Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/14—Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies
  • H10F77/143—Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies comprising quantum structures
  • H10F77/1433—Quantum dots
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/08—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials
  • C09K11/66—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials containing germanium, tin or lead
  • C09K11/661—Chalcogenides
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/12—Active materials
  • H10F77/123—Active materials comprising only Group II-VI materials, e.g. CdS, ZnS or HgCdTe
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/08—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials
  • C09K11/66—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials containing germanium, tin or lead
  • C09K11/661—Chalcogenides
  • C09K11/662—Chalcogenides with zinc or cadmium
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F10/00—Individual photovoltaic cells, e.g. solar cells
  • H10F10/10—Individual photovoltaic cells, e.g. solar cells having potential barriers
  • H10F10/16—Photovoltaic cells having only PN heterojunction potential barriers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F71/00—Manufacture or treatment of devices covered by this subclass
  • H10F71/129—Passivating
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/12—Active materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/12—Active materials
  • H10F77/127—Active materials comprising only Group IV-VI or only Group II-IV-VI chalcogenide materials, e.g. PbSnTe
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/14—Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/20—Electrodes
  • H10F77/206—Electrodes for devices having potential barriers
  • H10F77/211—Electrodes for devices having potential barriers for photovoltaic cells
  • H10F77/215—Geometries of grid contacts
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/20—Electrodes
  • H10F77/244—Electrodes made of transparent conductive layers, e.g. transparent conductive oxide [TCO] layers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/30—Coatings
  • H10F77/306—Coatings for devices having potential barriers
  • H10F77/311—Coatings for devices having potential barriers for photovoltaic cells
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/70—Surface textures, e.g. pyramid structures
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/70—Surface textures, e.g. pyramid structures
  • H10F77/707—Surface textures, e.g. pyramid structures of the substrates or of layers on substrates, e.g. textured ITO layer on a glass substrate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/773—Nanoparticle, i.e. structure having three dimensions of 100 nm or less
  • Y10S977/774—Exhibiting three-dimensional carrier confinement, e.g. quantum dots
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/84—Manufacture, treatment, or detection of nanostructure
  • Y10S977/89—Deposition of materials, e.g. coating, cvd, or ald
  • Y10S977/892—Liquid phase deposition
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/902—Specified use of nanostructure
  • Y10S977/932—Specified use of nanostructure for electronic or optoelectronic application
  • Y10S977/948—Energy storage/generating using nanostructure, e.g. fuel cell, battery

