WO2019232408A1 - Doped polycrystalline perovskite films with extended charge carrier recombination lifetimes and high power conversion efficiencies - Google Patents

Abstract

The present disclosure is directed to perovskite films comprising a polycrystalline perovskite composition, wherein the composition is doped with a plurality of ions selected from the group consisting of Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, and Ce³⁺. The plurality of ions reside in the grain boundaries and on the surface of the perovskite film. The doped polycrystalline perovskite films exhibit extended charge carrier recombination lifetimes and enhanced power conversion efficiencies in solar cells.

Description

DOPED POLYCRYSTALLINE PEROVSKITE FILMS WITH EXTENDED CHARGE CARRIER RECOMBINATION LIFETIMES AND HIGH POWER

CONVERSION EFFICIENCIES

GOVERNMENT INTEREST

This invention was made with government support under Grant No. FA9550- 16-1-0299 awarded by the Air Force Office of Scientific Research. The Government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Application No. 62/679,066, filed June 1, 2018, which is herein incorporated by reference in its entirety for all purposes.

FIELD

The presently disclosed subject matter relates generally to doped polycrystalline perovskite films that exhibit extended charge carrier recombination lifetimes and high power conversion efficiencies in solar cell devices.

BACKGROUND

Solar cells, which convert sunlight into electricity to provide clean and renewable energy, represent a promising long-term solution for the environmental issues caused by the mass production and burning of fossil fuels. The history of efficiency enhancement for thin-film solar cells has witnessed the importance of reducing charge -recombination loss within devices, including both at the electrode contacts and inside the photoactive layers.^1-5 Solution-processed organic-inorganic hybrid perovskite (OIHP) semiconductors have drawn tremendous attention to the field of optoelectronics,⁶ because they offer several valuable optical and electronic properties, such as large hole and electron mobility, strong light absorption, and long charge carrier diffusion length.^{7 11} Among these properties, the long charge recombination lifetime of polycrystalline OIHP thin films are particularly distinct and understood to be one reason for the success of these materials in solar cell applications.^{12 13} Though OIHP materials are shown to be more tolerant to defects, the point or extended defects in polycrystalline OIHP films still reduce the carrier recombination lifetime and impact device performance. Much effort has been dedicated to developing new methods to extend the carrier recombination lifetime in OIHP materials so as to improve their power conversion efficiencies, however, much to no success. The subject matter disclosed herein addresses this problem.

BRIEF SUMMARY

In one aspect, the subject matter described herein is directed to a perovskite film comprising a poly crystalline perovskite composition of formula (I):

ABX₃ (I)

wherein A is a cation selected from the group consisting of methylammonium (MA), tetramethylammonium, formamidinium (FA), cesium, rubidium, potassium, sodium, butylammonium, phenethylammonium, phenylammonium, guanidinium, and a combination thereof; B is a divalent metal selected from the group consisting of lead, tin, cadmium, germanium, zinc, nickel, platinum, palladium, mercury, titanium, silicon, and a combination thereof; and X is a halide selected from the group consisting of Cl, Br, F, I, and a combination thereof;

wherein said polycrystalline perovskite composition is doped with a plurality of ions selected from the group consisting of Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, and Ce³⁺;

wherein said plurality of ions reside in grain boundaries and on the surface of said perovskite film; and wherein said composition is doped with said plurality of ions in an amount selected from the group consisting of about 0.0001 wt% to about 0.40 wt% Ag⁺, from about 0.0001 wt% to about 5.0 wt% Ce³⁺, from about 0.0001 wt% to about 0.90 wt% Sr²⁺, from about 0.0001 wt% to about 0.90 wt% Cu⁺, and from about 0.0001 wt% to about 5.0 wt% Sm²⁺ relative to the weight of the perovskite film.

These and other aspects are described fully herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 A shows TRPL decay curves of MAPbE with or without metal ion additives. The percentages of the ions in the figure refer to the blended weight percent. Figure 1B shows J-V curves of FAo_.85MAo_.i5Pb(Io_.85Br_0.i5)3 based solar cells blending with metal ions. In the inset of Figure 1B is the device structure of perovskite a solar cell: ITO/PTAA/OIHP/PCBM/C60/BCP/Cu.

Figure 1C shows TRMC traces of MAPbF with or without blended metal ion additives.

Figure 1D shows a scheme of the metal ion doping of OIHPs described herein. Shown is MAPbF, where the metal ions gathered in GBs of the OIHP thin film. Further illustrated is down-shifted band bending towards GBs, where the charge separation increases and recombination decreases.

Figure 2 A shows the hole lateral conductivity of MAPbF with or without metal ion additives (blended weight 0.1% Ag⁺, 0.2% Sr²⁺, 0.1% Ce³⁺). The insets are lateral device structures, where the length of electrodes was 1 mm, and the spacing between the symmetrical electrodes was 50 pm.

Figure 2B shows the electron lateral conductivity of MAPbF with or without metal ion additives (blended weight 0.1% Ag⁺, 0.2% Sr²⁺, 0.1% Ce³⁺). The insets are lateral device structures, where the length of electrodes was 1 mm, and the spacing between the symmetrical electrodes was 50 pm.

Figure 2C shows a height image of Sr²⁺ treated MAPbF single crystal surface.

Figure 2D shows a CPD image of Sr²⁺ treated MAPbF single crystal surface.

Figure 2E shows cross sectional curves of a Sr²⁺ treated MAPbF single crystal surface.

Figure 3 shows height and CPD images of MAPbF thin films without and with 0.1% Ag⁺, 0.2% Sr²⁺ and 0.1% Ce³⁺, respectively (blended weight percentages). Eight grain boundaries are labeled in the CPD images, and their height, CPD across the grain boundaries are displayed.

Figure 4A shows calculated normalized total and partial DOS of Ag, Sr and Ce absorbed on MAI-terminated surfaces of MAPbF

Figure 4B shows calculated normalized total and partial DOS of Ag, Sr and Ce absorbed on PbF-terminated surfaces of MAPbF

Figure 4C shows an isosurface plot of the charge density of the highest occupied band (HOB) and the lowest unoccupied band (LETB) of Ag, Sr and Ce absorbed on MAI- terminated and PbF-terminated surfaces of MAPbF· Figure 5 shows a PL spectrum of MAPbL without and with metal ion additives (blended weight percentages 0. lwt.% Ag⁺, 0.2wt.% Sr²⁺, 0. lwt.% Ce³⁺).

Figure 6A shows J-V curves of MAPbL based solar cells blending with metal ions (ion percentages refer to the blended weight percentages).

Figure 6B shows an EQE spectrum of solar cells based on

FA_0.85MA_0.i5Pb(Io_.85Br_0.i5)₃ blending with 0.1 wt% Ce³⁺.

Figure 6C shows stable output photocurrent and PCE of solar cells based on FA_0.85MA_0.i5Pb(Io_.85Br_0.i5)₃ blending with 0.1 wt% Ce³⁺.

Figure 6D shows forward and reverse scan J-V curves of solar cells based on FA_0.85MA_0.i5Pb(Io_.85Br_0.i5)₃ blending with 0.1 wt% Ce³⁺.

Figure 6E shows statistics of the PCE distribution (30 devices) of

FA_0.85MA_0.i5Pb(Io_.85Br_0.i5)3 based solar cells blending without and with metal ion additives (blended weight ratios 0.1 wt% Ag⁺, 0.2 wt% Sr²⁺, 0.1 wt% Ce³⁺): over 60% of the devices doped by Sr²⁺ or Ce³⁺ showed PCEs higher than 19%, in contrast, most of the control devices with pristine OIHP show < 17.5% PCEs.

Figure 7 shows TRMC traces of MAPbL with or without metal ion additives (weight percentages refer to blended weight percent). The excitation light had a wavelength of 500 nm and fluence of 0.1410.04 nJ cm ².

Figure 8 A shows a height image of a Ag⁺ treated MAPbL single crystal surface. Figure 8B shows a CPD image a Ag⁺ treated MAPbL single crystal surface.

Figure 8C shows cross sectional curves of a Ag⁺ treated MAPbL single crystal surface.

Figure 8D shows a height image of a Ce³⁺ treated MAPbL single crystal surface. Figure 8E shows a CPD image a Ce³⁺ treated MAPbL single crystal surface.

Figure 8F shows cross sectional curves of a Ce³⁺ treated MAPbL single crystal surface.

Figure 9 shows XRD curves of MAPbL powder without and with Ag⁺, Sr²⁺ or Ce³⁺ additives (weight percentages refer to blended weight percent).

Figure 10 shows energy levels of MAPbL, MAI (PbL) terminal surfaces, atomic Ag, Sr, and Ce. DETAILED DESCRIPTION

The subject matter described herein relates to metal ion doped organic inorganic hybrid perovskite poly crystalline films that exhibit long charge recombination lifetimes. Many efforts have been devoted to elongate the carrier recombination lifetime in polycrystalline OIHP solar cells by increasing the grain size via film growth modification ^{13 15} as well as passivating charge traps on the surface and grain boundaries of perovskite films.^{16 20} However, it was unknown that the carrier recombination lifetime in polycrystalline OIHP could be lengthened by doping grain boundaries with extrinsic metal ions. The doped polycrystalline perovskite films described herein exhibit doping along their grain boundaries and on the surface of the film, which results in reduced charge recombination and increased efficiency of the OIHP films in solar cells. The results additionally provide insight to the defect tolerance of polycrystalline perovskite films.

