KR20050009982A - Semiconductor-nanocrystal /conjugated polymer thin films - Google Patents

Abstract

The present invention provides a thin film comprising an inorganic semiconductor-nanocrystal dispersed in a semiconductor-polymer at a high loading amount and a method of manufacturing the same. The present invention also discloses a photovoltaic device comprising a thin film.

Description

Semiconductor-nanocrystal / conjugated polymer thin films}

The first solar cells were fabricated in the mid-1950's from crystalline silicon wafers. At that time, the most effective devices converted 6% of solar power into electricity. Advances in solar cell technology over the past 50 years have resulted in 25% of the most efficient Si cells and 10% of commercially available Si modules in cell arrays. While crystalline and polycrystalline forms of Si are the most common material types in solar cells, other semiconductors such as gallium arsenide, indium phosphide and cadmium telluride are also being studied as next generation solar cells with higher efficiency. In particular, high-efficiency structures using GaInP, GaAs, and Ge, such as tandem cells where multiple band gaps are layered on a single device, have achieved a record efficiency of 34%.

Despite these impressive efficiencies, the manufacturing cost of the solar cells of the prior art is high, limiting their spread as a power source. The production of commercially available silicon solar cells of the prior art involves four main processes: growth of semiconductor materials, separation into wafers, formation and encapsulation of devices and their junctions. For cell manufacturing alone, 13 steps are required to make a solar cell, of which 5 steps require high temperature (300 ° C.-1000 ° C.), high vacuum, or both. In addition, growth of the semiconductor from the melt is carried out at a temperature higher than 1400 ° C. under an inert argon atmosphere. To obtain a high efficiency device (> 10%), a concentrator system that concentrates sunlight into the device, a plurality of semiconductors and a quantum well to absorb more light, or high performance semiconductors such as GaGs and InP It is necessary to include a structure. The performance advantage results in an increase in manufacturing cost due to the plural number of manufacturing steps. Until now, these high performance structures have been used primarily in space devices such as spacecraft and satellites where efficiency per unit weight is as important as manufacturing costs.

Another problem associated with prior art solar devices is the high cost of the fabrication material. The amount of silicon required for a module output of 1 kW is about 20 kg. At $ 20 / kg, the material cost for electronic grade silicon can be partially subsidized by inexpensive manufacturing. Other materials, such as GaAs synthesized with highly toxic gases, are about 20 times higher at a cost of $ 400 / kg. Since solar cells are large area devices, the cost of such materials hinders the production of inexpensive cells. As a result, thin film devices having active layers of several microns in thickness, such as amorphous Si, CdTe and CuInSe ₂ , have been studied. In 1991, O'Regan et al. Reported an invention on photochemical solar cells consisting of inexpensive TiO ₂ nanocrystals and organic dyes. O'Regan et al. Nature 353, 737 (1991).

By spin casting a derivative of polythiophene where the C ₆₀ layer was evaporated, the two layer apparatus could reach a maximum external quantum efficiency (EQE) of 23%. Higher efficiency, on the order of 50%, could be obtained by blending derivatives of C ₆₀ and MEH-PPV into homogeneous membranes for monolayer devices. Further improvements in efficiency are limited by hopping and poor electron transport properties of C ₆₀ , which is characterized by low overlap between device absorption and solar emission spectra. Greenham. NC et al., Phys Rev. B, Vol. 54 , No. 24, Dec 1996.

The use of CdSe particles in poly (3-hexylthiophene) has already been proposed. Alivisators et al. Adv. Mater. 1999 , 11, No. See 11. This only discloses the use of nanoparticles of less than 13 nm in size and the devices produced thereby do not reach the efficiency of the devices according to the invention. In addition, the prior art acknowledges the solution chemistry problem associated with nanorods and does not provide a solution to the problem solved by the present specification. Solar cells based on inorganic nanorods according to the present invention having good transport properties and an absorption spectrum that can be extended to near infrared light can reach efficiencies comparable to conventional solar cells based on high capacity inorganic semiconductors. To provide a solution to the above-mentioned problem is a thin film mixed with a semiconductor-nanocrystal according to an embodiment of the present invention.

The present invention relates to semiconductor nanocrystal / conjugate polymer thin films.

1 shows an energy level diagram for CdSe and P3HT schematically illustrating the charge transfer process between 5 nm CdSe and P3HT.

2 is a schematic diagram of the structure of a nanorod-polymer blend photovoltaic device according to one embodiment of the invention.

FIG. 3 shows low resolution TEM images of CdSe nanocrystals of a) 7 nm × 7 nm, b) 8 nm × 13 nm, c) 3 nm × 60 nm and d) 7 nm × 60 nm.

FIG. 4 shows AFM-TM imaging images of a film composed of 90% by weight 7nm × 7nm CdSe nanocrystals dispersed in P3HT spin casted from chloroform.

FIG. 5 shows AFM-TM a) topography and b) phase images of a film composed of 90 wt% 9 nm x 13 nm CdSe nanocrystals dispersed in P3HT spin cast from 1% to 8% by volume pyridine in chloroform. .

FIG. 6 shows the surface roughness (hollow circular dot) of a film composed of 90 wt% 9 nm x 13 nm CdSe nanocrystals dispersed in P3HT spin-cast from various concentrations of pyridine in chloroform. Maximum EQE (dark diamond) is shown for devices made with these membranes. The line acts as a guide to the eye.

FIG. 7A shows normalized photocurrent spectra (hollow circular dots) and photocurrent spectra (annealed square dots) after annealing at 120 ° C. for 90 wt% 3 nm × 60 nm CdSe nanorods in a P3HT device. FIG.

FIG. 7B shows the ratio of EQE before and after heat treatment as a wavelength function for 90 wt% 3 nm × 60 nm CdSe nanorods in P3HT and nanorod only devices. Inset shows individual 1-transmission spectra for 3 nm x 60 nm CdSe and P3HT.

FIG. 8 shows the absorption (dark diamond dot, dotted line), photocurrent (hollow circular point, dark line) of a series of 3 nm x 60 nm nanorod devices at various nanorod concentrations of P3HT, and photocurrent (dark square) after 120 ° C. heat treatment. The relative involvement of P3HT with respect to dots, dashed lines).

FIG. 9 shows EQE of 90 wt% 7 nm × 14 nm CdSe in P3HT at 515 nm under ˜0.1 mW / cm ² illumination. The inset shows the PL efficiency of 60 wt% 7 nm x 14 nm CdSe in 514 nm excitation and P3HT samples after heat treatment at various temperatures.

FIG. 10 shows the EQE spectrum (hollow circle) of 90 wt% 7 nm × 60 nm CdSe nanorods in P3HT and the EQE spectrum (dark square) after heat treatment at 120 ° C. FIG. Inset: For the device, under 0.1 mW / cm ² illumination, the corresponding current-voltage characteristics at 515 nm include an open circuit voltage of 0.4 V and a charge factor of 0.5.

FIG. 11A shows the EQE spectrum before heat treatment at 120 ° C. of a device made from 90 wt% 7 nm × 60 nm CdSe nanorods in P3HT at 212 nm, 271 nm and 346 nm in thickness.

FIG. 11B shows the EQE spectrum after heat treatment at 120 ° C. of a device made from 90 wt% 7 nm × 60 nm CdSe nanorods in P3HT at thicknesses 212 nm, 271 nm and 346 nm.

FIG. 12A shows the relative improvement in EQE before and after heating at 120 ° C. for the device shown in FIGS. 11A and 11B.

12B shows the absolute difference in EQE before and after heat treatment.

FIG. 13A shows the TEM of a thin film spin-cast from 20 wt% 3 nm × 60 nm CdSe nanorods and P3HT from chloroform.

FIG. 13B shows the TEM of the same nanocrystals of FIG. 13A when cast from 10% by volume pyridine in chloroform solution.

FIG. 14 shows a TEM of a cross section of a 100 nm film composed of 60 wt% 10 nm × 10 nm CdSe nanocrystals in P3HT.

15A depicts 7 nm × 60 nm CdSe nanorods.

FIG. 15B shows a TEM of a cross section of a 100 nm film composed of 40 wt% CdSe nanorods in P3HT.

FIG. 16 shows that the length of a 7 nm diameter nanorod increases continuously from 7 nm x 30 nm to 60 nm and the EQE for 90 wt% CdSe in the P3HT device is 3 to 515 nm under illumination of 0.084 mW / cm ² . 54% increase.

17A-17C show TEMs of 7 nm diameter nanocrystals with lengths of a) 7 nm, b) 30 nm and c) 60 nm. The scale bar is 50 nm and all TEMs are the same scale.

FIG. 18 shows EQE for 90 wt% 3 nm × 100 nm side chain CdSe nanorods in P3HT device as a function of pyridine concentration.

19A shows unaligned tetrapod nanocrystals.

19B shows aligned tetrapod nanocrystals.

FIG. 20 shows EQE spectra for 90 wt% 7 nm × 60 nm CdSe series in P3HT devices with different film thicknesses.

FIG. 21A shows EQE spectra for 90 wt% 7 nm × 7 nm CdSe in P3HT at various film thicknesses.

21b shows the corresponding absorption spectrum for the device as a function of increasing thickness.

FIG. 22A shows the TEM of 40 wt% 5 nm CdSe nanocrystals in P3HT for TOPO treated nanocrystals.

FIG. 22B shows the TEM of 40 wt% 5 nm CdSe nanocrystals in P3HT for T1 treated nanocrystals.

FIG. 22C shows the TEM of 40 wt% 5 nm CdSe nanocrystals in P3HT for pyridine treated nanocrystals.

FIG. 23A shows IV characterization of 90 wt% 7 nm × 60 nm CdSe nanorods in P3HT at 515 nm under 0.1 mW / cm ² illumination.

FIG. 23B shows the solar cell characteristics of the FIG. 23A device measured using a simulated AM 1.5 global light source, with 1.7% including short circuit current of 5.7 mA / cm ² , FF of 0.42, and open circuit voltage of 0.67V. Obtain solar power conversion efficiency.

FIG. 24 shows ideal I-V curves and typical I-V curves found experimentally.

Summary of the Invention

The invention described herein provides a thin film comprising an inorganic semiconductor-nanocrystal dispersed in a semiconducting-polymer at a high loading amount and a method for producing the same. The present invention also discloses a photovoltaic device comprising a thin film.

Detailed Description of the Preferred Embodiments

In one embodiment of the present invention, a thin film comprising a semiconducting conjugate polymer having at least 5% by weight of semiconductor-nanocrystals is disclosed.

In another embodiment, a photovoltaic device comprising the thin film of the present invention is disclosed.

In another embodiment of the invention, the surfactant coated semiconductor-nanocrystals are washed one or more times with a solvent, the washed semiconductor-nanocrystals and semiconducting polymers are dissolved together in a binary solvent mixture and the mixture is deposited. A method for producing a polymer thin film comprising depositing is disclosed.

In another embodiment of the present invention, a semiconductor-nanocrystal having an aspect ratio of greater than 2 is dispersed in a semiconducting conjugate polymer to obtain a polymer-nanocrystal composite, wherein the nanocrystal is polymer at 5 wt% or more. A method of making a photoactive thin film comprising depositing a thin film of the composite to be embedded therein is disclosed.