Definitions

• This invention resides in the fields of photovoltaic cells and quantum dots.
• the optimal light-harvesting material is one that achieves a high short-circuit current density J sc by maximizing the absorption of the sun's rays in both the visible and infrared spectra, and that one extracts a high level of work, in the form of a high open-circuit voltage V oc and a high fill factor FF, from each absorbed photon.
• V oc high open-circuit voltage
• FF fill factor
• colloidal quantum dot photovoltaics offer both the ability to form the light-harvesting layer by solution processing and the ability to tune the bandgap over a wide range, benefits that are available in both single-junction and multijunction cells.
• Nanocrystals Nano Lett. 9, 1699-1703 (2009), and others. Significant progress has also been achieved by sensitizing nanoporous Ti0 2 electrodes with a thin layer of colloidal quantum dots, with power conversion efficiencies of 3.2%. See for example Fan, S., et ah, "Highly efficient CdSe quantum-dot-sensitized Ti0 2 photoelectrodes for solar cell applications," Electrochem. Commun. 11, 1337-1330 (2009).
• photovoltaics as noted above can be significantly reduced or overcome by the pairing of a layer of light-harvesting nanoparticles with a layer of an electron-accepting material such that the junction between these layers is substantially depleted of both free electrons and free holes on at least one side of the junction when the device is not illuminated.
• An effective means of achieving this depletion is by selecting materials for these two layers that are of different bandgap magnitudes.
• Such a junction is thus a heterojunction by virtue of the two different materials on either side of the junction, and in particular a depleted heterojunction by virtue the low level or absence of both free electrons and free holes in the vicinity of the junction.
• the depletion arises from charge transfer from the electron-accepting contact to the to the nanoparticles.
• the nanoparticles are quantum dots, include p-type colloidal quantum dots, and the electron-accepting layer is, or includes, a metal oxide.
• the depletion is at least partly attributable to a relatively low charge density in the electron-accepting layer, as compared to that of the metal contact of a Schottky junction, which has a very high free electron density.
• photovoltaic devices within the scope of this invention offer further advantages over photovoltaic devices of the prior art.
• the use of a metal oxide as the electron-accepting layer allows the device to be configured with the electron-accepting layer as the front surface of the device or as the layer that the solar rays first penetrate upon entering the two semiconductor layers that form the photovoltaic junction.
• the electrons liberated by the rays are thus less susceptible to recombination with the holes since the electrons in these embodiments have a shorter distance to travel before reaching their destination electrode.
• the junction is that between a metal oxide and quantum dots
• the junction is better defined and easier to passivate, and thus less susceptible to defects, than a metal-semiconductor Schottky junction. This avoids the occurrence of Fermi-level pinning at the interface.
• these embodiments present less of a barrier to hole injection than a Schottky device by introducing a large discontinuity in the valence band and by minimizing the electron density at the interface.
• nanocrystals in photovoltaic devices and in optoelectronic devices in general, and particularly nanocrystals with surface anions is enhanced by depositing cations over the nanocrystals to form a first or inner shell and deposing anions over the first shell to form a second or outer shell.
• cation and anion shells in place of these ligands offers the advantages that the cation shells bind to the anions on the nanocrystal surface rather than to the cations, as organic ligands tend to do, and the ionic bonds are stable upon exposure to air and light, and particularly moisture, oxygen, and heat. Further advantages of these cation and anion shells are that by avoiding the need for organic ligands, these shells allow the nanocrystals to reside very close to each other in the light-absorbing film and thereby promote electron wave function overlap and carrier mobility, valuable features that are typically impeded by organic ligands. BRIEF DESCRIPTION OF THE FIGURES
• FIG. 1 is a plot of current density vs. voltage for examples of depleted
• heterojunction photovoltaic cells within the scope of the present invention.
• FIG. 2 is a plot of current vs. voltage for examples of depleted heterojunction photovoltaic cells within the scope of the present invention.
• FIG. 3 is a plot of external quantum efficiency vs. wavelength for examples of depleted heterojunction photovoltaic cells within the scope of the present invention.
• FIG. 4 is a plot of device capacitance vs. bias voltage and device resistance vs. bias voltage for examples of depleted heterojunction photovoltaic cells within the scope of the present invention.
• FIG. 5 shows absorption spectra of examples of depleted heterojunction
