Patent Description:
The United States Government has rights in this disclosure under Contract No. DE-AC36-08GO28308 between the United States Department of Energy and Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory.

<NPL>) describes the non-thermal annealing fabrication of triple-cation mixed-halide perovskites, FA<NUM>MA<NUM>Cs<NUM>PB(I<NUM>/<NUM>Br<NUM>/<NUM>)<NUM> by incorporation of a Pb(SCN)<NUM> additive. <CIT> describes the preparation of a crystalline compound comprising (i) cesium, (ii) formamidinium,(iii) one or more metal or metalloid dications [B], and (iv) two or more different halide anions [X]. <NPL>) describes a mixed-cation lead mixed-halide perovskite absorber for tandem solar cells. <NPL>) relates thermally stable MAPbI<NUM> perovskite solar cells. <CIT> relates to functional hole transport materials for optoelectronic and/or electrochemical devices.

The bandgap tunability from about <NUM> eV to <NUM> eV has enabled various perovskite-related tandem PVs such as perovskite/perovskite, perovskite/Si, perovskite/CIGS tandem solar cells which is strongly considered as an alternative direction to reach over <NUM>% efficiency. At present, the perovskite/perovskite tandem has reached <NUM>% for a <NUM>-terminal (<NUM>-T) device and <NUM>% for a <NUM>-terminal (<NUM>-T) structure, whereas the perovskite/Si tandem has reached <NUM>% for <NUM>-T and <NUM>% for <NUM>-T configurations. Therefore, a key effort for developing these tandem devices is to improve the wide-bandgap (WBG) perovskites with <NUM> eV to <NUM> eV of bandgap. Increasing the bromide portion at the halide anion position of perovskites is the common approach to developing WBG perovskite devices with various their compositions based on MA, FA, Cs or their mixtures on the A site of perovskites. In general, as the amount of substitution of iodide to bromide reaches certain range, the crystallographic, optoelectronic and chemical properties of perovskites exhibit undesired changes such as phase segregation, higher energetic disorder, and inferior light absorption. Thus, there remains a need for WBG perovskite films and devices having improved crystallographic and opto-physicochemical properties and/or performance metrics, as well as a need for improved methods for manufacturing such films and devices.

An aspect of the present invention is a method comprising treating a liquid comprising a first precursor at a concentration C<NUM>, a second precursor at a concentration C<NUM>, a third precursor at a concentration C<NUM>, a fourth precursor, and an additive at a concentration C<NUM>, wherein:the first precursor comprises at least one of cesium halide wherein cesium halide is cesium iodide or cesium bromide; the second precursor comprises at least one of formamidinium halide wherein formamidinium halide is formamidinium iodide or formamidinium bromide; the third precursor comprises PbBr<NUM> ;the fourth precursor comprises PbI<NUM>; the additive comprises at least one of methylammonium bromide (MABr), methylammonium chloride (MACl), and methylammonium iodide (MAI);the treating results in a perovskite having the formula FAxCs<NUM>-xPb(IyBr<NUM>-y)<NUM>, where <NUM> < x < <NUM> and <NUM> < y < <NUM>; each of C<NUM>, C<NUM>, and C<NUM> are independently between <NUM> and <NUM>; and at least one of C<NUM> /C<NUM> or C<NUM> /C<NUM> equals a ratio greater than zero and less than <NUM>.

A further aspect of the present invention is a perovskite having the formula FAxCs<NUM>-xPbzB'z-<NUM>(IyBr<NUM>-y)<NUM>, wherein each of x, y, and z are between zero and one, exclusively, and B' is selected from germanium and tin.

Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.

The present disclosure may address one or more of the problems and deficiencies of the prior art discussed above. However, it is contemplated that some embodiments as disclosed herein may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.

The present disclosure relates to high efficiency wide-bandgap (WBG) organic-inorganic perovskite materials, crystals, and/or solar cells, including tandem devices such as all perovskite and/or perovskite/Si tandem devices. The use of non-stoichiometric precursor chemistry with excess methylammonium halides (MAX; X = I, Br, or Cl) for preparing high-quality ~<NUM> eV FA<NUM>Cs<NUM>Pb(I<NUM>Br<NUM>)<NUM> organic-inorganic perovskite solar cells is demonstrated herein ("FA" refers to formamidinium). Among various methylammonium halides, some embodiments of the present disclosure utilized excess MABr in a non-stoichiometric precursor solution resulting in strong improvements to the final organic-inorganic perovskite crystallographic properties and device characteristics, without affecting the organic-inorganic perovskite composition. In contrast, other examples using excess MAI significantly reduced the bandgap of the final organic-inorganic perovskite due to the replacement of bromine with iodine. Using <NUM>% excess MABr, a single-junction organic-inorganic perovskite solar cell was demonstrated having a stabilized efficiency of <NUM>%. In addition, <NUM>% a <NUM>-terminal tandem device was demonstrated having a <NUM>% stabilized efficiency, using a <NUM>% semi-transparent WBG organic-inorganic perovskite top cell and an <NUM>% unfiltered (<NUM>% filtered) Si bottom cell.

As shown herein, the example organic-inorganic perovskite, FA<NUM>Cs<NUM>Pb(I<NUM>Br<NUM>)<NUM>, formed from a non-stoichiometric precursor solution having excess MABr demonstrated the highest intensity of main plane peaks in X-ray diffraction pattern (XRD) with the strongest degree of crystal orientation without morphological changes. This suggests that the excess MABr was more effective at healing defects/improving crystallographic properties during the formation of the organic-inorganic perovskite crystals presumably due to the high bromine content, when compared to the use of a precursor solution containing excess MACl. Further, it is confirmed that the use of excess MABr and MACl did not affect the final composition of perovskite, whereas the use of excess MAI in a precursor solution significantly changed the final perovskite composition. The use of the non-stoichiometric MABr precursor solution resulted in an average short-circuit current density (Jsc) and open-circuit voltage (Voc) for the final organic-inorganic perovskite-containing solar cell of increased by about <NUM> mA/cm<NUM> and <NUM> mV, respectively, resulting in average reverse stabilized efficiency increasing from <NUM> ± <NUM>% to <NUM> ± <NUM>%. The best organic-inorganic perovskite-containing device reached a stabilized PCE of <NUM>%.

