Sequential Organic Ligand Modifications to Dedicatedly Restructure Grain Boundary and Surface of Perovskites

The durability of perovskite solar cells (PSCs) is substantially limited by defects and imperfect structures at grain boundaries (GBs) and grain surfaces (GSs) of perovskites, where common single-step ligand passivation struggles due to ligand heterogeneous distributions and distinct chemical environments. Herein, we demonstrate a two-step sequential dedicated-ligand (TSS-DL) strategy that selectively targets GBs and GSs through spatially resolved interactions of the dedicated ligands. We identified two classes of dedicated ligands, including Ligand X, notably 2,2-difluoroacetamide bromide (DFABr) for GBs to restructure them into stable 2D perovskites and suppress defects, and Ligand Y, featuring 4-aminopiperidinium dibromide (4APPBr2) for GSs to create a rigid 2D perovskite overlayer that shields 3D perovskites from external stresses. TSS-DL-treated PSCs retain >93% of their power conversion efficiency (PCE) after 3,000 hours of operation and >90% after 4,000 hours under high humidity (>85% RH). By sequentially restructuring GBs and GSs using dedicated ligands, the work provides an effective way to overcome the instability of 3D PSCs while maintaining high performance. Single-step ligand passivation of grain boundary and surface defects often struggles with heterogeneous ligand distributions and distinct chemical environments. Here, the authors report a two-step sequential method to selectively target both types of defects, achieving a device efficiency of 26.06%.