• FIG. 6 is a plot of carrier lifetime vs. light intensity for examples of depleted heterojunction photovoltaic cells with dual-shell-passivated quantum dots within the scope of the present invention.
• FIG. 7 is a plot of current density vs. voltage for examples of depleted
• substantially depleted as used herein to characterize the region(s) adjacent to a heterojunction denotes that the charge density in the region(s) is orders of magnitude less than that of the metal side of a Schottky junction.
• the charge density is three or more orders of magnitude less than the charge density of conducting metals, and in many of these, the charge density is four or more, five or more, or six or more orders of magnitude less. Particularly effective results can be achieved when the depleted charge density is on the n-type electron accepting layer side of the junction.
• a range of charge density in the depleted region is about 1 x 10 12 cm “1 to about 1 x 10 18 cm “1 , or alternatively about 1 x 10 14 cm “1 to about 1 x 10 17 cm “1 , or as a further alternative about 1 x 10 15 cm “1 to about 1 x 10 1 ' cm “1 .
• bandgap difference i.e., the difference between the bandgap magnitude on one side of the junction and the bandgap magnitude on the other side of the junction
• a bandgap difference i.e., the difference between the bandgap magnitude on one side of the junction and the bandgap magnitude on the other side of the junction
• the bandgap of greater magnitude will reside in the n-type electron-accepting layer.
• Quantum dots are particularly useful as the nanoparticles, and colloidal quantum dots, i.e., quantum dots manufactured by colloid chemistry, are notable examples.
• metal chalcogenide quantum dots are well known in the art, and lead chalcogenide, and particularly lead sulfide, quantum dots are of particular interest.
• Quantum dots are known to absorb light at wavelengths related to the diameters of individual quantum dots, and this property can be used in the present invention to select or optimize the light-absorbing characteristics of the quantum dots.
• quantum dots with a number-average diameter within the range of about 2nm to about 15nm can be used effectively, while those with a number-average diameter within the range of about 3nm to about lOnm are often the most appropriate, and among these the range of about 3nm to about 6nm are often even more useful.
• the n-type electron-accepting layer can vary widely in composition, provided that the combination of n-type electron-accepting layer and light-absorbing nanoparticles when placed in contact form the depleted heterojunction described above.
• Metal oxides are examples of materials that can serve effectively as the n-type electron-accepting layer, and a particularly useful example of a metal oxide is titanium dioxide.
• the core of such a nanoparticle is generally a quantum dot having exposed anions at its surface.
• the quantum dot core is in many cases a metal chalcogenide colloidal quantum dot, most often a metal sulfide colloidal quantum dot.
• a noted example is lead sulfide, and lead sulfide quantum dots are often lead rich, with a surface composed primarily of exposed Pb 2+ ions but also containing exposed S 2" ions.
• the cations of the inner shell bind to, and thereby passivate, the S 2 ⁇ ions at the core surface, while the anions in the outer shell bind to, and thereby passivate, the cations of the inner shell.
• Examples of cations that can be used for the first shell are Cd 2+ , Pb 2+ , Zn 2+ , and Sn 2+ . Among these, Cd 2+ is particularly convenient and effective.
• Examples of anions effective for use as the second shell are halogen ions and the thiocyanate ion. Of these, halogen ions, and particularly bromine ion, are optimal or particularly convenient in certain cases.
• the present invention resides in the formation of passivated p-type semiconductor nanoparticles without using organic ligands as passivating agents.
• a Cd 2+ is cadmium(II) chloride-tetradecylphosphonic acid-oleylamine.
• anion-containing reagents are quaternary ammonium halides and thiocyanates, and specific examples are cetyltrimethylammonium bromide, hexatrimethylammonium chloride, tetrabutylammonium iodide, and tetrbutylammonium thiocyanate.
• Photovoltaic devices utilizing one or more of the features described above will typically contain at least two electrodes, one electrically connected to each of the two semiconductor layers of the heterojunction.
• a first electrode will be in direct electrical contact with the n-type metal oxide layer and a second electrode will be in contact with the colloidal quantum dot layer.
• the first electrode in many cases is a light-transmitting electrode, and examples are aluminum oxide, zinc oxide, indium tin oxide (ITO), and fluorine-doped tin oxide (FTO).
• the second electrode in many cases is either nickel, lithium fluoride, platinum, palladium, silver, gold, or copper, or alloys of two or more of these metals, such as alloys of silver, gold, and copper.
• a first electrode will be in direct electrical contact with the n-type metal oxide layer and a second electrode will be in contact with the colloidal quantum dot layer.
• the first electrode in many cases is a light-transmitting electrode, and examples are aluminum oxide, zinc oxide, in