A long photoluminescence decay lifetime is often regarded as an indication of a long charge carrier recombination lifetime in semiconductor materials. As described herein, however, after the addition of extrinsic metal ions to polycrystalline perovskite films, the charge carrier recombination lifetimes of the films measured by time-resolved microwave conductance (TRMC) were up to 100 times longer than those measured by photoluminescence decay. Regardless of their valence charge, the addition of the metal ions quench radiative charge recombination while dramatically slowing down the bimolecular charge recombination in the perovskite films. Without wishing to be bound by theory, it is understood that a lateral p-n homojunction at the individual grain level justifies the phenomenon as a result of doping of grain boundaries by metal clusters. The extrinsic metal ions gather in grain boundaries of the OIHP thin films and form metal clusters, which results in a band bending within the grain and the formation of p-n junctions within individual OIHP grains. The lateral homojunction structure facilities the exciton dissociation, and minimizes electron-hole recombination.

The presence of a homojunction in individual perovskite grains in doped films is advantageous in the light to current conversion process in solar cells. Although the exciton binding energies in three-dimensional hybrid perovskites are small enough for free carrier generation, doping provides a strategy to enhance the exciton dissociation for low dimensional perovskites with much larger exciton binding energy. Furthermore, the lateral homojunction separates photogenerated electrons and holes spatially, enhancing transport through different channels to electrodes. Electrons are extracted to the cathode through transportation along the grain boundaries to the electron transport layer, while holes flow to the hole transport layer within the grain interiors. This effectively reduces bimolecular charge recombination and enhances the device performance of polycrystalline OIHP solar cells. Additionally, controlled doping of OIHP materials is desired in solar cell applications to achieve the maximum open-circuit voltage, because a mild doping can enhance the quasi-Fermi level splitting without causing too much carrier charge recombination. As such, the lateral homojunction formed by controlled doping disclosed herein can be broadly applied to other OIHP applications where a long carrier recombination lifetime is needed, such as photodetectors and radiation detectors.

The presently disclosed subject matter will now be described more fully hereinafter. However, many modifications and other embodiments of the presently disclosed subject matter set forth herein will come to mind to one skilled in the art to which the presently disclosed subject matter pertains having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the presently disclosed subject matter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. In other words, the subject matter described herein covers all alternatives, modifications, and equivalents. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in this field. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In the event that one or more of the incorporated literature, patents, and similar materials differs from or contradicts this application, including but not limited to defined terms, term usage, described techniques, or the like, this application controls.

I. Definitions

As used herein, “and/or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

As used herein, the term“about,” when referring to a measurable value such as an amount of a compound or agent of the current subject matter, dose, time, temperature, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, ±1%, ±0.5%, or even ±0.1% of the specified amount. The terms “approximately,” “about,” “essentially,” and “substantially” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, in some embodiments, as the context may dictate, the terms“approximately”,“about”, and“substantially” may refer to an amount that is within less than or equal to 10% of the stated amount. The term“generally” as used herein represents a value, amount, or characteristic that predominantly includes or tends toward a particular value, amount, or characteristic.

The terms“comprising,”“including,”“having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term“or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term“or” means one, some, or all of the elements in the list.

As used herein,“n-type” refers to a structure, layer, or material wherein electrons are the majority carriers and holes are the minority carriers.

As used herein,“p-type” refers to a structure, layer, or material wherein holes are the majority carriers and electrons are the minority carriers.

As used herein“doped,” refers to a structure, layer, or material that is doped with a doping agent. A layer may be doped with an n-type dopant (also“n-doped” herein) or a p- type dopant (also“p-doped” herein).

As used herein,“dopant,” refers to a doping agent, such as an n-type dopant or a p-type dopant.

As used herein,“HTL” refers to hole transport layer.

As used herein,“ETL” refers to electron transport layer.

As used herein,“OIHP” refers to organic inorganic hybrid perovskite.

As used herein,“GB” refers to grain boundary.

As used herein,“PL” refers to photoluminescence.

As used herein,“resides” refers to an object that is situated in a particular location. In certain embodiments, a plurality of ions may be situated in or on a specific location, such as in a grain boundary of a film or on the surface of a film.

As used herein,“plurality” refers to more than one. In certain embodiments, a “plurality of ions” refers to a cluster of ions. II. Perovskite Film Compositions

The subject matter described herein is directed to a perovskite film comprising a polycrystalline perovskite composition of formula (I):

ABX₃ (I)

wherein A is a cation selected from the group consisting of methylammonium (MA), tetramethylammonium, formamidinium (FA), cesium, rubidium, potassium, sodium, butylammonium, phenethylammonium, phenylammonium, guanidinium, and a combination thereof; B is a divalent metal selected from the group consisting of lead, tin, cadmium, germanium, zinc, nickel, platinum, palladium, mercury, titanium, silicon, and a combination thereof; and X is a halide selected from the group consisting of Cl, Br, F, I, and a combination thereof;

wherein said polycrystalline perovskite composition is doped with a plurality of ions selected from the group consisting of Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, and Ce³⁺;

wherein said plurality of ions reside in grain boundaries and on the surface of said perovskite film; and wherein said composition is doped with said plurality of ions in an amount selected from the group consisting of about 0.0001 wt% to about 0.40 wt% Ag⁺, from about 0.0001 wt% to about 5.0 wt% Ce³⁺, from about 0.0001 wt% to about 0.90 wt% Sr²⁺, from about 0.0001 wt% to about 0.90 wt% Cu⁺, and from about 0.0001 wt% to about 5.0 wt% Sm²⁺ relative to the weight of the perovskite film.

a. ABX₃

In certain embodiments, in the polycrystalline perovskite composition of formula (I), A is selected from the group consisting of methylammonium, tetramethylammonium, formamidinium, cesium, rubidium, potassium, sodium, butylammonium, phenethylammonium, phenylammonium, guanidinium, and a combination thereof.

In certain embodiments, A comprises an ammonium, an organic cation of the general formula [NR4]⁺ where the R groups can be the same or different groups. Suitable R groups include, but are not limited to: methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; any alkane, alkene, or alkyne C_xH_y, where x=l-20, y=l-42, cyclic, branched or straight-chain; alkyl halides, C_xH_yX_z, x=l-20, y=0-42, z=l-42, X=F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenyl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., pyridine, pyrrole, pyrrolidine, piperidine, tetrahydroquinoline); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (e.g., acetic acid, propanoic acid); and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any alkoxy or group,— OC_xH_y, where x=0-20, y=l-42. In certain embodiments, A is methylammonium, (0¾N1¾⁺).

In certain embodiments, A comprises a formamidinium, an organic cation of the general formula [R₂NCHNR₂]⁺ where the R groups can be the same or different groups. Suitable R groups include, but are not limited to: hydrogen, methyl, ethyl, propyl, butyl, pentyl or an isomer thereof; any alkane, alkene, or alkyne C_xH_y, where x=l-20, y=l-42, cyclic, branched or straight-chain; alkyl halides, C_xH_yX_z, x=l-20, y=0-42, z=l-42, X=F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenyl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., imidazole, benzimidazole, dihydropyrimidine, (azolidinylidenemethyl)pyrrolidine, triazole); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen- containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (acetic acid, propanoic acid) and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any alkoxy or group,— OC_xH_y, where x=0-20, y=l-42. In certain embodiments A comprises a formamidinium ion represented by (H₂N=CH— NH₂ ')

In certain embodiments, A comprises a guanidinium, an organic cation of the general formula [(R₂N)₂C=NR₂]⁺ where the R groups can be the same or different groups. Suitable R groups include, but are not limited to: hydrogen, methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; any alkane, alkene, or alkyne C_xH_y, where x=l-20, y=l-42, cyclic, branched or straight-chain; alkyl halides, C_xH_yX_z, x=l-20, y=0-42, z=l-42, X=F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenyl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., octahydropyrimido[ 1 ,2-a]pyrimidine, pyrimido[ 1 ,2-a]pyrimidine, hexahydroimidazo[l,2-a]imidazole, hexahydropyrimidin-2-imine); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (acetic acid, propanoic acid) and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any alkoxy or group,— OC_xH_y, where x=0-20, y=l-42. In certain embodiments, A comprises a guanidinium ion of the type (H₂N=C— (NH₂)₂ ⁺).

In certain embodiments, A comprises an alkali metal cation, such as Li⁺, Na⁺, K⁺, Rb⁺, or Cs⁺.

In certain embodiments, A is selected from methylammonium (MA), formamidinium (FA), cesium, and a combination thereof. In certain embodiments, A is a combination of methylammonium (MA) and formamidinium (FA).

