Two-step growth of CsPbI3−xBrx films employing dynamic CsBr treatment: toward all-inorganic perovskite photovoltaics with enhanced stability

Abstract

Recently, CsPbI_3−xBr_x (x = 1–2) all-inorganic perovskites have been studied to overcome the phase instability of CsPbI₃. However, the addition of Br inevitably leads to a bandgap that is too wide (1.93–2.03 eV) compared to that of CsPbI₃ (1.73 eV). To avoid this, the present study focuses on developing stable α-CsPbI_3−xBr_x (x < 0.7) perovskite films with lower Br levels. Our dynamic CsBr treatment incorporates Br⁻ into the CsPbI₃ lattice, greatly enhancing the morphology, optical properties, stability, and photovoltaic performance of the resultant CsPbI_3−xBr_x (x < 0.7) perovskite films. At x = 0.66, the perovskite film with the relatively low bandgap of 1.84 eV contributes to achieving an impressive power conversion efficiency (PCE) of 14.08% and, after 1200 h storage under a nitrogen atmosphere without encapsulation, the PCE remains at around 70% of this initial level. This two-step growth using dynamic CsBr treatment opens up promising routes for the feasible fabrication of inorganic perovskite photovoltaics with exceptional stability.