<FIG> illustrates general structures of organic-inorganic perovskites <NUM> that may organize into cubic crystalline structures, as well as other crystalline structures such as tetragonal and orthorhombic, and may be described by the general formula ABX<NUM>, where X (<NUM>) is an anion and A (<NUM>) and B (<NUM>) are cations, typically of different sizes (A typically larger than B). In a cubic unit cell, the B-cation <NUM> resides at the eight corners of a cube, while the A-cation <NUM> is located at the center of the cube with twelve X-anions <NUM> centrally located between B-cations <NUM> along each edge of the unit cell. Typical inorganic perovskites include calcium titanium oxide (calcium titanate) minerals such as, for example, CaTiO<NUM> and SrTiO<NUM>. In some embodiments of the present invention, the A-cation <NUM> may include a nitrogen-containing organic compound such as an alkyl ammonium compound. The B-cation <NUM> may include a metal and the X-anion <NUM> may include a halogen.

Additional examples for the A-cation <NUM> include organic cations and/or inorganic cations. Organic A-cations <NUM> may be an alkyl ammonium cation, for example a C<NUM>-<NUM> alkyl ammonium cation, a C<NUM>-<NUM> alkyl ammonium cation, a C<NUM>-<NUM> alkyl ammonium cation, a C<NUM>-<NUM> alkyl ammonium cation, a C<NUM>-<NUM> alkyl ammonium cation, a C<NUM>-<NUM> alkyl ammonium cation, a C<NUM>-<NUM> alkyl ammonium cation, and/or a C<NUM> alkyl ammonium cation. Further examples of organic A-cations <NUM> include methylammonium (CH<NUM>NH<NUM>+), ethylammonium (CH<NUM>CH<NUM>NH<NUM>+), propylammonium (CH<NUM>CH<NUM> CH<NUM>NH<NUM>+), butylammonium (CH<NUM>CH<NUM> CH<NUM> CH<NUM>NH<NUM>+), formamidinium (NH<NUM>CH=NH<NUM>+), and/or any other suitable nitrogen-containing organic compound. In other examples, an A-cation <NUM> may include an alkylamine. Thus, an A-cation <NUM> may include an organic component with one or more amine groups. For example, an A-cation <NUM> may be an alkyl diamine halide such as formamidinium (CH(NH<NUM>)<NUM>). Thus, the A-cation <NUM> may include an organic constituent in combination with a nitrogen constituent. In some cases, the organic constituent may be an alkyl group such as straight-chain or branched saturated hydrocarbon group having from <NUM> to <NUM> carbon atoms. In some embodiments, an alkyl group may have from <NUM> to <NUM> carbon atoms. Examples of alkyl groups include methyl (C<NUM>), ethyl (C<NUM>), n-propyl (C<NUM>), isopropyl (C<NUM>), n-butyl (C<NUM>), tert-butyl (C<NUM>), sec-butyl (C<NUM>), iso-butyl (C<NUM>), n-pentyl (C<NUM>), <NUM>-pentanyl (C<NUM>), amyl (C<NUM>), neopentyl (C<NUM>), <NUM>-methyl-<NUM>-butanyl (C<NUM>), tertiary amyl (C<NUM>), and n-hexyl (C<NUM>). Additional examples of alkyl groups include n-heptyl (C<NUM>), n-octyl (C<NUM>) and the like. In still further general embodiments an A-cation <NUM> may include an inorganic constituent, with examples at least one of a Group I element. In some general embodiments an A-cation <NUM> may include at least one of cesium and/or rubidium. In some embodiments, an A-cation <NUM> may include a benzene ring, such as benzylamine and/or phenethylamine.

Examples of metal B-cations <NUM> include, for example, lead, tin, germanium, and or any other <NUM>+ valence state metal that can charge-balance the perovskite halide <NUM>. Examples for X-anions <NUM> include halogens: e.g. fluorine, chlorine, bromine, iodine and/or astatine. In some cases, the perovskite halide may include more than one X-anion <NUM>, for example pairs of halogens; chlorine and iodine, bromine and iodine, and/or any other suitable pairing of halogens. In other cases, the perovskite halide <NUM> may include two or more halogens of fluorine, chlorine, bromine, iodine, and/or astatine.

Thus, the A-cation <NUM>, the B-cation <NUM>, and X-anion may be selected within the general formula of ABX<NUM> to produce a wide variety of perovskite halides <NUM>, including, for example, methylammonium lead triiodide (CH<NUM>NH<NUM>PbI<NUM>), and mixed halide perovskites such as CH<NUM>NH<NUM>PbI<NUM>-xClx and CH<NUM>NH<NUM>PbI<NUM>-xBrx. Thus, a perovskite halide <NUM> may have more than one halogen element, where the various halogen elements are present in non-integer quantities; e.g. x is not equal to <NUM>, <NUM>, or <NUM>. In addition, perovskite halides, like other organic-inorganic perovskites, can form three-dimensional (<NUM>-D), two-dimensional (<NUM>-D), one-dimensional (<NUM>-D) or zero-dimensional (<NUM>-D) networks, possessing the same unit structure. Referring again to <FIG>, a perovskite having the basic crystal structure illustrated in <FIG>, having at least one of a cubic, orthorhombic, and/or tetragonal structure, may have other compositions resulting from the combination of the cations having various valence states in addition to the <NUM>+ state and/or <NUM>+ state of lead and alkyl ammonium cations; e.g. compositions other than AB<NUM>+X<NUM> (where A is one or more cations, or for a mixed perovskite where A is two or more cations). Thus, the methods described herein may be utilized to create novel mixed cation materials having the composition of a double perovskite (elpasolites), A<NUM>B<NUM>+B<NUM>+X<NUM>, with an example of such a composition being Cs<NUM>BiAgCl<NUM> and Cs<NUM>CuBiI<NUM> (embodiments not forming part of the claimed invention). Another example of a composition is described by A<NUM>B<NUM>+X<NUM>, for example Cs<NUM>PbI<NUM> and Cs<NUM>SnI<NUM> (embodiments not forming part of the claimed invention). Yet another example is described by A<NUM>B<NUM><NUM>+X<NUM>, for example Cs<NUM>Sb<NUM>I<NUM> (embodiments not forming part of the claimed invention). For each of these examples, A is one or more cations, or for a mixed perovskite, A is two or more cations.

