Surface Defect Passivation of Pb–Sn‐Alloyed Perovskite Film by 1,3‐Propanediammonium Iodide toward High‐Performance Photovoltaic Devices

The power conversion efficiency (PCE) of narrow‐bandgap Pb–Sn‐alloyed perovskite solar cells (PVSCs) is seriously impeded by the large open‐circuit voltage () deficit. Finding an effective approach to passivate defects in the perovskite film is critical to reduce the deficit. Herein, a linear organic cation 1,3‐propanediammonium iodide (PDAI 2 ) is used to passivate the surface defects of perovskite film, thus restraining the nonradiative recombination. After treating with PDAI 2 , the defect density of perovskite film is decreased to half and the carrier lifetime is prolonged more than 1.5 times. As a result, the champion Pb–Sn‐alloyed PVSC based on PDAI 2 treatment exhibits a small deficit of 0.39 V, and a high PCE of 20.2%.