US20190164699A1

US20190164699A1 - Perovskite surface defect passivation using zwitterionic amino acids

Info

Publication number: US20190164699A1
Application number: US16/248,420
Authority: US
Inventors: Xiao Cheng Zeng; Jinsong Huang; Dai Jun; Shuang Yang
Original assignee: University of Nebraska; NuTech Ventures Inc
Current assignee: University of Nebraska; NuTech Ventures Inc
Priority date: 2017-02-17
Filing date: 2019-01-15
Publication date: 2019-05-30
Also published as: US11335513B2; US20200035418A1; WO2018152494A1

Abstract

Semiconductor devices including a cathode layer, an anode layer, an active layer disposed between the cathode layer and the anode layer, wherein the active layer includes a perovskite layer, and a passivation layer disposed directly on a surface of the active layer between the cathode layer and the active layer, the passivation layer including a zwitterionic amino acid, such as valine or phenylalanine or other amino acid that passivates both cationic and anionic defects in the surface of the active layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application for Patent is a continuation-in part of, and claims priority to, U.S. International Patent Application No. PCT/US2018/018706 by Huang et al., entitled “Passivation of Defects in Perovskite Materials For Improved Solar Cell Efficiency and Stability,” filed Feb. 20, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62/460,266, filed Feb. 17, 2017, entitled “Passivation of Defects in Perovskite Materials For Improved Solar Cell Efficiency and Stability,” each of which is incorporated in its entirety herein by reference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under 01A1538893 and DMR1420645 awarded by the National Science Foundation and FA9550-16-1-0299 awarded by the Air Force Office of Scientific Research. The government has certain rights in the invention.

BACKGROUND AND SUMMARY

The present disclosure generally provides photodetector systems and methods, and more particularly photodetector systems and methods including perovskite photoactive or photoresponsive materials.
The ionic defects at the surfaces and grain boundaries of organic-inorganic halide perovskites (OIHPs) films are detrimental to both the efficiency and stability of OIHP devices such as solar cells. There are both negatively and positively charged defects in ionic OIHPs, while generally only one type of the defects is passivated. In certain embodiments, quaternary ammonium halides (QAHs), which are B-complex vitamins, are used to effectively passivate both cationic and anionic defects of OIHPs with negative- and positive-charged components, respectively. The dual-defect passivation advantageously reduces the charge trap density and elongates the carrier recombination lifetime. The dual-defect passivation also advantageously increases open-circuit-voltage of the device with bandgap of 1.55 eV to 1.15 V, and boosts the efficiency to 21.0%. QAHs universally passivate other types of OIHPs with bandgaps ranging from 1.51 eV to 1.72 eV and advantageously increase efficiency by 10-35%. Moreover, the defect healing also significantly enhances the stability of OIHP films. The various embodiments provide a new paradigm for defects passivation to further improve both the efficiency and stability of OIHPs devices such as solar cells.
According to an embodiment, a semiconductor device is provided that typically includes a cathode layer, an anode layer, an active layer disposed between the cathode layer and the anode layer, wherein the active layer includes a perovskite layer, and a passivation layer disposed directly on a surface of the active layer between the cathode layer and the active layer, the passivation layer comprising a layer of material that passivates both cationic and anionic defects in the surface of the active layer. In certain aspects, the perovskite layer includes organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃ ⁺), formamidinium (H₂NCHNH₂ ⁺), or an alkali-metal ion (e.g., Cs⁺, Rb⁺), B is a metal cation, and X is a halide anion (e.g., Cl, Br, I), thiocyanate (SCN-) or a mixture thereof. In certain aspects, the layer of material comprises a quaternary ammonium halide (QAH). In certain aspects, the layer of material comprises a zwitterion molecule. In certain aspects, the layer of material comprises a choline zwitterion molecule. In certain aspects, the layer of material comprises a zwitterionic amino acid. In certain aspects, the zwitterionic amino acid comprises one of valine or phenylalanine. In certain aspects, the semiconductor device further includes a first carrier transport layer disposed between the passivation layer and the cathode; and a second carrier transport layer disposed between the active layer and the anode, the first carrier transport layer having a higher electron conductivity than the second carrier transport layer, the second buffer layer having a higher hole conductivity than the first buffer layer.
According to another embodiment, a semiconductor device is provided that typically includes a cathode layer, an anode layer, and an active layer disposed between the cathode layer and the anode layer, wherein the active layer includes an organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃₊), an alkali metal ion (e.g., Cs⁺, Rb⁺) or formamidinium (H₂NCHNH₂ ⁺), B is a metal cation, and X is a halide anion(e.g., Cl, Br, I), thiocyanate (SCN-) or a mixture thereof. The semiconductor device also typically includes a passivation layer disposed directly on a surface of the active layer between the cathode layer and the active layer, the passivation layer including a layer of material that passivates both cationic and anionic defects in the surface of the active layer. In certain aspects, the layer of material comprises a zwitterionic amino acid. In certain aspects, the zwitterionic amino acid comprises one of valine or phenylalanine. The semiconductor device further typically includes an electron extraction layer disposed directly on the passivation layer between the passivation layer and the cathode layer, the electron extraction layer comprising a layer of C₆₀, a first charge transport layer comprising bathocuproine (BCP) and disposed between the electron extraction layer and the cathode, and a second charge transport layer comprising Poly [bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and disposed between the active layer and the anode. In certain aspects, the layer of C60 has a thickness of between about 1 nm and about 100 nm.
According to yet another embodiment, a method of making or of forming a semiconductor device is provided. The process typically includes providing an active layer, wherein the active layer includes a perovskite material, and applying a passivation layer directly on a surface of the active layer, the passivation layer comprising a first material that passivates both cationic and anionic defects in the surface of the active layer. In certain aspects, the method also typically includes forming a cathode layer on the passivation layer. In certain aspects, the method also typically includes forming an anode layer on a side of the active layer so that the active layer is disposed between the cathode layer and the anode layer. In certain aspects, the method also typically includes forming a first carrier transport layer disposed between the passivation layer and the cathode layer, and forming a second carrier transport layer disposed between the active layer and the anode layer, the first carrier transport layer having a higher electron conductivity than the second carrier transport layer, the second carrier transport layer having a higher hole conductivity than the first carrier transport layer. In certain aspects, the first material comprises a quaternary ammonium halide (QAH) or a zwitterion molecule. In certain aspects, the layer of material comprises a zwitterionic amino acid. In certain aspects, the zwitterionic amino acid comprises one of valine or phenylalanine. In certain aspects, the perovskite material includes organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃ ⁺), formamidinium (H₂NCHNH₂ ⁺), or an alkali-metal ion , B is a metal cation, and X is a halide anion, thiocyanate (SCN-) or a mixture thereof.
According to a further embodiment, a semiconductor device is provided that typically includes a cathode layer, an anode layer, an active layer disposed between the cathode layer and the anode layer, wherein the active layer includes a perovskite layer, and a passivation layer disposed directly on a surface of the active layer between the cathode layer and the active layer, the passivation layer comprising a zwitterionic amino acid that passivates both cationic and anionic defects in the surface of the active layer. In certain aspects, the perovskite layer includes organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃ ⁺), formamidinium (H₂NCHNH₂ ⁺), or an alkali-metal ion (e.g., Cs⁺, Rb⁺), B is a metal cation, and X is a halide anion (e.g., Cl, Br, I), thiocyanate (SCN-) or a mixture thereof. In certain aspects, the zwitterionic amino acid comprises one of valine or phenylalanine.
For the various semiconductor devices, and formation processes, in certain aspects, the anode layer includes indium tin oxide (ITO) and the cathode layer includes copper. In certain aspects, the active layer has a thickness of between about 1 nm and about 10 μm. In certain aspects, the passivation layer has a thickness of between about 1 nm and about 30 nm.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The detailed description is described with reference to the accompanying FIG.s. The use of the same reference numbers in different instances in the description and the FIG.s may indicate similar or identical items.