Thus, the present disclosure relates to methods for producing better performing perovskite materials, having better physical properties, where the method includes the use of at least one an additive alkylammonium halide in excess of the theoretical stoichiometric amounts needed to attain a targeted final perovskite composition. For perovskites having the general formula ABX<NUM>, the additive may be included in a starting solution that includes at least a first precursor AX at a first concentration C<NUM>, a second precursor A'X at a second concentration C<NUM>, and a third precursor BX<NUM> at a third concentration C<NUM>, where each of C<NUM>, C<NUM>, and C<NUM> are between <NUM> and <NUM>, or between <NUM> and <NUM>, and the combination of C<NUM>, C<NUM>, and C<NUM> result in a targeted perovskite composition defined by AxA'<NUM>-xBX<NUM>, where <NUM> ≤ x ≤ <NUM>, and W*C<NUM> = x, W*C<NUM> = <NUM>-x, W*C<NUM> = <NUM>, and W*(C<NUM> + C<NUM> + <NUM>*C<NUM>) = <NUM>, where <NUM> ≤ W ≤ <NUM>. W is a scaling factor having units of inverse concentration (e.g. <NUM>/M, <NUM>/mol/L, L/mol). The additive may include at least one of AX, A'X, and/or A"X at a concentration C<NUM>, where at least one of C<NUM>/C<NUM>, C<NUM>/C<NUM>, and/or C<NUM>/C<NUM> is between greater than zero and ten, or between greater than zero and one, and where the additive does not affect the target composition AxA'<NUM>-xBX<NUM> or the resultant bandgap of the target composition AxA'<NUM>-xBX<NUM>. Instead, the additive improves at least one physical property and/or performance metric of the target composition AxA'<NUM>-xBX<NUM>, for example at least one of an improved Tauc plot, an improved current density versus voltage plot, reduced hysteresis, and/or an improved external quantum efficiency (EQE), when the perovskite is used in a solar cell. Similar mixed A-cation perovskites may be produced according to the methods described herein, where the perovskites have the general formula of at least one of (AxA'<NUM>-x)<NUM>B<NUM>+B'<NUM>+X<NUM>, (AxA'<NUM>-x)<NUM>B<NUM>+X<NUM>, and/or (AxA'<NUM>-x)<NUM>B<NUM><NUM>+X<NUM>, where an additive is provided in addition to the stoichiometric amounts of the precursors needed to provide the targeted perovskite composition, where the additive does not affect the target composition or its bandgap (embodiments not forming part of the claimed invention).

In some embodiments of the present disclosure, for perovskites having the general formula ABX<NUM>, the additive may be included in a starting solution that includes at least a first precursor AX at a first concentration C<NUM>, a second precursor A'X at a second concentration C<NUM>, a third precursor BX<NUM> at a third concentration C<NUM>, and a fourth precursor BX'<NUM> at a fourth concentration C<NUM>, where each of C<NUM>, C<NUM>, C<NUM>, and C<NUM> are between <NUM> and <NUM>, or between <NUM> and <NUM>, and the combination of C<NUM>, C<NUM>, C<NUM>, and C<NUM> result in a targeted perovskite composition defined by AxA'<NUM>-xB(XyX'<NUM>-y)<NUM>, where <NUM> ≤ x ≤ <NUM>, and <NUM> ≤ y ≤ <NUM>, and where W*C<NUM> = x, W*C<NUM> = <NUM>-x, W*<NUM>*C<NUM> = y, W*<NUM>*C<NUM> = <NUM>-y, W*(C<NUM> + C<NUM> + <NUM>*C<NUM> + <NUM>*C<NUM>) = <NUM>, and W*(C<NUM> + C<NUM>) =<NUM>, where <NUM> ≤ W ≤ <NUM>. The additive may include at least one of AX, A'X, and/or A"X, at a concentration C<NUM>, where at least one of C<NUM>/C<NUM>, C<NUM>/C<NUM>, and/or C<NUM>/C<NUM> is between greater than zero and ten, or between greater than zero and one, and where the additive does not affect the target composition AxA'<NUM>-xB(XyX'<NUM>-y)<NUM> or the resultant bandgap of the target composition AxA'<NUM>-xB(XyX'<NUM>-y)<NUM>. Instead, the additive improves at least one physical property and/or performance metric of the target composition AxA'<NUM>-xB(XyX'<NUM>-y)<NUM>, for example at least one of an improved Tauc plot, an improved current density versus voltage plot, reduced hysteresis, and/or an improved external quantum efficiency (EQE), when the perovskite is used in a solar cell. Similar mixed A-cation, mixed B-cation, and/or mixed anion perovskites may be produced according to the methods described herein, where the perovskites have the general formula of at least one of (AxA'<NUM>-x)<NUM>B<NUM>+B'<NUM>+(XyX'<NUM>-y)<NUM>, (AxA'<NUM>-x)<NUM>B<NUM>++(XyX'<NUM>-y)<NUM>, and/or (AxA'<NUM>-x)<NUM>B<NUM><NUM>++(XyX'<NUM>-y)<NUM>, where an additive is provided in addition to the stoichiometric amounts of the precursors needed to provide the targeted perovskite composition, where the additive does not affect the target composition or its bandgap (embodiments not forming part of the claimed invention).