In another embodiment of the present invention, a photovoltaic device is disclosed, comprising a conjugated conductive polymer layer in which semiconductor-nanocrystals are dispersed, and having a power conversion efficiency of greater than 1% in AM 1.5 global illumination. .

In another embodiment of the present invention, a first planar electrode, a thin film deposited on the first planar electrode and including a semiconducting conjugate polymer embedded with semiconductor-nanocrystals, and a second electrode and a thin film opposed to the first electrode A photovoltaic device is disclosed that includes a hole injection layer disposed between a polymer layer and a first planar electrode.

In another embodiment of the invention, the semiconductor-nanocrystals have an aspect ratio of at least 2, preferably at least 5, more preferably from about 5 to 50. Most preferably about 10.

As a preferred embodiment of the present invention, a method of dispersing or embedding semiconductor-nanocrystals in a semiconducting polymer is disclosed. Preferably this "loading amount" is an amount of at least 5% by weight. More preferably, the amount is 20 to about 95 weight percent. More preferably the amount is from 50 to about 95% by weight. Most preferably the amount is about 90% by weight.

In a preferred embodiment of the present invention, the semiconductor polymer is trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluorene, polyaromatic Polymers or blends selected from amines, poly (thienylene-vinylene) and soluble derivatives thereof. (Poly (2-methoxy-5- (2'-ethylhexoxyoxy) p-phenylenevinylene) (MEH-PPV) and poly (3-hexylthiophene) (P3HT) are preferred, with P3HT being the most desirable.

In a preferred embodiment, the semiconductor-nanocrystals comprise rods having a length greater than about 20 nm. More preferred are rods having a length of 20 to 200 nm. More preferred are rods having a length of about 60 to 110 nm.

As a more preferred embodiment, the present invention discloses the use of group II-VI, group III-V, group IV semiconductors and tertiary chalcoprites. More preferred are CdSe, CdTe, InP, GaAs, CuInS2, CuInSe2, AlGaAs, InGaAs, Ge and Si, and even more preferred are CdSe.

The semiconductor nanocrystal may be a side chain nanocrystal. More preferred are nanocrystals with arm and tetrahedral symmetry.

Preferably, the thin film of the present invention has a thickness of about 200 nm.

The method of forming the thin film of the present invention uses a binary solvent mixture, at least one of the binary solvents being pyridine, chloroform, toluene, xylene, hexane, water, dichlorobenzene, methylene chloride, alkylamine, butanol, methanol and isopropane It is preferably selected from the group consisting of, wherein the alkyl chain is preferably branched or unbranched with 2 to 20 carbon atoms. Most preferred is pyridine in chloroform.

The amount of binary solvent mixture is 1-15% by volume, more preferably 4-12% by volume, most preferably 8% by volume.

As a preferred embodiment of the present invention, a method for preparing a polymer thin film incorporating semiconductor nanocrystals is disclosed, which comprises washing the surfactant-coated semiconductor nanocrystals preferably one or more times with a solvent in pyridine. .

In another embodiment of the present invention, a method of making a polymer thin film is disclosed that includes thermal annealing a deposited film at a temperature of about 60 ° C to about 200 ° C. About 120 ° C. is preferred.

In another embodiment of the present invention, a photovoltaic device is disclosed that includes a PEDOT: PSS (poly (ethylene-dioxy) thiophene: poly (styrene sulfonic acid)) hole transport layer on top of an ITO electrode.

"Semiconductor-nanocrystal" is understood to include semiconducting crystalline particles of all shapes and sizes. Preferably, they have a size of less than 100 nanometers, but are not limited thereto. "Nanocrystal", "nanorod" and "nanoparticle" can be used interchangeably herein. In some embodiments of the invention, the nanocrystalline particles may have larger than two sizes that are less than about 100 nanometers. Nanocrystals can be core / shell type or core type. For example, some side chain nanocrystal particles according to some embodiments of the present invention may have an arm having an aspect ratio of greater than about 1. In one embodiment, the cancer has an aspect ratio greater than about 5, and in some cases may be about 10 or more. The width of the arm may be less than about 200, 100, and 50 nanometers in some embodiments. For example, for a tetrapod with one core and four arms, the core has a diameter of about 3 to about 4 nanometers and each arm is about 4 to about 50, 100, 200, 500 and It may have a length greater than about 1000 nanometers. Of course, the tetrapods and other nanocrystalline particles described herein can have other suitable dimensions. As an embodiment of the present invention, the nanocrystalline particles may be monocrystalline or polycrystalline in nature. The present invention has an aspect ratio of at least 20, in particular greater than 50, 100 nm in length and is described in documents such as Peng, XG et al. Nature 404 , 59 (2000) and Peng, ZA et al. J. Am. Chem Soc. It is conceivable to use nanorods of CdSe and CdTe formed according to the method described in 123, 183 (2001).

As used herein, the length of a semiconductor-nanocrystalline rod is 20 to 200 nm. In a preferred embodiment, the semiconductor-nanocrystals comprise rods having a length greater than about 20 nm. More preferred are rods having a length of 20 to 200 nm. More preferably, it has a length in the range of about 60 to 110 nm.

"At least part of the semiconductor-nanocrystal has an aspect ratio greater than about 2" means that if the semiconductor-nanocrystal is an unbranched rod, at least a portion of the total amount of the rod will have an aspect ratio of greater than about 2. The amount may be 100%. This also means that when the nanocrystals are side chain semiconductor-nanocrystals (including tetrapods of course), "at least some" means that at least one side chain has an aspect ratio greater than two. The aspect ratio is defined as the length of the longest rod divided by its diameter. In the case of side chain nanocrystals, the aspect ratio of the side chain nanocrystals is defined as the length of the longest side chain divided by the longest side chain diameter.

"Some of the semiconductor-nanocrystals are side chain nanocrystals" means that at least 1% by weight of the nanocrystals are side chain nanocrystals. The term "some" is defined to include 100%, that is, "total part".

Although CdSe and CdTe semiconductor-nanocrystals are preferred, the nanocrystalline particles may also include other suitable semiconductor materials and may be rods, shaped particles, or spherical. For example, the particles may comprise a semiconductor, such as a compound semiconductor. Suitable compound semiconductors include group II-VI semiconductor compounds such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe and HgTe. Other suitable compound semiconductors include Group III-V semiconductors such as GaAs, GaP, GaAs-P, GaSb, InAs, InP, InSb, AlAs, AlP, AlGaAs, InGaAs and AlSb. The use of group IV semiconductors such as germanium or silicon is also possible under certain conditions. In another embodiment, the particles may comprise dielectric materials such as SiC, SiN or other materials that may exhibit polytypism. Tertiary chalcoprites such as CuInS ₂ and CuInSe ₂ are also included. Some metals such as Fe, Ni, Cu, Ag, Au, Pd, Pt, Co and others can be used in the examples because they may exhibit polymorphism. Rod, arrow, tear and tetrapod semiconductor nanocrystals are described in Manna et al. J. Am. Chem. Soc. 2000 , 12, 12700-12706.

Nanocrystalline particles according to the present invention can have unique optical, electrical, magnetic, catalytic and mechanical properties and can be used for many suitable end uses. They can be used, for example, as fillers in composite materials, as catalysts, as functional elements in optical devices, as functional elements in photovoltaic devices (eg solar cells), as functional elements in electrical devices, and the like.

"P3HT" means poly (3-hexylthiophene) and includes Reggioregular P3HT, which includes Head to Head and Head to Tail Reggio P3HT. Head to tail P3HT is preferred.

The present invention intends that semiconductor conjugate polymers that can be processed from solution can act in accordance with the present invention. By "semiconductor polymer" is meant all polymers having a pi-electron system. Non-limiting examples include trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluoroene, polyaromatic amine, poly (thienylene- Vinylene) and soluble derivatives of the above. Examples are (poly (2-methoxy, 5- (2'-ethylhexyloxy) p-phenylenevinylene) (MEH-PPV) and poly (3-alkylthiophene). (Offen), P3HT The present invention also relates to the large suspension (pendant) groups attached to the main conjugate chain, or that the conjugate polymer is incorporated into a copolymer structure in which at least one component is not conjugated, It is also contemplated to use conjugate polymers that are solution processable or melt processable, including, but not limited to, poly (, 4'-diphenylenediphenylvinylene), poly (1,4-phenylene-1-phenylvinylene and Poly (1,4-phenylenediphenylvinylene, poly (3-alkylpyrrole) and poly (2,5-dialkoxy-p-phenylenevinylene), which is a semiconductor conjugate polymer is a mixture of polymer blends One of them is a semiconductor conjugate polymer, so the nanocrystals do not fit into the blend or mixture. Or distributed.

The present invention also contemplates that semiconductor-nanocrystals, rods can be aligned by techniques known in crystal alignment techniques.

By "photovoltaic device" is meant to include the typical device structures known in the art. Examples of photovoltaic devices are described, for example, in Science , Vol 295, pp.2425-2427, March 29, 2002, the contents of which are incorporated herein by reference. An example of a photovoltaic device may have nanocrystalline particles in a binder. The combination can be sandwiched between two electrodes (aluminum electrode and indium tin oxide electrode) on a substrate to form a photovoltaic device.

"Binary solvent system" includes a system of two solvents, one of which may be a ligand that is a solvent. Pyridine in chloroform, for example. “Binary solvent systems” also include systems of at least one solvent and non-solvent ligands such as xylene and phosphonic acid. Xylene is a solvent for semiconductor nanocrystals and phosphonic acid is a ligand and not a solvent.

Suitable methods of making thin films as described herein are known. Non-limiting examples of various coatings and printing techniques from solution include spin coating, blade coating, dip coating, inkjet printing and screen printing. All of these techniques are generally referred to as "deposition". That is, the thin film of the present invention is deposited on a substrate of a predetermined form.

Supplementary electronic properties of inorganic and organic semiconductors can be used to form battery-active junctions. Charge transfer is preferred between high electron affinity inorganic semiconductors and relatively low ionization potential organic molecules and polymers. In one embodiment of the invention, semiconductor nanocrystals, such as CdSe nanocrystals, are combined with conjugate polymers such as P3HT to form charge interface junctions of high interface regions, forming photovoltaic devices with improved efficacy. From the energy level diagrams for CdSe nanocrystals and P3HT, it can be seen that CdSe is electron accepting and P3HT is hole accepting (FIG. 1). The presence of ligands on the surface of the nanocrystals mediates interaction with the polymer. We can replace or remove ligands on the surface of CdSe through chemical cleaning or nanocasting of the CdSe-P3HT blend film after the nanocrystals have been cast.

The efficacy of charge transfer and transport is determined by the form of the blend. Aggregation of nanocrystals in solutions and polymers depends on the strength of van der Waals action between particles and the separation between nanocrystals and their size. There is a need for a balance between aggregation for the transport of electrons and dispersion for more effective charge transfer. The inventors have surprisingly found that fine tuning of the form can be achieved through the use of solvent mixtures. The solvent mixture according to the invention containing the ligand pyridine and solubilizing the nanocrystals can affect the dispersion of the nanocrystals in solution. Since spin casting is a non-balancing process, the dispersion of nanocrystals in solution can be maintained in the polymer.

