Tetramethylurea Based Intermediate Phase Engineering for Efficient and Stable Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) are emerging photovoltaic devices renowned for their high efficiency and low cost. Efficient and stable PSCs depend on high‐quality perovskite films, which are strongly influenced by the excellent nucleation and growth. The choice of solvent is critical for the crystallization behavior of perovskite films. To improve film quality and address the uncontrollable fast crystallization, it is essential to replace traditional dimethyl sulfoxide (DMSO) solvent. In this work, tetramethylurea (TMU) ligand is successfully introduced into the solvent to replace DMSO for the first time. Through intermediate phase engineering, the crystallization of perovskite films is optimized. The stronger interaction between TMU and solutes versus DMSO can effectively delay the transition from intermediate to perovskite phase, yielding high‐quality perovskite films with larger grains and lower defects. Finally, the optimized perovskite films maintained excellent phase stability after aging for 150 h under 95% relative humidity (RH) or at 85 °C, while the device efficiency increased from 19.54% to 21.05%. Furthermore, the devices exhibited outstanding stability after aging for ≈1000 h under 50% RH. This research provides new insights and good example for achieving highly efficient and stable PSCs through intermediate phase engineering.