Similarly, for perovskites having the general formula ABX<NUM>, perovskites having the formula AxA'yA"(<NUM>-x-y)B(XaX'bX"(<NUM>-a-b))<NUM> may be produced using methods described herein, where x, y, a, and b are each greater than or equal to zero and less than or equal to one. For this example, the additive may be included in a starting solution that includes at least a first precursor AX at a first concentration C<NUM>, a second precursor A'X at a second concentration C<NUM>, a third precursor A"X at a third concentration C<NUM>, a fourth precursor BX<NUM> at a fourth concentration C<NUM>, a fifth precursor BX'<NUM> at a fifth concentration C<NUM>, a sixth precursor BX"<NUM> at a sixth concentration C<NUM>, where each of C<NUM>, C<NUM>, C<NUM>, C<NUM>, C<NUM>, and C<NUM> are between <NUM> and <NUM>, or between <NUM> and <NUM>, and the combination of C<NUM>, C<NUM>, C<NUM>, C<NUM>, C<NUM>, and C<NUM> result in a targeted perovskite composition defined by AxA'yA"(<NUM>-x-y)B(XaX'bX"(<NUM>-a-b))<NUM>, where W*C<NUM> = x, W*C<NUM> = y, W*C<NUM> = <NUM>-x-y, W*<NUM>*C<NUM> = a, W*<NUM>*Cs = b, W*<NUM>*C<NUM> = <NUM>-a-b, W*(C<NUM> + C<NUM> + C<NUM> + <NUM>*C<NUM> + <NUM>*C<NUM> + <NUM>*C<NUM>) = <NUM>, and W*(C<NUM> + C<NUM> + C<NUM>) = <NUM>, where <NUM> ≤ W ≤ <NUM>. The additive may include at least one of AX, A'X, A"X, and or A'"X at a concentration C<NUM>, where at least one of C<NUM>/C<NUM>, C<NUM>/C<NUM>, C<NUM>/C<NUM>, and/or C<NUM>/C<NUM> is between greater than zero and ten, or between greater than zero and one, and where the additive does not affect the composition AxA'yA"(<NUM>-x-y)B(XaX'bX"(<NUM>-a-b))<NUM> or the resultant bandgap of the composition AxA'yA"(<NUM>-x-y)B(XaX'bX"(<NUM>-a-b))<NUM>. Instead, the additive improves at least one physical property and/or performance metric of the target composition AxA'yA"(<NUM>-x-y)B(XaX'bX"(<NUM>-a-b))<NUM>, for example at least one of an improved Tauc plot, an improved current density versus voltage plot, reduced hysteresis, and/or an improved external quantum efficiency (EQE), when the perovskite is used in a solar cell. Similar mixed A-cation, and/or mixed anion perovskites may be produced according to the methods described herein, where the perovskites have the general formula of at least one of (AxA'yA"(<NUM>-x-y))2B<NUM>+B'<NUM>+(XaX'bX"(<NUM>-a-b)<NUM>, (AxA'yA"(<NUM>-x-y))<NUM>B<NUM>++( XaX'bX"(<NUM>-a-b))<NUM>, and/or (AxA'yA"(<NUM>-x-y))<NUM>B<NUM><NUM>++( XaX'bX"(<NUM>-a-b))<NUM>, where an additive is provided in addition to the stoichiometric amounts of the precursors needed to provide the targeted perovskite composition, where the additive does not affect the target composition or its bandgap (embodiments not forming part of the claimed invention).

Further, the present disclosure relates to methods for producing better performing perovskite materials having the general composition ABX<NUM>, having better physical properties, where the method includes the use of at least one an additive alkylammonium halide in excess of the theoretical stoichiometric amounts needed to attain a targeted final perovskite composition. The additive may be included in a starting solution that includes at least a first precursor AX at a first concentration C<NUM>, a second precursor A'X at a second concentration C<NUM>, a third precursor BX<NUM> at a third concentration C<NUM>, and a fourth precursor B'X<NUM> at a fourth concentration C<NUM>, where each of C<NUM>, C<NUM>, C<NUM>, and C<NUM> are between <NUM> and <NUM>, or between <NUM> and <NUM>, and the combination of C<NUM>, C<NUM>, C<NUM>, and C<NUM> result in a targeted perovskite composition defined by AxA'<NUM>-xByB'<NUM>-yX<NUM>, where <NUM> ≤ x ≤ <NUM> and <NUM> ≤ y ≤ <NUM>, and W*C<NUM> = x, W*C<NUM> = <NUM>-x, W*C<NUM> = y, W*C<NUM> = <NUM>-y, and W*(C<NUM> + C<NUM> + <NUM>*C<NUM> + <NUM>*C<NUM>) = <NUM>, where <NUM> ≤ W ≤ <NUM>. The additive may include at least one of AX, A'X, and/or A"X at a concentration C<NUM>, where at least one of C<NUM>/C<NUM>, C<NUM>/C<NUM>, and/or C<NUM>/C<NUM> is between greater than zero and ten, or between greater than zero and one, and where the additive does not affect the target composition AxA'<NUM>-xBX<NUM> or the resultant bandgap of the target composition AxA'<NUM>-xBX<NUM>. Instead, the additive improves at least one physical property and/or performance metric of the target composition AxA'<NUM>-xBX<NUM>, for example at least one of an improved Tauc plot, an improved current density versus voltage plot, reduced hysteresis, and/or an improved external quantum efficiency (EQE), when the perovskite is used in a solar cell. Similar mixed A-cation and/or mixed B-cation perovskites may be produced according to the methods described herein, where the perovskites have the general formula of at least one of (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM>+B"<NUM>+X<NUM>, (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM>+B"<NUM>+X<NUM>, (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM>++X<NUM>, and/or (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM><NUM>++X<NUM>, where an additive is provided in addition to the stoichiometric amounts of the precursors needed to provide the targeted perovskite composition, where the additive does not affect the target composition or its bandgap (embodiments not forming part of the claimed invention).