FIGS. 1A and 1B show embodiments of device structures of organic-inorganic halide perovskite (OIHP) devices.

FIG. 2 shows the passivation mechanism by quaternary ammonium halides (QAHs). The quaternary ammonium ions are expected to only passivate MA⁺vacancies by occupying cuboctahedral sites to compensate the MA⁺loss on the film surfaces, and the halide vacancies are compensated by additional halide ions from QAHs.

FIG. 3 shows trap density of states (tDOS) obtained by thermal admittance spectroscopy for devices with PCBM and Choline chloride passivation layers.

FIG. 4A shows current density-voltage (J-V) characteristics of two-step processed MAPbI₃devices with different passivation layers.

FIG. 4B shows J-V curves for the two-step processed MAPbI₃devices passivated by choline chloride and choline iodide.

FIG. 4C shows statistics of V_OCdistribution for devices with PCBM, L-α-Phosphatidylcholine, Choline iodide, and Choline chloride, where solid lines represent the Gauss distribution fitting for the statistic of V_OC.

FIGS. 5A-5D show stability assessment of perovskite solar cells with different passivation layers: Evolution of PCE (FIG. 5A), J_SC(FIG. 5B), V_OC(FIG. 5C), and FF (FIG. 5D) relative to the initial parameters for the device over 35 days of storage in air. Each average (symbol) and standard deviation (error bar) was calculated from three solar cells. The initial efficiency is 19.5% and 20.1% for devices with L-α-Phosphatidylcholine, Choline chloride, respectively.

FIG. 5E shows photographic images of the OIHP films with different treatments. The first and second rows show the images of the pristine films, with L-α-Phosphatidylcholine, and with Choline chloride from left to right, respectively, before after exposure to humidity of 90±5% for 2.5 h (the size of the film is 15 mm).

FIG. 6A shows a schematic of normal and zwitterionic forms of amino acids according to an embodiment.

FIG. 6B show a slab model of clean PbI₂-terminated MAPbI₃.

FIG. 6C shows calculated transition levels ϵ(q′/q) of intrinsic acceptors on MAPbI₃surface.

FIG. 6D shows calculated transition levels ϵ(q′/q) of intrinsic donors on MAPbI₃surface.

FIG. 6E shows the structure of valine and phenylalanine.

FIG. 6F shows I interstitial defects on a 9-layer PbI₂-terminated MAPbI₃surface.

FIG. 6G shows Pb interstitial defects on a 9-layer PbI₂-terminated MAPbI₃surface.

FIG. 6H shows Pb₂interstitial defects on a 9-layer PbI₂-terminated MAPbI₃surface.

FIG. 7A shows a schematic diagram of zwitterionic amino acids passivation of perovskite surface defects according to an embodiment.

FIG. 7B shows calculated transition levels ϵ(q′/q) of I_iand Pb_iafter valine and phenylalanine passivation according to an embodiment.

FIG. 8 shows in panels a)-c) density of states (DOS) for MAPbI₃surface with Pb interstitial defects, charge density of the highest occupied band (HOB) for unpassivated MAPbI₃surface with Pb interstitial defects, and charge density of HOB for passivated MAPbI₃surface with Pb interstitial defects, respectfully, and in panels d)-f) DOS for MAPbI₃surface with Pb₂interstitial defects, charge density of the highest occupied band (HOB) for unpassivated MAPbI₃surface with Pb₂interstitial defects, and charge density of HOB for passivated MAPbI₃surface with Pb₂interstitial defects, respectfully, and in panels g)-i), DOS for MAPbI₃surface with I interstitial defects, charge density of the highest occupied band (HOB) for unpassivated MAPbI₃surface with I interstitial defects, and charge density of HOB for passivated MAPbI₃surface with I interstitial defects, respectfully

FIG. 9A shows a device structure of a perovskite planar heterojunction solar cell including an amino acid passivation layer according to an embodiment.

FIG. 9B shows current density-voltage (J-V) characteristics of two-step-processed devices with different passivation layers, PCBM (control), phenylalanine (black), valine (blue).

FIG. 9C shows statistics of V_OCdistribution for devices with valine (black), phenylalanine (red) and PCBM (green).

FIG. 9D shows trap density of states obtained by thermal admittance spectroscopy for devices with PCBM (blue), valine (yellow) and phenylalanine (red).

