WO2009129540A1 - Photodétecteurs et éléments photovoltaïques basés sur des nanocristaux semi-conducteurs - Google Patents

Photodétecteurs et éléments photovoltaïques basés sur des nanocristaux semi-conducteurs Download PDF

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WO2009129540A1
WO2009129540A1 PCT/US2009/041153 US2009041153W WO2009129540A1 WO 2009129540 A1 WO2009129540 A1 WO 2009129540A1 US 2009041153 W US2009041153 W US 2009041153W WO 2009129540 A1 WO2009129540 A1 WO 2009129540A1
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semiconductor material
under
semiconductor
mobility
devices
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PCT/US2009/041153
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English (en)
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Edward Hartley Sargent
Ghada Koleilat
Jiang Tang
Keith William Johnstons
Andrea Geza Pattantyus-Abraham
Gerasimos Konstantatos
Ethan Jacob Dukenfield Klem
Stefan Myrskog
Dean Delehanty Macneil
Jason Paul Clifford
Larissa Levina
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Invisage Technologies, Inc.
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Priority claimed from US12/106,256 external-priority patent/US7923801B2/en
Application filed by Invisage Technologies, Inc. filed Critical Invisage Technologies, Inc.
Publication of WO2009129540A1 publication Critical patent/WO2009129540A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
    • 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

Definitions

  • the disclosure herein relates generally to optical and electronic devices, systems and methods that include optically sensitive material, such as nanocrystals or other optically sensitive material, and methods of making and using the devices and systems.
  • optically sensitive material such as nanocrystals or other optically sensitive material
  • Conjugated polymers have been widely investigated and have shown promising efficiencies. However, they remain transparent in most of the infrared spectral region Because half the sun's energy lies in the infrared, the optimal bandgap for a single-junction solar cell lies in the infrared, well beyond the sensitivity of today's organic solar cells,
  • colloidal quantum dots offer tuning to access different spectral regions through simple variation of their chemical synthesis.
  • lead salt colloidal quantum dots can be engineered to access the visible and the short-wavelength infrared spectral regions
  • organic polymers sensitized using infrared lead salt nanocrystals have been investigated; however, these devices did not exceed monochromatic power conversion efficiencies of 0.1%.
  • Solution-processed photovoltaics offer solar energy harvesting characterized by low cost, ease of processing, physical flexibility, and large area coverage
  • Conjugated polymers, inorganic nanocrystals (NCs), and hybrid materials have been widely investigated and optimized to this purpose.
  • Organic solar cells have already achieved 6 5% solar conversion efficiencies.
  • these devices fail to harvest most of the infrared (IR) spectral region.
  • High efficiency multijunction solar cells offer the prospect of exceeding 40% efficiency through the inclusion of infrared-bandgap materials.
  • infrared single junction solar cells should be optimized for infrared power conversion efficiency rather than solar power conversion efficiency.
  • the smallest-bandgap junction optimally lies at 1320 nm and 1750 nm respectively. Attempts to extend organic solar cell efficiency into the near infrared have so far pushed the absorption onset only to 1000 nm.
  • Figure IA shows the device architecture comprising Al on a PbS nanocrystal (NC) film, under an embodiment.
  • Figure IB shows the energy band model of the device, under an embodiment
  • Figure 2 shows the current-voltage curve and photovoltaic performance (under 975 nm, 12 mW cm "2 illumination) for a device, under an embodiment.
  • Figure 3A is a comparison of the current- voltage characteristics for a first cell configuration in the dark and under illumination from variations of the simulated solar illumination source, under an embodiment
  • Figure 3B is a comparison of current- voltage curves for a first cell configuration (under 975 nm illumination) and a second cell configuration (under 1550 nm illumination), under an embodiment.
  • Figure 3C shows EQE spectra for a first cell configuration and a second cell configuration, under an embodiment
  • Figure 4 shows a summary of the photovoltaic device performance parameters obtained from the various devices, under an embodiment
  • Figure 5A shows Transmission Electron Microscopy of as-synthesized oleic-acid capped PbSe NCs (diameter approximately 5 nm), under an embodiment
  • Figure 5B shows Transmission Electron Microscopy of PbSe NCs following octylamine ligand exchange (the inter -nanoparticle distance was reduced), under an embodiment.
  • Figure 5C shows Transmission Electron Microscopy of networks of PbSe NCs after benzenedithiol treatment due to the strong affinity of the thiol-end groups for the Pb atoms, under an embodiment
  • Figure 5D shows absorption of single treated (red) and double treated (blue) layers of PbSe NCs, under an embodiment.
  • Figure 6 shows the performance of three differently processed PbSe CQD devices, two of which exhibited similar external quantum efficiencies, under an embodiment.
  • Figure 7 shows a table summarizing the best performances of differently processed devices recorded under 12 mW cm "2 illumination at 975 nm, under an embodiment.
  • Figure 8A shows photovoltaic device performance, specifically current-voltage characteristics of a benzenedithiol treated two-layered device exhibiting 3 6% monochromatic power conversion efficiency at 975 nm under 12 mW cm " illumination, under an embodiment.
  • Figure 8B shows photovoltaic device performance, specifically simulated solar power conversion efficiency of more than 1.1% (i.e. AM 1.5 at 100 mW cm "2 ), under an embodiment.
  • Figure 8C shows photovoltaic device performance, specifically spectral external quantum efficiency of a device reaching 37% in the infrared and about 70% in the visible range, under an embodiment.
  • Figure 8D shows a spatial band diagram showing the device model, under an embodiment
  • Figure 9A is a plot of EQE stability comparison of benzenedithiol treated PbSe devices with previously reported amine-capped devices stored in air and in inert atmosphere, under an embodiment
  • Figure 9B is a plot of PCE stability comparison of benzenedithiol treated PbSe devices with previously reported amine-capped devices stored in air and in inert atmosphere, under an embodiment
  • Figure 1OA shows current- voltage characteristics of BDT treated PbSe CQD devices with bottom ITO contact and with Au top contact, under an embodiment.
  • Figure 1OB shows current-voltage characteristics of BDT treated PbSe CQD devices with bottom ITO contact and with Ag top contact, under an embodiment.