• This example illustrates the preparation of depleted heterojunction photovoltaic cells within the scope of the present invention, each formed by depositing a layer of PbS colloidal quantum dots (approximately 10 17 cm “3 n-type doping) of varying diameters— 3.7nm (bandgap 1.3eV), 4.3nm (bandgap 1.1 eV), and 5.5nm (bandgap 0.9eV)— over transparent Ti0 2 electrodes.
• PbS colloidal quantum dots approximately 10 17 cm "3 n-type doping
• the Ti0 2 electrodes were prepared on Sn0 2 :F (FTO)-coated glass substrates (Pilkington TEC 15, Hartford Glass, Inc., Hartford City, Indiana, USA) with a Ti0 2 paste (DSL-90T, Dyesol Ltd., Queanbeyan, NSW, Australia) as follows.
• the FTO substrates were first rinsed with toluene, then sonicated for twenty minutes in a mixture of Triton in de- ionized water (1-3% by volume).
• a Ti0 2 paste was prepared by combining one part by weight Ti0 2 nanoparticles with three parts by weight terpineol.
• the paste was then spin cast at 1500rpm for ninety seconds on the TiCU-treated FTO substrates. One edge of each substrate was then wiped free of the paste with a swab soaked in isopropyl alcohol to expose a section of claim FTO for electrical contacting. This was immediately followed by sintering for one hour on a hotplate at 400°C.
• the substrates were then placed in a bath of 60mM TiCl 4 in de-ionized water, and baked in the bath at 70°C for thirty minutes. They were then rinsed with de -ionized water, dried with nitrogen, and placed in a 520°C tube furnace for one hour, then cooled to room temperature. The sample was then allowed to cool, and the T1CI 4 treatment was repeated, followed by a final heating to 520°C.
• the substrates were then placed in individual substrate holders and stored in air for up to one week prior to further processing.
• PbS colloidal quantum dots were prepared as follows. Bis(trimethylsilyl)sulphide (TMS, synthesis grade) (0.18g, lmol) was added to 1-octadecene (lOmL), which had been dried and degassed by heating to 80°C under vacuum for 24 hours. A mixture of oleic acid (1.34g, 4.8mmol), PbO (0.45g, 2.0mmol), and 1-octadecene (14.2g, 56.2mmol) was heated to 95°C under vacuum for sixteen hours, then placed under Ar.
• TMS trimethylsilyl)sulphide
• the flask temperature was increased to 120°C and the TMS/octadecene mixture was injected, causing the temperature to drop to about 95°C, and the flask was allowed to cool to 36°C.
• the nanocrystals were precipitated with 50mL of distilled acetone and centrifuged under ambient conditions. The supernatant was then discarded, and the precipitate was redispersed in toluene, precipitated again with 20mL of acetone, centrifuged for five minutes, dried, and again dispersed in toluene (about 200mg mL "1 ).
• the nanocrystals were then placed in a N 2 -filled glove box, where they were precipitated twice with methane and then finally redispersed at 25 or 50mg mL "1 in octane.
• the resulting oleate-capped PbS quantum dots were deposited on the Ti0 2 by multilayer spin-coating of the Ti0 2 surface with 25 or 50 mg/mL solutions of the quantum dots in octane under ambient conditions. Each layer was deposited at 2500 rpm, then treated briefly with 10% 3-mercaptopropionic acid in methanol to displace the oleate ligand and thereby render the quantum dots insoluble, then rinsed with methanol and octane. Fifteen deposition cycles using the 25mg/mL dispersion produced thermally stable layers 22nm in thickness on the Ti0 2 substrate, and eight deposition cycles using the 50mg/mL dispersion also produced thermally stable layers of the same thickness.
• Each layered medium was then transferred to a glove box with N 2 atmosphere and left overnight.
• a gold contact was then deposited on the quantum dot layer by DC sputtering with 5mTorr Ar pressure at a power density of 1 W cm "2 through a shadow mask to thicknesses of 150nm to 200nm.
• Spatially- resolved X-ray elemental analyses and transmission electron microscopy were performed on a thin section sample prepared by focused-ion-beam milling, and revealed very little interpenetration of the quantum dot and Ti0 2 layers.
• FIG. 1 is a plot of the photovoltaic response of a depleted heterojunction solar cell as prepared above, expressed as current density in mA cm "2 vs. voltage, with the lower curve representing the dark current and the upper curve representing the illuminated current of a cell fabricated with 1.3eV-bandgap quantum dots (3.7nm).
• the data was measured using a Keithley 2400 source-meter under ambient conditions.
• the solar spectrum at AMI .5 was simulated to within class A specifications with a Xe lamp and filters with the intensity adjusted to lOOmW cm "2 .
• the source intensity was measured with a Melles-Griot broadband power meter (responsive from 300nm to 2000nm), through a circular 0.049cm 2 aperture at the position of the sample and confirmed with a calibrated solar cell.
• the accuracy of the power measurement was estimated to be ⁇ 7%.
• the average value of V oc was 0.53 ⁇ 0.02V
• the average value of J sc was 15.4 ⁇ 1.4mA cm "2
• the average value of FF was 57 ⁇ 4%.
• the average AMI .5 power conversion efficiency ⁇ was thus 4.9 ⁇ 0.3%.
• V oc was 0.52V
• J sc was 16.4mA cm "2