DETAILED DESCRIPTION

The history of power conversion efficiency (PCE) enhancement for thin-film and polycrystalline photovoltaic cells has witnessed the importance of reducing charge recombination loss both inside the photoactive layer and at the electrode contacts. Passivation of defects at the film surface becomes critical when the charge recombination inside the photoactive layer is negligible, which is the case for the organic-inorganic halide perovskite (OIHP) devices such as solar cells. Solution-processed OIHP devices embrace many intriguing optoelectronics attributes, such as strong light absorption, high charge carrier mobility, and long intrinsic carrier recombination lifetime. The insensitivity to point defects and easy crystallization of OIHP materials give rise to negligible charge recombination in perovskite polycrystalline thin films. However, the much shorter measured photoluminescence (PL) recombination lifetime of the polycrystalline films than the intrinsic carrier recombination lifetime from a single crystal interior indicates there is still high density of defects at the surface and grain boundaries of polycrystalline grains which are not benign electronically. These defects originate most likely from the low thermal stability, or low formation energy of OIHP materials containing organic components which tends to easily evaporate away from the surface during the thermal annealing process. These surface and grain boundary (GB) defects may not dramatically reduce device photocurrent output, because a portion of the trapped charges may still escape over a long time and be collected by the electrodes, as evidenced by the relative large short circuit current (J_SC) of many non-optimized devices, while they would significantly impact open circuit voltage (V_OC) of the devices due to their energy disorder and reduced carrier concentration which pull down the quasi-Fermi level splitting. In addition, these defects can cause other device instability issues, including ion migration and associated current hysteresis, and device degradation in ambient environment. A recent study of moisture dependent perovskite grain stability showed that the degradation of perovskite grains was initialized by the defective surface and GBs, while some single crystals with low surface defect density and no GBs could be stable in air for several years. The ionic defects (e.g., iodine or methylammonium vacancies) in the polycrystalline film have small migration activation energy (e.g., <0.1 eV) under 1 sun illumination. The defects could also initialize the permeation of moisture or oxygen into the perovskite films to accelerate the degradation of perovskite devices. Thus, it is desirable to electronically passivate the defects at the surface and GB to boost the PCE, and to heal these defects to prolong the durability of OIHP devices.
The ionic nature of OIHP materials imposes different requirements for the defects passivation with covalent-bonding semiconductors such as silicon (Si). The passivation of Si is mainly achieved by the elimination of the Si dangling bonds by formation of Si—O, Si—N or Si—H covalent bonds, which is however not applicable to strong ionic OIHPs. So far different passivation molecules have been reported to perform as electron donors or electron acceptors that can interact with the charged defects of OIHPs, and thereafter annihilate the relevant defect-induced charge traps. Lewis acids, such as phenyl-C61-butyric acid methyl ester (PCBM), as the good electron transporting materials could accept an electron from the negative charged Pb-I antisite defects, Pbl₃ ⁻or under-coordinated halide ions and thus passivate the halide-induced deep traps. Lewis base molecules, such as thiophene or pyridine, usually perform as the electron donors which could bind to the positively charged, under-coordinated Pb²⁺ions. However, these molecules could only passivate one type of defects, either positive charged or negative charged defects, but not both together. The defects in OIHP materials are charged, either positively or negatively, and therefore the passivation of them should take the charge neutrality into consideration.
In certain embodiments, a system of materials, including quaternary ammonium halides (QAHs), are used to passivate both cationic and anionic defects in OIHP with its negative- and positive-charged components. The dual-modality passivation remarkably reduces the trap density and prolongs the carrier lifetime, which universally enhances the V_OCof the OIHP planar heterojunction devices with different bandgaps and consequently increases the PCE by 10%-35%. This strategy can also enhance the stability of OIHPs devices, with almost no efficiency loss after 800 h of storage in ambient condition. The general rules for the passivation of ionic OIHPs include: the molecules or ions should have similar size with that of the ionic defects, and the molecules should have positive or negative charged components for self-assembling with the charged defects. These results highlight the importance of all-round passivation of charged ionic defects for improvement of the efficiency and durability of OIHPs devices.
Methods
Perovskite material layers are formed, e.g. a two-step method may be used to make MAPbI₃films, e.g., fabricated by a thermal annealing-induced interdiffusion method. See, e.g., U.S. Pat. No. 9,391,287, which is hereby incorporated by reference in its entirety. Perovskite materials may also be formed using a one-step, solvent engineering method, e.g., as described in Jeon, N. J. et al., “Solvent Engineering for High performance Inorganic-Organic Hybrid Perovskite Solar Cells,” Nat. Mater. 13, 897-903 (2014), which is incorporated by reference. The hole transport layer (HTL) poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) with concentration of 2 mg/ml dissolved in toluene were spin coated at the speed of 6,000 r.p.m for 35 s and then annealed at 100° C. for 10 min. PbI2 beads (99.999% trace metals basis) were purchased from Sigma-Aldrich. After dissolved in N,N-Dimethylformamide (DMF) at temperature of 100° C., around 50 μl of hot (−90 ° C.) 630 mg/ml PbI₂DMF precursor solutions was quickly dropped onto the substrate and spin coated at the speed of 6,000 r.p.m. The as-fabricated PbI₂films were dried and annealed at 90° C. for 10 min. After the PbI₂films cooled to 70° C., 60 μl of 63 mg/ml methylammonium iodide (MAI) 2-propanol (IPA) precursor solution at the temperature of 70° C. was spun on the PbI₂films. Subsequently, the sample was annealed at 70° C. for 20 min and 100° C. for 60 min. During the thermal annealing process, around 10 p.1 of DMF was added to the edge of the petri dish when the temperature reached 100° C.
The functional layer was applied to or disposed on the perovskite material layer (active layer). For example, the functional layer may be coated onto the perovskite substrate by spin coating, e.g., at 4,000 r.p.m. for 35 s, and annealing, e.g., at 100° C. for 30 min. The devices were finished by disposing or applying other layers thereto, e.g., thermally evaporating additional layers thereon, such as C₆₀(23 nm), BCP (8 nm) and copper (80 nm) in sequential order.
FIG. 1A illustrates a device structure of an OIHP photodetector device 1 according to an embodiment. As shown, device 1 includes a cathode layer 10, an anode layer 20, and an active layer 30 disposed between the cathode layer 10 and the anode layer 20. Device 1 also includes a passivation layer 40 disposed directly on a surface of the active layer between the active layer 30 and the cathode layer 10. The passivation layer 30 includes a layer of material that passivates both cationic and anionic defects in the surface of the active layer as discussed herein. The passivation layer 40 should generally have a thickness of between about 1 nm and about 30 nm or more, depending on the specific application. The active layer 30 in an embodiment includes a layer of perovskite material, where the perovskite material includes organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃ ⁺), formamidinium (H₂NCHNH₂ ⁺), or an alkali-metal ion (e.g., Cs⁺, Rb⁺), B is a metal cation, and X is a halide anion (e.g., Cl, Br, or I), thiocyanate (SCN-) or a mixture thereof. For example, in an embodiment, active layer 30 may include an organometal trihalide perovskite having the formula FA_xMA_1-xBX₃where FA is formamidinium (H₂NCHNH₂ ⁺), and MA is methylammonium (CH₃NH₃ ⁺) and x is a fractional value between (and including) 0 and 1. In an embodiment, X may be a mixture of two or more halides. For example, the active layer 40 may include FA_xMA_1-xB(Br_1-yI_y)₃where y is a fractional value between (and including) 0 and 1 and where x may have the same value of y or a different value. Specific examples might include FA_0.85MA_0.15B(Br_0.15I_0.85)₃, FA_0.83MA_0.17B(Br_0.17I_0.83)₃, and FA_0.83MA_0.17B(Br_0.4I_0.6)₃. The active layer 30 should generally have a thickness of between about 1 nm and about 10 μm depending on the specific application. For example, for typical photodetection applications, a perovskite active layer will have a thickness of about 100 nm to about 2 μm. Additionally, the active layer 30 should generally have an active device area e.g., the cross-sectional light-capturing area, of between about 0.04 mm²to about 7 mm², where a smaller active area may be more desirable as will be discussed below.