In certain embodiments, B comprises at least one divalent metal atom. In certain embodiments, B is selected from lead, tin, cadmium, germanium, zinc, nickel, platinum, palladium, mercury, titanium, silicon, and a combination thereof. In certain embodiments, the divalent metal (B) can be, for example, one or more divalent elements from Group 14 of the Periodic Table (e.g., divalent lead, tin, or germanium), one or more divalent transition metal elements from Groups 3-12 of the Periodic Table (e.g., divalent titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, palladium, platinum, and cadmium), and/or one or more divalent alkaline earth elements (e.g., divalent magnesium, calcium, strontium, and barium). In certain embodiments, B is lead. In certain embodiments, B is tin. In certain embodiments, B is a combination of lead and tin.

In certain embodiments, the variable X is independently selected from one or a combination of halide atoms, wherein the halide atom (X) may be, for example, fluoride (F ), chloride (CF), bromide (Br ), and/or iodide (G). In certain embodiments, X is iodide. In certain embodiments, X is bromide. In certain embodiments, X is a combination of bromide and iodide.

In certain embodiments, the poly crystalline perovskite composition is MAPbF. In certain embodiments, the polycrystalline perovskite composition is

FAo.85MAo.i5Pb(Io.85Bro.i5)3· b. Dopants

In certain embodiments, the polycrystalline perovskite compositions disclosed herein are doped with a plurality of ions selected from the group consisting of Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, and Ce³⁺.

As used herein, “blending ratio percent,” “blended weight percent ratio,” and “blending percent” refer to the weight ratio of the metal halide dopant (i.e. Agl) to metal halide (BX₂)in the precursor solution (i.e. Pbl₂, PbBr₂, Snl₂) to prepare the perovskite films, multiplied by 100%.

As used herein,“cation weight ratio %,” “metal cation ratio w%,” or“cation percent” refer to the weight ratio of the metal cation (i.e. Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, Ce³⁺) to the perovskite film, multiplied by 100%. The weight of the perovskite film in the cation weight ratio % refers to the weight of the perovskite ABX₃ composition without the added ion.

In certain embodiments, the plurality of ions reside in grain boundaries and on the surface of the perovskite film. In certain embodiments, the plurality of ions reside in grain boundaries or on the surface of the perovskite film.

In certain embodiments, the polycrystalline perovskite composition is doped with a plurality of ions in an amount selected from the group consisting of about 0.0001 wt% to about 0.40 wt% Ag⁺, from about 0.0001 wt% to about 5.0 wt% Ce³⁺, from about 0.0001 wt% to about 0.90 wt% Sr²⁺, from about 0.0001 wt% to about 0.90 wt% Cu⁺, and from about 0.0001 wt% to about 5.0 wt% Sm²⁺ relative to the weight of the perovskite film.

In certain embodiments, the polycrystalline perovskite composition is doped with a plurality of ions in an amount selected from the group consisting of about 0.02 wt% to about 0.04 wt% Ag⁺, from about 0.01 wt% to about 3.0 wt% Ce³⁺, from about 0.02 wt% to about 0.70 wt% Sr²⁺, from about 0.005 wt% to about 0.01 wt% Cu⁺, and from about 0.01 wt% to about 0.05 wt% Sm²⁺ relative to the weight of the perovskite film.

In certain embodiments, the polycrystalline perovskite composition is doped with Ag⁺ in an amount from about 0.005 wt% to about 0.45 wt%, from about 0.01 wt% to about 0.2 wt%, from about 0.05 wt% to about 0.3 wt%, from about 0.01 wt% to about 0.10 wt%, from about 0.02 wt% to about 0.07 wt%, from about 0.15 wt% to about 0.35 wt%, from about 0.025 wt% to about 0.035 wt%, from about 0.02 wt% to about 0.03 wt%, or from about 0.015 wt% to about 0.055 wt%.

In certain embodiments, the polycrystalline perovskite composition is doped with Ce³⁺ in an amount from about 0.001 wt% to about 5 wt%, from about 0.0001 wt% to about 2 wt%, from about 0.0001 wt% to about 1 wt%, from about 0.005 wt% to about 3 wt%, from about 0.01 wt% to about 1 wt%, from about 0.015 wt% to about 0.5 wt%, from about 0.001 wt% to about 0.10 wt%, from about 0.009 wt% to about 0.09 wt%, from about 0.01 wt% to about 0.07 wt%, from about 0.01 wt% to about 0.05 wt%, from about 0.005 wt% to about 0.05 wt%, or from about 0.01 wt% to about 0.03 wt%.

In certain embodiments, the polycrystalline perovskite composition is doped with Sr²⁺ in an amount from about 0.005 wt% to about 0.70 wt%, from about 0.007 wt% to about 0.5 wt%, from about 0.01 wt% to about 0.3 wt%, from about 0.015 wt% to about 0.2 wt%, from about 0.075 wt% to about 0.1 wt%, from about 0.001 wt% to about 0.10 wt%, from about 0.001 wt% to about 0.07 wt%, from about 0.01 wt% to about 0.05 wt%, from about 0.009 wt% to about 0.08 wt%, or from about 0.01 wt% to about 0.06 wt%.

In certain embodiments, the polycrystalline perovskite composition is doped with Cu⁺ in an amount from about 0.005 wt% to about 0.8 wt%, from about 0.0075 wt% to about 0.6 wt%, from about 0.001 wt% to about 0.5 wt%, from about 0.005 wt% to about 0.3 wt%, from about 0.001 wt% to about 0.2 wt%, from about 0.0015 wt% to about 0.3 wt%, from about 0.001 wt% to about 0.010 wt%, from about 0.001 wt% to about 0.025 wt%, from about 0.001 wt% to about 0.050 wt%, from about 0.001 wt% to about 0.009 wt%, from about 0.0001 wt% to about 0.5 wt%, from about 0.0005 wt% to about 0.010 wt%.

In certain embodiments, the polycrystalline perovskite composition is doped with Sm²⁺ in an amount from about 0.001 wt% to about 5 wt%, from about 0.0001 wt% to about 2 wt%, from about 0.0001 wt% to about 1 wt%, from about 0.005 wt% to about 3 wt%, from about 0.01 wt% to about 1 wt%, from about 0.015 wt% to about 0.5 wt%, from about 0.001 wt% to about 0.10 wt%, from about 0.009 wt% to about 0.09 wt%, from about 0.01 wt% to about 0.07 wt%, from about 0.01 wt% to about 0.05 wt%, from about 0.005 wt% to about 0.05 wt%, or from about 0.01 wt% to about 0.03 wt%.

In certain embodiments, when the perovskite composition is FA_0.85MA_0.i5Pb(Io_.85Br_0.i5)3, the perovskite film is doped with about 0.03 wt% Ag⁺ relative to the weight of the perovskite film. In certain embodiments, the perovskite film is doped with about 0.01 wt% Ag⁺, 0.02 wt% Ag⁺, 0.04 wt% Ag⁺, or 0.05 wt% Ag⁺ relative to the weight of the perovskite film. In certain embodiments, when the perovskite composition is

FA_0.85MA_0.i5Pb(Io_.85Br_0.i5)3, the perovskite film is doped with about 0.02 wt% Ce³⁺ relative to the weight of the perovskite film. In certain embodiments, the perovskite film is doped with about 0.009 wt% Ce³⁺, 0.01 wt% Ce³⁺, 0.03 wt% Ce³⁺, or 0.04 wt% Ce³⁺ relative to the weight of the perovskite film.

In certain embodiments, when the perovskite composition is

FA_0.85MA_0.i5Pb(Io_.85Br_0.i5)3, the perovskite film is doped with about 0.04 wt% Sr²⁺ relative to the weight of the perovskite film. In certain embodiments, the perovskite film is doped with about 0.02 wt% Sr²⁺, 0.03 wt% Sr²⁺, 0.05 wt% Sr²⁺, or 0.06 wt% Sr²⁺ relative to the weight of the perovskite film.

In certain embodiments, when the perovskite composition is MAPbF, the perovskite film is doped with about 0.025 wt% Ag⁺ relative to the weight of the perovskite film. In certain embodiments, the perovskite film is doped with about 0.023 wt% Ag⁺, 0.024 wt% Ag⁺, 0.026 wt% Ag⁺, or 0.027 wt% Ag⁺ relative to the weight of the perovskite film.

In certain embodiments, when the perovskite composition is MAPbF, the perovskite film is doped with about 0.02 wt% Ce³⁺ relative to the weight of the perovskite film. In certain embodiments, the perovskite film is doped with about 0.01 wt% Ce³⁺, 0.03 wt% Ce³⁺, 0.04 wt% Ce³⁺, or 0.05 wt% Ce³⁺ relative to the weight of the perovskite film.

In certain embodiments, when the perovskite composition is MAPbF, the perovskite film is doped with about 0.04 wt% Sr²⁺ relative to the weight of the perovskite film. In certain embodiments, the perovskite film is doped with about 0.02 wt% Sr²⁺, 0.03 wt% Sr²⁺, 0.05 wt% Sr²⁺, or 0.06 wt% Sr²⁺ relative to the weight of the perovskite film.

