Ammonium Sulfate to Modulate Crystallization for High‐Performance Rigid and Flexible Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) are attracting widespread research and attention as highly promising candidates in the field of electronic photovoltaics owing to their exceptional power conversion efficiency (PCE). However, rigid or flexible PSCs still face challenges in preparing full‐coverage and low‐defect perovskite films, as well as achieving highly reproducible and highly stable devices. Herein, a multifunctional additive 2‐aminoethyl hydrogen sulfate (AES) is designed to regulate the film crystallization and thereby form flat and pinhole‐free perovskite films. It is found that the introduction of AES can effectively passivate defects, restrain charge carrier recombination, and then achieve a higher fill factor. As seen with grazing incidence wide‐angle X‐ray scattering (GIWAXS), this approach does not affect the crystal orientation distribution. It is observed that AES addition shows a universality across different perovskite components since the PCE is improved up to 20.7% for FA_0.97MA_0.03Pb(I_0.97Br_0.03)₃‐AES, 22.85% for Cs_0.05FA_0.95PbI₃‐AES, 22.23% for FAPbI_2.7Br_0.3‐AES, and 23.32% for FAPI‐AES rigid devices. Remarkably, the non‐encapsulated flexible Cs_0.05 (FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃ device with AES additive delivers a PCE of 20.1% and maintains over 97% of its initial efficiency under ambient conditions (25 ± 5% relative humidity) over 2280 h of aging.