  • Figure 1OC shows current-voltage characteristics of BDT treated PbSe CQD devices with bottom ITO contact and with Al top contact, under an embodiment
  • Figure HB shows the output current density transient for typical CELIV transients
  • the hole mobility is determined from t max
  • Figure 12 summarizes the contribution of the depletion and quasi-neutral regions to the EQE under 12 mW cm "2 intensity at 975 nm, under an embodiment.
  • Figure 13 is a schematic diagram of the analytical model used in determining where electron-hole pairs were generated, under an embodiment
  • Figure 14 shows a representative ToF transient plot.
  • Figure 15 is a plot of carrier recombination lifetime (blue, left axis) and external quantum efficiency (red, right axis) versus illumination intensity at 975 nm, under an embodiment
  • Figure 16 shows a typical OCVD transient
  • Figure 17 shows transfer characteristics of PbSe NC thin film field-effect transistors, under an embodiment.
  • Figure 19A shows TEM images of chalcopyrite (CuGaSe 2 ) nanoparticles synthesized along with their corresponding SAED pattern, under an embodiment
  • Figure 19B shows TEM images of chalcopyrite (CuInSe 2 ) nanoparticles synthesized along with their corresponding SAED pattern
  • Figure 19C shows TEM images of chalcopyrite (CIGS) nanoparticles synthesized along with their corresponding SAED pattern
  • Figure 2OA shows powder XRD patterns of CuGaSe 2 , CuInSe 2 and CIGS nanoparticles, under an embodiment.
  • the vertical lines below indicate the corresponding reflection peaks for bulk CuIn 0 5 Ga 0 5 Se 2 (JCPDS 40-1488), CuGaSe 2 (JCPDS 79-1809) and CuInSe 2 (JCPDS 40-1487).
  • Figure 2OB shows an ensemble of UV-vis-NIR absorption spectrum of CuGaSe 2 , CuInSe 2 and CIGS nanoparticles in toluene, under an embodiment.
  • Figure 211 shows plots of size distribution of as-synthesized nanoparticles (data based on manual counts of 80 nanoparticles from TEM images), under an embodiment
  • Figure 22 A shows TEM images of CuGaSe 2 synthesized by cooking Cu(Ac),
  • Ga(acac) 3 and Se powder in oleylamine at 250 C under an embodiment.
  • Figure 22B and 22C show TEM images of CuInSe 2 synthesized by cooking Cu(Ac), In(Ac) 3 and Se powder in oleylamine at 250 C, under an embodiment
  • Figure 23A shows TEM images and corresponding SAED Of CuGaSe 2 hexagonal microplates obtained in oleylamine and oleic acid mixture, under an embodiment.
  • Figure 23B shows TEM images and corresponding SAED Of CuInSe 2 hexagonal microplates obtained in oleylamine and oleic acid mixture
  • Figure 24A shows TEM images of CuInSe 2 nanoparticles synthesized from Cu(acac) 2 and In(Ac) 3 precursors at 250 0 C (scale bars are 50 nm), under an embodiment
  • Figure 24B shows TEM images Of CuInSe 2 nanoparticles synthesized from Cu(Ac) and In(Ac) 3 precursors at 250 0 C (scale bars are 50 nm), under an embodiment
  • Figure 24C shows TEM images of CuInSe 2 nanoparticles synthesized from Cu(acac) 2 and In(acac) 2 precursors at 250 0 C (scale bars are 50 nm), under an embodiment
  • Figure 24D shows TEM images of CuInSe 2 nanoparticles synthesized from Cu(Ac) and In(acac) 3 precursors at 250 0 C (scale bars are 50 nm), under an embodiment
  • Figure 25A shows TEM images of CIGS nanoparticles synthesized by injection Cu(acac) 2 , In(acac) 3 and Ga(acac) 3 oleylamine solution into Se/oleylamine at an injection temperature of 270 0 C, under an embodiment.
  • Figure 25B shows TEM images of CIGS nanoparticles synthesized by injection Cu(acac) 2 , In(acac) 3 and Ga(acac) 3 oleylamine solution into Se/oleylamine at an injection temperature of 220 0 C, under an embodiment.
  • Figure 26A shows TEM images of CIGS nanoparticles synthesized with a precursor ratio CIGE3228-0,15mmol Cu(acac) 2 , O. lmmol Ga(acac) 3 and O.lmmol In(acac) 3 to 0 4mmol Se, under an embodiment.
  • Figure 26B shows TEM images of CIGS nanoparticles synthesized with a precursor ratio CIGE4138 - 0,20mmol Cu(acac) 2 , 0,15mmol Ga(acac) 3 and 0 05mmol In(acac) 3 to 0.40 mmol Se, under an embodiment.
  • Figure 26C shows XRD patterns of CIGS nanoparticles synthesized with precursor ratios CIGE3228-0 15mmol Cu(acac) 2 , O.lmmol Ga(acac) 3 and O.
  • Figure 27 shows XRD patterns of CIGS nanoparticles arrested for different reaction duration
  • Figure 28A shows representative TEM images and SAED pattern of CuInS 2 nanoparticles produced in oleylamine using sulfur powder instead of selenium powder, under an embodiment.
  • Figure 28B shows representative TEM images and SAED pattern Of CuGaS 2 nanoparticles produced in oleylamine using sulfur powder instead of selenium powder, under an embodiment.
  • Figure 29 shows composition of CIGS nanoparticles of an embodiment calculated from Inductively Coupled Plasma Atomic Emission Spectrometry (ICP)
  • High photocurrent including large external quantum efficiency (electrons of primary photocurrent per second per photon incident per second) and, in embodiments, large gain (electrons of total photocurrent per second per photon incident per second); low dark currents; a high ratio of photocurrent to dark current for a given level of illumination; rapid temporal response compatible with imaging.
  • Additional properties desired for energy harvesters include but are not limited to the following: efficient conversion of optical power of a particular wavelength into electrical power (a high monochromatic power conversion efficiency); efficient conversion of a band of wavelengths into electrical power (in the case of the totality of the sun's spectrum, a high solar AMI 5 power conversion efficiency); relatively large external quantum efficiency, relatively large open-circuit voltage; relatively large fill- factor
  • Embodiments described herein include the realization of materials having the aforementioned properties
  • Embodiments described herein include a composite material comprising semiconductor nanocrystal and organic molecules.