In certain embodiments, when the perovskite composition is MAPbF, the perovskite film is doped with about 0.007 wt% Cu⁺ relative to the weight of the perovskite film. In certain embodiments, the perovskite film is doped with about 0.004 wt% Cu⁺, 0.005 wt% Cu⁺, 0.006 wt% Cu⁺, 0.008 wt% Cu⁺, 0.009 wt% Cu⁺, or 0.010 wt% Cu⁺ relative to the weight of the perovskite film.

III. Devices

a. Charge Recombination Lifetime

In certain embodiments, the polycrystalline perovskite films disclosed herein can be used in a device, such as a solar cell, solar panel, light emitting diode, photodetector, x-ray detector, field effect transistor, memristor, or synapse. The perovskite films disclosed herein exhibit long charge recombination lifetimes. As used herein, carrier lifetime is the average time it takes for a minority carrier (i.e. free charge carriers, an electron and a hole) to recombine. The process through which this is carried out is referred to as carrier recombination or charge recombination. Techniques to obtain the free carrier recombination lifetime are described further herein.

In certain embodiments, the polycrystalline perovskite film exhibits a free carrier recombination lifetime of at least 2.0 ps. In certain embodiments, the polycrystalline perovskite film exhibits a free carrier recombination lifetime of at least 3.0 ps, 4 ps, 5 ps, 6 ps, 7 ps, 8 ps, 9 ps, 10 ps, 11 ps, 12 ps, 13 ps, 14 ps, 15 ps, 16 ps, 17 ps, 18 ps, 19 ps, or 20 ps.

b. Solar Cells

In certain embodiments, the subject matter disclosed herein is directed to a perovskite solar cell, comprising:

a conductive substrate;

a first transport layer disposed on said conductive substrate;

a doped polycrystalline perovskite film disclosed above disposed on said first transport layer;

a second transport layer disposed on said perovskite film; and

an electrode disposed on said second transport layer,

wherein said first transport layer or said second transport layer is an electron transport layer and the other of said first transport layer or said second transport layer is a hole transport layer.

In certain embodiments, the conductive substrate and electrode each comprise at least one of lithium, sodium, potassium, rubidium, cesium, francium, beryllium,

magnesium, calcium, strontium, barium, radium, boron, aluminum, gallium, indium, thallium, tin, lead, flerovium, bismuth, antimony, tellurium, polonium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium, seaborgium, bohrium, hassium, copernicium, samarium, neodymium, ytterbium, 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, carbon nanowire, carbon nanosheet, carbon nanorod, carbon nanotube, graphite, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum doped zinc oxide (AZO), antimony -tin mixed oxide (ATO), network of metal/alloy nanowire, or a combination of two or more of the above materials. In certain embodiments, the conductive substrate is selected from the group consisting of indium tin oxide (ITO), aluminum doped zinc oxide (AZO), and fluorine doped tin oxide (FTO). In certain embodiments, the conductive substrate is Indium Tin Oxide (ITO). In certain embodiments, the electrode is selected from Ag, Au, Cu, Al, Cr, Bi, Pt, graphite and a combination thereof. In certain embodiments, the electrode is Cu.

In certain embodiments, the hole transport layer comprises at least one of poly(3,4- ethylene dioxithiophene) (PEDOT) doped with poly( styrene sulfon icacid) (PSS), Spiro - OMeTAD, pm-spiro-OMeTAD, po-spiro-OMeTAD, dopants in spiro-OMeTAD, 4,4'- biskptrichlorosilylpropylphenyl)pheny laminoThiphenyl (TPD-Si2), poly(3 -hexyl-2, 5- thienylene vinylene) (P₃HTV), C₆o, carbon, carbon nanotube, graphene quantum dot, graphene oxide, copper phthalocyanine (CuPc), Polythiophene, poly(3,4- ( 1 hydroxymethyl)ethylenedioxythiophene (PHMEDOT), n-dodecylbenzenesulfonic acid/hydrochloric acid doped poly(aniline) nanotubes (a-PANIN)s, poly(styrene sulfonic acid)-graft-poly(aniline) (PSSA-g-PANI), poly(9. 9-dioctylfluorene)-co-N-(4-(l- methylpropyl)phenyl) diphenylamine (PFT), 4,4'-bis(p- trichlorosilylpropylphenyl) phenylaminobiphenyl (TSPP), 5,5'-bis(p-trichlorosilylpropylphenyl) phenylamino-2,20 bithiophene (TSPT), N-propyltriethoxy silane, 3,3,3-trifluo ropropyltrichloro silane or 3- aminopropyltriethoxysilane, Poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA), (Poly[[(2,4-dimethylphenyl)imino]-l,4-phenylene(9,9-dioctyl-9H-fluorene-2,7-diyl)- l,4phenylene], (PF8-TAA)), (Poly [[(2,4-dimethylphenyl)imino]-l,4-phenylene (6, 12- dihydro-6,6, 12, l2tetraoctylindeno[l,2-b]fluorene-2,8-diyl)-l,4-phenylene]) (PIF8-TAA), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[l,2-b:4,5-b]dithiophene-2,6-diyl][3-fluoro-2-[(2- ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), poly[N-90-heptadecanyl-2,7- carbazole-alt-5,5-(40,70-di-2-thienyl-20,l0,30-benzothiadiazole)] (PCDTBT), Poly[2,5- bis(2-decyldodecyl)pyrrolo[3,4-c]pyrrole-l,4(2H,5H)-dione-(E)-l,2-di(2,20-bithiophen-5- yl) ethene] (PDPPDBTE), 4,8-dithien-2-yl-benzo[l,2- d ;4,5- d 'jbistri azole- alt - benzo[l,2- b :4,5b'] dithiophenes (pBBTa-BDTs), pBBTa-BDTl, pBBTa-BDT2 polymers, poly(3-hexylthiophene) (P₃HT), poly(4,4’-bis(N-carbazolyl)-l, l’-biphenyl) (PPN), triarylamine (TAA) and/or thiophene moieties, Paracyclophane, Triptycene, and Bimesitylene, Thiophene and Furan-based hole transport materials, Dendrimer-like and star-type hole transport materials, VO, VOX, MoC, WO, ReO, NiOx, AgOx, CuO, Cu20, V205, Cul, CuS, CuInS2, colloidal quantum dots, lead sulphide (PbS), CuSCN, Cu2ZnSnS4, Au nanoparticles and their derivatives. Thiophene derivatives, Triptycene derivatives, Triazine derivatives, Porphyrin derivatives, Triphenylamine derivatives, Tetrathiafulvalene derivatives, Carbazole derivatives and Phthalocyanine derivatives. As used herein, when a material is referred to a“derivate” or as“derivatives,” such as Triphenylamine derivatives, the material contains Triphenylamine in its backbone structure. In certain embodiments, the hole transport layer is selected from the group consisting of poly(triaryl amine) (PTAA), poly(3-hexylthiophene) (P₃HT), poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), NiO_x, N4,N40-bis(4-(6-((3- ethyloxetan-3 -yl)methoxy)hexyl)phenyl)-N4, N40-diphenyl-biphenyl-4, 40-diamine (TPD), 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD), CuSCN, and a combination thereof. In certain embodiments, the hole transport layer comprises a material selected from the group consisting of poly(triaryl amine) (PTAA), polyp, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), NiO_x, N4,N40- bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4, N40-diphenyl-biphenyl-4, 40- diamine (TPD), 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD), CuSCN, and a combination thereof. In certain embodiments, the first transport layer is the hole transport layer. In certain embodiments, the hole transport layer comprises poly(triaryl amine) (PTAA).

In certain embodiments, the electron transport layer comprises at least one of LiF, CsP, LiCoO, CsCO, TiOX, TiO, nanorods (NRs), ZnO, ZnO nanorods (NRs), ZnO nanoparticles (NPs), ZnO, Al-O, CaO, bathocuproine (BCP), copper phthalocyanine (CuPc), pentacene, pyronin B, pentadecafluorooctyl phenyl-C60-butyrate (F-PCBM), C60, C6O/L1F, ZnO NRS/PCBM, ZnO/cross-linked fullerene derivative (C-PCBSD), single walled carbon nanotubes (SWCNT), poly(ethylene glycol) (PEG), poly(dimethylsi loxane-block-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), polyfluo rene 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 DBT15), fluorene alternating and random copolymer bearing cationic groups in the alkyl side chains (PFPNBr), poly (ethylene oxide) (PEO), and fullerene derivatives. In certain embodiments, the electron transport layer comprises a material selected from the group consisting of fullerene (C₆o), phenyl-C6i-butryric acid methyl ester (PCBM), phenyl-C_7i-butryric acid methyl ester (PC71BM), indene C₆o bis adduct (ICBA), Ti0₂, Sn0₂, ZnO, bathocuproine (BCP), and a combination thereof. In certain embodiments, the second transport layer is the electron transport layer. In certain embodiments, the electron transport layer comprises phenyl-C6i-butryric acid methyl ester (PCBM), fullerene (C₆o), and bathocuproine (BCP).