The anode layer 20 and the cathode layer 10 generally include conductive materials suited for the particular application. Useful materials for the anode layer 20 includes indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-tin mixed oxide (ATO), a conductive polymer, a network of metal nanowire, a network of carbon nanowire, nanotube, nanosheet, nanorod, carbon nanotube, silver nanowire, or graphene. Useful materials for the cathode layer include copper, aluminum, calcium, magnesium, lithium, sodium, potassium, strontium, cesium, barium, iron, cobalt, nickel, silver, zinc, tin, samarium, ytterbium, chromium, gold, graphene, an alkali metal fluoride, an alkaline-earth metal fluoride, an alkali metal chloride, an alkaline-earth metal chloride, an alkali metal oxide, an alkaline-earth metal oxide, a metal carbonate, a metal acetate, or a combination of at least two of the above materials.
FIG. 1B illustrates a perspective view of a specific device structure of an OIHP photodetector device 100 according to an embodiment. The specific structure of device 100 is composed of anode 20 including conductive layer 24: e.g., indium tin oxide (ITO) and second buffer layer 22: e.g., poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA)/active layer 30: e.g., CH₃NH₃PbI₃(MAPbI₃)/functional layer 40/and cathode layer 10 including electron extraction layer 12: e.g., fullerene, C₆₀, first buffer layer 14: e.g., 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and conductive material layer 16: e.g., Copper(Cu). As shown, the electron extraction layer 12 includes only fullerene (C₆₀), but may include a combination of material layers, such as a phenyl-C61-butyric acid methyl ester (PC₆₁BM)/C₆₀double layer. In this embodiment, the functional layer 40 is disposed directly on the organic-inorganic halide perovskite (OIHP) film 30 to passivate of the ionic defects of the perovskite film to enhance both the performance and the stability of the OIHP device.
In device 100, cathode layer 10 further includes an electron extraction layer 12 disposed between the cathode material layer 16 and the active layer 30. The electron extraction layer 12, in one embodiment, includes a layer of fullerene such as C₆₀directly disposed on the passivation layer 40.
Cathode layer 10 optionally includes a first charge transport layer 14 disposed between the electron extraction layer 12 and the cathode material layer 16. Anode layer 20 optionally includes a second charge transport layer 22 disposed between the active layer 30 and the anode material layer 24. When present, the first charge transport layer 14 should have a higher electron conductivity than the second charge transport layer 22, and the second charge transport layer 22 should have a higher hole conductivity than the first charge transport layer 14, e.g., the first transport layer 14 acts as an electron transport layer (ETL) and the second charge transfer layer 22 acts as a hole transport layer (HTL).
In certain embodiments, the first charge transport layer 14 includes at least one of C₆₀, a fullerene, a fullerene-derivative, LiF, CsF, LiCoO₂, CS₂CO₃, TiOx, TiO₂nanorods (NRs), ZnO, ZnO nanorods (NRs), ZnO nanoparticles (NPs), ZnO, Al₂O₃, CaO, bathocuproine (BCP), copper phthalocyanine (CuPc), pentacene, pyronin B, pentadecafluorooctyl phenyl-C₆₀-butyrate (F-PCBM), C₆₀/LiF, ZnO NRs/PCBM, ZnO/cross-linked fullerene derivative (C-PCBSD), single walled carbon nanotubes (SWCNT), poly(ethylene glycol) (PEG), Polyethylenimine (PEI), poly(dimethylsiloxaneblock-methyl methacrylate) (PDMS-b-PMMA), polar polyfluorene (PF-EP), polyfluorene bearing lateral amino groups (PFN), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-oxy-F), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-6-oxy-F), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFNBr-DBTI5), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFPNBr), or poly(ethylene oxide) (PEO). Representative fullerene groups include C₆₀, C70, C71, C76, C78, C80, C82, C84, and C92. C₆₀derivative is at least one C₆₀derivative selected from the group consisting of C₆₀PCBM, bis-adduct C₆₀PCBM, tris-adduct C₆₀PCBM, tetra-adduct C₆₀PCBM, penta-adduct C₆₀PCBM, hexa-adduct C₆₀PCBM, C₆₀ThCBM, bis-adduct C₆₀ThCBM, tris-adduct C₆₀ThCBM, tetra-adduct C₆₀ThCBM, penta-adduct C₆₀ThCBM, hexa-adduct C₆₀ThCBM, C₆₀mono-indene adduct, C₆₀bis-indene adduct, C₆₀tris-indene adduct, C₆₀tetra-indene adduct, C₆₀penta-indene adduct, C₆₀hexa-indene adduct, C₆₀mono-quinodimethane adduct, C₆₀bis-quinodimethane adduct, C₆₀tris-quinodimethane adduct, C₆₀tetra-quinodimethane adduct, C₆₀penta-quinodimethane adduct, C₆₀hexa-quinodimethane adduct, C₆₀mono-(dimethyl acetylenedicarboxylate) adduct, C₆₀bis-(dimethyl acetylenedicarboxylate) adduct, C₆₀tris-(dimethyl acetylenedicarboxylate) adduct, C₆₀tetra-(dimethyl acetylenedicarboxylate) adduct, C₆₀penta-(dimethyl acetylenedicarboxylate) adduct, C₆₀hexa-(dimethyl acetylenedicarboxylate) adduct, and a mixture thereof. C70 and C84 derivatives include PC70BM, IC70BA, and PC84BM.
In certain embodiments, the second charge transport layer 22 includes at least one of poly(3,4-ethylenedioxithiophene) (PEDOT) doped with poly(styrene sulfonicacid) (PSS), 4,4′ bis [(ptrichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2), poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) and C60, copper phthalocyanine (CuPc), poly[3,4-(lhydroxymethyl) ethylenedioxythiophene] (PHEDOT), n-dodecylbenzenesulfonic acid/hydrochloric acid-doped poly(aniline) nanotubes (a-PANIN)s, poly(styrenesulfonic acid)-graft-poly(aniline) (PSSA-g-PANI), poly [(9,9-dioctylfluorene)-co-N-(4-(1-methylpropyl)phenyl)diphenylamine] (PFT), 4,4′ bis [(p-trichlorosilylpropylphenyl)phenylamino] biphenyl (TSPP), 5,5′-bis[(p-trichlorosilylpropylphenyl) phenylamino]-2,20-bithiophene (TSPT), N-propyltriethoxysilane, 3,3,3 -trifluoropropyltrichlorosane or 3-aminopropyltriethoxysilanePoly [bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), V2O5, VOx, MoO3, WO3, ReO3, NiOx, AgOx/PEDOT:PSS, Cu2O, CuSCN/P3HT, or Au nanoparticles.
Functional layer 40 may include one or more different structured molecules with varied functional groups, including, for example, phenyl-C61-butyric acid methyl ester (PCBM), L-α-Phosphatidylcholine, Tween-20, Polyethylene-block-poly(ethylene glycol) (PE-PEG), Choline chloride, and/or Choline iodide. In certain embodiments, the functional layer includes a QAH having a structure of NR₄ ⁺X⁻, where R is an alkyl or aryl group and X is a halide.
FIG. 4A shows the current density-voltage (J-V) curves of the MAPbI₃(active layer) devices with deposition of different functional/passivation layers. The control device with PCBM layer showed typical performance with a short circuit current density (J_SC) of 22.5 mAcm⁻², a V_OCof 1.04 V, a fill factor (FF) of 73.0%, and a PCE of 17.1%. Compared to the device with PCBM layers, the performances of the MAPbI₃devices with Tween, and PE-PEG buffer layers were even worse with maximum PCE between 13.6% and 15.5%, even after optimization of the concentration of Tween and PE-PEG solution. It indicates that Tween and PE-PEG cannot passivate the surface defects on MAPbI₃. In striking contrast, the devices with L-α-Phosphatidylcholine layer showed a significantly improved performance with an average J_SCof 22.7 mA cm⁻², V_OCof 1.08 V, FF of 80.0%, and PCE of 19.6%. The performance enhancement and hysteresis-free behavior were tentatively attributed to the passivation effect of L-α-Phosphatidylcholine molecules.