  • the organic molecules passivate the surfaces of the semiconductor nanocrystals, and facilitate the transfer of charge between the semiconductor nanocrystals
  • Enhancements in the mobility of at least one type of charge carrier e g., electrons, holes, both electrons and holes
  • a p-type semiconductor material comprises semiconductor nanocrystals where the mobility of holes is greater than or equal to the mobility of electrons
  • at least one benzene ring forms at least a portion of the organic molecules and provides derealization of at least one type of charge carrier, such as electrons, thereby facilitating the transport of that type of charge carrier.
  • a semiconductor material is electrically addressed using a first and a second electrode.
  • the semiconductor material is a p-type semiconductor comprising semiconductor nanocrystals, wherein the mobility of electrons in the semiconductor material is greater than or equal to the mobility of holes.
  • a device, comprising a first and a second electrode, as well as a semiconductor material comprising semiconductor nanocrystals provides for the sensitive detection of light, including a combination of high external quantum efficiency, low dark current, and video- frame-rate-compatible temporal response
  • the device may further provide gain, wherein more than one electron of current flows per second for every photon per second of illuminating light.
  • a device, comprising a first and a second electrode, as well as a semiconductor material comprising semiconductor nanocrystals provide efficient conversion of optical power into electrical power
  • Materials from which the semiconductor nanocrystals of an embodiment are made may include one or more of the following, but the embodiment is not so limited: PbS, PbSe, PbTe; CdS; CdSe; CdTe; SnS; SnSe; SnTe; Si; GaAs; Bi2S3; Bi2Se3; CuInS2, CuInSe2; Cu(InGa)Se2 (CIGS); CuGaSe2.
  • Materials incorporated into the organic component of the film of an embodiment may include one or more of the following, but the embodiment is not so limited: Benzenedithiol; Dibenzenedithiol; Mercaptopropionic acid, Mercaptobenzoic acid, Pyridine; Pyrimidine; Pyrazine; Pyridazine; Dicarboxybenzene; Benzenediamine, Dibenzenediamine
  • the embodiments described herein provide planar, stackable PbS nanocrystal quantum dot photovoltaic devices with infrared power conversion efficiencies up to 4 2%. This represents a three-fold improvement over the previous efficiencies obtained in the more complicated, stacking-incompatible nanoporous architecture.
  • the planar Schottky photovoltaic devices described herein were prepared from solution-processed PbS nanocrystal quantum dot films with aluminum and indium tin oxide contacts. These devices exhibited up to 4.2% infrared power conversion efficiency, which is an approximate three-fold improvement over previous results, and solar power conversion efficiency reached 1.8%
  • the architecture of the devices described herein allows for direct implementation in multi- junction photovoltaic device configurations
  • Nanocrystal films were spin-coated in an inert atmosphere onto indium tin oxide (ITO)-coated glass substrates from a 150 mg mL "1 octane solution to produce films between 100 and 300 nm thick.
  • ITO indium tin oxide
  • the Schottky contact was formed using a stack of 0 7nm LiF/140 nm Al/190 nm Ag deposited by thermal evaporation through a shadow mask, all devices had a top contact area of 3.1 mm 2 . Photocurrents were seen to scale with device area up to 7.1 mm 2 , and negligible photocurrents were observed when the contacts were illuminated from the metallized side.
  • Figure IA shows the device architecture comprising Aluminum (Al) on a PbS nanocrystal (NC) film (the inset shows a SEM of the nanocrystal film), under an embodiment
  • the device comprises a first electrode that is the transparent conducting ITO contact
  • the device further comprises a second electrode that includes the Al
  • the device includes a semiconductor layer positioned between the first and second electrodes
  • the semiconductor layer of an embodiment includes colloidal quantum dots (CQDs) passivated with organic ligands, such as PbS CQDs passivated with butylamine, or passivated with benzenedithiol Spin-coating the nanocrystals from octane solutions led to smooth, densely-packed air ays, as shown by the scanning electron micrograph (SEM) of the inset (scale bar is 20 nm)
  • SEM scanning electron micrograph
  • Figure IB shows the energy band model of the device, under an embodiment.
  • a Schottky barrier was formed at the junction between thermally deposited Al and the p-type PbS colloidal nanocrystal film, and was the electron-extracting contact Photogenerated holes were extracted through the transparent conducting ITO contact
  • the energy band model illustrates the presence of bending in the conduction band (E c ), valence band (E v ), and vacuum energy (E vac ) near the Al/nanocrystal interface, under an embodiment
  • Photogenerated electron (e ⁇ ) and hole (h + ) transport is governed by the presence of a built-in electric field within the depletion layer (of width W) of the nanocrystal layer (of thickness d).
  • the Fermi level (Ef) is drawn to show the p-type conduction characteristics
  • the bandgap (E g ) of these nanocrystals is approximately 0 75 eV, defined by the first maximum in the absorption spectrum.
  • the PbS nanocrystals were synthesized using an organometallic route and ligand-exchanged to /?-butylamine as described previously.
  • Figure 2 shows the current-voltage curve and photovoltaic performance (under 975 nm, 12 mW cm "2 illumination) for a device processed using the optimized passivation (curve 2) procedure compared to the baseline (curve 1), showing an increase in V oc , under an embodiment.
  • Nanocrystals having undergone both the optimized passivation and ligand exchange procedures yielded devices with enhanced V oc and ⁇ Q ⁇ compared to the baseline; this is emphasized by the enclosure that represents the maximum power (P n ) load conditions Fill factor is represented as "FF” and power conversion efficiency is represented as "PC ⁇ ” Device open-circuit voltage (V oc ) was increased by a factor of two without lowering
  • the nanocrystals were passivated with ⁇ 2 5 nm long oleate ligands These long ligands pievent close nanocrystal packing and therefore impede charge transport in films, Many of the long oleate ligands were removed via repeated precipitations using methanol; a single precipitation was used for the baseline device.