In certain embodiments, the perovskite film is doped with a plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 17%. In certain embodiments, the perovskite film is doped with a plurality of ions in an amount sufficient to attain a Power Conversion Efficiency (PCE) of at least 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%.

The subject matter described herein is directed to the following embodiments:

1. A perovskite film comprising a polycrystalline perovskite composition of formula (I):

ABX₃ (I)

wherein A is a cation selected from the group consisting of methylammonium (MA), tetramethylammonium, formamidinium (FA), cesium, rubidium, potassium, sodium, butylammonium, phenethylammonium, phenylammonium, guanidinium, and a combination thereof; B is a divalent metal selected from the group consisting of lead, tin, cadmium, germanium, zinc, nickel, platinum, palladium, mercury, titanium, silicon, and a combination thereof; and X is a halide selected from the group consisting of Cl, Br, F, I, and a combination thereof;

wherein said polycrystalline perovskite composition is doped with a plurality of ions selected from the group consisting of Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, and Ce³⁺;

wherein said plurality of ions reside in grain boundaries and on the surface of said perovskite film; and wherein said composition is doped with said plurality of ions in an amount selected from the group consisting of about 0.0001 wt% to about 0.40 wt% Ag⁺, from about 0.0001 wt% to about 5.0 wt% Ce³⁺, from about 0.0001 wt% to about 0.90 wt% Sr²⁺, from about 0.0001 wt% to about 0.90 wt% Cu⁺, and from about 0.0001 wt% to about 5.0 wt% Sm²⁺ relative to the weight of the perovskite film. 2. The perovskite film of embodiment 1, wherein said poly crystalline perovskite composition is doped with said plurality of ions in an amount selected from the group consisting of about 0.02 wt% to about 0.04 wt% Ag⁺, from about 0.01 wt% to about 3.0 wt% Ce³⁺, from about 0.02 wt% to about 0.70 wt% Sr²⁺, from about 0.005 wt% to about 0.01 wt% Cu⁺, and from about 0.01 wt% to about 0.05 wt% Sm²⁺ relative to the weight of the perovskite film.

3. The perovskite film of embodiment 1 or 2, wherein A is a cation selected from the group consisting of methylammonium (MA), formamidinium (FA), cesium, and a combination thereof; B is selected from the group consisting of lead, tin, and a

combination thereof; and X is selected from I, Br, and a combination thereof.

4. The perovskite film of any one of embodiments 1-3, wherein said polycrystalline perovskite composition is MAPbF or FAo_.ssMAo_.isPbilo_.ssBro_.is^.

5. The perovskite film of any one of embodiments 1 -4, wherein said polycrystalline perovskite composition is FAo_.ssMAo_.isP Io_.ssBro_.is^ doped with a plurality of ions selected from the group consisting of Ag⁺, Sr²⁺, and Ce³⁺.

6. The perovskite film of any one of embodiments 1-5, wherein said film is doped with about 0.03 wt% Ag⁺ relative to the weight of the perovskite film.

7. The perovskite film of any one of embodiments 1-6, wherein said film is doped with about 0.02 wt% Ce³⁺ relative to the weight of the perovskite film.

8. The perovskite film of any one of embodiments 1-7, wherein said film is doped with about 0.04 wt% Sr²⁺ relative to the weight of the perovskite film.

9. The perovskite film of any one of embodiments 1-8, wherein said polycrystalline perovskite composition is MAPbF doped with a plurality of ions selected from the group consisting of Ag⁺, Sr²⁺, Ce³⁺, and Cu⁺.

10. The perovskite film of any one of embodiments 1-9, wherein said film is doped with about 0.025 wt% Ag⁺ relative to the weight of the perovskite film. 11. The perovskite film of any one of embodiments 1-10, wherein said film is doped with about 0.02 wt% Ce³⁺ relative to the weight of the perovskite film.

12. The perovskite film of any one of embodiments 1-11, wherein said film is doped with about 0.04 wt% Sr²⁺ relative to the weight of the perovskite film.

13. The perovskite film of any one of embodiments 1-12, wherein said film is doped with about 0.007 wt% Cu⁺ relative to the weight of the perovskite film.

14. The perovskite film of any one of embodiments 1-13, having a free carrier recombination lifetime of at least 2.0 ps, for use in a device selected from the group consisting of a solar cell, solar panel, light emitting diode, photodetector, x-ray detector, field effect transistor, memristor, and synapse.

15. The perovskite film of any one of embodiments 1-14, wherein said film exhibits a free carrier recombination lifetime of at least 4.0 ps.

16. A perovskite solar cell, comprising: a conductive substrate;

a first transport layer disposed on said conductive substrate;

the perovskite film of any one of embodiments 1-15 disposed on said first transport layer;

a second transport layer disposed on said perovskite film; and

an electrode disposed on said second transport layer,

wherein said first transport layer or said second transport layer is an electron transport layer and the other of said first transport layer or said second transport layer is a hole transport layer.

17. The perovskite solar cell of embodiment 16, wherein said conductive substrate is selected from the group consisting of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), cadmium oxide (CdO), zinc indium tin oxide (ZITO), and aluminum zinc oxide (AZO). 18. The perovskite solar cell of embodiment 16 or 17, wherein said conductive substrate is indium tin oxide (ITO).

19. The perovskite solar cell of any one of embodiments 16-18, wherein said first transport layer is a hole transport layer comprising a material selected from the group consisting of poly(triaryl amine) (PTAA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), NiO_x, N4,N40-bis(4-(6-((3-ethyloxetan-3- yl)methoxy)hexyl)phenyl)-N4, N40-diphenyl-biphenyl-4, 40-diamine (TPD), 2, 2', 7,7'- Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD), CuSCN, and a combination thereof.

20. The perovskite solar cell of any one of embodiments 16-19, wherein said hole transport layer comprises poly(triaryl amine) (PTAA).

21. The perovskite solar cell of any one of embodiments 16-20, wherein said second transport layer is an electron transport layer comprising a material selected from the group consisting of fullerene (C₆o), phenyl-C_6i-butryric acid methyl ester (PCBM), phenyl-C_7i- butryric acid methyl ester (PC₇₁BM), indene C₆o bis adduct (ICBA), Ti0₂, Sn0₂, ZnO, bathocuproine (BCP), and a combination thereof.

22. The perovskite solar cell of any one of embodiments 16-21, wherein said electron transport layer comprises phenyl-C_6i-butryric acid methyl ester (PCBM), fullerene (C₆o), and bathocuproine (BCP).

23. The perovskite solar cell of any one of embodiments 16-22, wherein said conductive electrode is selected from the group consisting of Ag, Au, Cu, Al, Cr, Bi, Pt, graphite and a combination thereof.

24. The perovskite solar cell of any one of embodiments 16-23, wherein said conductive electrode is Cu.

25. The perovskite solar cell of any one of embodiments 16-24, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 17%. 26. The perovskite solar cell of any one of embodiments 16-25, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 18%.

27. The perovskite solar cell of any one of embodiments 16-26, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 19%.

28. The perovskite solar cell of any one of embodiments 16-27, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 20%.

The following examples are offered by way of illustration and not by way of limitation.

EXAMPLES

Materials and Methods

FAI, MAI, and MABr were synthesized according to methods reported in the literature (Yang, W et al. Science 348, 1234-1237 (2015); Dong, Q. et al. Energy Environ. Sci. 8, 2464-2470 (2015); and Wei, H. et al. Nat. Photonics 10, 333-339 (2016)). The other raw materials and solvents were obtained commercially and were used without further purification.

Fabrication of OIHP thin film and solar cells

PTAA was chosen as the hole transporting layer because of the relatively large perovskite grain sizes that form on the non-wetting surface of PTAA. The fullerene derivative PCBM was used as the top passivation material and electron transporting layer in the devices disclosed herein. PTAA film was first deposited on cleaned ITO substrates by spin coating PTAA toluene solution (2 mg mL ¹) at 5000 rpm., and the as-prepared film was thermally annealed at 100 °C for 10 min. To improve the wetting property of the perovskite precursor on the PTAA film, the PTAA film coated ITO substrate was pre wetted by spinning 30 pL N, A-dimethylformamide (DMF) at 4000 rpm for 10 s. Then, the perovskite layer was fabricated by the anti-solvent method, and the compositions of MAPbE and FAo_.ssMAo_.isP Io_.ssBro_.is^ were used. The 80 pL precursor solution (1.3 M) was spun onto PTAA at 2000 rpm for 2s and 4000 rpm for 20 s. The sample was quickly washed with 130 pL toluene during spin-coating. Subsequently, the sample was annealed at 70 °C for 10 min and 100 °C for 10 min. The perovskite precursor solution was dissolved in a mixed solvent of DMF and dimethyl sulfoxide (DMSO), and the extrinsic metal iodides were dissolved in DMF, and then added to the perovskite precursor solution. The blending ratio as disclosed herein refers to the weight ratio of the metal iodide/lead iodide in the precursor solution. For the MAPbF composition, the volume ratio of DMF: DMSO was 9: 1; for FAo_.ssMAo_{. i}sPb^o_.ssBro_.15)3, this ratio was 4: 1. The PCBM (dissolved in 1, 2-dichlorobenzene, 20 mg mL ¹) was spin-coated on top of the perovskite layer at 6000 rpm for 35 s and annealed at 100 °C for 30 min. The devices were completed by the thermal evaporation of C₆o (20 nm), BCP (8 nm), and Cu (80 nm). The device area was 8 mm². The MAPbF thin film samples applied on the other substrates disclosed herein were fabricated using the same process described above in the solar cell preparation.

