MX2007001690A - Organic photosensitive devices - Google Patents

Abstract

The present invention generally relates to organic photosensitive optoelectronic devices. More specifically, it is directed to organic photosensitive optoelectronic devices having a photoactive organic region containing encapsulated nanoparticles that exhibit plasmon resonances. An enhancement of the incident optical field is achieved via surface plasmon polariton resonances. This enhancement increases the absorption of incident light, leading to a more efficient device.

Description

ORGANIC PHOTOSENSIBLE DEVICES FIELD OF THE INVENTION The present invention relates generally to organic photosensitive optoelectronic devices, More specifically, it relates to organic photosensitive optoelectronic devices having nanoparticles.

BACKGROUND OF THE INVENTION Optoelectronic devices are based on the optical and electronic properties of materials to produce or detect electromagnetic radiation in electronic form, or to generate electricity from the electromagnetic radiation of the environment.

Photosensitive optoelectronic devices convert electromagnetic radiation into electricity. Solar cells, also called photovoltaic (PV) devices, are a type of photosensitive optoelectronic device used specifically to generate electrical energy. PV devices, which can generate electrical power from light sources other than sunlight, can be used to drive loads that consume energy to provide, for example, lighting, heating or to power circuits or electronic devices such as calculators, radios, computers or remote communication or monitoring equipment. These power generation applications often also include charging batteries or other energy storage devices, so operation can continue when direct sunlight is not available, or from other sources, or balance the power output of the power source. PV device, with specific application requirements. As used herein, the term "resistive load" refers to any circuit, device, equipment or system that consumes or stores energy.

Another type of photosensitive optoelectronic device is a photoconductive cell. In this function, the signal detection circuit monitors the resistance of the device to detect changes due to the absorption of light.

Another type of photosensitive optoelectronic device is a photodetector. In operation, a photodetector is used in conjunction with a current sensing circuit which measures the current generated when the photodetector is exposed to electromagnetic radiation, and may have an applied bias voltage. Hereby, a detection circuit capable of providing a bias voltage to a photodetector and measure the electronic response of the photodetector to electromagnetic radiation. These three classes of photosensitive optoelectronic devices can be characterized according to the presence of a rectifying junction, as defined below, and also according to whether the device is operated with an external applied voltage, also called polarization or polarization voltage. A photoconducting cell lacks a rectifier junction, and it usually operates with a polarization. A PV device has at least one rectifying junction and is operated without polarization. A photodetector has at least one rectifier junction, and usually, but not always, one operates with a polarization. As a general rule, a photovoltaic cell provides power to a circuit, device or equipment, but does not provide a signal or current to control the detection circuit, or the information output of the detection circuit. In contrast, a photodetector or photoconductor provides a signal or current to control the detection circuit, or the information output of the detection circuit, but does not provide power to the circuit, device or equipment.

Traditionally, photosensitive optoelectronic devices of numerous inorganic semiconductors have been constructed, for example, crystalline, polycrystalline and amorphous silicon, arsenide of gallium, cadmium telluride and others. In the present, the term "semiconductor" denotes materials that can conduct electricity when the charge carriers are induced by thermal or electromagnetic excitation. In general, the term "photoconductor" refers to the process by which radiant energy is absorbed. electromagnetic, and thus becomes the excitation energy of electric charge carriers so that the carriers can conduct, ie transport, the electric charge in a material. The terms "photoconductor" and "photoconductive material" are used herein to refer to semiconductor materials that are chosen because of their property of absorbing electromagnetic radiation to generate electric charge carriers.

PV devices can be characterized by the efficiency with which they can convert incident solar energy into useful electrical energy. Devices that use crystalline or amorphous silicon dominate commercial applications, and some achieve efficiencies of 23% or higher. However, efficient crystalline-based devices, especially large-area ones, are difficult and burdensome to produce, due to the problems inherent in the production of large crystals without significant defects in efficiency degradation. On the other hand, amorphous silicon devices with high efficiency they still have stability problems. The current commercially available amorphous silicon cells have efficiencies stabilized between 4 and 8%. The most recent efforts have focused attention on the use of organic photovoltaic cells, in order to obtain acceptable photovoltaic conversion efficiencies with economic production costs.

PV devices can be optimized for maximum power generation under standard lighting conditions (ie, Standard Test Conditions that are 1,000 W / m2, AM 1.5 for spectral lighting), for the maximum production of photoelectric current per the photoelectric voltage. The energy conversion efficiency of these cells under standard lighting conditions depends on the following three parameters: 1) the zero-polarized current, ie the short-circuit current ISc, 2) the photoelectric voltage in open-circuit conditions, is say, the open circuit voltage V0c, and 3) the fill factor ff.

PV devices produce a photogenerated current when they are connected through a load and are irradiated by light. When irradiated with infinite charge, a PV device generates its maximum possible voltage, V of open circuit, or V0c- When it radiates with its electrical contacts in short, a PV device generates its maximum possible current, short circuit I, or Isc. When in reality it is used to generate energy, a PV device is connected to a finite resistance load, and the energy output is given by the product of current and voltage, I x V. The maximum total energy generated by a device PV is inherently capable of exceeding the product, Isc x V0c. When the load value is optimized to extract the maximum energy, the current and the test have the values Imax and Vmax, respectively.

A merit figure for PV devices is the fill factor ff, defined as: ff =. { Imax Vmax} /. { ISC Voc} (1) where ff is always less than 1, since Isc and voc are never achieved at the same time in actual use. However, as ff approaches 1, the device has less resistance in series or internal, so it provides a greater percentage of the product of Isc and V0c to the load, under optimal conditions. When Pj.nc is the energy incident on the device, can the energy efficiency of the device be calculated? by: When the electromagnetic radiation of an appropriate energy hits an organic semiconductor material, for example a Organic molecular crystal material (OMC), or a polymer, a photon can be absorbed to produce an excited molecular state. This is represented symbolically as S0 + hv = > . S0 *. Here S0 and S0 * denote the molecular states of earth and excited, respectively. This absorption of energy is associated with the promotion of an electron from a bound state at the HOMO energy level, which can be a n-link, with the LUMO energy level, which can be a n * link, or equivalently, the promotion from a gap from the LUMO energy level to the HOMO energy level. In thin film organic photoconductors, in general, it is believed that the generated molecular state is an exciton, that is, a pair of electron and gap in the bound state, that are transported as quasiparticles. The excitons can have an appreciable life time before the geminated recombination, which refers to the process of recombination of the original electron and hole with each other, as opposed to the recombination with holes or electrons of other pairs. In order to produce a photoelectric current, the electron-hole pair separates, generally in a donor-acceptor interface between two dissimilar organic thin films in contact. If the charges do not separate, they can recombine in a process of recombination geminada, also called tempered, either radioactive, by the emission of light of a lower energy to incident light, or non-radioactive, by heat production. Any of these results is undesirable in a photosensitive optoelectronic device. The electric fields or inhomogeneities in a contact can cause the tempering of an exciton instead of dissociating in the donor-acceptor interface, which results in a lack of net contribution to the current. Consequently, it is desirable to keep the photogenerated excitons away from the contacts. This has the effect of limiting the diffusion of the excitons to the region near the junction, whereby the associated electric field has a greater opportunity to separate the charge carriers released by the dissociation of the excitons near the junction.