• FIG. 2 is a plot of the photovoltaic response of a depleted heterojunction solar cell as prepared above, expressed as current in mA vs. voltage, with the lower curve representing cells fabricated with 0.9eV-bandgap (5.5nm) quantum dots, the middle curve representing the cells fabricated with l . leV-bandgap (4.3nm) quantum dots, and the upper curve representing the cells fabricated with 1.3eV-bandgap (3.7nm) quantum dots.
• FIG. 3 is a plot of external quantum efficiency (EQE) vs. wavelength and of absorption vs. wavelength, with the lower curve representing the EQE for the best-performing 1.3eV-bandgap quantum dot device and the upper curve representing the spectral absorption of the same device.
• the EQE is the ratio of extracted electrons to incident photons and the curve is also known as the incident photon conversion efficiency spectrum.
• the EQE was obtained by passing the output of a 400W Xe lamp through a monochromator and using appropriate order- sorting filters. The collimated output of the monochromator was measured through a 1.5nm aperture with a calibrated Newport 818-UV power meter.
• the measurement bandwidth was about 40nm and the intensity varied with the spectrum of the Xe lamp.
• the average intensity was 0.3mW cm "2 .
• the current-voltage response was measured with Keithley 2400 source-meters. The plot shows that at short wavelengths, the EQE reached values above 60%, while at longer wavelengths the EQE had a peak of 24%.
• FIG. 4 is a plot of device capacitance vs. bias voltage and of device resistance vs. bias voltage.
• the capacitance arises from the depletion layer due to charge transfer from Ti0 2 to the PbS colloidal quantum dot layer.
• Capacitance-voltage measurements were performed directly on the photovoltaic devices using an Agilent 4284A LCR meter.
• This example illustrates the preparation and use of nanoparticles containing a quantum dot core, an inner shell of cations and an outer shell of anions, within the scope of the present invention.
• Colloidal quantum dots capped with oleic acid ligands were synthesized and stripped of their oleate ligands, in the manner described in Example 1. These quantum dots were prepared with an excess of Pb during synthesis, resulting in a lead-rich bulk
• CdCl 2 -TDPA-OLA CdCl 2 -tetradecylphosphonic acid- oleylamine
• Photovoltaic devices utilizing these dual-shell-passivated quantum dots were fabricated in the same manner as described in Example 1 above.
• a scanning electron micrograph showed that the quantum dot layer was approximately 300nm in thickness and was free of the voids and cracks that often occur in films made from layer-by-layer deposition.
• Absorption spectra of the devices were obtained in a double pass by including reflection from the Au top contact.
• the spectra of devices made using 9, 11, and 13 quantum dot layers are shown in FIG. 5, which also includes corresponding spectra from the bare FTO/T1O 2 substrate.
• the absorption peak at 950nm is the excitonic peak of the PbS quantum dots. This indicates that quantum confinement of the core quantum dots was preserved in the shelled form.
• a reduction in interparticle distance is suggested by the red- shift (-lOOmeV) of the excitonic peak in the final film as compared to the excitonic peak of dots in solution.
• the device Upon exposure to 100 mW/cm 2 solar illumination, the device showed an open circuit voltage (V oc ) of 0.45V, a short-circuit current density (J sc ) of 21.8mA/cm 2 , and a fill factor (FF) of 59%, yielding a power conversion efficiency ⁇ of 5.76%.
• Integration of the net absorption of the quantum dot film over the AMI .5G spectrum indicates that a film having 100% quantum efficiency would have achieved a circuit current density (J c ) of 24.4mA/cm 2 . Comparing this with the measured circuit current density (J c ) of 21.8mA/cm 2 indicates that the internal quantum efficiency (IQE) averaged across the entire broadband absorbing region of 400-
• the doping density and carrier lifetime of the dual-shell-passivated quantum dot films were determined by capacitance-voltage (C-V) and V oc decay analyses, respectively.
• C-V analysis showed that doping was a full order of magnitude lower than in the lowest- doped organic ligand PbS and PbSe quantum dot films, and the carrier lifetime ⁇ , which is shown in FIG. 6, was approximately twice as long as that of a control device made using a bidentate organic ligand (3-mercaptopropionic acid, also shown in FIG. 6), reaching a remarkably long lifetime of over 40 ⁇ iSQC even under full solar 100 mW/cm 2 illumination.
• FIG. 7 is a plot of current density vs. voltage, comparing a layer of dual-shell- passivated quantum dots in accordance with the invention with quantum dots bearing 3- mercaptopropionic acid ligands, each shown both fresh (immediately after fabrication) and after ten days of storage under ambient conditions on a laboratory bench.
• the dual-shell- passivated quantum dots showed no significant change in performance over the ten-day period, while the organic ligand-capped quantum dots underwent a complete loss of efficiency over the same period.
• HTAC hexatrimethylammonium chloride
• CTAB cetyltrimethylammonium bromide
• TBAI tetrabutylammonium iodide
• TBAT tetrabutylammonium thiocyanate