Device characterization.

Simulated AM 1.5G irradiation (100 mW cm ²) was produced by a Xenon-lamp- based solar simulator (Oriel 67005, 150 W Solar Simulator) for current density -voltage (J- V) measurements. The light intensity was calibrated by a silicon diode (Hamamatsu Sl 133) equipped with a Schott visible-color glass-filtered (KG5 color-filtered). Keithley 2400 Source-Meter was used for J-V measurement. The scanning rate was 0.1 V s ¹. Unless stated otherwise, the scanning direction for the J-V measurements was from positive bias to negative bias (reverse scan). The absence of photocurrent hysteresis of the device was confirmed by changing the photocurrent scanning directions. The steady-state PCE was measured by monitoring the current with largest power output bias voltage and recording the value of the photocurrent. External quantum efficiency (EQE) curves were characterized with a Newport QE measurement kit by focusing a monochromatic beam of light onto the devices, where the photocurrent density calculated from the EQE had a < 3% mismatch with those measured from J-V scanning.

XRD Measurements

XRD measurements were performed with a Bruker-AXS D8 Discover Diffractometer. The Bruker-AXS D8 Discover Diffractometer was configured in parallel beam geometry with Cu Ka radiation. The perovskite thin films were scraped from the substrates, and then the XRD data of the powdered samples was obtained.

PL Measurements PL spectra were measured by iHR320 Photoluminescence Spectroscopy at room temperature. A 532 nm green laser from Laserglow Technologies was used as the excitation source in the PL measurements.

KPFM Measurements

To prepare the single crystal samples for KPFM studies, MAPbL thin single crystals were first grown on ITO/PTAA substrates. Following this, the metal iodide particles were placed on the single crystals, followed thermal annealing the substrates at 80 °C for 10 min. After blowing off the metal iodide particles using high-pressure flow, the surface potentials were measured by KPFM under nitrogen. To prepare the OIHP thin film samples, the top surface was mechanically polished by abrasive paper and the byproducts removed. KPFM is an Atomic Force Microscopy (AFM)-based surface imaging technique to acquire the work function or surface potential of a material. The KPFM measurements were performed using a commercial AFM (MFP3D-BIO, Asylum Research, USA), and Pt/Ir coated silicon probes (PPP-EFM, Nanosensors, Switzerland). The standard 2-pass KPFM technique was employed. The first pass acquired the morphology information, while during the second pass, the tip was lifted about 30 nm above the sample morphology based on the first pass so that the surface potential or contact potential difference (CPD) could be acquired. Meanwhile, IV DC and 2V AC biases were supplied to the probe. The CPD value was measured as the DC bias that nullify the first resonance component of the electrostatic force between tip and sample surface. The observed CPD is a relative potential difference with respect to the conductive probe. All measurements were conducted in dry N₂ to prevent sample degradation.

Computational Calculations

First-principles calculations were 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 is treated with the projector-augmented wave method. Grimme's DFT-D3 correction is adopted to describe the long-range van der Waals interactions. Surface slabs were modelled as Pbl -terminated or MAI-terminated symmetric (001) slabs of the tetragonal structure, which has a super cell of 2*2 and 9 layers of MAI and PbL in total. About 30 A vacuum was added on top of the slab surface to minimize the interaction between the adjacent slabs. A 5 *5 Monkhorst-Pack grid is used for all density of states calculations.

TRPL Measurements

TRPL of the perovskite films was obtained in a Horiba DeltaPro fluorescence lifetime system. The excitation was provided by a DeltaDiode (DD-405) pulse laser diode with a wavelength of 404 nm. The laser excitation energy was a 20 pj pulse. The 650 nm long pass filter was used. The PL lifetime was obtained by fitting the PL decay curve with a mono-exponential decay.

TRMC Measurements

For the TRMC measurements the perovskite films were mounted in a sealed microwave resonance cavity within a nitrogen glovebox. The TRMC technique monitors the change in reflected microwave power by the loaded microwave cavity upon pulsed laser excitation at 500 nm. The photo -conductance (AG) of the sample was deduced from the laser-induced change in normalized microwave power (A P/P) by

DR(ί)

-KAG(t) =

(1),

where K is the sensitivity factor. The yield of generated free charges Y and mobility å m = { + /½) was obtained from the maximum change in photoconductance, AG_ma by

where ¾ is the number of photons per pulse per unit area, b is ratio of the inner dimensions of the microwave cell, ^e is the elementary charge, and ¾ is the fraction of light absorbed by the sample. Normalized TRMC traces do not contain information on mobility, but allow for the comparison of samples in terms of charge carrier decay. The charge carrier lifetime was obtained by fitting the decay curve with a mono-exponential decay.

Example 1: Investigation of PL Decay

Several metal ions, including silver (Ag⁺), copper (Cu⁺), strontium (Sr²⁺), samarium (Sm²⁺), and cerium (Ce³⁺) ions, were incorporated into polycrystalline OIHP films to study their influence on the performance of OIHP solar cells. It was observed that addition of metal ions with different valence charges, including Ag⁺, Sr²⁺, Ce³⁺, into methylammonium lead iodide (MAPbL) thin films could quench their PL by 40-87% (Fig. 5). The PL quench effect was confirmed by the study of PL lifetime variation using time -resolved photoluminescence (TRPL) measurements. As shown by the PL decay curves in Fig. 1 A, the pristine MAPbF film deposited on glass showed a PL decay lifetime of up to ca. 2.0 ps, but the addition of metal ions (Ag⁺, Sr²⁺ and Ce³⁺) dramatically reduced PL decay lifetime to 40-130 ns. It was discovered that the metal ion additives increased the power conversion efficiencies (PCEs), rather than reduced the efficiency of the OIHP solar cells with modified ion contents.

Example 2: Study of Influence of Metal Ions on Perovskite Film Charge

Carrier Lifetime

The impact of ion addition on the device performance in solar cell devices with a p-i-n structure of indium tin oxide (ITO)/ poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) /OIHP/[6]-phenyl-C6l- butyric acid methyl ester (PCBM)/C60/bathocuproine (BCP)/copper (Cu) was evaluated, as shown in Fig. 1B. The OIHP layers had the composition of MAPbF and FAo_.ssMAo_.isPt^F_.ssBro_.isF (FA = formamidinium). The performance of the MAPbF devices doped by extrinsic metal ions (Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, Ce³⁺) with varying ion contents (0.03% to 0.2%, blending weight ratio) were improved with PCEs between 17.9% and 19.4%. The typical J-V curves are shown in Fig. 6A and the detailed parameters are summarized in Table 1. By contrast, a small amount of (0.1%) excess Pb²⁺ did not affect the device performance. Similar to that demonstrated by the MAPbF devices, the addition of metal ions increased the stabilized PCEs of the FAo_.ssMAo_.isPt^F_.ssBro_.isF based solar cells up to 20.8% (Fig. 1B), and the detailed parameters can be found in Table 2 and Fig. 2B through Fig. 2E.

Table 1. Summary of device performance for solar cells based on MAPbF blended by different metal ions. Jsc. short circuit current density; Voc· open circuit voltage; FF: fill factor.

