Dissolved-Cl2 Triggered Redox Reaction Enables High-performance Perovskite Solar Cells

Abstract Constructing 2D/3D perovskite heterojunction has been proven to be an effective strategy for fabricating high-performance perovskite solar cells (PSCs). However, previous reports only physically deposit a 2D perovskite passivation layer on the 3D perovskite layer. These methods are limited to surface passivation only, and the bulk 3D perovskite remains defective. Herein, we propose Cl2-dissolved chloroform as a multifunctional and reactive solvent for constructing the 2D/3D perovskite heterojunction. Specifically, the dissolved Cl2 reacts with the 3D perovskite, leading to Cl/I ionic exchange. The generated Cl- anions further diffuse to passivate the buried interface of PSCs, improving the bulk and interface quality. Additionally, hexylammonium bromide reacts with the residual PbI2 to form 2D/3D heterojunctions on the surface. As a result, we achieved high-performance PSCs with a champion efficiency of over 24% and substantially improved operational stability, retaining 80% of the initial efficiency after working for 905 h at the maximum power point.