In order to produce internally generated electric fields that occupy a substantial volume, the usual method consists of juxtaposing two layers of material with properly chosen conductive properties, especially with respect to their distribution of molecular quantum energy states. The interface of these two materials is called photovoltaic heterojunction. In the traditional theory of semiconductors, the materials for forming PV heterojunctions have generally been indicated as n or p type. Here the type n denotes that the type of major carrier is the electron. This could be visualized as the material with many electrons in relatively free energy states. The type p denotes that the type of major carrier is the hole. This material has many voids in relatively free energy states. The type of background, that is, the concentration of the non-photogenerated majority carrier depends mainly on an involuntary interruption due to defects or impurities. The type and concentration of the impurities determine the value or level of Fermi energy in the gap between the maximum level of occupied molecular orbital energy (HOMO) and the minimum level of unoccupied molecular orbital energy (LÜMO), called the HOMO- LUMO. The Fermi energy characterizes the statistical occupation of states of molecular quantum energy denoted by the energy value for which the probability of occupation is equal to half. A Fermi energy close to the LUMO energy level indicates that the electrons are the predominant carrier. A Fermi energy close to the HOMO energy level indicates that the gaps are the predominant carrier. Consequently, the Fermi energy is a main characterization property of traditional semiconductors, and the prototypical PV heterojunction has traditionally been the p-n interface.

The term "rectifier" denotes, among others, that an interface has an asymmetric driving characteristic, that is, the interface supports the electronic load transport, preference in one direction. Rectification is normally associated with an internal electric field that occurs in the heterojunction between appropriately selected materials.

As used herein, and would ordinarily be understood by one skilled in the art, a first energy level of "Greater occupied molecular orbital" (HOMO) or "Lower unoccupied molecular orbital" (LUMO) is "greater than" or "greater than" a second level of energy HOMO or LUMO, if the first energy level is closer to the level of vacuum energy. Since the ionization potentials (IP) are measured as negative energy with respect to a vacuum level, a higher energy level HOMO corresponds to an IP with a lower absolute value (a less negative IP). Similarly, a higher level of LUMO energy corresponds to an electronic affinity (AE) with a lower absolute value (a less negative AE). In a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A "higher" energy level HOMO or LUMO appears closer to the top of said diagram than a "lower" energy level HOMO or LUMO.

In the context of organic materials, the terms "donor" and "acceptor" refer to the relative positions of HOMO and LUMO energy levels of two organic materials in contact, but different. This contrasts with the use of these thermals in the inorganic context, where "donor" and "acceptor" can refer to types of switches that can be used to create inorganic layers of type n and p, respectively. In the organic context, if the LUMO energy level of a material in contact with another is lower, then that material is an acceptor. Otherwise, it is a donor. In the absence of external polarization, it is energetically favorable that the electrons of a donor-acceptor link move to the interior of the acceptor material, and that the voids move towards the interior of the donor material.

A significant property of organic semiconductors is the mobility of the carrier. Mobility measures the ease with which a load carrier can travel through a conductive material in response to an electric field. In the context of organic photosensitive devices, a layer that includes a material that is preferably driven by electrons, due to the high, mobility of the electrons, can be referred to as the electron transport layer, or ETL. A layer that includes a material that conducts preferably through voids, due to the high mobility of voids, can be referred to as a void transport layer, or HTL. Preferably, but not necessarily, an acceptor material is an ETL, and a donor material is an HTL. Conventional inorganic semiconductor PV cells employ a p-n junction to establish an internal field. The first thin organic film cells, such as those reported by Tang, Appl. Phys Lett. 48, 183 (1986), contain a heterojunction analogous to that used in a conventional inorganic PV cell. However, it is now recognized that, in addition to the establishment of a p-n type union, the compensation of the energy level of the heterojunction also plays an important role.

It is believed that the compensation of the energy level of the organic D-A heterojunction is important for the operation of organic PV devices, due to the fundamental nature of the photogeneration process in organic materials. After the optical excitation of an organic material, localized Frenkel excitons or charge transfer are generated. For the detection or generation of electric current to occur, the excitons bound in their electrons and constituent holes must be dissociated. This process can be induced by an internal electric field, but the efficiency of the electric fields that are usually found in organic devices (F ~ 106 V / cm) is low. The most efficient dissociation of excitons in Organic materials occur at the donor-acceptor interface (D-A). In said interface, the donor material with low ionization potential forms a heterojunction with an acceptor material with high electron affinity. According to the alignment of the energy levels of the donor and acceptor materials, the excitation of the exciton can be energetically favorable in this interface, which leads to a polaron of free electrons in the acceptor material, and a polaron of free holes in the material donor. Organic PV cells have many potential advantages, compared to traditional, silicon-based devices. Organic PV cells are lightweight, use inexpensive materials and can be deposited on low cost substrates, such as flexible plastic sheets. However, some organic PV devices in general have relatively low external quantum efficiency, in the order of 1%, or less. In part, it is believed that this is due to the second-order nature of the intrinsic photoconductive process. That is, the generation of carriers requires that they be generated; diffuse and ionize or join excitons. Is there an efficiency? associated with each of these processes. Sub-indices can be used as follows: P for energy efficiency, EXT for external quantum efficiency, A for photon absorption, ED for exciton diffusion, CC for charge gathering and INT for internal quantum efficiency. With this notation: ?? ~ ???? = ?? * ?? 0 r \ cc The diffusion length (LD) of an exciton is generally much lower (LD 50Á) than the optical absorption length (-500 Á), so a compensation is required between the use of a fast cell, and consequently resistant, with multiple or highly folded interfaces, or a thin cell with poor optical absorption efficiency.

In general, when light is absorbed to form an exciton in a thin organic film, a singlet exciton is formed. Because of the intersystem crosslinking mechanism, the singlet exciton can degrade to triplet exciton. Energy is lost in this process, which results in lower efficiency for the device. If it were not for the loss of energy due to intersystem cross-linking, it would be desirable to use materials that generate triplet excitons, since in general the triplet excitons have a longer life, and therefore a longer diffusion length than the singlet excitons.

By the use of organometallic material in the photoactive region, the devices of the present invention can efficiently use triplet excitons. It is believed that the singlet-triplet mixture can be so strong for the compounds organometallic that the absorptions involve the excitation from the singlet grounding states directly to the triplet excited states, eliminating the losses associated with the conversion from the excited singlet state to the triplet excited state. The longer life and longer diffusion length of the triplet excitons, compared to the singlet excitons, may allow the use of a thicker photoactive region, since triplet excitons may diffuse a greater distance to reach the donor-acceptor heterojunction, without sacrificing device efficiency.

Extract of the invention The present invention relates in general to organic photosensitive optoelectronic devices. More specifically, it relates to organic photosensitive optoelectronic devices with a photoactive organic region containing encapsulated nanoparticles exhibiting plasmon resonances. An increase in the incident optical field is achieved through resonances of surface plasmon polaritons. This increase increases the absorption of incident light, which leads to a more efficient device.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an organic PV device.

Figure 2 shows a schematic and electronic transmission micrograph of a cross section of a tandem organic photovoltaic cell.

Figure 3 shows the real (e?) And imaginary dielectric functions. { e2) for Ag, calculated as photon energy functions.

Figure 4 shows the simulated surface plasmon polariton resonance wavelength (SPP) for a spherical Ag particle of 5nm, as a function of the dielectric function em of the embedding medium.

Figure 5 shows the resonance wavelength of simulated SPP versus the axial ratio for an Ag particle in vacuum.

Figure 6 shows the absorbance spectra for Ag of 1 nm (dotted curve), CuPc of 7 nm (dashed curve) and film of CuMP of 7 nm in Ag of 1 nm (full curve) deposited on quartz substrates.

Figure 7 shows a contour map of the calculated intensity increase (I / Jo) of a chain of Ag particles with a diameter of 2R = 5 nm and a center-to-center spacing d = 10 nm a? = 690 nm.

Figure 8 shows the average calculated intensity increase (T / J0) at the surface of an Ag particle of 5 mm diameter as a function of the wavelength for the different incrustation media.

Figure 9 shows the absorption (dotted line) and the average intensity increase. { I / I0) (full lines) simulated on the surface of a spherical and elliptical particle of 5 nm in diameter (axial ratio of 0.5).