In comparison to Tween and PE-PEG, L-α-Phosphatidylcholine has the same long alkyl chain, while the difference is that L-α-Phosphatidylcholine has a choline phosphate zwitterion structure. The zwitterion structure with the choline group most likely passivates MAPbI₃. To verify, two other choline zwitterion molecules, also known as quaternary ammonium halides (QAHs), including choline iodide and choline chloride which have no long alkyl chain, were used as the interfacial layer. As shown in FIG. 4B, the V_OCof the perovskite devices was significantly increased by choline iodide and choline chloride as passivation layers without sacrificing the J_SCand FF of the devices, which confirmed the speculation. The devices with choline iodide and choline chloride showed higher V_OCof 1.14 and 1.15 V. Consequently, PCEs of the CH₃NH₃PbI₃devices with choline iodide and choline chloride passivation layers were increased to 20.1%, and 20.0%, respectively. FIG. 4C shows the V_OCdistribution of the devices with different passivation layers. The average V_OCvalues are 1.04, 1.09, 1.13, and 1.13 V for the statistic V_OCof the devices with PCBM, L-α-Phosphatidylcholine, choline iodide and choline chloride, respectively. The larger average V_OCof the devices passivated by QAHs than by L-α-Phosphatidylcholine indicates there is an additional passivation effect from the halide ions, because both of them have the quaternary ammonium component. There are both positively-charged cationic and negatively-charged anionic defects in OIHPs, such as I⁻and MA⁺vacancies, respectively, while quaternary ammonium ions are expected to only passivate MA⁺vacancies by occupying cuboctahedral sites to compensate the MA⁺loss on the film surfaces, as illustrated in FIG. 2. Loss of halide ions by the evaporation of MAI during thermal annealing process needs to be compensated by additional halide ions. Therefore, the dual passivation effect is critical in achieving the high efficiency devices according to various embodiments herein. The notable better passivation effect of choline chloride than choline iodide can be explained by the stronger Pb—Cl bonding than Pb—I bond, and small amount of Cl addition has been broadly reported to enhance the charge recombination lifetime in MAPbI₃. Based on the mechanism of passivation presented herein, any Zwitterion molecular structure should have a good passivation effect, because they have both negative and positive electric charges. A Zwitterion molecule may passivate both cationic and anion defects if the spacing of these defects is similar to or the same as the size of the Zwitterion molecule. However, the defects at the surface of perovskite films may have a very complicated distribution and compositions. The positive and negative charge defects may distribute away from each other, and their ratio may not be 1:1, because the perovskite film surface does not necessarily reach thermal dynamic stable states right after annealing processing, and the surfaces defects may pair up with bulk defects. In this context, the QAH molecule with separated positive and negative ions have the advantage of self-adaptive selection of defects with opposite charges for passivation, which is not limited by the complicated surface defect composition or distribution.
To further analyze the passivation effect of the QAH, measurements of the trap density of states (tDOS) were made for the devices fabricated by two-step processed MAPbI₃perovskite with choline chloride or PCBM passivation. The trap densities were extracted using thermal admittance spectroscopy (TAS) analysis, which is a well-established and effective technique to characterize both shallow and deep defects of thin film and organic solar cells. FIG. 3 shows that the device with choline chloride layers had overall the lowest tDOS over the whole trap depth region. The device with choline chloride layer had low tDOS in deeper trap region (0.40-0.52 eV) which were assigned to defects at the film surface. In addition, the density of shallower trap states (0.35-0.40 eV), which was assigned to traps at grain boundaries, in the choline chloride passivated devices was about three times smaller than in the PCBM passivated devices. This indicates that choline chloride may also diffuse into grain boundaries to passivate them. The better passivation effect of choline chloride than PCBM verifies that both cationic and anionic defects in OIHPs need to be considered in passivation techniques.
The stability of OIHPs devices in the ambient condition is challenged by their sensitivity to moisture and oxygen due to the hydroscopic nature of the OIHP films. Recent studies revealed that the degradation of perovskite films was generally initialized at the defects sites at the film surface and grain boundaries where the molecules have highest activity and diffusivity. The passivation may also enhance the stability of the perovskite films in ambient environment, because the healing of the defective sites on the film surface may inhibit the permeation of moisture and oxygen through the defects. To verify this, the stability of OIHPs devices with choline chloride and L-α-Phosphatidylcholine functional layers were monitored by placing the unencapsulated devices in ambient atmosphere at room temperature and relative humidity of 50%-85%; the device performance is summarized in FIGS. 5A-5D. The devices with choline chloride layers retained almost 100% of the initial PCEs after storage in the ambient condition for over one month. Interestingly, the V_OCof the devices increased during the first 5 days of storage in both types of devices with choline chloride passivation. This phenomenon may be caused by the additional passivation effect at the anode side by the diffusion of sodium ions into the perovskite films. The L-α-Phosphatidylcholine modified devices showed inferior performance, 30% loss of the initial PCE after 800 h storage in the ambient condition, despite that the long hydrophobic alkane tails could hinder the permeation of moisture. The difference in stability of the devices with two passivation layers highlighted the importance of healing both types of defects. The humidity stability test for the bare OIHP films (FIG. 5e ) shows that the films with QAHs have much slower degradation rate than the control films without QAHs when they were exposed to the humidity of 90±5% for same time intervals. This result confirmed that the healing of the defect sites by choline chloride effectively improves the moisture stability of OIHPs films.
Based on the passivation mechanism, there are at least two kinds of molecules that have the desired passivation effect. A first kind of molecule includes molecules that have a functional group (ammonium (—NH₂), halides, small atomic radius metal ions) which have the similar size to the corresponding vacancy, and thereafter fill these vacancies. The following molecules are expected to have the passivation effect because of this mechanism: Guanidine thiocyanate, aniline, benzylamine, and phenethylamine, Poly(ethylene glycol) bis(amine), (2-Methylbutyl)amine, 4-Pentyn-1-amine, N-Isopropylpyridin-2-amine, isochroman-6-amine, 2-phenylbutan-1-amine, 1-benzofuran-5-amine, 2-methylcyclopropan-1-amine, 3-Buten-1-amine, 1,4-Benzodioxan-6-amine, 5-methylpyrimidin-2-amine, 1-Methyl-1H-pyrazol-4-amine, 2,4,6-Trifluorobenzyl amine, 1,6-naphthyridin-2-amine, 1,2-benzisoxazol-3-amine, 1-Cyclohexyl-1H-pyrazol-5-amine, Methylammonium iodide, Methylammonium bromide, Methylammonium chloride, phenylethylammonium Iodide, phenylethylammonium bromide, phenylethylammonium chloride, n-butylammonium Iodide, n-butylammonium bromide, n-butylammonium chloride, NaCl, KCl, Ki, NaI, CsCl, CsI, RbCl, RbI, CoI₂, CoCl₂, SrCl₂, SrI₂. A second kind of molecule includes molecules that have the Zwitterionic structure which is composed of positive and negative charged components that could self-assemble with different charged defects, resulting in the healing of the charged defects. The following molecules are expected to have the passivation effect because of the above mechanism: Choline chloride, Choline iodide, Choline bromide, L-α-Phosphatidylcholine, Betaine, Tetrabutylammonium iodide, 1-Ethyl-3-methylimidazolium iodide, Tetrabutylammonium phosphate monobasic, 3-(4-tert-Butyl-1-pyridinio)-1-propanesulfonate, 3-(1-Pyridinio)-1-propanesulfonate, 3-(Benzyldimethylammonio)propanesulfonate, 3-(Decyldimethylammonio)-propane-sulfonate inner salt, Guanidinium iodide, Guanidinium thiocyanate, Guanidinium chloride. The functional molecules having at least one feature of the suitable size or Zwitterionic structure have the passivation effect on the OIHPs devices.