Metal Doped ratio Metal Foe (V) ./sc (mA cm ²) FF PCE (%) ion (blended) Cation ratio

(w/w) w%

L07 21.5 0.758 17.4

Ag⁺ 0.07% 0.025% 1.09 22.7 0.750 18.6

Cu⁺ 0.03% 0.007% 1.09 22.3 0.761 18.5

Sr²⁺ 0.2% 0.04% 1.11 22.5 0.742 18.6

Sm²⁺ 0.08% 0.02% 1.08 22.4 0.739 17.9

Ce³⁺ 0.1% 0.02% 1.11 22.6 0.773 19.4

Pb²⁺ 0.1% 0.03% 1.05 21.7 0.749 17.1 Table 2. Summary of the best device performance for solar cells based on

FA_0. MA_0.i Pb(Io_. Br_0.i blended by different metal ions. _

Metal Doped ratio Metal Loc (V) ./sc FF PCE (%) ion (blended) (w/w) Cation (mA cm ²)

Ratio w%

L09 223 0.769 187

Ag⁺ 0.1% 0.03% 1.10 22.6 0.786 19.5

Sr²⁺ 0.2% 0.04% 1.11 23.1 0.809 20.8

Ce³⁺ 0.1% 0.02% 1.10 23.2 0.816 20.8

To further investigate the enhanced device efficiency of the OIHP solar cells despite the reduced PL decay lifetime with the addition of extrinsic metal ions, the free carrier recombination lifetime was measured by TRMC in the doped OIHP films. The excitation light had a wavelength of 500 nm and a fluence of 7±4 nJ cm ². The fluence was close to that (4 nJ cm ²) in the TRPL measurement, so that the photo-induced charge carrier concentration would be comparable in both the TRPL and TRMC measurements. Univalent Ag⁺, divalent Sr²⁺, and trivalent Ce³⁺ were selected to be blended with MAPbL in this study. Fig. 1C shows the TRMC decay curves of the MAPbL films deposited on quartz with and without doped ions. The free carrier decay lifetime in pristine MAPbL as measured by TRMC was determined to be 2.1 ps, which is comparable to the measured PL decay lifetime of 2.0 ps, indicating a weak surface charge recombination. In contrast, the samples with extrinsic ion additives displayed very long free-carrier decay lifetimes of 4.1, 4.9 and 3.0 ps for the MAPbL films blended with 0.1 wt% Ag⁺, 0.2 wt% Sr²⁺ and 0.1 wt% Ce³⁺, respectively. Reducing the excitation light fluence to 0. l4±0.04 nJ cm ² increased the free carrier decay lifetimes to 11.2, 8.7 and 5.6 ps for 0.1 wt% Ag⁺, 0.2 wt% Sr²⁺ and 0.1 wt% Ce³⁺ blended MAPbL films, respectively, which were longer than that (4.2 ps) in pristine MAPbL (Fig. 7). These longer free carrier recombination lifetimes coincided with better device performance of OIHP solar cells with metal ion additives.

Example 3: Investigation of Lateral Homojunction within Perovskite Grains A model illustrated in Fig. 1D was proposed to reconcile the dramatically reduced PL lifetime yet increased free carrier recombination lifetime. Without wishing to be bound by theory, it is understood that the formation of a homojunction inside each individual perovskite grain arises as a result of n-doping of GBs by the added metal ions. Doping induced a built-in electric field in each grain along the in-plane direction that separates the photogenerated electron-hole pairs, which quenches PL and reduces PL lifetime, while the spatial separation of the free electrons and holes slows down the geminate recombination and increases the free carrier recombination lifetime.

In this model, the added metal ions n-dope perovskites at GBs. To verify it, MAPbL and several metal ions with different valence states, including Ag⁺, Sr²⁺ and Ce³⁺, were used to study the metal ion doping effect. First, the hole and electron conductivities of OIHP films were measured for the films deposited on glass substrates to check the doping concentration and the doping type. To separate the hole and electron conductivity, hole-only and electron-only devices were designed by depositing high work-function gold (Au) or low work-function PCBM/Cu on top of the perovskite films. The lateral device structures are shown in Fig. 2A and Fig. 2B. It should be noted that the electron mobility (10 ⁴- 10 ² cm² V ¹ s ¹) of PCBM is 3-5 orders of magnitude smaller than that of OIHP; thus, the measured electron conductivity should reflect the conductivity of perovskites. As shown in Fig. 2A, the added metal ions had no significant effect on the hole conductivity of MAPbL thin films at a bias from 0 to 10 V. However, the electron conductivities of all MAPbL films mixed with different types of metal ions (Ag⁺, Sr²⁺ and Ce³⁺) were ca. 1 order of magnitude larger than that of pristine MAPbL films, as shown in Fig. 2B. The improved electron conductivities can be attributed to the increased concentration of electrons in OIHPs due to metal ion doping or enhanced electron mobility. Surface contact potential difference (CPD) measurements that reveal the change of work function using Kelvin Probe Force Microscopy (KPFM) confirmed that the carrier concentration was increased by the extrinsic ion additives. The CPD in the measurements is defined as (<E>_{tiP -} Tkampic)/^. The same type of conductive tip (i.e. consistent F,_ir) was used, thus the CPD value should be directly related to the work function of the measured samples. The samples for KPFM measurements were prepared by depositing metal ions onto a certain area of the perovskite thin crystals, followed by thermal annealing and blowing off the residuals by an air knife. ²² The edge of the doped and undoped regions were measured so that the change of CPD among different regions could be quantified with an image. The height and CPD images of a Sr²⁺ treated MAPbL crystal at the edge of the treated area are shown in Fig. 2C and Fig. 2D, respectively. A clear boundary with a large CPD difference exists between the pristine MAPbL and the metal ion deposited regions. Across the boundary, the line scan curve shown in Fig. 2E revealed a higher CPD value for the Sr²⁺ treated area, indicating that the treated areas have a decrease in work function by ca. 260 meV. This directly confirmed n-type doping of MAPbF on the crystal surface by Sr²⁺.²³ Similarly, Ag⁺ and Ce³⁺ treated MAPbF also showed a reduced work function by 200 and 160 meV, respectively, compared to pristine MAPbF studied by KPFM measurements (Fig. 8A through Fig. 8F).

Example 4: X-Ray Diffraction Experiments

Experiments were conducted to confirm that the extrinsic metal ions did not substitute Pb²⁺ or MA⁺ ions to cause a bulk doping effect. First, monocationic ions typically cause n- type doping and tricationic ions typically cause p-type doping if the added metal ions substitute Pb²⁺. Second, X-ray diffraction (XRD) characterization showed no notable XRD peak shifts within its resolution limit after adding these ions into perovskites at a high concentration of 5 wt% (blending ratio) (Fig. 9). Since these metal ions were still in the polycrystalline perovskite films after deposition, it is understood that they accumulated in GBs and/or the surface of the OIHPs. As such, the metal ions doped the perovskite materials at the affinity of the grain boundaries or the surface. The non- uniform distribution of metal ions in polycrystalline perovskite films is expected to cause a band-bending within the grain along the lateral (or in-plane) direction. As a result, each grain has a p-n homojunction with a central area to be weakly p-type while a peripheral area to be n-type.

Example 5: Explanation of Band Bending

The band-bending was observed in the potential distribution of the perovskite polycrystalline films at the grain scale by KPFM. Here, the OIHP thin films were mechanically polished to avoid the impact of the surface composition heterogeneity on the surface work function distribution, which may be caused by thermal annealing in the process of thin film deposition or nonuniform surface doping by the metal ions. Fig. 3 shows the measured KPFM potential images of MAPbF thin films with and without Ag⁺, Sr²⁺ and Ce³⁺ ions. Compared to the grain interiors, both upward and downward bendings of energy level were observed in the same pristine MAPbF thin films, as indicated by the brighter and darker colors at the GBs, respectively. From the CPD image in Fig. 3, it can be determined that around 40 GBs in the pristine MAPbF thin-films are still darker (or have a larger work function) than the grain interior, while the other ten GBs are brighter (or have a smaller work function) than the grain interior. The CPD difference between GBs and their adjacent grains was between ca. -25 mV to 25 mV, (Fig. 3) which can be explained by the composition variation induced self-doping of perovskites.^25-27 Previous investigations showed that MAI rich MAPbF displays p-type behavior while Pbl₂ rich perovskite displays n-type behavior.²⁸ Thermal annealing may cause the evaporation of MAI, turning some GBs to be n-type, while the grain interior may remain weakly p-type. There was a variation of heterogeneity among the different films prepared under different thermal annealing conditions. In contrast, almost all MAPbF films blended with Ag⁺, Sr²⁺ and Ce³⁺ ions showed n-type GBs with energy level bending toward the Fermi level, i.e. brighter than grain interior as shown in Fig. 3, in agreement with the observed work function reduction and n-type electric conduction behavior shown above. In MAPbF thin films blended with all types of metal ions, the CPD at GBs were ca. 20 ± 10 mV larger than those of their grain interiors, and the cross sectional CPD curves can be seen in Fig. 3. This result demonstrated good reproducibility among all the measured samples, which confirmed the n-type doping of the perovskite along the GBs and the formation of lateral homojunctions at the grain level between the weakly p-doped grain center and the n-doped GBs by extrinsic metal ions. The pristine MAPbF thin films were shown to be slightly p- type with a hole concentration of 10¹⁶-10¹⁷,²⁸ and thus the calculated depletion width was ca. 80-250 nm according to the band bending of 0.2 eV. This calculated depletion width was close to what (80-150 nm) was observed in the KPFM study (Fig. 3).

Example 6: Studying the Doping Mechanism of Extrinsic Metal Ions

The electronic property studies disclosed herein demonstrated that all the metal ions increased the concentration of electrons in the OIHP films, and that these n-doping effects were independent of the valence electrons of the metal ions. This results indicate the influence of a doping mechanism different from traditional inorganic semiconductors.