  • the process of an embodiment included a solution-phase ligand exchange to the ⁇ 0.6 nm long n-butylamine ligand Nuclear magnetic resonance spectroscopy confirmed an increase in the extent of ligand exchange increased with the number of methanol precipitations, three methanol- induced precipitations proved to be an optimal compromise between charge transport efficiency and colloidal stability,
  • This solution-phase approach in contrast with solid state ligand exchanges, enabled the spin-coating of smooth, crack-free films necessary for high- yield, large-area devices,
  • a first cell configuration of an embodiment used 230 nm thick layers of PbS nanocrystals with a first excitonic transition at 1650 nm, which is close to the optimal infrared band gap (1750 nm) in a triple-junction cell
  • a second cell configuration of an embodiment provided maximum power conversion at 1550 nm, using smaller nanocrystals (with enhanced absorption at this wavelength) in slightly thicker films (250 nm).
  • Figure 3A is a comparison of the current- voltage characteristics for a first cell configuration in the dark and under illumination from variations of the simulated solar illumination source, under an embodiment.
  • Figure 3B is a comparison of current -voltage curves for a first cell configuration (under 975 nm illumination) and a second cell configuration (under 1550 nm illumination), under an embodiment.
  • Figure 3C shows EQE spectra for a first cell configuration and a second cell configuration, under an embodiment. The inset shows the absorption spectra of the ligand-exchanged nanocrystals in solution; excitonic peaks were also visible in the film absorption spectra au, arbitrary units.
  • Figure 4 shows a summary of the photovoltaic device performance parameters obtained from the various devices, under an embodiment While the V oc values are not large in absolute terms, they are high as a fraction of the material bandgap Device performance was maintained for up to 5 hours in air but degraded completely over 24 hours Nanocrystal films were stable in an inert environment for long durations (seven days), which indicates that encapsulation could improve long-term stability.
  • Short-circuit current density is represented as "Jsr”
  • power conversion efficiency is represented as "PCE”
  • the EQE spectrum of devices was measured by illuminating the devices with monochromatic light, measuring the current under short-circuit conditions, and scaling them with respect to the previously indicated EQEs measured at 975 nm and 1550 nm (for the first and second cell configurations, respectively)
  • the EQE spectra for devices of both designs are shown in Figure 3C
  • the features of the colloidal nanocrystal absorption spectrum (inset) are manifest in the EQE spectra wherein a well-defined first excitonic transition is retained even in densely-packed, conductive films.
  • the EQE reached values near 60% for visible wavelengths.
  • Film absorption data was also acquired by measuring the fraction of light reflected through the substrate and correcting for ITO and Al absorption
  • the film absorptions at 975 nm and 1550 nm were 41% and 14%, respectively, which indicates that the internal quantum efficiency exceeded 90% for the best devices.
  • Efficient, Stable Infrared Photovoltaics based on Solution-Cast Colloidal Quantum Dots The embodiments described below provide efficient solar cells (e g , 3 6% power- conversion efficiency) operating in the infrared to evince multi-week stability Since ligands previously employed in record-setting solar cells are labile and reactive with adjacent metal contacts, militating against long-lived device efficiency, a strongly-binding end functional group was selected to passivate the nanoparticle surfaces robustly in the solid state of an embodiment, while avoiding reactivity with the adjacent metal contact A further increase in proximity among the nanoparticles could be achieved, and could result in improved electron and hole transport, without sacrificing the highly desired quantum size-effect tuning offered by the use of colloidal quantum dots, so the devices described herein comprise a short bidentate linker having a conjugated, instead of an entirely insulating, moiety lying between the end groups.
  • the PbSe CQD based photovoltaic device of an embodiment achieves 3 6% infrared power conversion efficiency (PCE). This appears to be the first PbSe colloidal quantum photovoltaic to exceed one percent infrared PCE It also represents the first solution-processed infrared photovoltaic device to be stable over weeks without requiring fresh deposition of its top electrical contact. Thus, the devices described herein appear to be the first to manifest, and indeed exploit, a very surprising feature - the diffusion of charge carriers, within a colloidal quantum dot solid, over hundreds of nanometers
  • the PbSe NCs of an embodiment are synthesized using a modified version of the organometallic route reported for PbS NCs.
  • Figure 5A shows Transmission Electron Microscopy of as-synthesized oleic-acid capped PbSe NCs (diameter approximately 5 nm), under an embodiment
  • the as-synthesized NCs were capped with approximately 2 nm oleate ligands, previously reported to impede efficient charge transport in films
  • the benzenedithiol crosslinking was preceded with a solution-phase ligand exchange.
  • FIG. 5B shows Transmission Electron Microscopy of PbSe NCs following octylamine ligand exchange (the inter -nanoparticle distance was reduced), under an embodiment
  • Figure 5C shows Transmission Electron Microscopy of networks of PbSe NCs after benzenedithiol treatment due to the strong affinity of the thiol-end groups for the Pb atoms, under an embodiment.
  • the crosslinking process performed on the CQD films of an embodiment was optimized by varying the treatment durations through a 1 ,4-Benzenedithiol treatment optimization. After exposing the NC layers to BDT, films were blow dried with nitrogen and subjected to 30 min vacuum drying The crosslinking treatment was further optimized by varying its duration time for each of the two layers.
  • Figure 6 shows the performance of three differently processed PbSe CQD devices, two of which exhibited similar external quantum efficiencies, under an embodiment
  • the best passivated device 604 exhibits an IR PCE of 3 65 % with 40 % fill factor.
  • the fill factor decreases to 34 % when the treatment duration of the first layer 606 is increased
  • the highest fill factor (45 %) is registered for a reduced treatment time for both layers 602
  • the device with 20 min treatment duration for both layers 606 was deeply affected by processing defects because it exhibited the lowest open circuit voltage (V oc ) and fill factor.
  • Figure 6 also shows the best performance of an under-treated device 602 which had a better fill factor resulting from minimal defects but was not as efficient as the best passivated devices 604.
  • Figure 7 summarizes the best performances of differently processed devices recorded under 12 mW cm "2 illumination at 975 nm, under an embodiment
  • FIG. 5D shows absorption of single treated 502 and double treated 504 layers of PbSe NCs, under an embodiment.
  • Thin NC films (-110 nm) were spin-coated on ITO substrates and the samples were immersed in a dilute solution of benzenedithiol in acetonitrile (3.5 mM) for a duration ranging from 10 to 30 minutes This rendered the layer insoluble in the nonpolar solvents that were used for spin-coating the NCs.
  • a second thin layer was deposited on top to ensure the formation of a smooth, densely packed film.