Figure 10 shows (a) the increase of 'maximum calculated intensity (J / I0) at the center of a chain of particle IDs versus d; and (b) the peak wavelength of surface plasmon polariton (SPP) simulated as a function of the surface to surface spacing d, of a particle ID chain. spherical 5 nm diameter (full line) and elliptical particles (dotted lines).

Figure 11 shows the intensity increase (I / I0) calculated on the axis of a chain of IDs embedded in a medium n = 2 + 0.5 i, versus the wavelength of the medium.

Figure 12 shows the measured absorbance A, of variable thicknesses of CuPc on quartz at a wavelength of? = 690 nm with (triangles) and without (squares) a layer of Ag groups of 10 Á. The adjustments (whole curves) to the data are described in the text.

Figure 13 shows the measured difference of the absorbance (??) of the CuPc films with or without an Ag layer vs. Thickness CuPc t.

Figure 14 shows the effective increased length calculated for an ID chain of spherical particles of 5 nm diameter (full line) and ellipticals (axial ratio = 0.5) (dashed lines) embedded in a dielectric medium with n = 2 + 0.5i, as a function of the spacing between the surfaces of the chain particles.

Figure 15 shows the spectra of calculated external quantum efficiency (Í] EQE) for a tandem PV cell CuPc / PTCBI (a) with and b) without Ag groups.

Detailed description An organic photosensitive optoelectronic device is provided. The organic devices of the embodiments of the present invention can be used, for example, to generate a useful electric current from the incident electromagnetic radiation (e.g., PV devices) or they can be used to detect incident electromagnetic radiation. The embodiments of the present invention may comprise an anode, a cathode and a photoactive region between the anode and the cathode. The photoactive region is the portion of the photosensitive device that absorbs electromagnetic radiation to generate excitons that can be dissociated, in order to generate an electric current. The organic photosensitive optoelectronic devices may also include at least one transparent electrode to allow absorption of the incident radiation by the device. Various materials and configurations for PV devices are described in U.S. Patent Nos. 6,657,378, 6,580,027 and 6,352,777, which are hereby incorporated by reference in their entirety.

Figure 1 shows an organic photosensitive optoelectronic device 100. The figures are not necessarily drawn in scale. The device 100 may include a substrate 110, an anode 115 and an anode softening layer 120, a donor layer 125, an acceptor layer 1230, a blocking layer 135 and a cathode 140. The cathode 140 may be a cathode composed with a first conductive layer and a second conductive layer. The device 100 can be manufactured by depositing the layers described in order. The separation of charges can occur predominantly in the heterojunction between the donor layer 125 and the acceptor layer 130. The internal potential in the heterojunction is determined by the HOMO-LUMO energy difference between the two contact materials forming the heterojunction. The compensation of the HOMO-LUMO gap between the donor and acceptor materials produces an electric field at the donor / acceptor interface that facilitates the separation of the charges for the excitons created within a diffusion length of excitons of the interface.

The specific arrangement of the layers illustrated in Figure 1 is only shown by way of example, without limitations. For example, some of the layers (for example the blocking layers) can be omitted. Other layers (such as reflecting layers or other acceptor and donor layers) can be added. It can alter the order of the layers. Arrangements other than those specifically described may be used.

The substrate can be any suitable substitute that provides the desired structural properties. The substrate may be flexible or rigid, flat or non-planar. The substrate can be transparent, translucent or opaque. Plastic and glass are examples of rigid substrate materials of preference. Plastic and metal sheets are examples of flexible substrate materials of preference. The materials and thicknesses of the substrate can be chosen in order to obtain the desired structural and optical properties.

U.S. Patent No. 6,352,777, incorporated herein by reference, provides examples of electrodes, or contacts, that may be used in a photosensitive optoelectronic device. When used herein, the terms "electrode" and "contact" refer to the layers that provide a means to provide photogenerated current to an external circuit or provide a polarization voltage to the device. That is, an electrode, or contact, provides the interface between the active regions of an organic photosensitive optoelectronic device and a wire, cable, trace or other means for transporting the charge carriers to or from the external circuit. In a Photoelectric optoelectronic device is intended to allow the admission of the maximum amount of electromagnetic radiation from the environment from the outside of the device to the inner region with photoconductive activity. That is, electromagnetic radiation must reach a photoconductive layer (s), where it can be converted into electricity by photoconductive absorption. Often this implies that at least one of the electrical contacts must absorb a minimum and reflect a minimum of the incident electromagnetic radiation. That is, said contact should be substantially transparent. The opposite electrode can be a reflective material, so light passing through the cell without being absorbed is reflected back through the cell. As used herein, it is said that a layer of material or a sequence of several layers of different materials is "transparent" when the layer or layers allow at least 50% of the electromagnetic radiation from the environment to be transmitted in lengths relevant waveforms through the layer or layers. Similarly, layers that allow some transmission of ambient electromagnetic radiation, but less than 50%, at relevant wavelengths, are said to be "semitransparent." As used herein, "upper" means the furthest from the substrate, while "lower" means the most close to the substrate. For example, for a device having two electrodes, the lower electrode is the electrode closest to the substrate, and is usually the first fabricated electrode. The lower electrode has two surfaces, a lower surface closer to the substrate, and an upper surface remote from the substrate. When it is described that a first layer "is disposed on" a second layer, the first layer is disposed further away from the substrate. There may be other layers between the first and second layers, unless it is specified that the first layer is in "physical contact with" the second layer. For example, it can be described that a cathode "is disposed on" an anode, even when there are several layers in between.

Preferably, the electrodes are composed of metals or "metal substitutes". In the present, the term "metal" is used to encompass both materials composed of an elementally pure metal, for example, Mg, and alloys of metals that are materials composed of two or more elementally pure metals, for example, Mg together with Ag , which is denoted Mg: Ag. Herein, the term "metallic substitute" refers to a material that is not a metal, according to the normal definition, but that has properties similar to metals, which are desired in certain suitable applications. Substitutes for commonly used metals for electrodes and load transfer layers they include interrupted semiconductors with wide band gap, for example conductive transparent oxides such as indium tin oxide (ITO), gallium oxide, indium and tin (GITO), and zinc oxide, indium and tin (ZITO). The particular, ITO is a highly interrupted degenerate n + semiconductor with an optical band gap of about 3.23 eV, which makes it transparent for wavelengths greater than about 3,900 A. Another suitable metal substitute is the polyanaline conductive transparent polymer (PA I) and its related chemical compounds. Metal substitutes can be selected in addition to a wide range of non-metallic materials, where the term "non-metallic" means that it covers a wide range of materials, as long as the material does not contain metal in its non-combined chemical form. When a metal is present in its chemically uncombined form, either alone or in combination with one or more metals such as alloys, it can alternatively be said that the metal is present in its metallic form or as "free metal". Accordingly, the metal substitute electrodes of the present invention can sometimes be referred to as "metal free", wherein the term "metal free" expressly means that it encompasses a metal free material in its chemically uncombined form. In general, free metals have the form of metal bonds that are produced from a set of valence electrons that they are free to move in an electric conduction band, through the metallic lattice. Although metallic substitutes may contain metallic constituents, they are "non-metallic" in several bases. They are not pure free metals nor are alloys of free metals. When metals are present in their metallic form, the electric conduction bands tend to provide, among other metallic properties, a high electrical conductivity, in addition to high reflectivity for optical radiation.