Further, the present disclosure relates to methods for producing better performing perovskite materials, having better physical properties, where the method includes the use of at least one an additive alkylammonium halide in excess of the theoretical stoichiometric amounts needed to attain a targeted final perovskite composition. The additive may be included in a starting solution that includes at least a first precursor AX at a first concentration C<NUM>, a second precursor A'X at a second concentration C<NUM>, a third precursor BX at a third concentration C<NUM>, and a fourth precursor B'X' at a fourth concentration C<NUM>, where each of C<NUM>, C<NUM>, C<NUM>, and C<NUM> are between <NUM> and <NUM>, or between <NUM> and <NUM>, and the combination of C<NUM>, C<NUM>, C<NUM>, and C<NUM> result in a targeted perovskite composition defined by AxA'<NUM>-xByB'<NUM>-y(XzX'<NUM>-z)<NUM>, where <NUM> ≤ x ≤ <NUM>, <NUM> ≤ y ≤ <NUM>, and <NUM> ≤ z ≤ <NUM>. In some embodiments of the present disclosure, W*C<NUM> = x, W*C<NUM> = <NUM>-x, W*C<NUM> = y, W*C<NUM> = <NUM>-y, and W*(C<NUM> + C<NUM> + C<NUM> + C<NUM>) =<NUM>, where <NUM> ≤ W ≤ <NUM>. The additive may include at least one of AX, A'X, and/or A"X at a concentration C<NUM>, where at least one of C<NUM>/C<NUM>, C<NUM>/C<NUM>, and/or C<NUM>/C<NUM> is between greater than zero and tcn, or between greater than zero and one, and where the additive does not affect the target composition AxA'<NUM>-xByB'<NUM>-y(XzX'<NUM>-z)<NUM> or the resultant bandgap of the target composition AxA'<NUM>-xByB'<NUM>-y(XzX'<NUM>-z)<NUM>. Instead, the additive improves at least one physical property and/or performance metric of the target composition AxA'<NUM>-xBX<NUM>, for example at least one of an improved Tauc plot, an improved current density versus voltage plot, reduced hysteresis, and/or an improved external quantum efficiency (EQE), when the perovskite is used in a solar cell. Similar mixed A-cation, mixed B-cation, and/or mixed anion perovskites may be produced according to the methods described herein, where the perovskites have the general formula of at least one of (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM>+B"<NUM>+(XbX'b-<NUM>)<NUM>, (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM>+B"<NUM>+(XbX'b-<NUM>)<NUM>, (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM>++(XbX'b-<NUM>)<NUM>, and/or (AxA'<NUM>-x)<NUM>(BaB'<NUM>-a)<NUM><NUM>++(XbX'b-<NUM>)<NUM>, where an additive is provided in addition to the stoichiometric amounts of the precursors needed to provide the targeted perovskite composition, where the additive does not affect the target composition or its bandgap (embodiments not forming part of the claimed invention).

Further, in some embodiments of the present disclosure, the perovskite may be positioned on at least one of a silicon substrate, a CIGS substrate, a CdTe substrate, a III-V alloy, another substrate made of another perovskite material, and/or any other suitable substrate having a bandgap between <NUM> eV and <NUM> eV, inclusively. In accordance with the claimed invention, the final target perovskite includes FAxCs1-xPb(IyBr1-y)<NUM>, where x and y are all between greater than zero and less than or equal to one. In some embodiments of the present disclosure, the final target perovskite may include FA<NUM>CS<NUM>Pb(I<NUM>Br<NUM>)<NUM>. For any of the above described perovskite materials, produced by the methods described herein, may have a relatively wide bandgap; e.g. greater than or equal to <NUM> eV, or between <NUM> eV and <NUM> eV, inclusively. However, depending on the specifics of the fabrication method, perovskite materials having a relatively low bandgap may also be produced; e.g. less than or equal to <NUM> eV, or between <NUM> eV and <NUM> eV, inclusively.

<FIG> illustrates a method <NUM> for producing an organic-inorganic perovskite layer <NUM>, according to some embodiments of the present disclosure. The method <NUM> may begin with the combining <NUM> of various precursors, for example a first precursor <NUM>, a second precursor <NUM>, up to a predetermined number, n, of precursors, thus including an nth precursor <NUM>. Each of these precursors (<NUM>, <NUM>, and <NUM>) may provide one or more of the compounds and/or elements required to achieve the final targeted organic-inorganic perovskite composition, e.g. FA<NUM>Cs<NUM>Pb(I<NUM>Br<NUM>)<NUM>. Thus, for this particular example, the first precursor <NUM> includes CsI, the second precursor <NUM> includes formamidinium iodide (FAI), a third precursor (not shown) includes PbBr<NUM>, and an nth precursor <NUM> for n equal to four includes PbI<NUM>. Again for the specific example of an organic-inorganic perovskite defined by FA<NUM>Cs<NUM>Pb(I<NUM>Br<NUM>)<NUM>, this final composition may be achieved by combining <NUM> the desired stoichiometric amounts of each of the first precursor <NUM> of CsI, the second precursor <NUM> of FAI, the third precursor (not shown) of PbBr<NUM>, and the fourth (n=<NUM>) precursor <NUM> of PbI<NUM> to form a precursor solution <NUM> having molar concentrations of <NUM>, <NUM>, <NUM>, and <NUM> for each of the four precursors, respectively. In addition, the combining <NUM> includes an additive <NUM>, which provides an excess (e.g. above the stoichiometric amount) of at least one of element and/or constituents making up the final composition of the organic-inorganic perovskite layer <NUM>. For example, for the case of FA<NUM>CS<NUM>Pb(I<NUM>Br<NUM>)<NUM>, the additive <NUM> includes at least one of MAI, MABr, and/or MACl at a molar concentration between <NUM> and <NUM>. The precursor solution <NUM> may be formed using any suitable solvent, with examples including water and/or organic solvents (not shown). However, this composition is provided for exemplary purposes and other compositions for organic-inorganic perovskites are within the scope of the present disclosure. For example, compositions defined by FAxCs<NUM>-xPb(IyBr<NUM>-y)<NUM>, where <NUM> ≤ x ≤ <NUM> and <NUM> ≤ y ≤ <NUM>, may be produced according to some of the embodiments described herein. More generally, AxA'<NUM>-xB(XyX'<NUM>-y)<NUM>, where A and A' are both A-cations, X and X' are both anions, and B is a cation as described above, <NUM> ≤ x ≤ <NUM>, and <NUM> ≤ y ≤ <NUM>, may be produced according to some of the embodiments described herein. Similarly, perovskites having the general formula AxA'yA"(<NUM>-x-y)B(XaX'bX"(<NUM>-a-b))<NUM> may also be produced using methods described herein, where each of x, y, a, and b are greater than or equal to zero and less than or equal to one.