According to one embodiment of the invention, the solvent mixture is used to control the phase separation down the nanometer scale. The inventors have surprisingly found that solvent mixtures can be used for phase separation in membranes with high concentrations of nanocrystals (up to 90-95% by weight) in polymers, and in particular, P3HT can be controlled down to the nanometer scale. It is an object of the present invention to improve the solubility of nanocrystals by simultaneously using good solvents and ligands for nanocrystals, in particular by using good solvents for polymers for CdSe and solution processing. A preferred example is the weak binding Lewis base, pyridine, having a relatively low boiling point of 116 ° C. selected as a ligand for the nanocrystals for easy removal. Pyridine treated nanocrystals of various shapes and sizes (FIG. 3) were co-dissolved with P3HT in a mixture of 4% to 12% by volume of pyridine dissolved in chloroform to form a uniform membrane consisting of particles dispersed in the polymer when spin cast. Create The preferred amount of pyridine to cover the nanocrystalline surface is determined by the number of unpassivated Cd surface sites on the nanoparticles. Since pyridine can be mixed with chloroform, solubility in nanocrystals is increased by twofold: (a) pyridine coated nanocrystals are more soluble in chloroform than untreated and (b) they bind to nanocrystals. Solubility is high in excess of pyridine. But too much pyridine should be avoided because it mediates the precipitation of P3HT, which is soluble in cloform and insoluble in pyridine. Thus, there are three solubility forms:

I. Low Pyridine Concentration Form: Inadequate solubility of nanocrystals causes large-scale phase separation in the blend membrane due to aggregation of nanocrystals.

II. Moderate pyridine concentration form: As long as the polymer can be sufficiently dissolved in the miscible blend of the two solvents, improving solubility of the nanocrystalline components of the blend solution results in intimate mixing of the two semiconductors, thus preventing phase separation during spin coating. .

III. High Pyridine Concentration Form: Since pyridine is non-solvent to the polymer component, we believe that large scale phase separation will occur by aggregation of the polymer chains.

In order to investigate the morphology of nanocrystal-polymer membrane sensitive techniques such as atomic force microscopy (AFM), bulk sensitive techniques such as transmission electron microscopy (TEM) are used. An example of Form I is shown in FIG. 4 for a blend of 90 wt% of 7 nm x 7 nm crystals in P3HT spun from a single solvent of chloroform. 4 shows a phase separation on the micron scale, which can be detected under an optical microscope and also with the naked eye, such as film scattered light. Light scattering is undesirable in thin film photovoltaic cells because it can reduce the absorbed light portion.

The study of the surface of the nanocrystal-polymer blend film can be improved by using AFM in taping mode (TM) because local differences in film composition can be identified by comparing the phase and topographic images. To illustrate the transition from Form I to Form II, FIG. 5 shows the AFM-TM for a 5 μm scan region of a 9 nm × 13 nm Nanorod-P3HT blend membrane spun from a solvent mixture of low and medium pyridine concentrations. Topography and image images are shown. Topography of these membranes is very rough for low pyridine concentrations, but intermediate concentrations yield much softer membranes. The corresponding AFM-TM phase image shows that surface roughness is related to phase separation. Phase separation between nanocrystals and polymers does not yield a single material domain, and therefore individual polymers and nanocrystal regions cannot be identified. At low pyridine concentrations, there is clear evidence for local changes in membrane composition, but at moderate pyridine concentrations, phase separation is very smooth. Thus these two concentrations can be seen as a result of the I and II states.

In another embodiment of the present invention, loading a large amount of semiconductor-nanocrystals into the conjugate polymer in accordance with the present invention results in a "smooth" thin film surface. This can be quantified. To quantitatively display these results, the root mean square of the film roughness (RMS) is determined as a function of pyridine concentration from the AFM topography image (FIG. 6). RMS roughness increases in magnitude as the pyridine concentration increases from 0 to 5% by volume. Between 5 and 12% by volume pyridine concentration, there is only a slight increase in RMS roughness, while increasing in size order as the pyridine concentration is selected from 12 to 20% by volume. Using this configuration, concentrations of 0-5% by volume may be attributed to Form I, 5-12% by volume may be attributed to Form II and 12-20% by volume may be attributed to Form III. . The concentration is for a fixed total concentration of nanocrystals and polymers in binary solution. When 90% by weight of CdSe nanocrystals were used in P3HT herein, the partial concentrations were 45 g / l and 5 g / l. It should be understood that the concentrations indicated for the washes can vary by 20% and are still effective.

The separation of charges can only occur in excitons which occur within the exciton diffusion range of the nanocrystal-polymer interface. Since single material domain size is reduced as a result of better nanocrystal dispersion, an increase in external quantum efficiency (EQE) is expected. EQE is a measure of charge separation efficiency, given that the charge collection efficiency at the electrode set is comparable to the following amounts: (i) incident light intensity, (ii) fraction of absorbed light, and (iii) electrode selection. Can be used. These three conditions are met for the device in which EQE data is presented in FIG. 6. 6 shows the pyridine dependence of EQE on a blend of P3HT and 9 nm × 13 nm CdSe nanocrystals. EQE increases by 1.4 times as it moves from state I to state II, and then decreases again for state III. As a preferred embodiment, up to 35% EQE can be obtained when the pyridine concentration is 8 volumes in the solvent mixture, ie binary solvent system.

Similar dependence of EQE on pyridine concentration in binary solvent systems exists for spherical nanocrystals dispersed in P3HT. The maximum EQE is 8 vol% pyridine concentration, which is comparable to the value measured on the low aspect ratio nanorods described above. For fixed nanocrystal concentrations, the optical concentration of pyridine is determined by the surface to volume ratio of the nanocrystals. For devices consisting of 3 nm x 100 nm nanorods, the best device is a solution containing 12% by volume pyridine Although cast from, a device consisting of 7 nm x 60 nm nanorods only requires 4% by volume pyridine. 3 nm diameter nanorods have a surface-to-volume ratio about two times higher than 7 nm nanorods. Since the bound pyridine molecules are in dynamic balance with the free pyridine in solution, more pyridine is required to maintain the surface of the thinner nanorods covered with pyridine.

As another embodiment of the present invention, the binary solvent mixture used in accordance with the present invention can be varied by replacing pyridine with another ligand. For example, CdSe, CdTe and InP nanocrystals are mostly synthesized as a mixture of TOPO or TOP and various phosphonic acids. After the nanocrystals are recovered and stored, there is a large amount of TOPO (or TOP) in the product and the nanocrystals are passivated by the organic surfactant. Nanocrystals with TOPO shells tend to be less oxidized and readily soluble in various solvents including toluene, chloroform, hexane, THF, pyridine and butanol. TOPO may be substituted with thiols, amines and other ligands for cadmium such as phosphine oxides and phosphonic acids (see below).

Non-conjugated ligands do not absorb in the visible part of the electromagnetic spectrum and are not added to the photovoltaic current of the solar cell. Oligothiophenes with phosphine oxide or phosphonic acid functionality attached may be bonded to the surface of CdSe and other semiconductor-nanocrystals. Longer conjugates, the conjugate ligands having the four monomer units, are absorbed in the visible region of the electromagnetic spectrum and are conducive to photocurrent, so their use can be considered as an embodiment of the present invention. Phenylphosphonic acid is a non-limiting example of a ligand of preferred use. The energy level of oligothiophene with 10 monomer units reaches the energy level of the parent polymer, P3HT. TnPA is known as thiefene (n is the number of thiefene rings) phosphonic acid shown below. There are three forms of preferred thiophene derivative ligands that may be contemplated by the present invention. The number of thiophene rings can vary and they utilize phosphonic acid, phosphine oxide or oligothiophene amines.

Since large oligomers can be tightly bound to the nanocrystals and interact intimately with the polymer, they help to improve the charge transfer rate between the two semiconductors. Oligomers with similar side chains for the polymer allow large nanocrystals to repel one another and disperse well in the polymer. If desired, the nanocrystals are blended with polymers containing chemical functional groups such as phosphine and phosphine oxides that are bound to the nanocrystals. In this case, the polymer is very close to the nanocrystals, which promotes charge transfer quickly and efficiently.

The nanocrystals are washed with a solvent suitable for the specific surfactant in the nanocrystals to replace TOPO, or other synthetic solvents. The nanocrystals are then dissolved in a solvent with excess of the desired ligand to be used and refluxed at high temperature for several hours. High temperatures ensure the movement of ligands on or off the nanocrystal surface and excess balances the new ligand on the nanocrystal surface. Another effective chemical treatment that reduces the exposure of the nanocrystals to oxygen and water at high temperatures is to dissolve the nanocrystals in excess replacement ligand and then precipitate the particles in a solvent for TOPO or other synthetic solvents and discard the supernatant after centrifugation. Pyridine with a boiling point of 116 ° C. is one of the easiest ligands to replace and is preferred for use with CdSe. Pyridine-passivated nanocrystals are less soluble than TOPO-coated nanocrystals, but pyridine can be stripped off easily by drying or heating the nanocrystals.

In photovoltaic devices made with nanocrystalline-polymer blends, the ligands of the nanocrystalline phase determine the morphology and microphase separation of the membrane. The form of the blend of CdSe with various ligands of TOPO, pyridine and modified TOPO (one octyl moiety is substituted with thiophene ring (T1)) is compared in FIG. 22.

As a non-limiting example, CdSe nanocrystals passivated with a nonpolar alkyl chain by TOPO may be uniformly dispersed in a nonpolar matrix of P3HT. The apparent spacing between the particles corresponds to 11 μs, the approximate length of the TOPO molecule (FIG. 22A). If TOPO is modified by substitution of one octyl chain with a thiophene ring to produce T1, these nanocrystals behave differently from TOPO coated particles when dispersed in P3HT (FIG. 22B). Nanocrystals coated with T1 aggregate more than TOPO coated particles, and aggregates of CdSe nanocrystals make lines of nanocrystals. Without wishing to be bound by any particular theory or principle, the thiophene ring on the T1 molecule is pi-stacked with the thiophene ring on the polymer, causing the nanocrystals to align along the polymer chain. The presence of the surfactant on the nanocrystalline surface is identified from the separation between the particles between the aggregates and between the chains of the nanocrystals. In contrast, nanocrystals coated with pyridine aggregate in P3HT (FIG. 22C). Although not limited to any particular theory or principle, since pyridine is a weak Lewis base, some of the pyridine may be removed from the nanocrystalline surface during solvent evaporation as the film is cast. As a result, van der Waals action between large polar nanoparticles in nonpolar P3HT results in microscale phase separation between the organic and inorganic components of the composite. Pyridine washed nanocrystals are in intimate contact with adjacent particles such that there is no apparent separation between nanocrystals in the membrane, as observed in TOPO coated particles. Similar differences in aggregation characteristics between TOPO and pyridine coated nanocrystals are also observed for the polymer MEH-PPV, which is more polar than P3HT.

As a preferred embodiment, the present invention contemplates substantially no substitution of 95% of the surfactant on the rods from synthetic processing. Advantageously, three washes will remove more residual surfactant and would be desirable because the surfactant interferes with charge transfer. However, the inventors have found that one washing step with some surfactant left behind results in photovoltaic devices that are much better and have unexpected results than people would expect. The EQE for such a device is 3 to 5 times better than the device washed three times.