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Photovoltaic Devices (AREA)

Priority Applications (9)

Applications Claiming Priority (6)

Publications (1)

Family

ID=44708204

Family Applications (1)

Country Status (11)

Cited By (3)

Families Citing this family (26)

Citations (2)

Family Cites Families (24)

• 2010
  • 2010-09-27 US US12/890,797 patent/US9382474B2/en active Active
• 2011
  • 2011-03-25 BR BR112012025386A patent/BR112012025386A2/pt not_active Application Discontinuation
  • 2011-03-25 SG SG2012073268A patent/SG184407A1/en unknown
  • 2011-03-25 KR KR1020127029025A patent/KR101894408B1/ko not_active Expired - Fee Related
  • 2011-03-25 EP EP11711741.6A patent/EP2556131B1/en active Active
  • 2011-03-25 CA CA3061443A patent/CA3061443C/en active Active
  • 2011-03-25 CN CN201610694633.6A patent/CN106167704B/zh not_active Expired - Fee Related
  • 2011-03-25 CN CN201180017884.6A patent/CN102859710B/zh not_active Expired - Fee Related
  • 2011-03-25 RU RU2012131848/28A patent/RU2012131848A/ru not_active Application Discontinuation
  • 2011-03-25 CA CA2795719A patent/CA2795719C/en active Active
  • 2011-03-25 JP JP2013503781A patent/JP6117693B2/ja not_active Expired - Fee Related
  • 2011-03-25 WO PCT/US2011/030074 patent/WO2011126778A1/en not_active Ceased
  • 2011-03-25 AU AU2011238678A patent/AU2011238678A1/en not_active Abandoned
• 2016
  • 2016-06-24 US US15/192,361 patent/US10784388B2/en active Active
  • 2016-11-18 JP JP2016225169A patent/JP6360130B2/ja not_active Expired - Fee Related

Patent Citations (2)

Non-Patent Citations (8)

Also Published As

Similar Documents

Legal Events