Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

•A key phase transition intermediate (8H phase) was isolated and identified•Complete evolution of FAPbX3 by the 8H single crystal is provided•Effects doping anions cations on stabilization are revealed•Rational design for fabrication highly efficient stable PSCs suggested The stability formamidinium lead halide (FAPbX3) perovskites crucial to long-term perovskite solar cells, while a molecular-level understanding process mechanism still lacking. We crystal, phase, which composed both face-sharing corner-sharing octahedrons and, thus, creates cubic, olive-like peanut-like cages. helps complete from viewpoint structural chemistry also reveals underlying roles in stabilizing FA-based according Pauling’s rules. could indicate novel interfacial structure phase. These findings insights will form practical guidance rationally preparing high-quality devices. FAPbI3 (FA+ = formamidinium) perovskite, one most basic components nowadays cells (PCSs), undergoes spontaneous investigations Here, we report study based isolation identification series intermediates. A with unique discovered, elucidate perovskites. Our new insight rules not only deepens maximizing concentrations halogens cubic cages but forms suggestion high-performance PCSs controlling factors such as composition, precursor solution, stoichiometry, additives. Metal materials have attracted tremendous attention optoelectronic device applications, especially (PSCs), because their high performance photoelectric conversion efficiency1Kim G. Min H. Lee K.S. D.Y. Yoon S.M. Seok S.I. Impact strain relaxation ?-formamidinium iodide cells.Science. 2020; 370: 108-112https://doi.org/10.1126/science.abc4417Crossref PubMed Scopus (309) Google Scholar, 2Yoo J.J. Seo Chua M.R. Park T.G. Lu Y. Rotermund F. Kim Y.-K. Moon C.S. Jeon N.J. 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And spaces, created octahedron framework, occupy.19Stoumpos Thus distinctive features (3C Meanwhile, al.,19Stoumpos all repeat every reverse layers type location orientations AA? resultant z-direction channels reside 1B). Besides, pulverization observed process. Several sets spots reciprocal space appeared when 3C-FAPbI3 undergoing scanned globally diffractometer (Figures 1C S1). contrast, FAPbBr3 do transform 2H-FAPbBr3 even after exposure water oxygen S2A). traditional concepts like factor cannot explain bears parameter larger S2B). globularity should taken account that size rigidity, symmetry, chemical environment (halide ions) important.40Gholipour Ali A.M. Turren-Cruz Tajabadi Taghavinia al.Globularity-selected molecules generation multication perovskites.Adv. 29: 1702005https://doi.org/10.1002/adma.201702005Crossref (54) how efficiently Br? suppress partly substituted FAPb(I1-xBrx)3, further studied. gradually changed yellow ones contents bromine 33% 17% solutions, respectively S3). One FAPb(I1-xBrx)3 systems obtained. elucidated SCXRD detail below adopting above-presented linkage model. First, grown (100°C) solution bromide content. then transformed mother liquor 2 h temperature. After isolating quickly removing residual solvents, analyzed SCRXD. this solved refined, it named [PbX6] 1D, S4, S5), stacked eight sequence … ABCAA?C?B?A?ABCAA?C?B?A?…. ratio halogen Xcorner: Xface 3:1. More importantly, contains addition types cages, i.e., cage 2A, 2B, S6). enhances relationship filling three 1:2:1. indeed feature This exhibits characteristic powder XRD peaks 2? 13.24°, those S7 S8; Table Second, orange about S9–S11).32Gratia shows solvents accelerate explaining why so sensitive solvent atmosphere storage time. immediate removal crystals, slowed down became obvious weeks under influence air. Analogous six ABCC?B?A?ABCC?B?A?…, 2:1. Without occupy 1:1. Note exhibiting 12.27° directly containing reactant. Finally, small 4H 13.06° S12–S14) formed transformation or aging S15). four AA?B?BAA?B?B…, 1:1, leaving similar filled unavailable together long-range ordered far predict closer relationship. stack ABCABC...or...C?B?A?C?B?A?, generating number stacking three. exist AA?, BB?, CC?, resulting being produced whenever appear. As shown Figure 3, arrange ABCABC... continuously upper line reversing A?B?C?A?B?C?... line, letters pattern octahedrons. extend generate semicircles A, B, C units; they continue another semicircle reversed C?, B?, A? units crossing lines ends A?. circle means layer numbers phases. It noteworthy represent having identical orientation. change layers. way, depict correlation among discovered Moreover, may potential deactivation process, 10H-FAPbX3 12H-FAPbX3 4). Hence, intermediates set (3C) (2H). map fact iodine family (see supplemental information). mentioned above, very fast pulverization, making difficult capture without introduction bromide. likely present interfaces grain boundary, help S16). review our manuscript, presence 4H-FAPbI3 6H-FAPbI3 in-situ synchrotron GIWAXD technique.41Park B.-w. Kwon K.-j. Y.K. Im Shin T.J. S.Il. triiodide ?-phase isopropylammonium chloride 419-428https://doi.org/10.1038/s41560-021-00802-zCrossref (22) They found boundary FAPbI3, strongly support perovskites.Figure 4Summary Pb atoms five predicted FAPbX3View Large Image ViewerDownload Hi-res image Download (PPT) evolves fraction reduced S17; Tables S2 determined investigating electron cloud S18–S20; S4–S6) combining DFT calculations. Significantly lower densities, higher occupancies, sites sites, Pb–Br–Pb bond angle greater Pb–I–Pb refined structures. results show Cl? energies 5A, 5B, S21–S26; S7) repulsive forces adjacent Pb2+ arranged 5C). suggest locate rather ones, increasing thermodynamic system. agree third rule accommodating oxidation state tend share corners faces, order increase distances cations. chlorine stabilize octahedron, thereby preferential 3C-FAPbBr3 thermodynamically bromine-substituted eventually transforms That is, face-sharing, would unstable bromine-containing temporarily intermediates, enabled successful isolations According discipline above crystallographic changes, 3C- 2H-phase deduced FAPbI3. generated lead-halide changes framework evolves. (3C, 8H) (4H, 2H) (8H, 6H) 6H, 4H). transitions MAPb(I1-xBrx)3 CsPb(I1-xBrx)3 systems. Thus, assume influenced interactions verify conjecture, models 8H-CsFA7Pb8I24 8H-MAFA7Pb8I24 5D–5F, S27–S29, S30–S32) built as, isomers 2×2×1 supercells 8H-CsFA31Pb32I96 8H-MAFA31Pb32I92 S33–S35 S36–S38), analyze calculations (?E). note isomer accurately compare energy differences ?E increases slightly Cs+ MA+ significantly 5G), case S29). prefer occupying PWT program FA+. result smallest (56.6 Å3) largest (84.0 5G). rule, vice versa S39; S8).42Zhang Larson B.W. Dunfield S.P. Reid O.G. 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Huh al.Methylammonium induces cells.Joule. 2179-2192https://doi.org/10.1016/j.joule.2019.06.014Abstract (616) guidance, quality optimized 1.59 eV bandgap reach 21% any interface passivation. best negligible hysteresis effect keeps 90% initial 1,000 20% humidity S43). successfully include kinds (cubic, peanut-like, olive-like) structure. discoveries 8H-FAPbX3 bridge establish picture correlates experimentally view. combined revealing intrinsic proven preference anions’ cations’ occupation obey rules, namely energetically keys maximize Further, fabricated optimizing presented work provide basis cells.