Intermediate State Formation Extends the Ambient Temperature Processing Window of Solution-Processed Perovskite Solar Cells

Solution-processed perovskites offer tremendous potential for low-cost, high-throughput photovoltaic production. However, high-quality perovskite films typically require stringent processing conditions, compromising reliability in large-scale production. Here, we discover that the initial nucleation process during the spin-coating is critical in determining the film quality. This process is highly sensitive to ambient temperature (T_A) and associated with the effectiveness of intermediate phase formation. Besides the general wisdom that the intermediate phase regulates the initial nucleation by temporarily consuming precursor ions, we find that the intermediate phase plays a key role in guaranteeing high film quality by spatially separating the nuclei to mitigate thermally activated nuclei aggregation. By stabilizing a strongly coordinated intermediate phase, we achieve perovskite solar cells (PSCs) with power conversion efficiencies of 24% to 25%, even T_A elevated to 28 °C. This work offers valuable insights into enhancing the reliability of PSCs and provides a deeper understanding of the role of the intermediate phase in the solution-processing of perovskite films.