Embodiments of the present invention may include, as one or more of the transparent electrodes of the photosensitive optoelectronic device, a highly transparent, non-metallic, low-resistance cathode such as that described in United States Patent No. 6,420,031 of Parthasarathy et al. ("Parthasarathy? 031") or a cathode of a highly efficient, low strength metal / non-metallic compound, such as that described in U.S. Patent No. 5,703,436 to Forrest et al. ("Forrest 36"), both incorporated herein by reference in their entirety. Each type of cathode is preferably prepared in a manufacturing process which includes the step of depositing by splashing an ITO layer on an organic material, such as copper phthalocyanine (CuPc), to form a highly transparent cathode, not metallic and low resistance, or in a thin layer of g: Ag, to form a highly efficient and low resistance metallic / non-metallic composite cathode.

In the present, the term "cathode" is used in the following manner. In a non-stacked PV device or an isolated unit of a PV device stacked under ambient irradiation and connected with a resistive load and without applied external voltage, for example, a PV device, the electrons move towards the cathode from the photoconductive material. Similarly, the term "anode" is used herein in such a way that in a PV device under illumination the voids move toward the anode from the photoconductive material, which is equivalent to the electrons traveling in the opposite direction. It should be noted that according to the terms used herein, the anodes and cathodes may be electrodes or load transfer layers.

An organic photosensitive device comprises at least one photoactive region, in which light is absorbed to form an excited state, or "exciton", which can then be dissociated into an electron and a gap. The dissociation of exciton in general occurs in the heterojunction formed by the juxtaposition of an acceptor layer and a donor layer. For example, in the device of the Figure 1, the "photo-active region" may include the donor layer 125 and the acceptor layer 130.

The acceptor material may comprise, for example, perylenes, naphthalenes, fullerenes or nanotubules. An example of acceptor material is bis-benzimidazole 3, 4, 9, 10-perylentetracarboxylic acid (PTCBI). Alternatively, the acceptor layer may comprise a fullerene material as described in U.S. Patent No. 6,580,027, incorporated herein by reference in its entirety. Adjacent to the acceptor layer is a layer of donor-type organic material. The limit of the acceptor layer and the donor layer form the heterojunction that can produce an internal generation electric field. The material for the donor layer can be a phthalocyanine or a porphyrin, or one of its derivatives or transition metal complexes, for example copper phthalocyanine (CuPc). Other suitable acceptor and donor materials can be used. In a preferred embodiment of the invention, the stacked organic layers include one or more exciton blocking layers (EBL) as described in U.S. Patent No. 6,097,147, Peumans et al., Applied Physics Letters. 2000, 76, 2650-52, and the pending application act number 09 / 449,801, filed on November 26, 1999, both incorporated herein by reference. They have been achieved higher external and internal quantum efficiencies by including an EBL to confine the photogenerated excitons to the region near the dissociation interface, and prevent the parasitic tempering of excitons at the organic photosensitive interface / electrode. In addition to limiting the volume over which excitons can diffuse, an EBL can also act as a barrier. of diffusion for the substances introduced during the deposition of the electrodes. In some circumstances, an EBL of sufficient thickness can be prepared to fill point gaps or short circuit defects - which would otherwise render the organic PV device non-functional. Consequently, an EBL can help to protect fragile organic layers from the damage produced when the electrodes are deposited on the organic materials.

It is believed that EBLs derive their property from exciton blockers from having a LUMO-HOMO energy gap substantially greater than that of the adjacent organic semiconductor, from which the excitons are blocked. Consequently, confined excitons can not exist in the EBL, due to energy considerations. While it is desirable for the EBL to block the excitons, it is not desirable for the EBL to block all charges. However, due to the nature of the adjacent energy levels, an EBL can block a carrier sign of charges. According to the design, an EBL will exist between two other layers, usually an organic photosensitive semiconductor layer and an electrode or charge transfer layer. The adjacent charge transfer electrode or layer will be in the context a cathode or an anode. Accordingly, the material of an EBL in a particular position in a device will be chosen so that the desired sign of the carrier is not impeded in transport to the electrode or load transfer layer. The adequate alignment of the energy level ensures that there is no barrier to the transport of loads, which prevents an increase in the resistance in series. For example, it is desirable that the material used as a cathode EBL have a LUMO energy level that is quite coincident with the LUMO energy level of the adjacent material, in order to minimize any unwanted barrier of the electrons.

It will be appreciated that the nature of exciton blocking by a material is not an intrinsic property of its HOMO-LUMO energy gap. That certain material acts as an exciton blocker depends on the relative HOMO and LUMO energy levels of the adjacent organic photosensitive material. Consequently, it is not possible to identify a class of compounds isolated as excitone blockers, without considering. the context of the device in which it will be used. However, with As taught herein, one skilled in the art will be able to identify whether a particular material will act as an exciton blocking layer when used with a selected set of materials, to build an organic PV device.

In a preferred embodiment of the invention, an EBL is located between the acceptor layer and the cathode. A preferred EBL material comprises 2,7-dimethyl-4,7-diphenyl-1,10-phenanthroline (also referred to as batrocuproin or BCP), which is considered to have a LUMO-HOMO energy level separation of about 3.5 eV, or aluminum bis (2-methyl-8-hydroxyquinoline) -fenolate (III) (Alq20PH). BCP is an effective exciton blocker that can easily transport electrons to the cathode from an acceptor layer.

The EBL layer can be interrupted with a suitable switch, for example, but without limitations 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA), 3,4,9,10-perylentetracarboxylic dimide (PTCDI), bis-benzimidazole 3, 4,9,10-perylentetracarboxylic acid (PTCBI), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) and its derivatives. It is believed that the BCP deposited in the present devices is amorphous. The present amorphous BCP exciton blocking layers can exhibit film recrystallization, which is especially fast under high light intensities. The morphology change obtained in the polycrystalline material results in a lower quality film, with possible defects such as shorts, errors and intrusions of the electrode material. Accordingly, it was found that the disruption of certain EBL materials, such as BCP, which exhibit this effect with a suitable, relatively large and stable molecule, can stabilize the structure of the EBL to prevent morphology changes with performance degradation. It will also be appreciated that the interruption of an EBL that carries electrons in a given device, with a material with an energy level close to that of the EBL, will help to ensure that no electron traps are formed that can produce space charge accumulation and reduce performance. . In addition, it will be appreciated that relatively low interruption densities should minimize the generation of excitons at isolated switch sites. Since said excitons are prevented from diffusing into the surrounding EBL material, said absorptions reduce the photoconversion efficiency of the device.

Representative embodiments may also comprise transparent load transfer layers or charge recombination layers. As described herein, charge transfer layers are distinguished from the donor and acceptor layers by the fact that the charge transfer layers are often, but not always, inorganic (often metals) and can be chosen to have no photoconductive activity. The term "charge transfer layer" is used herein to refer to similar but different layers of the electrodes, in that the charge transfer layer only delivers the charge carriers from a subsection of an optoelectronic device to the section following. The term "charge recombination layer" is used herein to refer to similar but different layers of electrodes in which a charge recombination layer always allows the recombination of electrons and gaps between photosensitive devices in tandem, and may also increase the Internal optical field strength near one or more active layers. You can build a. charge recombination layer from nanoparticles, semi-transparent metal nanoparticles or nanorods, as described in U.S. Patent No. 6,657,378, incorporated herein by reference in its entirety.

In another preferred embodiment of the invention, an anode softener layer is located between the anode and the donor layer. A preferred material for this layer comprises a film of 3,4-polyethyldioxythiopentene: olistyrenesulfonate (PEDOT: PSS). The introduction of the PEDOT: PSS layer between the anode (ITO) and the donor layer (CuPc) can lead to much improved manufacturing yields. This is attributed to the ability of the PEDOT: PSS film layer to make ITO plane, whose rough surface would otherwise form short in the thin molecular layers.

In another embodiment of the invention, one or more of the layers can be treated with plasma before depositing the new layer. The layers can be treated, for example, with a mild plasma of argon or oxygen. This treatment is beneficial, since it reduces the resistance in series. It is particularly advantageous to subject the PEDOT: PSS layer to gentle treatment with plasma, before depositing the next layer.