  • the second layer was also subjected to a linking treatment
  • the total thickness of the NCs active layer ranged between 210 and 250 nm.
  • Figure 8A shows photovoltaic device performance, specifically current- voltage characteristics of a benzenedithiol treated two-layered device exhibiting 3 6% monochromatic power conversion efficiency at 975 nm under 12 mW cm "2 illumination, under an embodiment.
  • Figure 8B shows photovoltaic device performance, specifically simulated solar power conversion efficiency of more than 1 1% (i e AMI 5 at 100 mW cm "2 ), under an embodiment From total absorbance measurements at 975 nm, the IQE was found to approach 90%
  • Figure 8C shows photovoltaic device performance, specifically spectral external quantum efficiency of a device reaching 37% in the infrared and about 70% in the visible range, under an embodiment.
  • the spectrally resolved EQE is presented between 400 to 1600 nm.
  • the EQE follows closely the features of the absorption spectrum shown in Figure ID, a well-defined first excitonic peak is observable at 1250 nm. In the visible wavelengths, a peak EQE of 70% is recorded.
  • Figure 8D shows a spatial band diagram showing the device model, under an embodiment.
  • a Schottky barrier is formed at the Mg/p-type semiconducting NCs interface.
  • the majority of the photogenerated carriers diffuse through the quasi-neutral region (L QN ⁇ 145 nm and are separated in the depletion region (W ⁇ 65 nm) A fraction of the carriers is lost to recombination.
  • Figure 9A is a plot of EQE stability comparison of benzenedithiol treated PbSe devices with previously reported amine-capped devices stored in air and in inert atmosphere, under an embodiment.
  • Figure 9B is a plot of PCE stability comparison of benzenedithiol treated PbSe devices with previously reported amine-capped devices stored in air and in inert atmosphere, under an embodiment This data compares the stability of the devices fabricated as described herein with previously reported high-efficiency devices (e g , devices fabricated by spin-coating butylamine-capped PbS NCs on ITO substrates and evaporating Al contacts on top).
  • high-efficiency devices e g , devices fabricated by spin-coating butylamine-capped PbS NCs on ITO substrates and evaporating Al contacts on top.
  • the benzenedithiol-crosslinked PbSe NC devices of an embodiment retained their high EQE values for over ten days when stored in a nitrogen filled glovebox (solid red line), and their PCE maintains 90% of its initial value for more than 2 days
  • the amine-capped devices (dashed red line) severely deteriorated within the first 24 h (e.g , lost half of their EQE and more than 75% of their power conversion efficiency)
  • the benzenedithiol treated devices (solid blue lines) registered greater stability than the amine-capped devices (dashed blue lines) (e g , the dithiol-capped PbSe NC based devices retained their high EQE and ⁇ 80% of their PCE over 48 hours, whereas the amine- capped devices lost all performance within the same period of time). Note that all the testing was done in air, and all the devices in this study were exposed to a minimum of 15 hours of oxygen and moisture. Several high efficiency benzenedithiol treated devices retained over 75% of their EQE for more than two weeks The reported EQE and PCE values were taken under 12 mW cm "2 at 975 nm
  • the depth of the depletion region was then determined The capacitance was measured at zero bias (under short-circuit conditions). The static relative permittivity via the charge extraction was found by linearly increasing voltage (CELIV) method to be 15 ⁇ 1.
  • d is the film thickness (-230 nm), and a is the majority carrier mobility.
  • the mobility was found to be 2.4xlO "3 cm 2 V " 's " ' in the PbSe NC based solar cells of an embodiment
  • the static relative permittivity was found to be 15 ⁇ 1.
  • a typical CELIV transient is represented in figure S6
  • Figure HB shows the output current density transient for typical CELIV transients Hole mobility is determined from tmax-
  • the capacitance was measured at zero bias under short circuit conditions in order to determine the device depletion width (W)
  • the capacitance value per unit area (C,) was determined to be 2 x 10 "7 F cm "2
  • the fraction of light absorbed incident from the ITO side in double pass is:
  • a 1 -2 ⁇ d totai l -e where d is the thickness of the CQD film, and ⁇ is the absorbance.
  • the percentage of photons absorbed through the depletion region of 65 nm width near the Mg contact in double-pass is estimated to be 13%. Accordingly, the electron-hole pairs generated in the depletion region, believed to be efficiently extracted (> 90 %) , only contributed to less than half of the photocurrent.
  • the quasi-neutral region absorbed the remaining 30 % of the incident light In order to account for the 32 % EQE at 975 nm, 20 % of the photogenerated carriers created in the quasi-neutral portion of the device must have diffused to the depletion region to be separated therein. The rest was lost to carrier recombination. Diffusion therefore must be playing a large role in the devices of an embodiment.
  • Figure 13 is a schematic diagram of the analytical model used in determining where electron-hole pairs were generated, under an embodiment
  • the electron-hole pairs generated within the depletion region (W) are efficiently separated
  • the electrons generated within L QN2 diffuse to the depletion region where they are separated by the built-in field while the electrons generated within L QN I of the ITO contact are mostly lost to recombination
  • the photons absorbed in L QN2 of thickness ⁇ 95 nm account for the rest of the EQE
  • the required diffusion length for the least mobile carrier electros in this case
  • it is assumed that only the photogenerated carriers in the quasi- neutral region that have a transit time of 0 1 r in the depletion region (L QN2 ⁇ 95 nm) are largely not lost to recombination where T is the recombination lifetime
  • the model is estimated to be plausible within experimental uncertainty if the minority carrier diffusion length is
  • the electron mobility was found to be 1.4x10 "3 Cm 2 V 1 S "1 for a benzenedithiol treated device CELIV experiments conducted on the photovoltaic devices allowed us to estimate the hole mobility to be 2 4x10 " 3 Cm 2 V 1 S "1 in the dithiol treated NC based devices.
  • the electron and the hole mobility in the devices of an embodiment are within the same order of magnitude, in contrast with recent findings in PbS colloidal quantum dots devices, where the minority electrons were ⁇ 8 times less mobile
  • Time of flight was performed on a sample with a geometry identical to the photovoltaic device, i.e. a layer of NCs sandwiched between the ITO and magnesium contacts, with the exception that the total NC layer in this case was thicker (> 700 nm).
