Shallow Iodine Defects Accelerate the Degradation of α-Phase Formamidinium Perovskite

Shallow defects are mostly benign in covalent semiconductors, such as silicon, given that they do not constitute non-radiative recombination sites. In contrast, the existence of shallow defects in ionic perovskite crystals might have significant repercussions on the long-term stability of perovskite solar cells (PSCs) because of the metastability of the ubiquitous formamidinium lead triiodide (FAPbI₃) perovskite and the migration of charged point defects. Here, we show that shallow iodine interstitial defects (I_i) can be generated unintentionally during commonly used post-fabrication treatments, which can lower the cubic-to-hexagonal transformation barrier of FAPbI3-based perovskites to accelerate its phase degradation. We demonstrate that concurrently avoiding the generation of I_i and the more effective passivation of iodine vacancies (V_ī) can improve the thermodynamic stability of the films and operational stability of the PSCs. Our most stable PSC retained 92.1 % of its initial performance after nearly 1,000 h of continuous illumination operational stability testing. ; © 2020 Elsevier. Received 14 June 2020, Revised 4 August 2020, Accepted 24 August 2020, Available online 23 September 2020. This work was supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office under award number DE-EE0008751. Computing resources used in this work were provided by the National Center for High-Performance Computing of Turkey (UHEM) with grant number 5005902018. M.H.W. would like to acknowledge the detailed discussions with the late Kelvin G. Lynn. M.H.W.'s contributions and the PAS work was supported by subcontract to Washington State University from the University of California, Los Angeles of a grant by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office under award number DE-EE0008751 awarded to Dr. Yang Yang. This work was also supported by the National ...