5 nm diameter nanocrystals were washed three times in methanol to remove excess TOPO and then dissolved in a minimum amount of pyridine (50 μl / 100 mg CdSe) and precipitated three times in hexane to give particles with pyridine on the surface. Methanol washed nanocrystals were first refluxed with pyridine to replace TOPO, precipitated with hexane and then refluxed for 12 hours in a solution of T1 dissolved in toluene to give T1 coated particles. Membranes were obtained by spin casting in a NaCl IR window from a solution consisting of 40 wt% nanocrystals in P3HT dissolved in chloroform. These samples were immersed in water to float the blend membrane and copper TEM grid and to obtain the membrane using perforated carbon.

In another embodiment of the present invention, the present inventors have found that heat treatment is an effective way to improve the mobility of organic molecules bound to an inorganic surface, and that treatment of nanocomposites around the glass transition temperature of a polymer causes the molecules in the film to be directed to the surface. It was surprisingly found to be able to move. In organic blends, thermal annealing has been used to enhance the balance morphology of spin cast membranes and in some cases to enhance phase separation and crystallization in composites. In the case of nanocrystal-polymer blends, heat treatment improves the performance of the photovoltaic device by the deformation of the nanocrystal-nanocrystal and nanocrystal-polymer interfaces surprisingly improving charge transfer and transport. Excess pyridine in the binary solvent used to control the dispersion of nanocrystals in the polymer will appear to act as a non-radioactive recombination center for excitons made in P3HT. As a result, these excitons do not contribute to the photocurrent. Thermal annealing of the membranes according to embodiments of the present invention results in the removal of excess unbound pyridine in the interfacial pyridine and polymer regions. Significant improvements in EQE are observed in the apparatus after heating, which is also related to the recovery of these lost excitons for charge transfer and photocurrent generation.

The normalized photocurrent measured for 90 wt% 3 nm x 60 nm CdSe nanorods in P3HT spin cast from a solvent of 10 vol% pyridine in chloroform is shown in FIG. 7A (the hollow circle is the value before annealing; Color square is the value measured after annealing). The absolute maximum EQE is 15% at 455 nm under flow argon, 0.1 mW / cm ² illumination. By heating at 120 ° C. for 3 hours and cooling to room temperature for 8 hours under a reduced pressure of about 50 mTorr, the photocurrent of the same device is much higher than would be expected by the average person (FIG. 7A).

Without being limited to any particular theory or principle, these unexpected results may be explained as follows. The ratio of the photocurrent of the heated device to the photocurrent of the device before heating shows a total improvement of 2.5 times, particularly a strong increase of more than 6 times near 650 nm with shoulder at 700 nm. To understand the origin of this red EQE enhanced peak, a device with 3 nm x 60 nm CdSe nanorods was fabricated and heated under the same conditions. Analysis of photocurrent before and after heat treatment indicates that there is an enhancement characteristic at the center of 700 nm. Thus, we can assume that this red shift in the blend photocurrent is due to the nanorods. Thus, regardless of the specific theory or mechanism of operation, heat treatment is believed to help remove interfacial pyridine and bring the nanorods closer, bringing unexpected surprisingly good effects. This agglomeration of adjacent nanorods will improve electron transport between nanorods, so the separation distance between hopping steps will be reduced. In addition, the removal of interfacial pyridine will have the effect of enhancing charge transfer between the materials by connecting CdSe and P3HT to more intimate electronic contact. These two effects will result in a photocurrent improvement of about 2.5 times over all absorption wavelengths.

The maximum photocurrent increase will occur in the region between 500 nm and 700 nm, more than six times can be obtained for a 90 wt% CdSe blend device and CdSe and P3HT make a significant contribution to the absorption of light. To determine the relative contribution, one can compare the fraction of absorbed light to the fraction of photocurrent generated by each material component. Absorption spectra of a series of devices with varying CdSe concentrations can be fixed to a linear combination of individual CdSe and P3HT spectra (FIG. 8).

There is no noticeable change in absorption in the 400 nm to 700 nm range of the blend apparatus after heating. For concentrations above 40% by weight, the contribution of P3HT to the photocurrent is much less than the proportion of light absorbed by the polymer. For a 90 wt% CdSe device, P3HT is responsible for 61% of the absorbed light, but the polymer only contributes 8% of the photocurrent. This indicates that the actual amount of light absorbed by P3HT does not contribute to the generation of current and is not affected by non-radioactive or radioactive recombination pathways. However, when these devices are heat treated at 120 ° C., changes in the photocurrent spectrum yield a P3HT contribution close to the ratio of light absorbed. In the case of a 90 wt% CdSe device, the P3HT portion of the photocurrent increases significantly by 66%, comparable to 61% of the light absorbed in P3HT. This amplification of external quantum efficiency is observed at 60 ° C. to 160 ° C. and is reduced once at 180 ° C. as aluminum moves through the film and the device degrades (FIG. 9). Thus, the PL efficiency of the 60 wt% CdSe blend film, which is a function of the processing temperature, is increased to 120 ° C. and then decreased and kept constant at high temperatures (FIG. 9 inset). The present invention contemplates that the thermal annealing temperature may be at least 200 ° C.

This unexpected result can be explained as follows. Since the PL efficiency of CdSe in the blend is less than 0.1%, the PL of the sample is significantly increased from P3HT. Heating of P3HT is known to result in an improvement in crystallinity and to suppress PL efficiency. This effect is observed in the heating film of P3HT at temperatures as low as 40 ° C. The increased crystallinity thus accounts for a slight decrease in PL efficiency observed in blend films higher than 120 ° C., but does not account for a substantial increase in PL efficiency below 120 ° C. Removing excess pyridine in the polymer at low temperatures may be the cause of increased P3HT PL efficiency with increasing treatment temperature. This seems to be because some photons absorbed in P3HT do not contribute to PL because they undergo non-radioactive recombination at the pyridine sites in the polymer in the untreated membrane. After heat treatment, the photons can contribute to radioactive corrosion and charge transfer. Thus, removal of excess pyridine results in a greater P3HT contribution to photocurrent, leading to an increase in the EQE observed in the 500 nm to 700 nm region.

Heat treatment according to a preferred embodiment of the present invention is particularly important for improving EQE in high aspect ratio nanorod devices having a high surface to volume ratio and requiring high concentrations of pyridine (> 8% by volume) in spin casting solutions. . Devices comprised of nanorods contain large nanorods-nanorods, nanorod-polymer interface regions containing pyridine as well as excess pyridine. This removal of pyridine results in a six-fold greater EQE improvement as seen in FIG. In contrast, 7 nm x 60 nm nanorods were blended with P3HT in a solvent with 4% by volume of pyridine and the initial EQE increase after heating was about 1.3-fold (FIG. 10).

The present invention contemplates the use of nanorods with a low surface-to-volume ratio, so the removal of pyridine from the thin film (<200 nm) is due only to pumping the sample at low pressure (<10 ^-6 mbar) Not observed. Heat treatment of thin films is also dangerous for open circuits and filling factors because aluminum diffuses through some critical devices.

In the 90 wt% 7 nm x 60 nm nanorod CdSe series in P3HT devices ranging from 100 nm to 350 nm thickness, the 200 nm thickness is improved upon heat treatment at 120 ° C. (FIG. 11).

As the thickness of the device increases, the relative improvement in EQE also increases (FIG. 12A). The absolute increase in EQE after treatment increases with thickness (FIG. 12B) but is limited to 346 nm thickness due to the poor transport properties of the thickest device. Hybrid nanorod-polymer solar cells become more efficient through nanorod alignment, but the synthesis of rods larger than 100 nm in length and the synthesis of thicker films with higher optical densities to absorb more sunlight can be used. In these thick films, heat treatment is desirable to realize high performance devices.

As another embodiment of the present invention, the inventors have realized a surprising strategy for increasing charge collection to increase carrier mobility and obtain improved cell performance. In the case of a blend of electron transport material and hole transport material, the generation of an osmotic path is required for the transfer of charge. In dispersions of nanocrystals and polymers, termination in the path to electrons acts as a trap or recombination center. Increasing the size of the nanocrystals improves their performance by reducing the number of such terminations. However, in order to achieve the efficiency observed in commercially available solar cells, it is desirable to have higher carrier mobility and lower recombination ratio. In the case of nanorods having a length similar to the thickness of the device, it is preferred that the carrier mobility has an indicated path similar to the carrier mobility of the one-dimensional wire. By controlling the aspect ratio of CdSE nanorods dispersed in P3HT, the inventors have surprisingly found that the length scale and direction of electron transport can be adapted through thin film PV devices.

As the nanocrystals increase the aspect ratio on the spherical to rod, they move closer from the molecular region to the 1-dimension wire region and they become less soluble. In FIG. 13A, the nanorods form a single island of several microns spacing when the membrane is cast from chloroform. However, at the same concentration, nanorods are uniformly dispersed in the polymer membrane when cast from a pyridine / chloroform solvent mixture (FIG. 13B). Dispersion of nanorods in pyridine and chloroform is important to create a charge transfer interface with P3HT for reduced exciton recombination as well as uniform membrane casting.

It is important to characterize the morphology of the blend film in the cross region because the structure of the solar cell extends toward the thickness of the device rather than from the side of the device. To achieve this, a solution in which 60% by weight of 10 nm x 10 nm CdSe nanocrystals are dissolved in P3HT is spin casted from solution onto a polybed epoxy disk. The disc is finely cut with a diamond knife to obtain a 60 nm thick film. The thin film on one edge contains the cross section of the nanocrystal-P3HT blend. In the TEM image of the film (FIG. 14), the dark part without nanocrystals is an epoxy substrate, on top of which is a P3HT film, about 100 nm containing nanocrystals are seen. Nanocrystals follow a uniform overall film thickness with no significant phase separation laterally.

It was very difficult to get cross sections for long nanorod-polymer membranes. Nanorods did not cut due to their large size and the blend film showed a tendency to tear and was dragged by the knife. Thus, the membranes, once they are spun onto epoxy disks, are well embedded in epoxy resin over 2 days and cured to provide additional support during microcutting. The cross section for the 40 wt% 7 nm × 60 nm CdSe nanorods in P3HT shows the nanorods filling a significant portion of the thickness of the film shown in FIG. 15B.

As the length of the nanorods increases to fill the thickness of the photovoltaic device, electron transport is also expected to substantially improve. However, the expected improvement in transport assumes that the nanorods are aligned perpendicular to the plane of the substrate and that the nanorods are long enough to transport electrons entirely in one nanorod. 15 shows that the nanorods are randomly dispersed, but nevertheless some particles are oriented with important components along the electron transport direction. Other evidence for some alignment of the nanorods and beneficial effects on electron transport can be observed at the photocurrent.

