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Controlling competing photochemical reactions stabilizes perovskite solar cells

Abstract

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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Data availability

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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Acknowledgements

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.

Author information

S.G.M. performed the photoluminescence measurements. D.M. and E.M. performed the first-principles calculations. C.A.R.P., J.M.B., M.G. and M.K. were responsible for fabrication of the thin films. M.K. fabricated the solar cell devices and M.K and A.J.B. characterized the solar cell. A.P., S.G.M., A.J.B., D.M. and F.D.A. analysed the data. S.G.M., F.D.A. and A.P. wrote the first draft of the manuscript and all authors contributed to the discussions and finalized the manuscript. A.P. supervised the project.

Correspondence to Filippo De Angelis or Annamaria Petrozza.

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Fig. 1: Transient integrated photoluminescence intensity from MAPbI3 and MAPbBr3 thin films as a function of excitation repetition rate and temperature.
Fig. 2: Transient integrated photoluminescence intensity from MAPbI3 thin films as a function of excitation penetration depth and excitation geometry.
Fig. 3: Defect dynamics.
Fig. 4: Photoluminescence enhancement and quenching mechanisms.
Fig. 5: Thin film passivation.