Defect Passivation Using Zwitterionic Amino Acids

Amino acids are known to have two forms, namely, regular form and zwitterion form (see FIG. 6A on the right). In the regular form, the N atom in the —NH₂functional group has a lone pair of electrons which can passivate positive charged metal cations. Meanwhile, the oxygen site in carboxyl group (—COOH) can passivate the positively charged defects. While in the zwitterion form, amino acids have a positive charged —NH₃end and a negative charged —COO end, thereby may passivate both positive and negative charged defects
In certain embodiments, zwitterionic amino acids are used for passivating ionic defects in perovskite materials, including hybrid perovskite materials, at both surface and grain boundaries. Specific examples of zwitterionic amino acids include valine (VA) and phenylalanine (PA), which both are representative of amino acids with a hydrophobic side chain (see, FIG. 6E). For example, DFT calculations show that valine and phenylalanine are able to passivate both positively and negatively charged defects. Experiments have confirmed that the charge trap density in a valine- or phenylalanine-passivated device is reduced, e.g. as compared to a PCBM passivated device, that an improved open-circuit-voltage results, and that efficiency is enhanced up to 21.2%.
In certain embodiments, non-zwitterion amino acids (e.g., having unionized structure) may be used to passivate defects in perovskite materials.
Advantages of amino acids include their ability to behave as either electron donor or acceptor, as the amino acid has both electron rich and electron deficient ends in its zwitterionic form (as shown in FIG. 6A), thus allowing them to passivate both positive charged and negative charged defects. Further, the sizes of amino acids are relatively small, therefore enabling efficient penetration into the grain boundaries to passivate the defects. Moreover, with a proper choice of the side chain, amino acids can be hydrophobic, thus enabling enhancement of moisture resistance. Valine (VA) and phenylalanine (PA), two typical hydrophobic amino acids, are discussed herein. Theoretical results predicted that these molecules could effectively passivate both negatively charged iodide and positively charged lead ions, which is further confirmed from the experiment, showing that amino acids passivation remarkably reduced the trap density and enhanced the V_OC, consequently, the PCE of valine and phenylalanine passivated devices were boosted to 20.6% and 21.2%, respectively. These results highlight the importance of dual passivation of the surface and grain boundary defects to improve the efficiency of OIHP devices.

Valine and Phenylalanine Passivation

To simulate the surface defects, a 9-layer PbI₂-terminated slab model of the tetragonal structure of MAPbI₃as shown in FIG. 6B is used. The MAPbI₃in this example was synthesized under the condition of slightly excess of PbI₂. Six intrinsic point defects at the surface were considered, including two vacancies (V₁, V_Pb), two interstitials (Pb_i, I_i) and two antisites (Pb_i, I_Pb). The calculated transition levels (ϵ(q′/q)) of donor-like and acceptor-like defects are plotted in FIG. 6C and FIG. 6D. V_Iis a shallow donor with a ϵ(0/+1) lies 0.04 eV below conduction band minimum (CBM), while V_Pbhas a (0/−1) transition level at 0.09 eV above valance band maximum (VBM) and a (−1/−2) transition level at 0.62 eV above VBM, acting as deep acceptors. I and Pb interstitials, and Pb₂interstitials are shown in FIGS. 6E-6H; I interstitial is a typical negative charged defect, while the other two are representative positive charged defects. For two interstitials, Pb_iexhibits deep transition levels in the band gap, including ϵ(0/+1)=1.09 eV, and ϵ(+1/+2)=1.52 eV, thus acting as deep donors, while L has a (0/−1) transition level at 0.35 eV above VBM, makes it a deep acceptor defect. For the antisite IPb, it has (−1/−2) and (−2/−3) transition levels above CBM, but the (0/−1) transition level lies at 0.48 eV above VBM, making it a deep acceptor. Pb_Iis deep donor, with (0/1+) and (1+/3+) transition levels at 0.29 eV and 0.43 eV below CBM. As compared to the transition levels of intrinsic point defects in bulk MAPbI₃(see, Yin W-J, Shi T, Yan Y. Unusual defect physics in CH3NH3PbI3 perovskite solar cell absorber. Applied Physics Letters 104, 063903 (2014)), the transition levels of points defects at the surface shows a quite different picture, for example, both I_iand Pb_iare benign in bulk but have deep transition levels on the surface. This could be accounted from the missing of space confinement effect as well as the different bonding nature of defect sites with its neighbors on the surface as compared to its bulk counterpart.
Although I_i, V_Pb, Pb_i, Pb_I, I_Pball have deep transition levels, I_iand Pb_idefects were used for the amino acid passivation, for the reason that under the condition of slight excess of PbI₂, the formation energy of I_iand Pb_idefects are relatively lower than others. A schematic passivation diagram can be found in FIG. 7A, where the electron-rich —NH₃end is supposed to passivate the positive charged defects, while the electron deficient —COO end is presumed to neutralize the negative charged defects. The calculated transition levels of I_iand Pb_idefects on valine and phenylalanine passivated MAPbI₃surfaces are plotted in FIG. 7B. It can be clearly seen that upon valine or phenylalanine passivation, both the deep acceptor and deep donor states become shallower. For example, the (0/1−) transition level of I_iare at 0.15 eV and 0.18 eV above VBM for valine and phenylalanine passivated models, respectively, while it is 0.35 eV in the unpassivated model. For the Pb_idefect, the (1+/2+) transition level at 0.18 eV below CBM goes to above CBM after valine or phenylalanine passivation, while the (0/1+) transition level goes to 0.17 eV and 0.15 eV below CBM upon valine or phenylalanine passivation, respectively, in comparison with 0.61 eV when the surface is unpassivated.
For the I interstitial defect, additional calculations were performed for the electronic properties of the aforementioned passivated and unpassivated three defected surface models. From the density of states (DOS) as plotted in FIG. 8, panels a), d) and g), one can see that PbI₂-terminated MAPbI₃surface with I and Pb₂interstitial appear to have deep trap states (as marked with arrows), the deep acceptor states (unoccupied) of I interstitial are located at about 0.6 eV above the valence band maximum (VBM), while the deep donor states (occupied) of Pb₂interstitial are located at about 0.7 eV below the conduction band maximum (CBM). While for the Pb interstitial the defect donor state is quite shallow, lies at about 0.04 eV below CBM. The charge density of these defect states are plotted in FIG. 8, panels b), e) and h), from which one can clearly see that these states are relatively localized around the defects. For the valine passivated ones, it is found that I interstitial can interact with the —NH₂end in valine. The interstitial I defect gains electron from valine, thus the deep acceptor state in the unpassivated structure becomes an occupied state, and the new acceptor state in the passivated structure becomes a rather delocalized one, as shown in FIG. 8, panel i). Similarly, for the Pb₂interstitial defect, one finds the Pb₂bond with the two O atoms in the carboxyl group of valine in its zwitterion form, the valine gains electron from the Pb₂, and the localized donor state becomes much more delocalized states after passivation, as shown in FIG. 8, panel f). For the Pb interstitial defect, although the computed energy level of the donor state is quite shallow, the charge density of the state as plotted in FIG. 8, panel a) shows that it is still a relatively localized state, although the passivation does not significantly change the energy level, the new donor state after valine passivation shows it is a delocalized one.

