Metal halide perovskites have become a popular material system for fabricating photovoltaics and various optoelectronic devices. However, long-term reliability must be assured. Instabilities are manifested as light-induced ion migration and segregation, which can lead to material degradation. Discordant reports have shown a beneficial role of ion migration under illumination, leading to defect healing. By combining ab initio simulations with photoluminescence measurements under controlled conditions, we demonstrate that photo-instabilities are related to light-induced formation and annihilation of defects acting as carrier trap states. We show that these phenomena coexist and compete. In particular, long-living carrier traps related to halide defects trigger photoinduced material transformations, driving both processes. Defect formation can be controlled by blocking under-coordinated surface sites, which act as a defect reservoir. By use of a passivation strategy we are thus able to stabilize the perovskite layer, leading to improved optoelectronic material quality and enhanced photostability in solar cells.
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The data that support the plots within this paper and other findings of this study are available from the corresponding authors on reasonable request.
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This work has been funded by the European Union project PERT PV under grant no. 763977, ERC project SOPHY under grant no. 771528 and PERSEO ‘PERrovskite-based solar cells: towards high efficiency and long-term stability’ (Bando PRIN 2015—Italian Ministry of University and Scientific Research (MIUR) Decreto Direttoriale 4 Novembre 2015 no. 2488, project no. 20155LECAJ). The Ministero Istruzione dell’Università e della Ricerca (MIUR) and the University of Perugia are acknowledged for the financial support through the program “Dipartimenti di Eccellenza 2018-2022” (Grant AMIS) to F.D.A. S.G.M. thanks the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico—Brasil) for a scholarship (206502/2014-1). M.K. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant no. 797546 of the FASTEST project. The authors thank G. Paternò for his support in setting up the transient Voc characterization.
The authors declare no competing interests.
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Simulations and temporal dynamics.