EQE can be used as a measure of charge transport efficiency when the following amounts are comparable to a set of devices: (i) the angle of incidence, (ii) the fraction of absorbed light, and (iii) the electrode primarily determined by the selection of the electrode Charge collection efficiency, and (iv) charge transfer efficiency determined from photoluminescence inhibition. These four conditions are met for the device with EQE data provided in FIG. Thus, we expect that as the aspect ratio of the nanorods increases from 1 to 10 (FIG. 17), the charge transport should be significantly improved to obtain about 3 times the EQE improvement. In a network composed of shorter nanoparticles, electron transport is predominant by hopping between fractional particles, including passages for electron collection electrodes. However, in devices composed of longer particles, band conductance predominates as the path is formed from a single nanorod. Since the thickness of the nanorod-polymer membrane in the device is about 200 nm, 60 nm long nanorods can penetrate through a significant portion of the device, while 30 nm x 7 nm length particles are progressively less as shown in FIG. 16. effective. The best devices containing 7 nm x 60 nm nanorods are run with a maximum EQE of 55% under 0.1 mW / cm ² illumination at 485 nm, which is reproducibly reproducible. The reported results represent the average of five device sets in separate cases from three different synthetic batches of 57 individual solar cells. The average external quantum efficiency of these 57 devices is within 10% of the average with maximum efficiency at 59% under ˜0.1 mW / cm ² monochrome illumination. Individual devices were repeatedly characterized over a time scale of months and showed no significant difference between measurements.

Due to the excellent carrier transport properties of inorganic semiconductor nanorods compared to semiconductive organic polymers and small molecules, these hybrid nanorod-polymer solar cells exhibit the best EQE reported so far in polymer containing cells.

Photovoltaic devices according to the present invention are thought to include high side chain nanorods. The high side chain nanorods were synthesized according to a technique known in the art from injection of the precursor ten times. During injection during synthesis, these nanorods produced multiple nuclear sites for side chain and length increase. Since many of these side chain nanorods have lengths greater than 100 nm, further increases in EQE are expected when used in nanorod-polymer PV devices. The side chains are caused by low energy zincblende defects in the wurtzite structure of the rods, similar to the stacking defects that cause the defective nanorods along their length. As a result, the mobility of the carriers in the side chain nanorods is similar to the unbranched rods. The interaction between the side chains and the body of the nanorods is also stronger in the two distinct nanorods in physical contact. Thus, band transport is more prevalent in the side chain nanorods and electron hopping occurs between discrete nanorods.

Embodiments of the present invention are understood to include nanocrystalline particles of even more complex shapes. As an embodiment of the present invention, initial nucleation yields a core having a cubic crystal structure (eg, zinc blende crystal structure). Thereafter, cancers with hexagonal crystal structures (eg wurtzite) can grow out of the core. However, different growth conditions can produce cubic and hexagonal crystal structures alternately, resulting in irregular side chains. By precise control of the temperature through the reaction, side chain “inorganic dendrimers” can be obtained. Mana et al . , J. Am. Chem. Soc ., 2000 , 122, 12700-2706 and US Ser. No. 10 / 301,510, filed November 20, 2002, currently pending.

The inherent properties of tetrapods self-aligning on a substrate with one arm, which always faces only one electrode, combined with a low band gap material such as CdTe, makes tetrapod semiconductor-nanocrystals embedded in the conjugate polymer of a particularly preferred embodiment. In contrast to randomly oriented nanocrystals, tetrapods according to embodiments of the present invention can be aligned and provide a one-way current path as compared to randomly oriented nanocrystal particles.

The photocurrent spectra for 90 wt% CdSe side chain nanorod blends in P3HT for various pyridine concentrations are shown in FIG. 18. Preferred pyridine concentrations for the side chain nanorods occur at 12%, which is much higher than pyridine concentrations for shorter non-branched rods up to 8%. The maximum EQE for these devices is 31% at 450 nm under about 0.1 mW / cm ² illumination. Contrary to the expected results, the EQE is about twice as low as a device made with 60 nm nanorods.

The dispersion of longer nanorods (> 100 nm) in P3HT is limited by its solubility in pyridine-chloroform. When dissolved in pyridine-chloroform, the side chain nanorods formed a gelatinous, viscous solution. This results in lower solubility of the side chain materials and higher nanorod-nanorod interactions compared to nanorod-solvent interactions. Using these side chain materials, the CdSe-P3HT membrane cast was heterogeneous and diffused, which clearly shows macrophase separation. The improvement in transport efficiency is compensated by a decrease in charge separation efficiency due to a decrease in the interface area between the nanorods and P3HT.

Long cadmium selenide nanorods in high concentration solution and passivated by pyridine are separated at small intervals, in some cases by the diameter of pyridine. Under this approach, van der Waals forces, both volume and distance scale, are very strong and promote cohesion. It is challenging to dissolve long nanorods at high concentrations needed to produce sufficiently thick films for PV devices. Larger and longer chain ligands are needed to extend the length of the nanorods added to the polymer. In order to prevent the ligand from acting as a barrier layer, they must be electrically active and the energy level should also be to facilitate charge transfer between CdSe and P3HT.

Full band conduction of electrons requires that the transport be contained entirely within a single nanocrystal. Another improvement in transport depends on the alignment of the nanorods across the film thickness. Nanorod alignment methods include field and stretch alignment, both of which require significant modification of current device processing and construction. Tetrapods with four identical nanorod arms attached to the cubic center are naturally oriented on the surface with one arm perpendicular to the substrate plane as shown in FIG. 19. Thus, the next generation of hybrid solar cells incorporate tetrapods as self-aligning nanocrystals for the efficient transport of electrons.

Another embodiment of the present invention is the surprising film thickness at which the nanorod / polymer photovoltaic device of the present invention operates. One of the many advantages of using nanocrystals and polymers is a high absorption coefficient compared to bulk inorganic semiconductors. They form thin films of less than 300 nm that can absorb more than 90% of incident radiation. Unlike conventional inorganic semiconductor solar cells, which require more than a few microns in thickness to absorb light, nanocrystals and polymers can be used to obtain devices with low material usage and flexibility. Regardless of the particular theory or mechanism, the efficiency dependence of nanorod-polymer PV devices with sufficient thickness depends on the nature of the carrier transport, since the good transport properties of the nanorods can be exploited when the nanorod length reaches a significant portion of the film. It also provides information.

The photocurrent spectrum of the device for which absorption is discussed is shown in FIG. 20. As the film thickness increases from 100 nm to 350 nm, the corresponding increase and subsequent decrease in EQE is not only due to the increase in absorbed light. The shape of the spectrum depends on the thickness of the device and the photosensitivity in the red region of the spectrum increases with thicker film. This may be due to a weak filter effect resulting from the part of the film that does not contribute to the photocurrent. In thick films, electrons generated near the PSS electrode reach the aluminum electrode that is collected because the network of nanorods in physical contact transports electrons with low carrier mobility compared to transport in the case of being completely contained in one particle. In order to traverse multiple nanorods. Blue light absorbed close to the transparent electrode is not so strongly involved in the photocurrent. In addition, the electric field across the device involved in charge separation is reduced with a predetermined voltage bias for thicker films as compared to thinner films.

The inventors have found that nanorod-polymer devices can be made significantly thicker at 200 nm to achieve more light absorption because the nanorod dispersion properties are well controlled and the transport properties at the nanorods are more effective than the organic materials described above. Found that.

The photocurrent spectrum of the 90 wt% 7 nm spherical nanocrystals in the P3HT device also shows similar properties (FIG. 21A). Absorption spectra of a set of devices of varying thickness are shown in FIG. 21B. As the thickness of the device increases, EQE as a function of wavelength shows a more pronounced response than in the red region of the spectrum. For these spherical nanocrystals, the optimum device thickness is 160 nm, which can be compared with the optimal 212 nm for long nanorod devices. Since long nanorods exhibit enhanced electron transport compared to shorter dimension spheres, the device can be made thicker to absorb more light before hopping transport becomes dominant. This provides evidence of the effect of enhancing transport using one-dimensional nanorods.

In another embodiment of the present invention, a photovoltaic device is disclosed that incorporates a PEDOT: PSS (ethylene-dioxy) thiophene: poly (styrene sulfonic acid) hole transport layer on top of an ITO electrode. Incorporating a hole conductive layer on top of the ITO electrode provides a number of advantages, such as providing a smoother surface when depositing the nanocomposite layer by spin casting, and its effect is much better than that of ITO conductive polymer (P3HT). Matching with the balance band of the facilitates the hole conduction. Of course, a number of different hole conductive layers can be selected depending on the action of the electrode material applied. Non-limiting examples of such devices are shown in FIG. 4. The most preferred embodiment of the invention is a semiconductor nanocrystal made by spin casting a solution of 90 wt% 7 nm x 60 nm CdSe nanorods in P3HT onto an ITO glass substrate coated by PEDOT: PSS with aluminum as the top contact point. It is a polymer solar cell. A power conversion efficiency of 6.9% was obtained at 515 nm under 0.1 mW / cm ² in an inert atmosphere of flowing argon. At this intensity, as shown in Fig. 23A, the open circuit voltage is 0.5V, the light voltage is 0.4V at the maximum power point and the charge factor is 0.6. For plastic PV devices, monochromatic power conversion efficiency is one of the highest reported. Solar cells based on very few polymers can achieve monochromatic power conversion efficiencies greater than 2%. The most reliable example is a blend obtained from soluble derivatives of C ₆₀ and MEH-PPV, reaching an efficiency of 5%.

As another embodiment of the present invention, the alignment of semiconductor-nanocrystals across the film thickness can be controlled with external assistance. Alignment aids may include help known to those skilled in the art. These can help to obtain electric field, magnetic field or stretch alignment, and include help that can be used to align nanocrystals. For the purposes of the present invention, the alignment can be defined when 10 to 99% of the nanocrystals have a longitudinal axis aligned no more than 20 ° from the normal to the thin film plane.

Experimental Example

The above description has numerous embodiments of the present invention. Some variables of the above examples are summarized in Table 1 below. Non-limiting examples of the invention are described below. Pyr / Chlor means a pyridine mixture in chloroform.

Nanocrystals were synthesized using pyrolysis of organometallic precursors by techniques known in the art, mainly in mixtures consisting of trioctylphosphine oxide (TOPO) and tributyl- or trioctylphosphine and small amounts of various phosphonic acids. Peng et al ., Nature 2000, 404 , 59; And Peng et al . , J. Am. Chem. Soc. See 2001 , 123, 1389. The recovered product was dispersed and washed three times with methanol to remove excess surfactant. Pyridine treatment of nanocrystals to remove surfactants used in the synthesis of nanorods was achieved by dissolving the particles in pyridine and then precipitation in hexane. TOPO coated CdSe nanocrystals were soluble in hexane, while pyridine coated particles were insoluble in hexane. Repeating the pyridine treatment two to three times can effectively replace at least 95% of the TOPO with pyridine on the nanocrystal surface.