Photovoltaic Device Architecture and Performance

To confirm the predicted passivation effects of valine and phenylalanine amino acids, experimental studies of the valine and phenylalanine amino acid passivated perovskites were conducted. The planar heterojunction perovskite solar cells in this specific embodiment were built as poly [bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)/CH3NH3PbI3/amino acid passivation layer/fullerene (C60)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/copper (Cu), as shown in FIG. 9A. The low-temperature two-step inter-diffusion of lead iodide (PbI₂) and a methyl ammonium iodide (MAI) stacking layer followed by a solvent annealing process was used to synthesize the perovskite layer. PCBM is used in the control device here. The current density-voltage (J-V) curves of the devices with different passivation are shown in FIG. 9B. The control device with PCBM layer shows a performance with a short circuit current density (J_SC) of 22.4 mA cm⁻², an open circuit voltage (V_OC) of 1.06 eV, a fill factor (FF) of 78.4%, and a PCE of 18.63%. Both valine and phenylalanine show significantly improved performance, with a J_SCof 22.41 mA cm⁻², a V_OCof 1.14 eV, a FF of 80.5% and a PCE of 20.57% for valine; and a J_SCof 22.5 mA cm⁻², a V_OCof 1.19 eV, a FF of 79% and a PCE of 21.2% for phenylalanine. The V_OCof the perovskite devices was significantly increased with valine and phenylalanine as passivation layers without sacrificing the J_SCand FF of the devices. FIG. 9C shows the V_OCdistribution of the devices with different passivation layers. The average V_OCvalues are 1.06, 1.14, and 1.19V for the devices with PCBM, valine and phenylalanine as passivation layer, respectively. To further verify the passivation effect of valine and phenylalanine amino acids, the trap density of states (tDOS) was also measured for the devices with PCBM, valine or phenylalanine passivation. The trap densities were extracted from the thermal admittance spectroscopy analysis. As shown in FIG. 9D, the devices with valine and phenylalanine have lower tDOS than PCBM over the entire trap depth region, specifically, the device with phenylalanine owns the lowest tDOS over the deeper trap region (0.40-0.52 eV) and the shallower trap region (0.30-0.40 eV). It is noted that the deeper trap states were assigned to the surface defects, while the shallower trap region was assigned to the defects at grain boundaries. In the shallower trap region, tDOS of the valine passivated device is about one order lower than the PCBM passivated device, while the phenylalanine passivated device is strikingly more than two orders lower than that of PCBM, indicating valine and phenylalanine amino acids can also efficiently diffuse into the grain boundary regions, and passivate the defects there.

Example Methods

First principles calculations. First-principles calculation was carried out in the framework of density functional theory as implemented in the VASP program. The generalized gradient approximation in the form of Perdew-Burke-Ernzerhof (PBE) was used for the exchange-correlation function. The ion-electron interaction was treated with the projector-augmented wave method. Surface slabs were modelled as PbI₂-terminated slabs of the tetragonal structure as the MAPbI₃was synthesized with slight excess PbI₂, the slab model has 9 layers of MAI and PbI₂in total. About 30 Å vacuum was added on top of the slab surface to minimize the interaction between the adjacent slabs. An energy cutoff of 500 eV was employed, and atomic positions were optimized until the maximum force on each atom is less than 0.02 eV/Å. Grimme's DFT-D3 correction was also adopted to describe the long-range Van der Waals interaction. The thermodynamic transition levels between different charge states of the defects were calculated according to: (q′/q)=[DFE(q′, E_F=0)−DFE(q, E_F=0)]/(q−q′), where DFE(q, E_F=0) is the formation energy of defect at q charge state.
Device fabrication: Patterned ITO substrates were cleaned by ultra-sonication with soap, acetone and isopropanol for 15 minutes, respectively. The hole transport layer poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) with a concentration of 2 mg.ml⁻¹dissolved in toluene was spin-coated at a speed of 4,000 RPM for 35 s, followed by annealing at 100° C. for 10 min. The PTAA film was pre-wetted by spinning 75 μl dimethyl formamide (DMF) at 4,000 RPM for 15 s to improve the wetting property of the perovskite precursor solution. The perovskite precursor solution composed of mixed cations (lead (Pb), cesium(Cs), formamidinium (FA) and methylammonium (MA)) and halides (I, Br) was dissolved in mixed solvent (DMF/DMSO=4:1) with a chemical formula of Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45. The amino-acid was added into perovskite precursor solution with the concentration of 1.5 mg/mL. Then 80 μl precursor solution was spin-coated at 2000 RPM for 2 s and 4000 RPM for 25 s, and the film was quickly washed with 130 μl toluene at 20 s during the procedure. The sample was annealed at 65° C. and 100° C. each for 10 min. C₆₀(30 nm), BCP (8 nm) and copper layers (140 nm) were thermally evaporated in sequential order to finish the devices.
Characterization: J-V analysis of solar cells was performed using a solar light simulator (Oriel 67005, 150 W Solar Simulator) and the power of the simulated light was calibrated to 100 mW.cm⁻²by a silicon (Si) diode (Hamamatsu S1133) equipped with a Schott visible-color glass filter (KG5 color-filter). All cells were measured using a Keithley 2400 source-meter with a scan rate of 0.1 V.s⁻¹. External quantum efficiency curves were characterized with a Newport QE measurement kit by focusing a monochromatic beam of light onto the devices. The tDOS of solar cells were derived from the frequency-dependent capacitance (C-f) and voltage dependent capacitance (C-V), which were obtained from the TAS measurement performed by a LCR meter (Agilent E4980A).
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the disclosed subject matter (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or example language (e.g., “such as”) provided herein, is intended merely to better illuminate the disclosed subject matter and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Certain embodiments are described herein. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments to be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A semiconductor device, comprising:

a cathode layer;

an anode layer;

an active layer disposed between the cathode layer and the anode layer, where the active layer includes a perovskite layer; and

a passivation layer disposed directly on a surface of the active layer between the cathode layer and the active layer, the passivation layer comprising a layer of material that passivates both cationic and anionic defects in the surface of the active layer, wherein the layer of material comprises a zwitterionic amino acid.