The simple layer structure illustrated in Figure 1 is provided as a non-limiting example, and it is understood that the embodiments of the invention can be used in connection with a wide variety of other structures. The specific materials and structures described are of an exemplary nature, and other materials and structures can be used. Functional devices can be obtained by combining the various layers described in different ways, or by omitting layers completely, based on design, performance and cost factors. You can also include other layers not specifically described. Materials other than those specifically described can be used. While many of the examples provided herein describe various layers comprising a single material, it is understood that combinations of materials may be used, such as a mixture of host and switch, or more generally a mixture. In addition, the layers may have several sublayers. The names given to the various layers in the present are not intended to be strictly limiting. Organic layers that are not part of the photoactive region, i.e., organic layers that do not generally absorb photons, which make significant contributions to the photoelectric current may be referred to as "non-photoactive layers". Examples of non-photoactive layers include EBL and anode softener layers. Other types of non-photoactive layers can also be used.

Preferred materials for use in the photoactive layers of a photosensitive device include cyclometalized organometallic compounds. As used herein, the term "orgnometallic" will generally be understood by one skilled in the art, and given, for example, in "Inorganic Chemistry" 2nd edition, by Gary Miessler and Donald A. Tarr, Prentice Hall (a998) ). Accordingly, the term "organometallic" refers to compounds that have an organic group attached to a metal through a carbon-metal bond. This class does not include per se the coordination compounds which are substances that only have donor bonds in heteroatoms, such as metal complexes of amines, halides, pseudohalides (CN, etc.) and the like. In practice, organometallic compounds generally comprise, in addition to one or more carbon-metal bonds with an inorganic species, one or more donor bonds from a heteroatom. The carbon-metal bond with an organic species refers to a direct bond between a metal and a carbon atom of an organic group, such as phenyl, alkyl, alkenyl, etc., but does not refer to a metal bond as "carbon inorganic ", for example the carbon of CN or CO. The term "cyclometalic" refers to compounds comprising a bidentate organometallic ligand, such that upon joining a metal a ring structure is formed, which includes the metal as one of the ring members.

The organic layers can be manufactured by vacuum deposition, spin coating, organic vapor phase deposition, ink jet printing and other methods known in the art.

The organic photosensitive optoelectronic devices of the embodiments of the present invention can act as PV, photodetector or photoconductor. Provided that the organic photosensitive optoelectronic devices of the present invention act as a PV device, the materials used in the photoconductive organic layers and their thickness should be selected, for example, in order to optimize the external quantum efficiency of the device. Provided that the organic photosensitive optoelectronic devices of the present invention act as photodetectors or photoconductors, the materials used in the photoconductive organic layers and their thicknesses can be selected, for example, to maximize the sensitivity of the device in the desired spectral regions.

This result can be achieved by considering several patterns that can be used in the selection of the thickness of the layer. It is desirable that the diffusion length of the exciton LD be greater or comparable to the thickness of the layer L, since it is believed that the greater dissociation of the excitons takes place at the interface. If LD is less than L, many excitons can recombine before dissociation. It is also desirable that the total thickness of the photoconductive layer be of the order of the absorption length of the electromagnetic radiation I / a (where a is the absorption coefficient), so that almost all of the radiation incident on the PV device is absorbed to produce excitons. In addition, the thickness of the photoconductive layer must be as thin as possible, in order to avoid excess resistance in series, due to the high resistance in mass organic semiconductors.

Consequently, these competition patterns require inherent compensations when selecting the thickness of the photoconductive organic layers of a photosensitive optoelectronic cell. Accordingly, on the one hand, a thickness comparable to or greater than the absorption length (for a single cell device) is desirable in order to absorb the maximum amount of incident radiation. On the other hand, as the thickness of the photoconductive layer increases, two undesirable effects increase. One is due to the high series resistance of organic semiconductors, so the increased thickness of the organic layer increases the strength of the device and reduces efficiency. Another undesirable effect is that increasing the thickness of the photoconductive layer increases the probability that the excitons are generated far from the effective field at a load separating interface, which results in a higher probability of recombination and, again, lower efficiency . Accordingly, a configuration of the device that balances these competing effects in a manner such that high external quantum efficiency for the device in general is produced is desirable.

The organic photosensitive optoelectronic devices of the present invention can function as photodetectors. In this embodiment, the device can be a multi-layer organic device, for example as described in United States patent application act No. 10 / 723,953, filed on November 26, 2003, and incorporated in its entirety to the present as a reference. In this case, an external electric field is usually applied to facilitate the extraction of the different loads. A concentrator or trap configuration can be employed to increase the efficiency of the organic photosensitive optoelectronic device, where the photons are forced to make multiple passages through the thin regions of absorption. The United States Patents Nos. 6,333,458 and 6,440,769, hereby incorporated by reference in their entirety, resolve this issue through the use of structural designs that increase the efficiency of photoconversion by photosensitive optoelectronic devices, by optimizing the optical geometry for high absorption and for use with optical concentrators that increase the efficiency of the recovery. Said geometries of the photosensitive devices substantially increase the optical path through the material, by trapping the incident radiation within a cavity reflector or waveguide structure, so that light is recycled through multiple reflections by the photosensitive material. The geometries described in U.S. Patent Nos. 6,333,458 and 6,440,769 accordingly increase the external quantum efficiency of the devices, without causing a substantial increase in overall strength. The geometry of said devices includes a first reflective layer, a transparent insulating layer, which should be longer than the optical coherence length of the incident light in all dimensions, in order to prevent interference effects by optical microcavities; a layer of transparent first electrode, adjacent to the transparent insulating layer; a photosensitive heterostructure adjacent to the transparent electrode and a second electrode, which is also a reflector.

Covers can be used to focus the optical energy on the desired regions of a device. U.S. Patent Application No. 10 / 857,747, incorporated herein by reference in its entirety, provides examples of coatings.

In tandem bilayer solar cells, each subcell can be thin enough to allow a large percentage of exeitons to dissociate, while the device has enough thickness to achieve a high absorption efficiency. Figure 2 shows a schematic diagram 200 and transmission electron micrographs with high resolution 290 of a cross section of a tandem organic PV cell. The two cells 210 and 220 are contacted by an indium tin oxide (ITO) anode 230 and an Ag 240 cathode, and are separated by a layer of Ag 250 nanoparticles. As used herein, the term "nanoparticle" refers to a particle that fits within and / or between the organic layers of an organic device, a size preferably of nanoparticles is approximately 300 A or less, although the nanoparticles may be encapsulated within other materials, which You can increase this size. The increase distances and the LDD diffusion lengths and ??? of the donor layer (D) and the acceptor layer (A) of each device are labeled. The Ag groups are visible in the micrograph and are shown (full circles) in the scheme. The diagram shows a representation of the generation of current in the tandem cell. Upon absorption of light, the excitons are formed in both photovoltaic cells 210 and 220. After dissociation at a DA 270 · or 280 interface, the gap is collected in the subcell PV 210 and the electrons in the subcell PV 220 in the adjacent electrodes 230 and 240. To prevent the accumulation of charge within the cells, the electron of the subcell 210 PV and the hollow of the subcell PV 220 they diffuse to the layer of 250 metal nanoparticles, where they recombine. The attraction of the initial charge towards the nanoparticle is mainly a consequence of image loading effects. Once the metal particle has an isolated charge, the Coulomb attraction of the free counter charge produces the rapid recombination of the surface of Ag 250.