The method <NUM> may then continue by applying <NUM> the precursor solution <NUM> to a substrate (not shown), for example by spin-coating, dip-coating, curtain-coating, blade-coating, and/or any other suitable solution-processing method, resulting in the formation of a liquid film <NUM>. After the liquid film <NUM> has been formed, the method <NUM> may proceed with treating <NUM> the liquid film <NUM>, resulting in the removal of volatiles <NUM> (e.g. water and/or organic solvents) to form the final organic-inorganic perovskite layer <NUM>. For example, the treating <NUM> may include thermal treating, where the liquid film <NUM> is heated to a temperature of up to <NUM> to remove the volatiles <NUM>. Further, the treating <NUM> may include exposing the liquid film <NUM> to a local pressure that is less than one atmosphere; e.g. a vacuum. In addition, the treating <NUM> may be performed for a period of time between one minute and one hour. In some embodiments of the present disclosure, the treating <NUM> may include exposing the liquid film <NUM> to a gas stream such as nitrogen and/or dry air.

<FIG> illustrates the UV-vis absorption spectrum for organic-inorganic perovskite films prepared with and without the use of excess of methylammonium halides in the precursor solution. For this example, the pristine organic-inorganic perovskite sample (FA<NUM>Cs<NUM>Pb(I<NUM>Br<NUM>)<NUM>), which was prepared according to the procedure described below, used a stoichiometric perovskite precursor consisting of <NUM> CsI, <NUM> FAI, <NUM> PbBr<NUM>, <NUM> PbI<NUM> in DMF solution with HI and HBr acid additives, exhibited the absorption spectrum corresponding to an optical bandgap of <NUM> eV. The absorption spectra were barely affected using <NUM>% excess of MABr or MACl additives in the precursor solution, suggesting that the perovskite structure was not altered. This suggests that non-stoichiometric solution strategies having excess methylammonium halides may be used to improve the characteristics and/or properties of organic-inorganic mixed-halide (e.g. bromine and iodine) perovskites. In contrast, the use of <NUM>% of MAI additive, resulted in a significant red shift of the absorption onset by about <NUM>. Tauc plots in <FIG> further confirm the decrease of the optical bandgap of the organic-inorganic perovskite materials from <NUM> eV (for the reference and MABr/MACl samples) to <NUM> eV when <NUM>% MAI additive was used. The degree of bandgap shift (~<NUM> eV) is consistent with the incorporation of about additional <NUM> iodide per <NUM> halides (I and Br). The X-ray diffraction (XRD) patterns in <FIG> and <FIG> and <FIG> also agreed with the bandgap change as reflected from the UV-vis spectra. The main peak position of the sample produced using excess MAI additive shifted slightly to a lower diffraction angle by about <NUM>°. These results suggest that when excess MAI is used as an additive in the precursor solution to produce Br-I (e.g. (XyX'<NUM>-y)<NUM>) mixed perovskite materials, the iodide ion may be more stable in the lattice than the bromide ion. Consequently, the final amount of iodide ion in I-Br mixed-halide organic-inorganic perovskite was increased depending on the amount of iodide ion in the precursor solution. In contrast, the excess bromide (or chloride) resulting from the MABr additive (or the MACl additive) was less stable than iodide when competing for the lattice sites, and consequently, the final bandgap of the resultant organic-inorganic perovskite prepared using excess MABr or MACl additives was not affected by the removal of the bromine and iodine during the subsequent treating, e.g. annealing. This is important for developing alloyed perovskite samples (especially for WBG organic-inorganic perovskite materials having a high bromine content) since the bandgap may be easily affected by halide-based precursor precursors and/or additives.

It is noteworthy that the intensity of the main organic-inorganic perovskite (<NUM>) peak was enhanced with the use of excess methylammonium halides additives, especially for the MABr additive, which leads to an order of magnitude increase in the peak intensity. In comparison to the use of the MACl additive, the MABr additive presumably reduces to a lesser degree the perovskite lattice structure with a bromide rich condition during the transition from a precursor state to the intermediate phase, and ultimately to the final organic-inorganic perovskite crystal structure. In addition, the chlorine in the MACl additive could form a relatively stable Br-Cl alloy state during the intermediate film formation stage. The enhanced XRD peak intensity is normally associated with higher crystallinity and/or more aligned grain orientation (texture). The full-width half-maximum (FWHM) of the (<NUM>) plane decreased from <NUM>° for the reference sample, to <NUM>° with <NUM>% MAI additive in the precursor solution, <NUM>° with <NUM>% MACl additive, and <NUM>° for <NUM>% MABr additive (see <FIG> and Table <NUM>). In general, the sharp XRD peak with small FWHM means high crystallinity, increased crystal size, and decreased bulk defect. Thus, the organic-inorganic perovskite prepared from non-stoichiometric precursor, e.g. containing excess MABr additive, showed the most improved crystallographic properties in comparison to using other excess halide-containing additives. The degree of grain orientation is another parameter that shows the crystallographic properties of polycrystalline thin films. Through determining the intensity ratio of peaks for the (<NUM>) plane to the (<NUM>) plane (see Table <NUM>), the degree of orientation was qualitively assessed. The (<NUM>)/(<NUM>) intensity ratio increased from about <NUM> for the pristine organic-inorganic perovskite film using stoichiometric amounts of precursors to <NUM> for the film prepared using excess MABr additive in the precursor solution.

<FIG> shows a top view of SEM images of organic-inorganic perovskite films prepared with and without the use of excess methylammonium halide additives (<NUM>% MAI, MABr, or MACl), according to some embodiments of the present disclosure. Analysis of these images shows that the average grain size was about <NUM> ± <NUM> for all these films. There is no clearly discernable difference in the average grain size among these films. This could be caused by the use of an acid additive (e.g., HI or HBr) in the precursor chemistry (not shown in <FIG>). It is often found that larger grain size leads to improved carrier lifetime, higher carrier mobility, and improved device characteristics. This is frequently attributed to the reduction of the number of grain boundaries. However, the larger grain size is also frequently connected to enhanced film crystallinity and preferred orientation, which also affect device performance.