CdTe tetrapods were synthesized as described in currently pending US application 10 / 301,501, filed November 20, 2002. Cadmium oxide (CdO) (99.99 +%), tellurium (Te) (99.8%, 200 mesh) and tri-n-octylphosphine oxide (C24H51OP or TOPO, 99%) were purchased from Aldrich. n-octadecylphosphonic acid (C18H39O3P or ODPA, 99%) was purchased from Oriza Laboratoris Inc. Trioctylphosphine (TOP) (90%) was purchased from Fluka. All solvents used were anhydrous from Aldrich and used without further purification. All work was done using standard airless techniques. The Cd / Te molar ratio varied from 1: 1 to 5: 1 and the Cd / ODPA molar ratio varied from 1: 2 to 1: 5. Te precursor solution was prepared by dissolving tellurium powder in TOP (concentration 10% by weight of Te). The mixture was stirred at 250 ° C. for 30 minutes, then cooled and centrifuged to remove residual insoluble particles. In a typical synthesis of CdTe tetrapods, a mixture of ODPA, TOPO and CdO was degassed in 50 ml three flasks connected to a Liebig condenser at 120 ° C. for 20 minutes. The mixture was heated slowly under Ar until CdO decomposed and the solution became clear and colorless. Then 1.5 g of trioctyl phosphine (TOP) was added and the temperature was further raised to 320 ° C. Thereafter, the Te: TOP precursor solution was injected rapidly. The temperature was lowered to 315 ° C. and maintained at this value during synthesis. All synthesis was stopped after 5 minutes by removing the heating mantle and rapidly cooling the flask. After cooling the solution to 70 ° C., 3-4 ml of anhydrous toluene was added to the flask and the dispersion was transferred to an Ar dry box. The minimum amount of anhydrous methanol used to precipitate the nanocrystalline particles after centrifugation was added to the dispersion. This prevented co-precipitation of the Cd-phosphonate complex. After removing the supernatant, the precipitate was dissolved twice in toluene and re-precipitated with methanol. After removing the supernatant, the final precipitate was stored in a dry box. All the resulting CdTe tetrapods could easily be dissolved in a solvent such as chloroform or toluene.

Example 1 . According to one embodiment of the invention, a solution of CdSe nanocrystals and P3HT dissolved in a pyridine-chloroform solvent mixture is spun onto an ITO coated glass substrate under an inert atmosphere, pumped for 12 hours under <10 ^-6 mbar Photovoltaic devices were fabricated by evaporating the upper aluminum to obtain the structure shown in FIG. 2.

Example 2 . a. Nanocrystalline Synthesis: According to another embodiment of the present invention, long CdSe nanorods (90 wt.% CdSe) in P3HT were synthesized as follows: Cd stock: 0.161 g of dimethylcadmium 0.34 g of trioctylphosphine (TOP )). Se stock: 0.2 g of Se was dissolved in 2.367 g of TOP. In three flasks, 3.536 g trioctylphosphine oxide (TOPO), 0.187 g hexylphosphonic acid (HPA) and 0.357 g tetradecylphosphonic acid (TDPA) were mixed. This mixture was heated to 360 ° C. and degassed under argon. Cd stock was slowly injected, then the temperature was lowered to 330 ° C. and Se stock was injected quickly. The reaction was run at 290 ° C. for 18 minutes and then heat was removed. About 15 mL of methanol was added to the flask at 40 ° C. The mixture was centrifuged and the supernatant was discarded. 8 mL of methanol was added, shaken and centrifuged again to remove supernatant.

b. Substrate Preparation: Indium tin oxide (ITO) on a glass substrate was washed by sonication with a series of solvents. After the final solvent wash, the samples were dried and placed in a pre-cleaned plasma chamber. These samples were treated with plasma for 4 minutes. As soon as the sample is removed from the chamber, deposition of PEDOT: PSS (purchased from Bayer-electronic grade) begins. PEDOT: PSS is deposited by filtration through a 0.2 micron acetate filter followed by spin casting at 3000 rpm. The membrane was dried by heating at 120 ° C. for 1 hour under flowing argon.

c. Nanocrystal Wash: The synthesized nanocrystals were divided into 2 portions and 8 mL of methanol was added to each half portion. Centrifugation, the supernatant removed and the procedure repeated again. 0.35 mL of pyridine was added to each half to dissolve the nanorods, heated at 120 ° C., and occasionally shaken for 10 minutes. Precipitates with 8 mL of hexane for each half. Centrifuged and the supernatant was discarded. Nanorods were dissolved in a chloroform / pyridine mixture with 9.2% pyridine to produce 83 mg / mL nanocrystals.

d. Active layer deposition: Regioregular poly (3-hexylthiophene) (P3HT) was dissolved in chloroform at 30 mg / mL. Using this solution and the nanorod solution described above (see III above), the nanorods and P3HT dissolved in a TOPchloroform / pyridine mixture such that the weight ratio of nanorods to P3HT is 9: 1 and the P3HT concentration is 4.55 mg / ml. The solution was prepared. The thin film was spin cast at 1350 rpm onto a substrate prepared from this solution (see II above).

e. Electrode deposition: The sample was placed in an evaporation chamber and pumped under vacuum for at least 8 hours to reach below 10 ^-6 Torr. An aluminum film is thermally deposited to a thickness of about 100 nm through a shadow mask to form an upper electrode.

Example 3 CdTe Tetrapod in P3HT

CdTe tetrapod nanocrystals with one core and four arms of about 80 nm in length were synthesized and then washed with tetrahydrofuran (THF) and ethyl acetate in the dissolution / precipitation step. Nanocrystals were co-dissolved in solvent chloroform with ligand phenylphosphonic acid and heated at 100 ° C. for several hours. The nanocrystals were precipitated with methanol and then redissolved in chloroform. The nanocrystalline solution was mixed with the P3HT solution and spin cast as described in Example 2 to produce a thin film. The substrate and the electrode were processed as in Example 2. The EQE for the sample was less than 10%.

Example 4 CdTe Tetrapod in P3HT

CdTe tetrapods were synthesized and washed with toluene and methanol (THF and ethyl acetate) as in Example 3.

Nanocrystals (about 50 mg) were dissolved in about 2 ml of solvent chloroform with about 1000 mg of ligand hexylphosphonic acid (HPA) and heated for several hours. The rest of the procedure followed Example 3. The EQE for the sample was less than 10%.

Example 5 CdTe Tetrapod in P3HT

Although carried out as described in Example 4, additionally the nanocrystals were dissolved in tributylphosphine (TBP) and stirred for 20 minutes before precipitation with methanol. The reaction was then carried out as in Example 3. The EQE for the sample was less than 10%.

Example 6 CdTe Tetrapods in MEH-PPV

Although carried out as described in Example 3, the nanocrystals were redissolved in solvent p-xylene after the final methanol precipitation. This example will have the ligand phenylphosphonic acid. A solution in which MEH-PPV is dissolved in p-xylene can be prepared, mixed with nanocrystals and then cast blended into a membrane as described in Example 2.

Example 7 CdTe Nanocrystals in P3HT

All steps were performed in the same manner as in Example 2 except that the ligand pyridine was replaced with n-butylamine or n-hexylamine.

Example 8 CdSe Nanocrystals in P3HT

The CdTe nanocrystals were replaced with CdSe nanocrystals in the same manner as in Example 4. In addition, the HPA used as a ligand is replaced with T1.

Example 9 CdSe or CdTe Nanocrystals in P3HT

It was carried out as in Example 8 using CdSe or CdTe nanocrystals.

Replace HPA with T5-PA.

Characterization of the Sample

Nanocrystal size, morphology and structure were measured by TEM using a FEI Tecnai 12 120 kV microscope. A thin film of CdSe-P3HT (Regioregular P3HT from Aldrich), about 50-100 nm thick, was cast using a TEM by casting a film on a NaCl IR window, floating the film in water, and then selecting it using a copper TEM grid. The study was carried out. The shape of the blend membrane was characterized directly on the device via an atomic force microscope in taping mode using Nanoscpoe IIIa purchased from digital instruments. The film thickness was measured by AFM.

Absorption of the CdSe-P3HT blend membrane was measured using an Agilent Chemstation UV / Vis spectrophotometer. Photocurrent measurements were obtained with current and voltage using a 250 Watt tungsten light source coupled to an Action SP150 monochromator and Keithley 236 source measurement unit as illumination source. Light intensity was measured using a Calibrated Graseby silicon photodiode.

Photoluminescence stopping experiments were completed on a CdSe-P3HT film 100-200 nm thick cast on a glass substrate. Absolute photoluminescence of the sample at 514 nm under excitation from an argon ion laser was obtained by deMello et al . , Adv. Mater. It measured according to the method described in 1997, 9, 230.

The efficiency of photovoltaic devices is described in Rostalski, J. Sol. Energy Mater. Sol. As described in Cells 61, 87 (2000). The first is number efficiency and external quantum efficiency (EQE), which represents the number of photons that are converted to electrons. The second is power conversion efficiency, which indicates how much power is produced per unit of incident radiated power. EQE is important for understanding the mechanism of current generation, but is rarely used as a measure of the efficiency of commercial solar cells. More important in commercial devices is the power conversion efficiency of the device under solar conditions.

In commercial applications, the most important variable is the power conversion efficiency of photovoltaic cells. to be. Since power is the product of current and voltage, power conversion efficiency is determined by measuring the current as a function of voltage. The power conversion efficiency can be expressed using the power P _light and electrical output P _out of the incident light of the cell:

The maximum theoretical output is expressed as the product of the short photocurrent I _sc and the open circuit voltage V _oc . 24 shows a typical IV curve found experimentally. The inner rectangular area corresponds to the maximum output (at the maximum power point) of the actual device, while the outer rectangular area formed by the axis and ideal IV corresponds to the maximum ideal output. Curve the actual IV characteristic and maximize the product of current and voltage for maximum output. The ratio between the maximum theoretical output and the actual maximum output is an important characteristic of the IV feature. This ratio is called the filling factor (FF) and is defined as:

When indicating the maximum output of a photovoltaic cell using the charge factor, the power conversion efficiency becomes:

A lot of information is contained within the IV characteristics of the device. I _sc is proportional to EQE and is coupled to V _oc and FF and provides all the variables needed to characterize the battery's power efficiency.

The present invention described herein has a power conversion efficiency of A.M. 15 globular illumination provides more than 1% photovoltaic cells. More preferably the amount is at least 5%. Even more preferably the amount is at least 10%. Most preferably 30% or less.

Power conversion efficiency is measured by monochromatic or white light illumination. Monochromatic light power conversion efficiency is not sufficient to characterize solar cells, but is a measure of device performance at specific wavelengths. This is useful when, for example, small electronic components that operate under ambient room lighting and when the device is to be used under conditions other than the sun, such as watches or power meters for laser irradiation. Standard methods for characterizing solar cells are carried out under Air Mass 1.5 or A.M 1.5 conditions (1.5 times the emission spectrum of the sun after traveling through the Earth's atmosphere). Such solar illumination is generally simulated virtually, which is standard A.M. This is because conditions are difficult to obtain stably due to non-ideal climatic conditions.

The terms and expressions used herein are for the purpose of description and should not be regarded as limiting, and the use of such terms and expressions does not exclude a significant term or a part of the features shown, and various modifications within the claims of the present invention It should be understood that it is possible. Also, one or more features of an embodiment of the present invention may be combined with one or more features of another embodiment of the present invention without departing from the scope of the present invention.

All patents, patent applications, and references mentioned herein are incorporated herein by reference.