  • the devices were held under reverse bias by applying a positive potential to the Mg contact and a negative potential to the ITO A 10 ns pulse of 532nm light was incident on the sample from the transparent ITO side.
  • the recombination lifetime ⁇ was estimated at relevant solar intensities through the technique of transient open circuit voltage decay (OCVD).
  • OCVD transient open circuit voltage decay
  • the device was illuminated using a digitally modulated 975nm diode laser at different intensities.
  • the lifetime was found to be on the order of 10-20 ⁇ s
  • Figure 15 is a plot of carrier recombination lifetime (dots, with reference to left axis) and external quantum efficiency (squares, with reference to right axis) versus illumination intensity at 975 nm, under an embodiment.
  • the decrease in the EQE (>10 mW cm "2 ) corresponds to the limit where the minority carrier transit time exceeds the recombination lifetime
  • the transit time should be shorter than the characteristic time for carrier relaxation at the relevant intensities, which was measured using the technique of transient open circuit voltage decay (OCVD)
  • OCVD transient open circuit voltage decay
  • the OCVD method was performed on a photovoltaic device by abruptly turning off the illumination and recording the V oc decay The device was illuminated using a 975 nm laser at different intensities The voltage generated across the device was recorded as the illumination was abruptly removed (within 3 us).
  • the recombination lifetime at every intensity was determined by applying a linear fit to the initial V oc decay Figure 16 shows a typical OCVD transient. The recombination was evaluated from the following relation
  • Thin film field-effect transistors were fabricated on highly conductive silicon wafers with 100 nm of thermally grown oxide as the gate dielectric. The source and drain electrodes were separated by a 10 ⁇ m gap.
  • the octylamine-capped PbSe NCs was diluted to a concentration of 10 mg ml/'and the benzenedithiol solution to 1 mM
  • a range of gate voltages was applied and recorded the current modulation through the NC film
  • Figure 17 shows the FET transfer characteristics of PbSe NC thin film field-effect transistors, under an embodiment.
  • Thin films field-effect transistors were fabricated on highly doped n-type silicon wafers with 100 nm of thermally grown oxide as the gate dielectric. The source and drain electrodes were separated by a 10 um gap. The FET devices were completed by spin- coating thin layers of PbSe NCs The PbSe CQD films exhibited p-type behavior both before and after treatment.
  • Carriers in the depletion region are separated via the action of the built-in field resultant from the metal-semiconductor, or Schottky, junction
  • the drift length is given by
  • ⁇ is the carrier mobility
  • V b is the built in potential
  • W is the depletion
  • M q - diffusion length is in excess of 220 nm, which allows a substantial fraction of the minority carriers to diffuse out of the neutral region, and allows accounting for the high observed EQE
  • Figure 18 summarizes the calculated charge transport characteristics, under an embodiment From the transport parameters calculated, the hole diffusion length was estimated to be 350 nm and the electron minority diffusion length was estimated to be 220 nm (equations included in the main text) These values are evaluated in low injection mode with the minimal value of the recombination lifetime 13 ⁇ s; thus, the minimum value of the minority diffusion length is 220 nm Referring to Figure 13, the latter value is found to be very close to the required diffusion length
  • the devices described herein exhibited a photovoltaic response only after being subjected to the benzenedithiol crosslinking process It is herein proposed that the as- exchanged NCs were dominated by a large density of unpassivated surface states As with previously-reported chemical processes on PbSe and CdSe NCs, benzenedithiol offers passivation of dangling bonds. Additionally, as seen in the stability study, benzenedithiol appears to offer a longer-lived NCs/metal interface than do amine ligands The latter are believed to react with the top metal contact
  • Another feature of the device processing architecture described herein is the use of two superimposed layers of colloidal quantum dot solids to increase absorbing thickness and minimize pinholes. Preceding the solid-state treatment with a solution-phase exchange to a somewhat shorter ligand helped to reduce volume contraction upon crosslinking of the film This contributed to the realization of densely-packed, high-mobility films in situ on a substrate
  • the devices of an embodiment are stable, high-efficiency infrared solution- processed photovoltaic devices. Further, it was shown herein that minority carrier diffusion can occur efficiently over hundreds of nanometers in such films Strongly-passivating, short, electron-transport-assisting bidentate linkers appear to play a key role in achieving these properties.
  • the chemicals used in producing an embodiment include one or more of the following, but are not so limited.
  • Lead (II) oxide powder PbO, 99%
  • Oleic acid OA, technical grade 90%
  • 1-Octadecene ODE, technical grade 90%
  • anhydrous toluene octane, methanol
  • isopropanol acetonitrile
  • ethyl acetate Bis(trimethylsilyl)selenide (TMSe); 1,4 benzenedithiol (97%).
  • ODE was degassed by pre-pumping at 8O 0 C for 16 hours and TMSe source was pre-filtered with 0.1 and 0.02 ⁇ m Whatman syringe filters before use.
  • the synthesis was performed in a single, three-neck, round bottom flask
  • the Pb precursor was prepared by pumping the mixture of PbO and OA at 8O 0 C for 16 hours
  • the resulting transparent solution of lead oleate precursor was stirred vigorously while being heated under Ar for about 30 min
  • the stock solution of selenium precursor was prepared by mixing TMSe with ODE in a glove box and the portion cotxesponding to a 2: 1 (Pb.
  • PbSe NCs particularly in their solution phase, were observed to be extremely sensitive to both air and moisture and as a result all post-synthetic treatments were performed in a glove box with anhydrous reagents.
  • the oleate-capped PbSe NCs were isolated from any remaining starting materials and side products by precipitating the solution with a mixture of equal volumes of methanol (5 mL) and ethylacetate (5 mL), The precipitate was then re-dispersed in toluene and re-precipitated with methanol After the second precipitation, the NCs were vacuum- dried for 10 min and redispersed in toluene
  • the solution exchange procedure was carried out inside a nitrogen filled glovebox,
  • the as-synthesised NCs were precipitated with methanol, vacuum-dried for 10 min, and redispersed in octylamine After three days, the NCs were precipitated with anhydrous isopropanol, vacuum-dried for 10 min and redispersed in octane solution to achieve a typical concentration of 80 mg mL "1 .
  • the octylamine-exchanged PbSe NCs were spin-coated on ITO-coated glass substrate inside the glovebox.
