Brominated PEAI as Multi‐Functional Passivator for High‐Efficiency Perovskite Solar Cell

The interfaces of perovskite solar cells (PSCs) are well known to be rich in deep‐level carrier traps, which serve as non‐radiative recombination centers and limit the open‐circuit voltage ( V oc ) and power conversion efficiency (PCE) of PSCs. Defect chemistry and surface passivators have been researched extensively and mainly focused on the neutralization of uncoordinated lead or anion defects. Herein, a novel brominated passivator 2‐bromophenethylammonium iodide (2‐Br‐PEAI) is introduced for a multi‐functional passivation effect at the perovskite interface. The brominated species readily form 2D perovskite on top of the 3D perovskite and multi‐interact with the 3D perovskite surface. Apart from the halide vacancy filling and anion bonding ability, the Br atoms on the benzene ring can interact with the FA cations via strong hydrogen bonding N‐H ⋯ Br and interact with the [PbI 6 ] 4− inorganic framework. The interface defects in the PSCs are well passivated, minimizing non‐radiative recombination and enhancing device performance. As a result, a champion PCE of 24.22% was achieved with high V oc and fill factor. In addition, modified devices also showed enhanced operational stability (retention of >95% initial PCE after 400 h) and humidity resistance (>90% initial PCE maintained after 1500 h under ~50% RH).