Claims (179)

A thin film comprising semiconducting conjugate polymer embedded with at least 5 wt.% Semiconductor-nanocrystals, wherein at least a portion of the semiconductor-nanocrystals have an aspect ratio of greater than about 2. 3. The thin film of claim 1, wherein at least some of the semiconductor-nanocrystals have an aspect ratio of greater than about 5. 5. The thin film of claim 1, wherein at least some of the semiconductor-nanocrystals have an aspect ratio of greater than about 10. The thin film of claim 1, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of about 5 to about 50. The thin film of claim 1, wherein at least some of the semiconductor-nanocrystals have an aspect ratio of about 2 to about 10. The thin film of claim 1, wherein the semiconducting conjugate polymer has from about 5 to about 99 weight percent of embedded semiconductor-nanocrystals. The thin film of claim 1, wherein the semiconducting conjugate polymer has about 20 to about 95 weight percent of embedded semiconductor-nanocrystals. The thin film of claim 1, wherein the semiconducting conjugate polymer has about 50 to about 95 weight percent of embedded semiconductor-nanocrystals. The thin film of claim 1, wherein the semiconducting conjugate polymer has about 90% of the embedded semiconductor-nanocrystals. The method of claim 1 wherein the semiconducting conjugate polymer is trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluorene, polyaromatic Thin films selected from amines, poly (thienylene-vinylene) and soluble derivatives thereof. The process of claim 10 from (poly (2-methoxy-5- (2'-ethylhexyloxy) p-phenylenevinylene) (MEH-PPV) and poly (3-hexylthiophene) (P3HT) Thin film chosen. The thin film of claim 1, wherein the semiconductor-nanocrystal comprises a rod having a length greater than about 20 nm. The thin film of claim 1, wherein the semiconductor-nanocrystal comprises a rod having a length of about 20 nm to about 200 nm. The thin film of claim 13, wherein the semiconductor-nanocrystal comprises a rod having a length of about 60 nm to about 110 nm. The thin film of claim 1, wherein the semiconductor-nanocrystal comprises a rod that is about 7 nm x 60 nm. The thin film of claim 1, wherein the semiconductor-nanocrystal comprises a semiconductor selected from the group consisting of Group II-VI, Group III-V, Group IV semiconductors, and tertiary chalcoprites. The thin film of claim 16, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe, CdTe, InP, GaAs, CuInS 2, CuInSe 2, AlGaAs, InGaAs, Ge, and Si. The thin film of claim 1, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe and CdTe. The thin film of claim 1, wherein a portion of the semiconductor-nanocrystal is a side chain nanocrystal. 20. The thin film of claim 19 wherein the portion of the side chain nanocrystals has more than two arms, wherein the arms are not the same length. The thin film of claim 19, wherein the side chain nanocrystals do not have the same shape. 20. The thin film of claim 19 wherein the side chain nanocrystals have four arms and have tetrahedral symmetry. The thin film of claim 22 wherein the side chain nanocrystals are CdSe or CdTe and are embedded in an amount of about 90% by weight. The thin film of claim 1, wherein the film has a thickness of about 100 nm to about 350 nm. The thin film of claim 22 wherein the film has a thickness of about 200 nm. A photovoltaic device comprising the thin film of claim 1. 27. The photovoltaic device of claim 26, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of greater than about 5. 27. The photovoltaic device of claim 26, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of greater than about 10. 27. The photovoltaic device of claim 26, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of about 5 to about 50. 27. The photovoltaic device of claim 26, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of about 2 to about 10. 27. The photovoltaic device of claim 26, wherein the semiconducting conjugate polymer has about 5 to about 99 weight percent of embedded semiconductor-nanocrystals. 27. The photovoltaic device of claim 26, wherein the semiconducting conjugate polymer has about 20 to about 95 weight percent of embedded semiconductor-nanocrystals. 27. The photovoltaic device of claim 26, wherein the semiconducting conjugate polymer has about 50 to about 95 weight percent of the embedded semiconductor-nanocrystal. 27. The photovoltaic device of claim 26, wherein the semiconducting conjugate polymer has about 90% of embedded semiconductor-nanocrystals. 27. The method of claim 26, wherein the semiconducting conjugate polymer is trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluorene, polyaromatic A photovoltaic device selected from amines, poly (thienylene-vinylene) and soluble derivatives thereof. The method of claim 35, wherein the poly (2-methoxy-5- (2'-ethylhexyloxy) p-phenylenevinylene) (MEH-PPV) and poly (3-hexylthiophene) (P3HT) Photovoltaic device chosen. 27. The photovoltaic device of claim 26, wherein the semiconductor-nanocrystal comprises a rod having a length greater than about 20 nm. 27. The photovoltaic device of claim 26, wherein the semiconductor-nanocrystal comprises a rod having a length of about 20 nm to about 200 nm. The photovoltaic device of claim 38, wherein the semiconductor-nanocrystal comprises a rod having a length of about 60 nm to about 110 nm. 27. The photovoltaic device of claim 26, wherein the semiconductor-nanocrystal comprises a rod about 7 nm x 60 nm. 27. The photovoltaic device of claim 26, wherein the semiconductor-nanocrystal comprises a semiconductor selected from the group consisting of Group II-VI, Group III-V, Group IV semiconductors, and tertiary chalcoprites. 42. The photovoltaic device of claim 41, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe, CdTe, InP, GaAs, CuInS2, CuInSe2, AlGaAs, InGaAs, Ge, and Si. 27. The photovoltaic device of claim 26, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe and CdTe. 27. The photovoltaic device of claim 26, wherein a portion of the semiconductor-nanocrystal is a side chain nanocrystal. 45. The photovoltaic device of claim 44, wherein the portion of the side chain nanocrystals has more than two arms, wherein the arms are not the same length. 45. The photovoltaic device of claim 44, wherein the side chain nanocrystals do not have the same shape. 45. The photovoltaic device of claim 44, wherein the side chain nanocrystals have four arms and have tetrahedral symmetry. The photovoltaic device of claim 47, wherein the side chain nanocrystals are CdSe or CdTe and are embedded in an amount of about 90% by weight. 27. The photovoltaic device of claim 26, wherein the film has a thickness of about 100 nm to about 350 nm. The photovoltaic device of claim 49, wherein the film has a thickness of about 200 nm. The surfactant coated semiconductor-nanocrystals are washed one or more times with a solvent, The washed semiconductor-nanocrystal and semiconducting polymer are dissolved together in a binary solvent mixture, and A method of making a polymer thin film, comprising depositing the mixture. 52. The method of claim 51, wherein at least a portion of the semiconductor-nanocrystals have an aspect ratio of greater than about 2. 52. The method of claim 51, wherein at least a portion of the semiconductor-nanocrystals have an aspect ratio of greater than about 5. 52. The method of claim 51, wherein at least a portion of the semiconductor-nanocrystals have an aspect ratio of greater than about 10. 53. The method of claim 51, wherein at least a portion of the semiconductor-nanocrystals have an aspect ratio of about 5 to about 50. 52. The method of claim 51, wherein at least a portion of the semiconductor-nanocrystals have an aspect ratio of about 2 to about 10. 52. The method of claim 51, wherein the semiconducting conjugate polymer has about 5 to about 99 weight percent of embedded semiconductor-nanocrystals. 52. The method of claim 51, wherein the semiconducting conjugate polymer has about 20 to about 95 weight percent of the embedded semiconductor-nanocrystals. 53. The method of claim 51, wherein the semiconducting conjugate polymer has about 50 to about 95 weight percent of the embedded semiconductor-nanocrystals. The method of claim 51, wherein the semiconducting conjugate polymer has about 90% of the embedded semiconductor-nanocrystals. 52. The method of claim 51, wherein the semiconducting conjugate polymer is trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluorene, polyaromatic A process for producing a polymer thin film selected from amines, poly (thienylene-vinylene) and soluble derivatives thereof. 62. The composition of claim 61 from (poly (2-methoxy-5- (2'-ethylhexyloxy) p-phenylenevinylene) (MEH-PPV) and poly (3-hexylthiophene) (P3HT) Method for producing the polymer thin film selected. The method of claim 51, wherein the semiconductor-nanocrystal comprises a rod having a length greater than about 20 nm. The method of claim 51, wherein the semiconductor-nanocrystal comprises a rod having a length of about 20 nm to about 200 nm. 65. The method of claim 64, wherein the semiconductor-nanocrystal comprises a rod having a length of about 60 nm to about 110 nm. The method of claim 51, wherein the semiconductor-nanocrystal comprises a rod about 7 nm x 60 nm. The method of claim 51, wherein the semiconductor-nanocrystal comprises a semiconductor selected from the group consisting of Group II-VI, Group III-V, Group IV semiconductors, and tertiary chalcoprite. 67. The method of claim 67, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe, CdTe, InP, GaAs, CuInS2, CuInSe2, AlGaAs, InGaAs, Ge, and Si. The method of claim 51, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe and CdTe. The method of claim 51, wherein a portion of the semiconductor-nanocrystal is a side chain nanocrystal. The method of claim 70, wherein the portion of the side chain nanocrystals has more than two arms, wherein the arms are not the same length. The method of claim 70, wherein the side chain nanocrystals do not have the same shape. The method of claim 70, wherein the side chain nanocrystals have four arms and have tetrahedral symmetry. 74. The method of claim 73, wherein the side chain nanocrystals are CdSe or CdTe and are embedded in an amount of about 90% by weight. The method of claim 51, wherein the film has a thickness of about 100 nm to about 350 nm. 76. The method of claim 75, wherein the film has a thickness of about 200 nm. The compound of claim 51, wherein at least one of the binary solvents is selected from the group consisting of pyridine, chloroform, toluene, xylene, hexane, water, dichlorobenzene, methylene chloride, alkylamine, butanol, methanol and isopropane, wherein the alkyl chain is A method for producing a polymer thin film having 2 to 20 carbon sources in a branched or unbranched chain. The method of claim 51, wherein the concentration of the binary solvent mixture is about 1 to about 15 volume percent. 79. The method of claim 78, wherein the concentration of the binary solvent mixture is about 4 to about 12 volume percent. 80. The method of claim 79, wherein the concentration of the binary solvent mixture is about 8% by volume. 78. The method of claim 77, wherein the binary solvent mixture comprises pyridine in chloroform. 52. The method of claim 51, wherein the deposited thin film is heated at a temperature of about 60 ° C to about 200 ° C. 83. The method of claim 82, wherein the deposited thin film is heated at a temperature of about 80 ° C to about 130 ° C. 84. The method of claim 83, wherein the deposited thin film is heated at a temperature of about 120 ° C. Dispersing the semiconductor-nanocrystal in the semiconducting conjugate polymer to obtain a polymer-nanocrystal composite, Depositing a thin film of the composite such that the nanocrystals are embedded in the polymer at least 5% by weight, At least a portion of the semiconductor-nanocrystal has an aspect ratio of greater than two. 86. The method of claim 85, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio greater than about 5. 86. The method of claim 85, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio greater than about 10. 86. The method of claim 85, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of about 5 to about 50. 86. The method of claim 85, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of about 2 to about 10. 86. The method of claim 85, wherein the semiconducting conjugate polymer has about 5 to about 99 weight percent of embedded semiconductor-nanocrystals. 86. The method of claim 85, wherein the semiconducting conjugate polymer has about 20 to about 95 weight percent of the embedded semiconductor-nanocrystal. 