<FIG> shows the typical photocurrent density-voltage (J-V) curves for perovskite solar cells (PSCs) using organic-inorganic perovskite films prepared with and without the use of excess methylammonium halide additives (<NUM>% MAI, MABr, or MACl), according to some embodiments of the present disclosure. When the MAI additive was used, the Jsc was clearly higher than that of the other devices. This is consistent with the reduced bandgap as we discussed above in connection with the absorption spectra shown in <FIG> and <FIG>. Because of the minimum impact to the bandgap when <NUM>% MABr or MACl additive was used, the Jsc values of these devices are essentially the same as the reference device. Regardless which methylammonium halide additive was used, the device hysteresis was clearly reduced. This can be attributed to the improved crystallographic properties as discussed in connection with <FIG> and <FIG>. The details of the PV parameters including Jsc, Voc, fill factor (FF), and power conversion efficiency (PCE) are summarized in Table <NUM>. Based on these results, it is clear that the MABr additive had the strongest positive effect on the final device performance, especially the Voc, without changing the organic-inorganic perovskite composition (and bandgap). This is consistent with the structure effect as discussed above. It should be noted that the use of excess MAI additive can also significantly improve device performance and reduce hysteresis, but at a cost of shifting the bandgap from <NUM> to <NUM> eV.

The impact of different MABr additive concentrations on the final organic-inorganic perovskites, including film morphology, optical absorption, crystal structure, and device characteristics were also studied. <FIG>, <FIG>, and <FIG> show SEM images of the organic-inorganic perovskite films produced using different amounts of MABr additives, from <NUM>% to <NUM>% excess of stoichiometric amounts. There was no significant variation of the grain morphology when MABr additive was changed from <NUM>% to <NUM>%. However, when <NUM>% MABr additive was used, the film morphology was changed significantly with clear evidence of void formation. This is likely caused by the release of large amounts of MABr additive during the film formation process. The deterioration of film morphology with <NUM>% MABr additive is consistent with the much higher base line of the absorption spectrum shown in <FIG>. In contrast, the films prepared with <NUM>% and <NUM>% MABr additive showed similar optical absorption spectra as the reference film. <FIG> shows that the XRD peak intensity increased with the amount of MABr additive without clearly affecting the peak locations. The typical J-V curves of devices based on organic-inorganic perovskites using non-stoichiometric precursor with different amounts of MABr additive are shown in <FIG>. The corresponding statistics of PV parameters are summarized in Table <NUM> below. When the MABr additive concentration was increased from <NUM>% excess to <NUM>% excess, there was a clear increase in both Voc and FF, leading to improved device efficiency and reduced J-V hysteresis. With a further increase to <NUM>% MABr additive, the average device efficiency dropped substantially from about <NUM>% to <NUM>%. This is consistent with the observed deterioration of the film morphology when <NUM>% MABr was used. <FIG> shows the J-V curves of the best-performing device using <NUM>% MABr additive with both forward and reverse scans. This device was composed of about <NUM>-nm organic-inorganic perovskite and a cross-section of the device stack is shown in <FIG>. The reverse and forward J-V scans yield conversion efficiencies of <NUM>% and <NUM>%, respectively. Because of the hysteresis, the stabilized power output (SPO) near the maximum power point under continuous one-sun illumination was also evaluated. The result is shown in the inset of <FIG>, where the SPO of ~<NUM>% is established. The SPO value is close to the efficiency determined from the reverse J-V scan. The EQE spectrum of the champion device is shown in <FIG>. The integrated current density from EQE spectrum is <NUM> mA/cm<NUM>, which is consistent with the Jsc value (~<NUM> mA/cm<NUM>) from the J-V curve.

In order to investigate the contribution of the organic-inorganic perovskites used in tandem solar cells, an organic-inorganic perovskite-Si <NUM>-terminal tandem cell was prepared by mechanically stacking a Si bottom cell with a semi-transparent wide-bandgap (~<NUM> eV) organic-inorganic perovskite top cell. <FIG> and Table <NUM> show the corresponding J-V curves and PV parameter summary. For the tandem study, SnO<NUM> was used rather than TiO<NUM> as the electron transport material for the PSC. The use of SnO<NUM> can further increase the Voc. For the transparent top contact a stack of <NUM> MoOx, <NUM> Au and <NUM> MoOx was used. A stack of MoOx/Au/MoOx not only facilitates the maximization of semi-transparent top cell efficiency due to the formation of continuous ultrathin Au metal layer and reasonable conductivity, but also enables the relatively high transmittance for the top electrode/cell. The semi-transparent WBG PSC exhibited a PCE of <NUM>% with a Voc of <NUM> V, a Jsc of <NUM> mA cm-<NUM>, and a FF of <NUM>% when measured under reverse voltage scan. With the filter of the semi-transparent WBG top solar cell, the efficiency of the Si bottom cell decreases from <NUM>% to <NUM>% due to the large reduction in the incident light harvesting by Si active layer. The perovskite-Si <NUM>-terminal tandem cell yields a PCE of <NUM>%, which is higher than the semitransparent perovskite top cell (<NUM>%) and the unfiltered Si bottom cell (<NUM>%). As shown in <FIG>, the measured EQE-integrated Jsc's of the organic-inorganic perovskite top cell and the filtered Si bottom cell are <NUM> and <NUM> mA cm-<NUM>, respectively, in agreement with the Jsc's obtained from their respective J-V curves. It is worth noting that these perovskite-Si <NUM>-terminal tandem cells still have potential to be further improved by using more transparent eletrode stack for semi-transparent perovskite top cells, Si bottom cell with higher efficiency, and more effective optical coupling scheme.