2. The semiconductor device of claim 1, wherein the perovskite layer includes organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃ ⁺), formamidinium (H₂NCHNH₂ ⁺), or an alkali-metal ion , B is a metal cation, and X is a halide anion, thiocyanate (SCN-) or a mixture thereof.

3. The semiconductor device of claim 1, further comprising:

a first carrier transport layer disposed between the passivation layer and the cathode; and

a second carrier transport layer disposed between the active layer and the anode, the first carrier transport layer having a higher electron conductivity than the second carrier transport layer, the second carrier transport layer having a higher hole conductivity than the first carrier transport layer.

4. The semiconductor device of claim 3, wherein:

the first carrier transport layer comprises at least one C60, a fullerene, a fullerene-derivative, LiF, CsF, LiCoO2, CS2CO3, TiOx, TiO2 nanorods (NRs), ZnO, ZnO nanorods (NRs), ZnO nanoparticles (NPs), ZnO, Al2O3, CaO, bathocuproine (BCP), copper phthalocyanine (CuPc), pentacene, pyronin B, pentadecafluorooctyl phenyl-C60-butyrate (F-PCBM), C60, C60/LiF, ZnO NRs/PCBM, ZnO/cross-linked fullerene derivative (C-PCBSD), single walled carbon nanotubes (SWCNT), poly(ethylene glycol) (PEG), Polyethylenimine (PEI), poly(dimethylsiloxaneblock-methyl methacrylate) (PDMS-b-PMMA), polar polyfluorene (PF-EP), polyfluorene bearing lateral amino groups (PFN), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-oxy-F), polyfluorene bearing quaternary ammonium groups in the side chains (WPF-6-oxy-F), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFNBr-DBTI5), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFPNBr), or poly(ethylene oxide) (PEO).; and

the second carrier transport layer comprises at least one poly(3,4-ethylenedioxithiophene) (PEDOT) doped with poly(styrene sulfonicacid) (PSS), 4,4′bis[(ptrichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2), poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) and C60, copper phthalocyanine (CuPc), poly[3,4-(1hydroxymethyl) ethylenedioxythiophene] (PHEDOT), n-dodecylbenzenesulfonic acid/hydrochloric acid-doped poly(aniline) nanotubes (a-PANIN)s, poly(styrenesulfonic acid)-graft-poly(aniline) (PSSA-g-PANI), poly[(9,9-dioctylfluorene)-co-N-(4-(1-methylpropyl)phenyl)diphenylamine] (PFT), 4,4′bis[(p-trichlorosilylpropylphenyl)phenylamino] biphenyl (TSPP), 5,5′-bis[(p-trichlorosilylpropylphenyl) phenylamino]-2,20-bithiophene (TSPT), N-propyltriethoxysilane, 3,3,3-trifluoropropyltrichlorosilane or 3-aminopropyltriethoxysilanePoly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), V2O5, VOx, MoO3, WO3, ReO3, NiOx, AgOx/PEDOT:PSS, Cu2O, CuSCN/P3HT, or Au nanoparticles.

5. The semiconductor device of claim 1, further comprising a fullerene layer disposed on the passivation layer between the passivation layer and the first carrier transport layer.

6. The semiconductor device of claim 5, wherein the fullerene layer comprises a layer of C₆₀having a thickness of between about 1 nm and about 100 nm.

7. The semiconductor device of claim 1, wherein the anode layer includes at least one of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-tin mixed oxide (ATO), a conductive polymer, a network of metal nanowire, a network of carbon nanowire, nanotube, nanosheet, nanorod, carbon nanotube, silver nanowire, or graphene.

8. The semiconductor device of claim 1, wherein the cathode layer includes at least one of copper, aluminum, calcium, magnesium, lithium, sodium, potassium, strontium, cesium, barium, iron, cobalt, nickel, silver, zinc, tin, samarium, ytterbium, chromium, gold, graphene, an alkali metal fluoride, an alkaline-earth metal fluoride, an alkali metal chloride, an alkaline-earth metal chloride, an alkali metal oxide, an alkaline-earth metal oxide, a metal carbonate, a metal acetate, or a combination of at least two of the above materials.

9. The semiconductor device of claim 1, wherein the passivation layer has a thickness of between about 1 nm and about 30 nm.

10. The semiconductor device of claim 1, wherein the zwitterionic amino acid comprises one of valine or phenylalanine.

11. A semiconductor device, comprising:

a cathode layer;

an anode layer;

an active layer disposed between the cathode layer and the anode layer, where the active layer includes an organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃ ⁺), an alkali metal ion or formamidinium (H₂NCHNH₂ ⁺), B is a metal cation, and X is a halide anion, thiocyanate (SCN-) or a mixture thereof;

a passivation layer disposed directly on a surface of the active layer between the cathode layer and the active layer, the passivation layer comprising a layer of material that passivates both cationic and anionic defects in the surface of the active layer, wherein the layer of material comprises a zwitterionic amino acid;

an electron extraction layer disposed directly on the passivation layer between the passivation layer and the cathode layer, the electron extraction layer comprising a layer of C₆₀;

a first carrier transport layer comprising bathocuproine (BCP) and disposed between the electron extraction layer and the cathode; and

a second carrier transport layer comprising Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and disposed between the active layer and the anode.

12. The semiconductor device of claim 11, wherein the anode layer includes indium tin oxide (ITO) and wherein the cathode layer includes copper.

13. The semiconductor device of claim 11, wherein the layer of C₆₀has a thickness of between about 1 nm and about 100 nm.

14. The semiconductor device of claim 11, wherein the active layer has a thickness of between about 1 nm and about 10 μm.

15. The semiconductor device of claim 11, wherein the passivation layer has a thickness of between about 1 nm and about 30 nm.

16. The semiconductor device of claim 11, wherein the zwitterionic amino acid comprises one of valine or phenylalanine.

17. A method of making a semiconductor device, the process comprising:

providing an active layer, where the active layer includes a perovskite material; and

applying a passivation layer directly on a surface of the active layer, the passivation layer comprising a first material that passivates both cationic and anionic defects in the surface of the active layer, wherein the first material comprises a zwitterionic amino acid.

18. The method of claim 17, further comprising forming a cathode layer on the passivation layer.

19. The method of claim 18, further comprising forming an anode layer on a side of the active layer so that the active layer is disposed between the cathode layer and the anode layer.

20. The method of claim 19, further comprising

forming a first carrier transport layer disposed between the passivation layer and the cathode layer; and

forming a second carrier transport layer disposed between the active layer and the anode layer, the first carrier transport layer having a higher electron conductivity than the second carrier transport layer, the second carrier transport layer having a higher hole conductivity than the first carrier transport layer.

21. The method of claim 17, wherein the perovskite material includes organometal trihalide perovskite having the formula ABX₃, or A₂BX₄, wherein A is methylammonium (CH₃NH₃ ⁺), formamidinium (H₂NCHNH₂ ⁺), or an alkali-metal ion , B is a metal cation, and X is a halide anion, thiocyanate (SCN-) or a mixture thereof.

22. The method of claim 17, wherein the zwitterionic amino acid comprises one of valine or phenylalanine.