To investigate the origin of the n-doping effect of the excess metal ions in OIHPs, first- principles calculations were carried out in the framework of density functional theory. It is understood that Ag has a 5 5 outer shell electron, while Sr and Ce have 4.v² and 4 5 /' 6.v², respectively. Without wishing to be bound by theory, these outer shell electrons require less energy to be lifted from the valence band into the conduction band; consequently, Ag, Sr and Ce can easily lose outer-shell electrons and behave like n-type dopants. This is supported by DFT calculations, the results for which indicate that the highest occupied level of Ag, Sr and Ce are closer to the conduction band minimum (CBM) of MAI- or PbF-terminated surface (Fig. 10). The normalized total density of states and the density of states contributed from Ag (Sr or Ce) are plotted in Fig. 4 A and Fig. 4B. It can be seen that Ag (Sr or Ce) introduces some occupied states below the Fermi energy in the doped samples. It can also be noted that the Fermi level in all of the density of states (DOS) figures of the doped samples is closer to the CBM or stays in the conduction band of the perovskites. Thus, the extrinsic metal ions accumulating at GBs leads to Fermi level pinning of the perovskite at the GBs, which causes the observed band bending and n-type doping behavior in the peripheral area of the perovskite grains. The charge density of the highest occupied and lowest unoccupied level of the Ag, Sr and Ce adsorbed on MAI- terminated and Pbl₂-terminated surfaces are also plotted in Fig. 4C. From these plots, the contributions of Ag, Sr and Ce states to the charge density of the highest occupied states near the Fermi level can be discerned, which corresponds with the charge transfer from Ag, Sr and Ceto the conduction bands of MAPbR.

REFERENCES

The references listed below as well as all references cited in the specification are incorporated herein by reference to the extent that they supplement, explain, provide a background for or teach methodology, techniques and/or compositions employed herein. All cited patents and publications referred to in this application are herein expressly incorporated by reference.

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Efforts have been made to ensure accuracy with respect to numbers used (e.g, amounts, temperature, etc.) but some experimental errors and deviations should be accounted for.

One skilled in the art will recognize many methods and materials similar or equivalent to those described herein, which could be used in the practicing the subject matter described herein. The present disclosure is in no way limited to just the methods and materials described. Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this subject matter belongs, and are consistent with: Singleton et al (1994) Dictionary of Microbiology and Molecular Biology, 2nd Ed., J. Wiley & Sons, New York, NY; and Janeway, C., Travers, P., Walport, M., Shlomchik (2001) Immunobiology, 5th Ed., Garland Publishing, New York.

Throughout this specification and the claims, the words“comprise,”“comprises,” and “comprising” are used in a non-exclusive sense, except where the context requires otherwise. It is understood that embodiments described herein include“consisting of’ and/or“consisting essentially of’ embodiments.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limit of the range and any other stated or intervening value in that stated range, is encompassed. The upper and lower limits of these small ranges which may independently be included in the smaller rangers is also encompassed, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

Many modifications and other embodiments set forth herein will come to mind to one skilled in the art to which this subject matter pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the subject matter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

What is claimed is:

1. A perovskite film comprising a polycrystalline perovskite composition of formula

(I):

ABX₃ (I)

wherein A is a cation selected from the group consisting of methylammonium (MA), tetramethylammonium, formamidinium (FA), cesium, rubidium, potassium, sodium, butylammonium, phenethylammonium, phenylammonium, guanidinium, and a combination thereof; B is a divalent metal selected from the group consisting of lead, tin, cadmium, germanium, zinc, nickel, platinum, palladium, mercury, titanium, silicon, and a combination thereof; and X is a halide selected from the group consisting of Cl, Br, F, I, and a combination thereof;

wherein said polycrystalline perovskite composition is doped with a plurality of ions selected from the group consisting of Ag⁺, Cu⁺, Sr²⁺, Sm²⁺, and Ce³⁺;

wherein said plurality of ions reside in grain boundaries and on the surface of said perovskite film; and wherein said composition is doped with said plurality of ions in an amount selected from the group consisting of about 0.0001 wt% to about 0.40 wt% Ag⁺, from about 0.0001 wt% to about 5.0 wt% Ce³⁺, from about 0.0001 wt% to about 0.90 wt% Sr²⁺, from about 0.0001 wt% to about 0.90 wt% Cu⁺, and from about 0.0001 wt% to about 5.0 wt% Sm²⁺ relative to the weight of the perovskite film.

2. The perovskite film of claim 1, wherein said poly crystalline perovskite composition is doped with said plurality of ions in an amount selected from the group consisting of about 0.02 wt% to about 0.04 wt% Ag⁺, from about 0.01 wt% to about 3.0 wt% Ce³⁺, from about 0.02 wt% to about 0.70 wt% Sr²⁺, from about 0.005 wt% to about 0.01 wt% Cu⁺, and from about 0.01 wt% to about 0.05 wt% Sm²⁺ relative to the weight of the perovskite film.

3. The perovskite film of claim 1, wherein A is a cation selected from the group consisting of methylammonium (MA), formamidinium (FA), cesium, and a combination thereof; B is selected from the group consisting of lead, tin, and a combination thereof; and X is selected from I, Br, and a combination thereof.

4. The perovskite film of claim 3, wherein said poly crystalline perovskite composition is MAPbF or FAo_.ssMAo_.isP Io_.ssBro_.is^·

5. The perovskite film of claim 4, wherein said polycrystalline perovskite composition is FAo_.ssMAo_.isP Io_.ssBro_.is^ doped with a plurality of ions selected from the group consisting of Ag⁺, Sr²⁺, and Ce³⁺.

6. The perovskite film of claim 5, wherein said film is doped with about 0.03 wt% Ag⁺ relative to the weight of the perovskite film.

7. The perovskite film of claim 5, wherein said film is doped with about 0.02 wt% Ce³⁺ relative to the weight of the perovskite film.

8. The perovskite film of claim 5, wherein said film is doped with about 0.04 wt% Sr²⁺ relative to the weight of the perovskite film.

9. The perovskite film of claim 4, wherein said poly crystalline perovskite composition is MAPbF doped with a plurality of ions selected from the group consisting of Ag⁺, Sr²⁺, Ce³⁺, and Cu⁺.

10. The perovskite film of claim 9, wherein said film is doped with about 0.025 wt% Ag⁺ relative to the weight of the perovskite film.

11. The perovskite film of claim 9, wherein said film is doped with about 0.02 wt% Ce³⁺ relative to the weight of the perovskite film.

12. The perovskite film of claim 9, wherein said film is doped with about 0.04 wt% Sr²⁺ relative to the weight of the perovskite film.

13. The perovskite film of claim 9, wherein said film is doped with about 0.007 wt% Cu⁺ relative to the weight of the perovskite film.

14. The perovskite film of claim 1, having a free carrier recombination lifetime of at least 2.0 ps, for use in a device selected from the group consisting of a solar cell, solar panel, light emitting diode, photodetector, x-ray detector, field effect transistor, memristor, and synapse.

15. The perovskite film of claim 14, wherein said film exhibits a free carrier recombination lifetime of at least 4.0 ps.

16. A perovskite solar cell, comprising: a conductive substrate;

a first transport layer disposed on said conductive substrate;

the perovskite film of claim 1 disposed on said first transport layer;

a second transport layer disposed on said perovskite film; and

an electrode disposed on said second transport layer,

wherein said first transport layer or said second transport layer is an electron transport layer and the other of said first transport layer or said second transport layer is a hole transport layer.

17. The perovskite solar cell of claim 16, wherein said conductive substrate is selected from the group consisting of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), cadmium oxide (CdO), zinc indium tin oxide (ZITO), and aluminum zinc oxide (AZO).

18. The perovskite solar cell of claim 17, wherein said conductive substrate is indium tin oxide (ITO).

19. The perovskite solar cell of claim 16, wherein said first transport layer is a hole transport layer comprising a material selected from the group consisting of poly(triaryl amine) (PTAA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), NiO_x, N4,N40-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4, N40-diphenyl- biphenyl-4, 40-diamine (TPD), 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'- spirobifluorene (spiro-OMeTAD), CuSCN, and a combination thereof.

20. The perovskite solar cell of claim 19, wherein said hole transport layer comprises poly(triaryl amine) (PTAA).

21. The perovskite solar cell of claim 16, wherein said second transport layer is an electron transport layer comprising a material selected from the group consisting of fullerene (C₆o), phenyl-C_6i-butryric acid methyl ester (PCBM), phenyl-C_7i-butryric acid methyl ester (PC₇₁BM), indene C₆o bis adduct (ICBA), Ti0₂, Sn0₂, ZnO, bathocuproine (BCP), and a combination thereof.

22. The perovskite solar cell of claim 21, wherein said electron transport layer comprises phenyl-C_6i-butryric acid methyl ester (PCBM), fullerene (C₆o), and

bathocuproine (BCP).

23. The perovskite solar cell of claim 16, wherein said conductive electrode is selected from the group consisting of Ag, Au, Cu, Al, Cr, Bi, Pt, graphite and a combination thereof.

24. The perovskite solar cell of claim 23, wherein said conductive electrode is Cu.

25. The perovskite solar cell of claim 16, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 17%.

26. The perovskite solar cell of claim 16, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 18%.

27. The perovskite solar cell of claim 16, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 19%.

28. The perovskite solar cell of claim 16, wherein said perovskite film is doped with said plurality of ions in an amount sufficient to attain a Power Conversion Efficiency of at least 20%.