DMSO‐Assisted Control Enables Highly Efficient 2D/3D Hybrid Perovskite Solar Cells

Abstract Building 2D/3D heterojunction is a promising approach to passivate surface defects and improve the stability of perovskite solar cells (PSCs). Developing effective methods to build high‐quality 2D/3D heterojunction is in demand. The formation of 2D/3D heterojunction involves both the diffusion of 2D spacer molecules and phase transition from 3D to 2D structure. Herein, a DMSO‐assisted method is demonstrated to simultaneously regulate both the 2D/3D formation kinetics, yielding high‐quality 2D top layer with continuous coverage, which enhances the photovoltaic performance of PSCs. It is found that the presence of DMSO significantly facilitates the diffusion of 2D spacer cation. Meanwhile the residual DMSO may partially dissolve the surface perovskite, facilitating the reaction between 2D molecules with 3D perovskite and ultimately leading to sequential secondary crystal growth and the appearance of a distinct 2D layer. The formation of high‐quality 2D layer effectively passivates the surface defects thus suppresses the interfacial charge recombination. As a result, the champion PSC based on optimal 2D/3D heterojunction exhibits a high fill factor of 85% and a power conversion efficiency of 24%. The work offers a novel perspective for the construction of 2D/3D perovskite heterojunctions.