Root cause for the difference in photovoltaic parameters of perovskite solar cells prepared by one- and two-step processes

Benefiting from good solubility of metal halide perovskites, low-temperature solution processes (including one- and two-step spin-coating) have become the most common approach for perovskite solar cells (PSCs). However, one confusing issue is that what are specifically effective strategies for the one-step process may not be applicable for the two-step process, and vice versa. Herein, the PSCs with the same perovskite composition and device configuration were prepared by one- and two-step processes, respectively. The results indicated that high performance PSCs with comparable power conversion efficiency over 22% were achieved by both methods, while the detailed photovoltaic parameters varied greatly depending on the one- or two-step process. Compared to the one-step counterpart, the two-step processed PSCs exhibit lower open-circuit voltage and fill factor, but superior short-circuit current, which was in-depth interpreted in terms of the crystalline growth mode, optical properties, defect types, and carrier transport mechanisms related to a perovskite film surface (including a top and a bottom surface). Understanding the root cause for such differences would be central toward identifying what is really crucial for further producing high performance PSCs.