86. The method of claim 85, wherein the semiconducting conjugate polymer has about 50 to about 95 weight percent of the embedded semiconductor-nanocrystal. 86. The method of claim 85, wherein the semiconducting conjugate polymer has about 90% of the embedded semiconductor-nanocrystals. 86. The method of claim 85, wherein the semiconducting conjugate polymer is trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluorene, polyaromatic A process for producing a photoactive thin film selected from amines, poly (thienylene-vinylene) and soluble derivatives thereof. 95. The method of claim 94, wherein the poly (2-methoxy-5- (2'-ethylhexyloxy) p-phenylenevinylene) (MEH-PPV) and poly (3-hexylthiophene) (P3HT) Method for producing a photoactive thin film selected. 86. The method of claim 85, wherein the semiconductor-nanocrystal comprises a rod having a length greater than about 20 nm. 86. The method of claim 85, wherein the semiconductor-nanocrystal comprises a rod having a length of about 20 nm to about 200 nm. 98. The method of claim 97, wherein the semiconductor-nanocrystal comprises a rod having a length of about 60 nm to about 110 nm. 86. The method of claim 85, wherein said semiconductor-nanocrystal comprises a rod about 7 nm x 60 nm. 86. The method of claim 85, wherein the semiconductor-nanocrystal comprises a semiconductor selected from the group consisting of Group II-VI, Group III-V, Group IV semiconductors, and tertiary chalcopyrite. 101. The method of claim 100, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe, CdTe, InP, GaAs, CuInS2, CuInSe2, AlGaAs, InGaAs, Ge, and Si. 86. The method of claim 85, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe and CdTe. 86. The method of claim 85, wherein a portion of the semiconductor-nanocrystal is a side chain nanocrystal. 107. The method of claim 103, wherein the portion of the side chain nanocrystals has more than two arms, wherein the arms are not the same length. 107. The method of claim 103, wherein the side chain nanocrystals do not have the same shape. 107. The method of claim 103, wherein the side chain nanocrystals have four arms and have tetrahedral symmetry. 107. The method of claim 106, wherein the side chain nanocrystals are CdSe or CdTe and are embedded in an amount of about 90% by weight. 86. The method of claim 85, wherein the film has a thickness of about 100 nm to about 350 nm. 109. The method of claim 108, wherein the film has a thickness of about 200 nm. 86. The method of claim 85, wherein the semiconductor-nanocrystal and the semiconducting polymer are dissolved in a binary solvent mixture, The binary solvent mixture comprises at least one solvent selected from the group consisting of pyridine, chloroform, toluene, xylene, hexane, water, dichlorobenzene, methylene chloride, alkylamine, butanol, methanol and isopropane, wherein the alkyl chain is A method for producing a photoactive thin film having 2 to 20 carbon atoms in a branched or unbranched chain. 111. The method of claim 110, wherein the concentration of the binary solvent mixture is about 1 to about 15 volume percent. 112. The method of claim 111, wherein the concentration of the binary solvent mixture is about 4 to about 12 volume percent. 118. The method of claim 112, wherein the concentration of the binary solvent mixture is about 8% by volume. 119. The method of claim 110, wherein the binary solvent mixture comprises pyridine in chloroform. 86. The method of claim 85, wherein the deposited thin film is heated at a temperature of about 60 ° C to about 200 ° C. 86. The method of claim 85, wherein the deposited thin film is heated at a temperature of about 80 ° C to about 130 ° C. 86. The method of claim 85, wherein the deposited thin film is heated at a temperature of about 120 ° C. A photovoltaic device comprising a conjugated conductive polymer layer in which semiconductor-nanocrystals are dispersed, and having a power conversion efficiency of greater than 1% in AM 1.5 global illumination. 118. The photovoltaic device of claim 118, wherein the device has a power conversion efficiency of greater than 5%. 119. The photovoltaic device of claim 119, wherein the device has a power conversion efficiency of greater than 10%. 118. The photovoltaic device of claim 118, wherein the device has a power conversion efficiency of about 1% to about 30%. 126. The photovoltaic device of claim 121, wherein the device has a power conversion efficiency of about 2% to about 30%. 123. The photovoltaic device of claim 122, wherein the device has a power conversion efficiency of about 5% to about 15%. 118. The photovoltaic device of claim 118, wherein the device has a power conversion efficiency of about 1.7%. 118. The photovoltaic device of claim 118, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of greater than about 5. 118. The photovoltaic device of claim 118, wherein at least some of the semiconductor-nanocrystals have an aspect ratio greater than about 10. 118. The photovoltaic device of claim 118, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of about 5 to about 50. 118. The photovoltaic device of claim 118, wherein at least some of the semiconductor-nanocrystals have an aspect ratio of about 2 to about 10. 118. The photovoltaic device of claim 118, wherein the semiconducting conjugate polymer has from about 5 to about 99 weight percent of embedded semiconductor-nanocrystals. 118. The photovoltaic device of claim 118, wherein the semiconducting conjugate polymer has about 20 to about 95 weight percent of the embedded semiconductor-nanocrystal. 118. The photovoltaic device of claim 118, wherein the semiconducting conjugate polymer has about 50 to about 95 weight percent of the embedded semiconductor-nanocrystal. 118. The photovoltaic device of claim 118, wherein the semiconducting conjugate polymer has about 90% of embedded semiconductor-nanocrystals. 119. The semiconducting conjugate polymer of claim 118 comprising trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluorene, polyaromatic A photovoltaic device selected from amines, poly (thienylene-vinylene) and soluble derivatives thereof. 133. The composition of claim 133, which is obtained from (poly (2-methoxy-5- (2'-ethylhexyloxy) p-phenylenevinylene) (MEH-PPV) and poly (3-hexylthiophene) (P3HT) Photovoltaic device chosen. 118. The photovoltaic device of claim 118, wherein the semiconductor-nanocrystal comprises a rod having a length greater than about 20 nm. 118. The photovoltaic device of claim 118, wherein the semiconductor-nanocrystal comprises a rod having a length of about 20 nm to about 200 nm. 137. The photovoltaic device of claim 136, wherein the semiconductor-nanocrystal comprises a rod having a length of about 60 nm to about 110 nm. 118. The photovoltaic device of claim 118, wherein the semiconductor-nanocrystal comprises a rod about 7 nm x 60 nm. 118. The photovoltaic device of claim 118, wherein the semiconductor-nanocrystal comprises a semiconductor selected from the group consisting of Group II-VI, Group III-V, Group IV semiconductors, and tertiary chalcoprites. 141. The photovoltaic device of claim 139, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe, CdTe, InP, GaAs, CuInS2, CuInSe2, AlGaAs, InGaAs, Ge, and Si. 118. The photovoltaic device of claim 118, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe and CdTe. 118. The photovoltaic device of claim 118, wherein a portion of the semiconductor-nanocrystal is a side chain nanocrystal. 146. The photovoltaic device of claim 142, wherein the portion of the side chain nanocrystals has more than two arms, wherein the arms are not the same length. 143. The photovoltaic device of claim 142, wherein the side chain nanocrystals do not have the same shape. 145. The photovoltaic device of claim 142, wherein the side chain nanocrystals have four arms and have tetrahedral symmetry. 145. The photovoltaic device of claim 145, wherein the side chain nanocrystals are CdSe or CdTe and are embedded in an amount of about 90% by weight. 118. The photovoltaic device of claim 118, wherein the film has a thickness of about 100 nm to about 350 nm. 148. The photovoltaic device of claim 147, wherein the film has a thickness of about 200 nm. First planar electrode, A thin film comprising a semiconducting conjugate polymer embedded with a semiconductor-nanocrystal and deposited on a first planar electrode, A second electrode opposite the first electrode, and A photovoltaic device comprising a hole injection layer disposed between the thin film polymer layer and the first planar electrode. 149. The photovoltaic device of claim 149, wherein the hole injection layer comprises PEDOT: PSS. 149. The photovoltaic device of claim 149, wherein the first electrode comprises ITO and the second electrode comprises Al. 149. The photovoltaic device of claim 149, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of greater than about 5. 149. The photovoltaic device of claim 149, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of greater than about 10. 149. The photovoltaic device of claim 149, wherein at least some of the semiconductor-nanocrystals have an aspect ratio of about 5 to about 50. 149. The photovoltaic device of claim 149, wherein at least a portion of the semiconductor-nanocrystal has an aspect ratio of about 2 to about 10. 149. The photovoltaic device of claim 149, wherein the semiconducting conjugate polymer has about 5 to about 99 weight percent of the embedded semiconductor-nanocrystal. 149. The photovoltaic device of claim 149, wherein the semiconducting conjugate polymer has about 20 to about 95 weight percent of the embedded semiconductor-nanocrystal. 149. The photovoltaic device of claim 149, wherein the semiconducting conjugate polymer has about 50 to about 95 weight percent of the embedded semiconductor-nanocrystal. 149. The photovoltaic device of claim 149, wherein the semiconducting conjugate polymer has about 90% of embedded semiconductor-nanocrystals. 149. The semiconducting conjugate polymer of claim 149 comprising trans-polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene) and poly (p-phenylene-vinylene), polyfluorene, polyaromatic A photovoltaic device selected from amines, poly (thienylene-vinylene) and soluble derivatives thereof. 161. The process of claim 160 from (poly (2-methoxy-5- (2'-ethylhexyloxy) p-phenylenevinylene) (MEH-PPV) and poly (3-hexylthiophene) (P3HT) Photovoltaic device chosen. 149. The photovoltaic device of claim 149, wherein the semiconductor-nanocrystal comprises a rod having a length greater than about 50 nm. 149. The photovoltaic device of claim 149, wherein the semiconductor-nanocrystal comprises a rod having a length of about 20 nm to about 200 nm. 163. The photovoltaic device of claim 163, wherein the semiconductor-nanocrystal comprises a rod having a length of about 60 nm to about 110 nm. 149. The photovoltaic device of claim 149, wherein the semiconductor-nanocrystal comprises a rod about 7 nm x 60 nm. 149. The photovoltaic device of claim 149, wherein the semiconductor-nanocrystal comprises a semiconductor selected from the group consisting of Group II-VI, Group III-V, Group IV semiconductors, and tertiary chalcopyrite. 167. The photovoltaic device of claim 166, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe, CdTe, InP, GaAs, CuInS2, CuInSe2, AlGaAs, InGaAs, Ge, and Si. 149. The photovoltaic device of claim 149, wherein the semiconductor-nanocrystal is selected from the group consisting of CdSe and CdTe. 149. The photovoltaic device of claim 149, wherein a portion of the semiconductor-nanocrystal is a side chain nanocrystal. 172. The photovoltaic device of claim 169, wherein the portion of the side chain nanocrystals has more than two arms, wherein the arms are not the same length. 172. The photovoltaic device of claim 169, wherein the side chain nanocrystals do not have the same shape. 172. The photovoltaic device of claim 169, wherein the side chain nanocrystals have four arms and have tetrahedral symmetry. 172. The photovoltaic device of claim 172, wherein the side chain nanocrystals are CdSe or CdTe and are embedded in an amount of about 90% by weight. 158. The photovoltaic device of claim 149, wherein the film has a thickness of about 100 nm to about 350 nm. 174. The photovoltaic device of claim 174, wherein the film has a thickness of about 200 nm. A film comprising a polymer in which nanocrystals are embedded. (a) washing the nanocrystals at least once with a solvent; (b) dissolving the washed nanocrystals and polymer in a solvent to obtain a mixture; And (c) at least one of the steps of depositing the mixture. A photovoltaic device comprising a polymer layer in which nanocrystals are dispersed. First electrode, A film comprising a polymer on the first electrode, and A photovoltaic device comprising a second electrode.