Charge‐State‐Controlled Surface Modifiers for High‐Voltage and Stable Wide‐Bandgap Perovskite Solar Cells

For wide‐bandgap mixed‐halide perovskites, quasi‐two‐dimensional (quasi‐2D) surface reconstruction using bulky‐cation spacers is widely employed to passivate surface defects and disrupt halide migration pathways. Nevertheless, under operational stress, conventional ammonium‐based spacers can undergo deprotonation, destabilizing the low‐dimensional surface layer and weakening its function. Herein, we report an organic‐spacer charge‐state control strategy for the surface modification of Cs 0.2 FA 0.8 PbI 1.8 Br 1.2 wide‐bandgap perovskites. This strategy involves combining octylammonium (OA) with N ‐methylsulfanilic acid (NMSA) to form NMSAO, a charge‐neutralized ammonium–sulfonate modifier state. This configuration induces an associated Ruddlesden–Popper‐like quasi‐2D phase at the perovskite surface that suppresses trap‐mediated recombination, facilitates interfacial charge extraction, and disrupts halide‐ion migration pathways. As a result, the NMSAO‐treated perovskite solar cells (PSCs) achieved a power conversion efficiency (PCE) of 19.83% and an open‐circuit voltage ( V OC ) of 1.326 V, compared with 17.30% and 1.197 V for the untreated control PSCs. Furthermore, the NMSAO‐treated PSCs retain 93.59% of their initial PCE after 500 h of continuous illumination under ISOS‐L‐1 conditions and more than 93% after 500 h of thermal aging at 85°C. This study demonstrates the effectiveness of a charge‐neutralized organic spacer for quasi‐2D surface reconstruction in wide‐bandgap mixed‐halide PSCs, improving both photovoltaic performance and operational stability.