This structure of tandem cells connected in series is advantageous because it leads to an increase in the open circuit voltage V0cr compared to the case of the isolated bilayer cell. Dice ?? = JscV0cFF / Pinc (-in- where JSc is the short circuit current density, FF is the fill factor, and Pinc is the incident optical energy density), this can lead to an increase of ??, given that the others parameters remain unchanged. The challenge of making cells in tandem, therefore, is to balance the photoelectric current of each cell, since the current of the device is limited by the smallest of the two currents produced in subcell PV 210 or subcell PV 220. This can be achieved by varying the thicknesses or compositions of the materials of the various layers of the device, but is complicated by the effects of optical interference. Serial tandem cells can also comprise multiple electrically connected sub-cells, even with more than two sub-cells, where each subcell comprises an acceptor layer and a donor layer. Other arrangements of sub-cells may be used, as will be apparent to those skilled in the art.

In addition to functioning as an efficient recombination carrier layer, to prevent cell loading, the nanoparticles can also increase the incident electric field, which in turn can increase absorption in the nearby organic thin film. The shaded surface 260 in the diagram of Figure 2 indicates the region where the electric field receives influence from the Ag 150 nanoparticles. The field increase is a consequence of the surface plasmon polariton (SPP) resonances optically excited on the surfaces of the nanoparticles. As used herein, and as will be understood by one skilled in the art, "surface plasmon polariton resonance" refers to the coupling of the incident photons to the plasma oscillation of the surfaces of the particles, where "oscillation" occurs. Plasma "refers to the collective excitation of conduction electrons in the particle. The resonance of SPP originates in the displacement of the negative conduction electrons against the background with positive charge, due to the applied electric field. This results in polarization charges on the surface of the nanoparticles, which leads to a restoration force and consequently a resonance frequency. This property of the metal nanoparticles can also be applied to Schottky cells and PV cells sensitized to dyes, wherein the photosensitized region is in contact with the nanoparticle layer.

The SPP resonance position of the nanoparticles or aggregates of nanoparticles may be influenced by the irregular shape of the particles, the various dielectric fouling media and the effects of the substrate, as well as the coupling between particles. By taking advantage of these various effects, the resonance of a nanoparticle or nanoparticle arrangement can be tuned according to the wavelengths in the visible and infrared spectrum.

Since the SPP resonance increases the local electromagnetic field, the nanoparticle and the photoactive region do not need to be in direct contact to obtain the benefits of SPP resonance. In one embodiment of the invention encapsulated nanoparticles are dispersed within an active organic region disposed between two electrodes. The nanoparticles can be distributed randomly or evenly throughout the region. Other arrangements of nanoparticles are also possible, and may be advantageous for specific applications. In a form of Preferred embodiment of the invention, the photoactive region comprises one or more PV cells. In this embodiment, the encapsulated nanoparticles can be arranged in planar layers between adjacent PV cells. The photoactive region may comprise other suitable organic materials, such as dye-sensitized materials. The dispersion of the nanoparticles within the photoactive region increases the electric field incident in the surrounding region, due to the resonances of SPP on the surface of the particles. Preferably, the nanoparticles comprise a metal, with particular preference for Ag, Cu and Au. The use of these materials provides an SPP resonance that causes greater absorption with visible wavelengths. The nanoparticles may also comprise an interrupted degenerative semiconductor or other semiconductor material.

The resonance wavelength occurs when the following equation is minimized: t e1 (?) + 2em (?)] 2 + e2 (?) 2 = constant where t (?) And e2 (?) Correspond to the metal, and sm (?) corresponds to the embedding medium. This can be simplified to e? (?) = -2 sm (?) given that tz (?) or d Zz / d? they are small, which is generally true for, for example, Ag, in the resonance region of 3, 0 to 3.5 eV. Figure 3 shows the actual dielectric function 310 and the imaginary dielectric function 320 for Ag as photon energy functions. The mass of Ag is shown as a full line and Ag groups with diameters of 10 nm (dashed line) and 5 nm (dashed line) are also shown. Figure 4 shows the effect of the embedding medium with the SPP resonance of nanoparticles of 2R = 5 nm of Ag, where changes in dielectric function have been taken into account. The dashed lines indicate the resonance wavelengths for a particle with an axial particle ratio of b / a = 0.6. The box shows the geometry of the simulation.

The shape of a nanoparticle is another factor that can particularly affect the resonance of SPP. For example, for elliptical nanoparticles, the SPP can be divided into two modes, one corresponding to the major axis a, and the other to the minor axis b of the spheroid. Figure 5 shows the SPP peak position for an elliptical nanoparticle in vacuum. As used herein, the term "axial ratio" refers to the ratio between the minor axis and the major axis, ie, b / a. For small values of axial ratio, the wavelength spacing between the two resonance peaks it reaches values of 300 nm, and for b / a = 1, the position of SPP corresponds to that of a spherical nanoparticle in vacuum to ?? = 338 nm. For example, the dashed lines of Figure 5 show that an axial ratio of 0.6 leads to SPP modes at h = 334 and at-360 nm. This division of dipole modes can be generalized to cases of any non-spherical particle shape, due to the resulting distribution of the charge in the asymmetric nanoparticle. In preferred embodiments of the invention, the nanoparticles have the minor axis no greater than about 300A, and an axial ratio not less than about 0.1. For more spherical particles (ie, those having an axial ratio of about 1), it is preferred that the average separation between surfaces does not exceed about 100A. The particles of larger size and / or smaller average separations decrease the amount of organic material available for absorption, which can decrease the increase of the optical field of incidence due to the resonances of SPP. However, for some purposes other dimensions than those specifically described may be used. In addition, it is preferred that the nanoparticles are not spherical, and are arranged with the major axes parallel to the interface. It is believed that this provision increases the increase of the optical field of incidence which results from the interactions of dipoles and SPP resonances of the nanoparticles. For non-spherical particles (those with an axial ratio less than 1) the coupling between particles may have less influence on the local field increments. Accordingly, it is preferred that the average separation between non-spherical particle surfaces is not greater than about 300A. Other arrangements and separations may be used for some purposes! In some cases, the encapsulated nanoparticles may comprise a significant percentage of the volume of the active region. For PV cell applications it is advantageous to introduce field increments over the entire range of the solar spectrum that overlaps with the absorption spectra of the photoactive materials. Next, the spectral dependence is analyzed. of absorbance.

Figure 6 shows representative absorption spectra measured from three quartz films with nanoparticles and without them. The nanoparticles in the Ag layer of 1 nm thickness have an average diameter of approximately 2R = 5 nm, and an inter-center spacing of approximately d = 10 nm. The curve 610 of an insular Ag film of 10 A thickness has a peak of 100 nm (total width at half of the maximum) centered on a wavelength of ?? = 440 nm, due to the excitation of Surface plasmon of the nanoparticles. The position and intensity of the peak indicate the distribution of the size and shape of the particles, in addition to the bipolar coupling between nanoparticles that broadens the optical response by decreasing the spacing of the particles. Also shown is the absorption of a 7 nm thick film of CuPc (curve 620) and a CuPc film of 7 nm deposited on the top of the insular Ag film of coverage thickness of 1 nm (curve 630). The plasmon peak of the Ag nanoparticle layer shifts to red at 30 nm at? = 470 nm due to the presence of the surrounding dielectric CuPc, although the positions of the CuPc peaks to? = 625 nm and 690 nm are not modified. However, the most notorious feature is the increase in CuPc absorption at wavelengths? > 470 nm. This broadband, non-resonant improvement can lead to an increase of approximately 15% in the efficiency of the tandem PV cells over that which is expected simply by combining the efficiencies of several accumulated CuPc / PTCBI bilayers.

The improvement may occur below the surface plasmon frequency, ?? Below ??, a collection of randomly distributed nanoparticles can generate "hot spots" in the electric field due to interactions between particles, while the absorption of nanoparticle films is due to the dipolar plasmon modes formed on the surface of the particles.

