Solar Cells & Photonics Research Laboratory

School of Chemistry
University of Hyderabad, Hyderabad, India

Double Charged Surface Layers in Lead Halide Perovskite Crystals

Authors: Smritakshi P Sarmah, Victor M Burlakov, Emre Yengel, Banavoth Murali, Erkki Alarousu, Ahmed M El-Zohry, Chen Yang, Mohd S Alias, Ayan A Zhumekenov, Makhsud I Saidaminov, Namchul Cho, Nimer Wehbe, Somak Mitra, Idris Ajia, Sukumar Dey, Ahmed E Mansour


defects; ion migration; lead halide perovskite crystal; Nanometer surface layers; one vs two-photon excitat

Year: Nano Lett., 2017, 17 (3), pp 2021–2027​​

Abstract: Understanding defect chemistry, particularly ion migration, and its significant effect on the surface’s optical and electronic properties is one of the major challenges impeding the development of hybrid perovskite-based devices. Here, using both experimental and theoretical approaches, we demonstrated that the surface layers of the perovskite crystals may acquire a high concentration of positively charged vacancies with the complementary negatively charged halide ions pushed to the surface. This charge separation near the surface generates an electric field that can induce an increase of optical band gap in the surface layers relative to the bulk. We found that the charge separation, electric field, and the amplitude of shift in the bandgap strongly depend on the halides and organic moieties of perovskite crystals. Our findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surface passivation strategies to remediate them.​​


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