In summary, the use of non-stoichiometric precursor solutions having excess methylammonium halides additives (MAI, MABr, and MACl) for preparing high-quality organic-inorganic perovskite thin films (~<NUM> eV FA<NUM>Cs<NUM>Pb(I<NUM>Br<NUM>)<NUM>) for solar cell applications has been demonstrated. In contrast to the standard iodine-based perovskites, the composition of the perovskites containing high bromine content can be affected significantly by the use of excess methylammonium halides additives due to the competition of different halides in the organic-inorganic perovskite lattice. For organic-inorganic mixed-halide perovskites based on Br-I mixtures, excess MAI additive significantly reduced the bandgap due to more iodide incorporation, whereas the use of both MABr and MACl additives showed little impact on the organic-inorganic perovskite composition and crystal structures. Interestingly, excess MABr additive (rather than excess MACl additive) in the non-stoichiometric precursor showed the strongest effect on improving both the crystallographic properties (e.g., crystallinity and orientation) and the device characteristics.

Organic-Inorganic perovskite and device fabrication. Fluorine doped tin oxide (FTO, TEC15, Hartford glass Co) was patterned using Zn powder and HCl (~<NUM>). Compact TiO<NUM> (c-TiO<NUM>) film was deposited on thoroughly cleaned substrate by spray pyrolysis using <NUM> titanium diisopropoxide bis(acetylacetonate) in <NUM>-butanol solution. PCBM (<NUM>/ml in dichlorobenzene) was span at <NUM> rpm for <NUM> on top of c-TiO<NUM>, followed by <NUM> hr annealing at <NUM>. Organic-inorganic perovskite precursor solutions, targeting a final organic-inorganic perovskite composition of FA<NUM>Cs<NUM>Pb(I<NUM>Br<NUM>)<NUM>, was composed of <NUM> CsI, <NUM> FAI, <NUM> PbBr<NUM>, <NUM> PbI<NUM> precursors in a DMF solution. <NUM>µl of HI acid and <NUM>µl of HBr acid were added into <NUM> precursor. Different amounts of additives, eg. <NUM> MAI, MABr, MACl, were added to the prepared precursor solution. The precursor solution was deposited by spin-coating <NUM>µl precursor at <NUM> rpm for <NUM>. The resultant transparent yellow liquid film was transferred onto a hotplate at <NUM> for <NUM>, and then at <NUM> with a petri-dish covered for <NUM>, resulting in the final, solid organic-inorganic perovskite layer. A hole transport layer (HTL) was spin-coated at <NUM> rpm for <NUM> with a HTL solution consisting of <NUM> <NUM>,<NUM>',<NUM>,<NUM>'-tetrakis(N,N-dip-methoxyphenylamine)-<NUM>,<NUM>'-spirobifluorene (Spiro-OMeTAD; Merck), <NUM>µL bis(trifluoromethane) sulfonimide lithium salt stock solution (<NUM> Li-TFSI in <NUM> acetonitrile), and <NUM>µl <NUM>-tert-butylpyridine (TBP), and <NUM> chlorobenzene solvent. Finally, a <NUM> Ag layer was deposited on the HTL layer by thermal evaporation for the top contact.

Semi-transparent device fabrication. For the (~<NUM> eV) semi-transparent top organic-inorganic perovskite cell, SnO<NUM> was used as the electron transport material (ETM). The SnO<NUM> ETM was deposited onto pre-patterned and cleaned FTO substrates by plasma-enhanced atomic layer deposition (Ensure Scientific Group AutoALD-PE V2. The substrate was then sequentially deposited by a C<NUM>-SAM layer, organic-inorganic perovskite film, and spiro-OMeTAD as the hole transport material (HTM). Finally, the sequence of <NUM> MoOx, <NUM> Au, and <NUM> MoOx were thermally evaporated through a patterned mask onto the HTM.

Film and device characterization. The optical absorption spectra of the organic-inorganic perovskite films were measured using a UV-vis spectrophotometer with the aid of an integrated sphere (Cary-6000i, Agilent) The morphologies of the prepared organic-inorganic perovskite films and the cross-sectional structure and thickness of the solar cells were investigated using a feld-emission scanning electron microscopy (FESEM, Quanta <NUM>, FEI). J-V curves were measured in air under <NUM> mW/cm<NUM> simulated AM1. <NUM> solar irradiation with a Keithley <NUM> Source Meter. The light intensity for J-V measurements was calibrated by a standard Si solar cell. EQE spectra were measured from <NUM> to <NUM> for perovskite solar cells and from <NUM> to <NUM> for Si cells using a QE system from PV Measurements Inc. All characterizations and measurements were performed in the ambient condition. The stabilized current and power output were measured using a potentiostat (Princeton Applied Research, VersaSTAT MC).

<NUM>-terminal tandem cell measurements. The measurements were performed using the standard methods. In brief, the J-V curves of semitransparent top organic-inorganic perovskite cells were measured under <NUM> mW/cm<NUM> AM1. <NUM> solar irradiation. EQE spectra were performed on a QE system. Each semitransparent wide-bandgap top cell consists of multiple subcells with small and large active areas as defined by the areas of the metal electrodes. The small subcells have similar active areas as the bottom cells and are used for J-V measurements.

The large subcells are used to filter the bottom cells for easy cell alignment. The J-V curve and EQE spectrum of Si bottom cell were taken by putting such a semitransparent wide-bandgap top cell with a large active area on top as a filter.

Claim 1:
A method comprising:
treating a liquid comprising a first precursor at a concentration C<NUM>, a second precursor at a concentration C<NUM>, a third precursor at a concentration C<NUM>, a fourth precursor, and an additive at a concentration C<NUM>, wherein:
the first precursor comprises at least one of cesium halide wherein cesium halide is cesium iodide or cesium bromide;
the second precursor comprises at least one of formamidinium halide wherein formamidinium halide is formamidinium iodide or formamidinium bromide;
the third precursor comprises PbBr<NUM>;
the fourth precursor comprises PbI<NUM>;
the additive comprises at least one of methylammonium bromide (MABr), methylammonium chloride (MACl), and methylammonium iodide (MAI);
the treating results in a perovskite having the formula FAxCs<NUM>-xPb(IyBr<NUM>-y)<NUM>, where <NUM> < x < <NUM> and <NUM> < y < <NUM>;
each of C<NUM>, C<NUM>, and C<NUM> are independently between <NUM> and <NUM>; and
at least one of C<NUM>/C<NUM> or C<NUM>/C<NUM> equals a ratio greater than zero and less than <NUM>.