Alleviating halide perovskite surface defects

Surface defects acutely influence perovskite solar cell performance. In this issue of Matter, Wang et al. developed a novel and compelling molecular “defect indicator” approach, notable for minimizing surface evaluating passivation strategies. The performance metal halide cells has improved rapidly in the past decade, with certified power-conversion efficiency now exceeding 25%.1Yoo J.J. Seo G. Chua M.R. Park T.G. Lu Y. Rotermund F. Kim Y.-K. Moon C.S. Jeon N.J. Correa-Baena J.-P. al.Efficient via carrier management.Nature. 2021; 590: 587-593https://doi.org/10.1038/s41586-021-03285-wCrossref PubMed Scopus (802) Google Scholar One source impressive progress is unique material properties semiconductors. It predicted theory that, bulk crystals, point low formation energies create only shallow trap states, that are likely to deep states have high energies.2Yin W.-J. Shi T. Yan Unusual defect physics CH3NH3PbI3 absorber.Appl. Phys. Lett. 2014; 104: 063903https://doi.org/10.1063/1.4864778Crossref (1794) On other hand, it generally accepted at grain boundaries surfaces not as benign and, fact, limit device stability. Therefore, considerable attention focused on defects.3Xue J. R. Yang perovskites from nano bulk.Nat. Rev. Mater. 2020; 5: 809-827https://doi.org/10.1038/s41578-020-0221-1Crossref (106) often acknowledged two kinds dominate lead films: undercoordinated I Pb atoms.4Wang Bai S. Tress W. Hagfeldt A. Gao Defects engineering high-performance cells.npj Flex. Electron. 2018; 2: 22https://doi.org/10.1038/s41528-018-0035-zCrossref (216) As such, most strategies include treatment thin films Lewis bases acids.5Chen B. Rudd P.N. Yuan Huang Imperfections their cells.Chem. Soc. 2019; 48: 3842-3867https://doi.org/10.1039/C8CS00853ACrossref This because Pb2+ or clusters act acids, which can be passivated by binding base. Undercoordinated sites therefore various acids. Molecular passivate atoms simultaneously also been proposed. Zwitterions, example, possess both acid basic functional groups thus capability positively negatively charged ionic defects.6Zheng X. Chen Dai Fang Lin Wei H. Zeng X.C. Defect hybrid using quaternary ammonium anions cations.Nat. Energy. 2017; 17102https://doi.org/10.1038/nenergy.2017.102Crossref Despite extensive efforts committed defects, neither comprehensive understanding origins nor definitive solution yet achieved. difficulty identify types corresponding mechanisms. demonstrate “positively approach ability contribute better means strategies.7Wang Xue Yao C. Z.-K. Weber M.H. Rose A.H. Nuryyeva Zhu al.Unraveling photovoltaic film.Matter. 4: 2417-2428Abstract Full Text PDF (7) authors studied two-step sequential deposited formamidinium-methylammonium (FA-MA) mixed cation suggest where FAI antisite dominant trap. use rationally designed molecule interact able target specifically identified defect, providing future strategy study defects. conditions highly dependent film deposition techniques; thus, distinct expected film-processing approaches compositions. For process FA-MA films, found distribution FA MA cations uniform, whereby preferentially accumulate surface.5Chen result, first principles near surface. contrast case may different prepared techniques. fluorinated organic these defects.7Wang cannot penetrate film, confirmed characterization will enables isolated passivation. further conducted systematic characterization, combining theoretical calculations surface-sensitive experimental measurements understand chemical interactions efficacy molecule. With treatment, energy dramatically increased total density significantly reduced. result passivation, power conversion 21.01% 23.19% work shows importance comprehensively complex, processing composition dependent, very bulk. Defects, especially difficult characterize. Novel important Two directions perovskites. “direct” visualization low-damage damage-free imaging While some encouraging results achieved atomic resolution,8Rothmann M.U. J.S. Borchert Lohmann K.B. O’Leary C.M. Sheader A.A. Clark L. Snaith H.J. Johnston M.B. Nellist P.D. Herz L.M. Atomic-scale microstructure perovskite.Science. 370: eabb5940https://doi.org/10.1126/science.abb5940Crossref (14) Scholar,9Yu Zhang D. Kisielowski Dou Kornienko N. Bekenstein Wong A.B. Alivisatos A.P. P. Atomic Resolution Imaging Halide Perovskites.Nano 2016; 16: 7530-7535https://doi.org/10.1021/acs.nanolett.6b03331Crossref (90) many observed. Another direction developing indicators” specific types, combined techniques efficacy.10Wang K.-L. Luo Fenning Xu Zhao al.Constructive configurations surface-defect photovoltaics.Science. 366: 1509-1513https://doi.org/10.1126/science.aay9698Crossref (429) demonstrated contributes toward latter atomistic origins.7Wang Unraveling state filmWang al.MatterMay 28, 2021In BriefAn uneven was uncovered mixed-cation leading energetics. Based recombination velocity 20 cm/s over 23% were Full-Text Open Archive