Fig. 1: Device properties of FA_0.99Cs_0.01PbI₃ PeSCs.

a Device architecture of the surface-passivated device. The pristine device has a similar architecture but without the OAI layer. b Current density versus voltage of the pristine and surface-passivated devices measured during forward and reverse voltage sweeps at a scan rate of 40 mV s^–1. c Configuration of the surfaces of pristine and surface-passivated perovskites. The OA chains mount to the perovskite surface via their NH₃⁺ groups, which also passivate the FA⁺ vacancies simultaneously, while the I^– vacancies can be passivated by the I^– in OAI⁶⁴.