Optimized Crystallization of CsPbI2Br Films through the Incorporation of H2O for High-Efficiency All-Inorganic Perovskite/Organic Tandem Solar Cell

Abstract

Among all-inorganic perovskites, CsPbI₂Br possesses excellent photovoltaic performance, intrinsic thermal stability and suitable bandgap and superior phase-stability, demonstrating large application potential for single-junction perovskite solar cells (PSCs) and perovskite/organic tandem solar cells (TSCs). However, a critical challenge persists in the effective control of the crystallization process of the CsPbI₂Br film, as inadequate crystallization can result in a substantial decrease in the photoelectric efficiency of solar cells. Herein, a simple approach utilizing a small amount of H₂O additive is introduced to optimize the crystallization process of CsPbI₂Br film. Specifically, the introduction of water facilitates the formation of numerous CsPbI₂Br seed crystals within the precursor solution, promoting subsequent Ostwald ripening process of the perovskite film. Additionally, the presence of water enhances the desorption of DMSO from CsPbI₂Br, further improving overall crystallization. As a result, a CsPbI₂Br-basedPSC exhibits a high power conversion efficiency (PCE) of 16.7% and an open-circuit voltage (V_OC) of 1.36 V. By integrating these CsPbI₂Br-based front sub-cells with narrow-bandgap PM6:Y6-based rear sub-cells, a high PCE of 23.21% and V_OC of 2.17 V is achieved, illustrating the potential of TSCs for high-efficiency tandem solar cells. Furthermore, the unencapsulated TSCs display superior stability under ambient air conditions and operation.