Figure 7 shows a distribution of. representative field for a planar arrangement of Ag cylinders, on a quartz substrate surrounded by a dielectric CuPc, of diameter 2R = 5 nm and a uniform spacing from surface to surface d = 5 nm. The particles are on a quartz substrate (n = 1.46, z = 0) and are embedded in a dielectric medium (CuPc). Contour labels represent the calculated intensity improvement and are spaced 0.5. The polarization vector is indicated by the arrow, and the propagation is in the + z direction. The field distribution is for an excitation wavelength of? = 690 nm and polarization parallel to the nanoparticle chain. The contours indicate the intensity of the electric field improvement,, (I / Io), where I is the local field strength and I0 is the field strength incident. These intensities are proportional to respectively, where 'is the local field amplitude and is the amplitude of the incident field. It is possible to find me prayers from. the intensity up to twelve times greater in the interstices of the cylinders. The dipolar nature of The intensity of the field is evident, and there is an attenuation of the field in the "shadow" of the sphere.

The effect of the embedding medium on the position of the SPP resonance and also on the spectral bandwidth of the improvement is of particular importance for the application to solar cells, where improving a wide range of wavelengths is of interest. Figure 8 shows the improvement of intensity of an integrated incident field on the surface of a single spherical particle, 2R = 5 nm. The resonance peak shifts towards red as a consequence of the increasing dielectric constant of the embedding medium. As n increases from 1 to 2, the resonance peak becomes more important, while the degree of the enhancement plateau on the long wavelength side of the SPP peak is reduced. Embedding the particle in a material with n = 2 + 0.5t, a typical value for a very absorbent thin organic film, causes the peak of dipolar SPP to be suppressed by more than one order of magnitude compared to a nonabsorbent dielectric.

Figure 9 shows the spectra of a spherical nanoparticle (2R = 5 nm) and an elliptical b / a = 0.5 of area equal to the spherical nanoparticle embedded in a dielectric with n = 2 + 0.5i. Both particles have the same area, and are embedded in a dielectric with n = 2 + 0.5i. The absorption (dotted lines) of elliptical nanoparticles reaches a peak a? = 470 nm, and it moves towards red from that of the spherical a? = 392 nm. The polarization of the incident light is parallel to the major axis of the elliptical particle, and therefore that mode is excited. The elliptical particle has a red-shifted breeding tail that extends beyond the absorption of most organic PV materials, which makes this particle form more suitable for use in organic PV cells.

The charge recombination layer in a tandem organic PV cell may consist of a thermally evaporated random arrangement of nanoparticles of various sizes, shapes and spacing from each other. Figure 10 shows the improvement of the intensity in the center of an arrangement of spherical Ag nanoparticles 1010, 1020 and elliptical nanoparticles 1030, 1040 in a medium with n = 2 + 0.5i. For d > .10 nm, the improvement decreases monotonously and the spacing increases rapidly for o < 10 nm due to the non-linear increase in the dipolar coupling between neighboring nanoparticles. The SPP resonance position shifts towards red for d = 10 nm, while for d greater the resonance of SPP converges to the wavelength of the single particle.

Figure 11 shows the spectral response for d = 10 nm 1110 and 1120, 5 nm 1130 and 1140, and 2.5 nm 1150 and 1160, for both spherical (full lines) 1110, 1130 and 1150 arrangements, as well as elliptical (dotted lines) ) 1120, 1140 and 1160. The full lines indicate a group arrangement of 5 nm in diameter, while the dotted lines indicate elliptical particles of axial ratio 0.5 with the same area. The surface spacings with surface area of d = 10 nm (open squares), 5 nm (filled circles) and 2.5 nm (open triangles) are shown. In each case, the elliptical arrangement has a greater maximum improvement than for the spherical case. As d is reduced, the effects of the coupling are stronger than the effect of the form. The improvement plateau for these structures is wide due to the coupling between particles. In addition, there is a region of attenuation in the wavelength just below the resonance of SPP. The solar spectral intensity in? < 350-400 nm is weak and therefore this does not cause a significant impact on the performance of the device compared to the improvements recorded at high wavelengths.

The distance over which an improvement occurs from the recombination layer of a tandem organic PV cell is also of interest. Figure 12 shows the measured absorbance, A, of various thicknesses of CuPc in quartz at a wavelength of? = 690 nm with (triangles) and without (squares) a layer of Ag groups of 10 A. The measured absorbance values of CuPc films of various thicknesses (t) deposited directly on quartz substrates, as well as on island films of Ag, at a non-resonant wavelength? = 690 nm are shown in Figure 12. At this wavelength, the absorption due to Ag nanoparticles can be neglected, which provides a direct comparison of changes in CuPc uptake. The absorbency increases more rapidly for the CuPc film absorbed in the Ag islands 1210 than for the pure film 1220 when t = 10 nm. When t 'is large, absorption no longer increases. Figure 13 shows the measured difference in the absorbency (?) Of the CuPc films with and without Ag layer compared to the thickness of CuPe, t.

Nano-sized Ag nanoparticle films have scattering and reflection efficiencies close to zero. The loss by spreading from the dipole mode can only be greater than the loss by absorption for the particles with 2R = 30 nm.

Figure 14 shows the effective thickness of a thin film dielectric region with n = 2 + 0.5i surrounding a particle arrangement that is within the "enhancement zone" of that arrangement, including the area within that array of particles. For very small d, the improvement in the interstices of the nanoparticle is great, although it is mostly confined to this small region. The improvement for the spherical arrangement 1410 and the elliptical arrangement 1420 reaches a peak at approximately or = 25 nm, and extends at distances of about 7 and 9 nm, respectively.

A tandem PV cell consisting of two DA / CuPc / PTCBI heterojunctions located in series and separated by a thin layer of Ag nanoparticle recombination has a power efficiency of approximately. (2.5 + 0.1)% while ?? for a single cell of CuPc / PTCBI it is (1.1 + 0.1)% under an illumination AM1.5G (mass of air 1.5 global) simulated of 1 sun (100 mW / cm2). V0'c for the tandem cell is approximately twice the value of a single cell. An increase in Jsc can explain an increase of approximately 15% in ?? to 2.5%. Jsc is determined using: (3) where S (?) is the simulated AM 1.5G solar irradiation spectrum, q is the charge of the electron, c is the speed of light, and h is the Planck constant.

Figure 15 shows? 0 (?) Calculated with the nanoparticle layer of Ag 1510 and without the nanoparticle layer of Ag 1520 for the tandem structure: 150 n ITO / 10 nm CuPc / 13 nm PTCBI / 1 nm Ag / 13 nm CtiPc / 30 nm PTCBI / 100 nm Ag. The open circles show ??? 2? for the anterior cell (PV 1, closer to the anode) while filled squares show nEQE for the posterior cell (PV 2, closer to the cathode). The contributions to nEQE are also shown on the part of the CuPc and PTCBI layers for PV 1 (full curves) and PV 2 (dotted curves). The posterior cell is thicker than the anterior cell to compensate for the reduction in field strength due to absorption in the anterior cell, as well as due to the effects of parasitic optical interference. In the structure without nanoparticles of Ag 1520, for PV 1 (open circles) and PV 2 (full squares) they have similar forms, although PV 1 has a higher Jsc due to its greater nEQE (?) in most of the photoactive region. This current imbalance limits the Jsc to a smaller current in PV 2. For both PV 1 and PV 2, the main contribution with nEQE (?) is from the CuPc layer, since the diffusion length for CuPc, Lc ^ Pc = (100 ± 30) A, is greater than PTCBI with LPCBI = (30 ± 3) A. The short circuit current density is balanced for the improved case, although nEQE (?) For PV 1 and PV 2 have different shapes. Due to the improvement of the nanoparticle field, there is a large contribution with nEQE (X) from - the PTCBI layer for PV 1, and from the CuPc layer for PV 2.