  • the devices had a typical thickness of 210 to 250 nm as measured with a surface profiler (Veeco Dektak3).
  • the benzenedithiol treatment was done in a fumehood in air, Approximately 100 nm Mg/190 nm Ag were deposited by thermal evaporation through a shadow mask, leading to a contact area of 3 1 mm 2 .
  • the devices were stored in a nitrogen filled glovebox for 24 h before initial testing, All device characterizations were carried out in dark shielded enclosures in air ,
  • the OCVD curves were recorded using a digital oscilloscope with a 1 M ⁇ input impedance
  • the illumination source (975 nm diode laser) was modulated using a Stanford Research Systems DG535 digital pulse generator
  • An Agilent 4284A LCR meter was used to measure the capacitance at zero bias in order to determine the device depletion width
  • the incident light was chopped at 100 Hz and the short-circuit current was measured with a Stanford Research SR830 lock-in amplifier.
  • Illumination was provided by a white light source dispersed by a Jobin-Yvon Triax 320 monochromator. The light intensity was kept constant for all wavelengths
  • the measured spectrum was then scaled to match the value of the monochromatic EQE obtained at 975 nm.
  • the total film absorbance was obtained by measuring the reflectivity of the substrate and correcting for the ITO and Mg contact absorption in an integrating sphere A Cary 500 UV-Vis-IR Scan photospectrometer in the reflective mode was used to measure the reflectivity spectra. TEM images were taken using a Hitachi HD-2000
  • third-generation solar cells having greater than 30% AMI .5 power conversion efficiencies can be achieved by stacking differ ent-bandgap semiconductors on one another to form tandem (e g., two-junction) or multijunction cells
  • tandem e g., two-junction
  • a first cell of the stack absorbs higher-energy photons only, and provides a large open-circuit voltage; the next cells of the stack absorb the lower-energy photons, and, series-connected, provide additive contributions to the open-circuit voltage.
  • the layers of the optimal tandem cell (two- junction) have bandgaps at 1 3 urn and 800 nm and take the limiting efficiency up to 44% compared to the 32% limiting efficiency of an optimal single-junction device.
  • Quantum size-effect tuning provides one means of deploying materials of a single composition to address the different needed spectral regions
  • the use of ternary and quaternary chalcopyrite nanoparticles adds a further degree of freedom in harnessing efficiently the various band's within the sun's spectrum reaching the earth: the tuning of stoichiometry With bandgaps 740 nm and 1.23 eV, CuGaSe 2 and CuInSe 2 are excellent candidates for the two junctions of a near-optimal tandem cell Tuning CIGS stoichiometry along the continuum between CuGaSe 2 and CuInSe 2 provides continuous optimization over the intervening spectral range
  • CGS, CIS, and CIGS colloidal nanoparticles exhibiting one of more of the following characteristics: purity of phase (to generate a single bandgap within each junction), colloidal stability and a lack of aggregation (to ensure practical processing), excellent crystallinity (to provide sharp absorption onsets needed in optimized multijunction devices).
  • monodisperse chalcopyrite nanoparticles were synthesized under the hypotheses that: there is rapid formation of chalcopyrite compounds in mixtures of appropriate precursors with liquid Se; Cu, In, and Ga salts as well as selenium powders dissolve in oleyamine at elevated temperatures to enable chalcopyrite nanoparticle formation; the injection ratio of precursors must favor of ternary and quaternary compound formation and avoid binary compounds in a successful synthesis
  • FIG. 19A shows TEM images of chalcopyrite (CuGaSe 2 ) nanoparticles synthesized along with their corresponding SAED pattern, under an embodiment.
  • CuGaSe 2 nanoparticles were plate-like with irregular morphology and average size 11 nm.
  • Figure 19B shows TEM images of chalcopyrite (CuInSe 2 ) nanoparticles synthesized along with their corresponding SAED pattern, under an embodiment CuInSe 2 nanoparticles were a mixture of triangular, deformed hexagonal, and round plate-like nanoparticles with average size 16 nm
  • Figure 19C shows TEM images of chalcopyrite (CIGS) nanoparticles synthesized along with their corresponding SAED pattern, under an embodiment CIGS nanoparticles had average diameter 15 nm
  • Figure 21 shows plots of size distribution of as-synthesized nanoparticles (data based on manual counts of 80 nanoparticles from TEM images), under an embodiment
  • Each of these samples showed a narrow size distribution and their average sizes agree well with those calculated based on XRD.
  • the spacing among nanoparticles in all samples was approximately 2.4 nm, twice the length of their passivating oleylamine ligand
  • Figure 2OA shows powder XRD patterns of CuGaSe 2 2004, CuInSe 2 2002 and CIGS 2006 nanoparticles, under an embodiment; the vertical lines below indicate the corresponding reflection peaks for bulk CuIn 0 5 Ga 0 5 Se 2 (JCPDS 40-1488), CuGaSe 2 (JCPDS 79-1809) and CuInSe 2 (JCPDS 40-1487).
  • Figure 22A shows TEM images of CuGaSe 2 synthesized by cooking Cu(Ac), Ga(acac) 3 and Se powder in oleylamine at 250 C
  • Figure 22B and 22C show TEM images Of CuInSe 2 synthesized by cooking Cu(Ac), In(Ac) 3 and Se powder in oleylamine at 250 C
  • Figure 23A shows TEM images and corresponding SAED of CuGaSe 2 hexagonal microplates obtained in oleylamine and oleic acid mixture, under an embodiment.
  • Figure 23B shows TEM images and corresponding SAED Of CuInSe 2 hexagonal microplates obtained in oleylamine and oleic acid mixture
  • Figure S4A shows TEM images of CuInSe 2 nanoparticles synthesized from Cu(acac) 2 and In(Ac) 3 precursors at 250 0 C (scale bars are 50 nm), under an embodiment.
  • Figure 24B shows TEM images Of CuInSe 2 nanoparticles synthesized from Cu(Ac) and In(Ac) 3 precursors at 250 0 C (scale bars are 50 nm)
  • Figure 24C shows TEM images Of CuInSe 2 nanoparticles synthesized from Cu(acac) 2 and In(acac) 2 precursors at 250 0 C (scale bars are 50 nm)
  • Figure 24D shows TEM images Of CuInSe 2 nanoparticles synthesized from Cu(Ac) and In(acac) 3 precursors at 250 0 C (scale bars are 50 nm), under an embodiment.
  • Figure 25B shows TEM images of CIGS nanoparticles synthesized by injection Cu(acac) 2 , In(acac) 3 and Ga(acac) 3 oleylamine solution into Se/oleylamine at an injection temperature of 220 0 C, under an embodiment
  • Figure 26A shows TEM images of CIGS nanoparticles synthesized with a precursor ratio CIGE3228- 0 15mmol Cu(acac) 2 , 0 lmmol Ga(acac) 3 and 0 lmmol In(acac) 3 to 0.4mmol Se, under an embodiment.
  • Figure 26B shows TEM images of CIGS nanoparticles synthesized with a precursor ratio CIGE4138 - 0 20mmol Cu(acac) 2 , 0.15mmol Ga(acac) 3 and 0 05mmol In(acac) 3 to 0.40 mmol Se, under an embodiment.
  • Figure 26C shows XRD patterns of CIGS nanoparticles synthesized with precursor ratios CIGE3228-0 15mmol Cu(acac) 2 , 0. lmmol
  • Table 21 shows composition of CIGS nanoparticles of an embodiment calculated from Inductively Coupled Plasma Atomic Emission Spectrometry (ICP) In the embodiments desciibed herein, temperature provided for tuning of the size and composition of the CIGS particles.
  • ICP Inductively Coupled Plasma Atomic Emission Spectrometry
  • Figure 27 shows XRD patterns 2702-2706 of CIGS nanoparticles arrested for different reaction duration, under an embodiment
  • the XRD characterization of products obtained one (1) minute after injection in CIGS synthesis showed exclusively Cu(In 0 5 Ga 0 5 )Se 2 diffraction peaks, implying that chalcopyrite nanoparticles formed essentially immediately upon injection
  • Figure 28A shows representative TEM images and SAED pattern of CuInS 2 nanoparticles produced in oleylamine using sulfur powder instead of selenium powder
  • Figure 28B shows representative TEM images and SAED pattern of CuGaS 2 nanoparticles produced in oleylamine using sulfur powder instead of selenium powder
  • CuInSe2 and CIGS nanoparticles_ all synthesis were carried out with standard schlenk line.
  • a round two-necked flask was located in a heating mantle, and one neck was connected to a condenser while the other neck was sealed by septum and one thermocouple was used to control the temperature
  • 0 2 mmol Cu(acac) 2 , 0 2mmol Ga(acac) 3 and 5ml oleylamine were mixed at room temperature and kept at 80 °C under vacuum for Ih to dissolve all the precursors completely This solution was marked as solution A
  • 10ml oleylamine and 0 4 mmol Se powder were filled in a separate flask, and pumped at 120 0 C for 0.5h to further degas any residual air and/or moisture and then N 2 was introduced for the left whole reaction.
  • the solution was heated up to 250 0 C in around lOmin and it gradually changed from colorless to orange to brownish red due to the dissolution of Se powder in oleylamine, which generally took about one hour.
  • 5ml solution A in a syringe with 17 gauge needle was swiftly injected into the solution at 250 0 C in about 5 second under vigorous stirring.
  • the solution turned into black at once and turned off the heating mantle immediately (without removal of heating mantle).
  • the at least one property of an embodiment includes derealization of at least one type of charge carrier across at least a portion of the organic molecules, wherein the at least one type of charge carrier includes at least one of electrons and holes
  • the composite material of an embodiment comprises at least one benzene ring forming at least a portion of the organic molecules, wherein the at least one benzene ring results in the derealization of the at least one type of charge carrier.
  • the semiconductor nanocrystals of an embodiment comprise at least one of PbS,
  • the organic molecules of an embodiment comprise at least one of Benzenedithiol, Dibenzenedithiol, Mercaptopropionic acid, Mercaptobenzoic acid, Pyridine, Pyrimidine, Pyrazine, Pyridazine, Dicarboxybenzene, Benzenediamine, and Dibenzenediamine.
  • the embodiments described herein include a semiconductor material, the semiconductor material comprising a p-type semiconductor material including semiconductor nanocrystals, wherein at least one property of the semiconductor material results in a mobility of electrons in the semiconductor material being greater than or equal to a mobility of holes.
  • the embodiments described herein include a semiconductor material, the semiconductor material comprising an n-type semiconductor material including semiconductor nanocrystals, wherein at least one property of the semiconductor material results in a mobility of holes in the semiconductor material being greater than or equal to a mobility of electrons
  • the embodiments described herein include a device comprising a semiconductor material in contact with a first electrode and a second electrode, wherein the semiconductor material is a p-type semiconductor material comprising semiconductor nanocrystals, wherein properties of the semiconductor material result in a mobility of electrons in the semiconductor material being greater than or equal to a mobility of holes
  • the embodiments described herein include a device comprising a semiconductor material in contact with a first electrode and a second electrode, wherein the semiconductor material is an n-type semiconductor material comprising semiconductor nanocrystals, wherein properties of the semiconductor material result in a mobility of holes in the semiconductor material being greater than or equal to a mobility of electrons

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Abstract

La présente invention concerne un matériau composite. Le matériau composite comprend des nanocristaux semi-conducteurs et des molécules organiques qui passivent les surfaces des nanocristaux semi-conducteurs. Une ou plusieurs propriétés des molécules organiques facilitent le transfert de charge entre les nanocristaux semi-conducteurs. La présente invention décrit un matériau semi-conducteur qui comprend un matériau semi-conducteur de type P incluant des nanocristaux semi-conducteurs. Au moins une propriété du matériau semi-conducteur entraîne une mobilité des électrons dans le matériau semi-conducteur qui est supérieure ou égale à la mobilité des trous. La présente invention concerne un matériau semi-conducteur qui comprend un matériau semi-conducteur de type N incluant des nanocristaux semi-conducteurs. Au moins une propriété du matériau semi-conducteur entraîne une mobilité des trous dans le matériau semi-conducteur supérieure ou égale à la mobilité des électrons.
PCT/US2009/041153 2008-04-18 2009-04-20 Photodétecteurs et éléments photovoltaïques basés sur des nanocristaux semi-conducteurs WO2009129540A1 (fr)

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