In the CuPc / PTCBI architecture, the small LD of these materials allows the deposition of thin layers in the anterior and posterior cells and, thus, the DA interface is within the improvement zone. For materials with a large LD, such as C60, the present architecture does not allow a significant improvement in the DA interface when the thickness of the layer is about LD, since it is the optimum layer thickness for a bi-layer organic PV cell. For these materials, it may be possible to produce tandem devices from thin coevaporated films of materials D and A, where the excitation of the excitons is not limited by LD. In this case, the PV sub-cells can be kept thin to preserve a high FF, while the enhancement of the nanoparticle charge recombination layer increases the absorption in the cell.

The intensity of the optical field in the near field of a metallic nanoparticle chain can be increased by a factor of up to one hundred compared to the intensity of the incident light. This improvement covers a wide range of spectra and can be extended to distances of up to 100 A, allowing greater absorption in thin organic films placed in contact with nearby nanoparticles or nanoparticles. The improvement may result in higher power efficiencies in tandem bilayer organic PV cells.

The relatively small diffusion lengths in the CuPc / PTCBI PV cells allow thin layers with better absorption at the current generating DA interface. For materials with LD > 100 A, the tempering of excitons. in Ag nanoparticles can limit the potential for efficiency improvements by means of increased absorption. A possible means to prevent the exciter tempering from competing with the increase in efficiency is to encapsulate the metal nanoparticles in an insulating layer. These encapsulated nanoparticles can then be dispersed in all organic films, improving absorption without degrading the electrical efficiency of the cell. The Encapsulated nanoparticles can comprise a significant percentage of the volume of the organic film.

The encapsulated nanoparticles can be created using a self-assembly layer by layer, as described in Ung et al., J Phys. Chem. B 2001, 105, 3441-52 and Salgueirino-Maceira et al., J: Phys. Chem. B 2003, 107, 10990-10994, the Turkevich method as described therein, and other methods as described in Liz-Marian and Mulvaney, J. Phys. Chern. B 2003, 107, 7312-26, all three incorporated herein by reference. Other methods for creating and encapsulating nanoparticles can be employed, as will be appreciated by one skilled in the art.

The use of these encapsulated nanoparticles will allow the adjustment of the effects of particle coupling with particle, macroscopic properties of the host material and other effects. In one embodiment of the invention, the nanoparticles are encapsulated within the insulating material. In a preferred embodiment of the invention, the nanoparticles are encapsulated within an oxide. It is especially preferred that the insulating layer is not less than about 10 A and not greater than about 100 A. Less than about 10 A, the quantum effects will become non-trivial and, at more than 100 A, the separation of the nanoparticles can begin to cushion the resonance effects of SPP. The nanoparticles may not need to be in physical contact with the organic photoactive region. In another embodiment of the invention, the nanoparticles can be arranged throughout the "active zone". As used herein, "active zone" is a region slightly larger than the "photoactive region". Specifically, the "active zone" is a region from which the nanoparticles can have a significant positive effect on absorption in the photoactive region. In general, the "active zone" includes organic materials comprising the photoactive region, as well as organic materials within approximately 100 A of the photoactive region. The active zone may include non-photoactive materials and may include, more commonly, for example, blocking layers arranged adjacent to the photoactive region.

Once manufactured according to any of the various methods, the encapsulated nanoparticles can be incorporated into a device by any appropriate method. In a preferred embodiment, the nanoparticles are incorporated into an organic layer deposited in solution by suspension in the solution before deposition. Other methods can also be used, such as co-depositing encapsulated particles with an organic layer deposited by evaporation. The orientation of such nanoparticles (where the particles are non-spherical) can be controlled by mechanical means, such as spin coating, and / or by the application of a field, such as a magnetic or electric field, during the Deposition process. In some embodiments, the encapsulated nanoparticles can be manufactured in situ.

Although the present invention is described with respect to particular examples and preferred embodiments, it is understood that the present invention is not limited to these examples and embodiments. The present invention as claimed includes variations of the particular examples and preferred embodiments described therein, as will be obvious to one skilled in the art.

Claims (29)

1. CLAIMS 1. A device comprising: a first electrode a second electrode a photoactive region comprising an organic material disposed between and electrically connected to the first electrode and the second electrode; and a plurality of encapsulated nanoparticles disposed within the photoactive region, wherein the nanoparticles have a plasmon resonance.
2. 2. The device according to claim 1, wherein the nanoparticles are composed of metal.
3. 3. The device according to claim 1, wherein the nanoparticles are encapsulated within an oxide.
4. 4. The device according to claim 1, wherein the nanoparticles are encapsulated within an insulating material.
5. 5. The device according to claim 1, wherein the nanoparticles are distributed throughout the photoactive region.
6. 6. The device according to claim 1, wherein the photoactive region comprises a first subcell that, further, comprises: a first donor layer; and a first acceptor layer in contact. direct physical with the first donor layer.
7. 7. The device according to claim 6, wherein the photoactive region also comprises a second subcell which, furthermore, comprises: a second donor layer; and a second acceptor layer in indirect physical contact with the first donor layer, wherein the second subcell is disposed between the first subcell and the second electrode.
8. 8. The device according to claim 6, wherein the nanoparticles are disposed within the first acceptor layer and the first donor layer.
9. 9. The device according to claim 7, wherein the nanoparticles are disposed between the first subcell and the second subcell.
10. 10. The device according to claim 1, wherein the nanoparticles are non-spherical.
11. The device according to claim 10, wherein the photoactive region is planar, and the longest axis of each nanoparticle is approximately parallel to the plane of the photoactive region.
12. 12. The device according to claim 10, wherein the axial ratio of each nanoparticle is not less than about 0.1.
13. 13. The device according to claim 1, wherein the average surface-to-surface separation between nanoparticles is not greater than about 300 A.
14. 14. The device according to claim 1, wherein the smallest axis of each nanoparticle is not greater than about 300 A.
15. 15. The device according to claim 4, wherein the thickness of the insulating material is not less than about 10 A.
16. 16. The device according to claim 4, wherein the thickness of the insulating material is not greater than about 100 A.
17. 17. The device according to claim 2, wherein the nanoparticles comprise Ag.
18. 18. The device according to claim 2, wherein the nanoparticles comprise Au.
19. 19. The device according to claim 2, wherein the nanoparticles comprise Cu.
20. 20. The device according to claim 1, wherein the photoactive region comprises a bulk heterojunction.
21. 21. The device according to claim 1, wherein the photoactive region comprises a material sensitive to dyes.
22. 22. The device according to claim 1, wherein the nanoparticles comprises a conductive material.
23. 23. The device according to claim 1, wherein the nanoparticles comprise a semiconductor material.
24. 24. The device according to claim 1, wherein the nanoparticles comprise an interrupted degenerative semiconductor.
25. 25. A device comprising: a first electrode; a second electrode; an active zone disposed between and electrically connected to the first electrode and to the second electrode, wherein the active zone also comprises: a photoactive region disposed within the active zone and disposed between and electrically connected to the first electrode and the second electrode; and organic materials disposed within 100 A of the photoactive region; and a plurality of nanoparticles encapsulated within the active zone, wherein the nanoparticles have a plasmon resonance.
26. 26. The device according to claim 25, wherein the active zone also comprises a blocking layer of the organic exciton disposed adjacent to the photoactive region.
27. 27. A method for manufacturing a device comprising: obtaining encapsulated nanoparticles; manufacture a first electrode; manufacturing an organic photoactive region, wherein the encapsulated nanoparticles are disposed within the photoactive region; and fabricate a second electrode.
28. 28. The method according to claim 27, which also comprises a method for depositing the photoactive region by a solution process, wherein the nanoparticles are dispersed within the solution comprising the photoactive materials.
29. 29. The method according to claim 27, wherein the encapsulated particles are co-deposited with an organic layer deposited by evaporation.