Sequential Processing: Spontaneous Improvements in Film Quality and Interfacial Engineering for Efficient Perovskite Solar Cells

Planar perovskite solar cells (PSCs) represent a promising alternative to solar cells due to their many advantages. To improve device performance, it is necessary to develop PSCs with good interfacial engineering and film crystallinity, which are two critical aspects of high‐performance PSCs. However, both aspects are relatively independent and difficult to simultaneously enhance. This study reports an effective and universal sequential solution deposition process to specifically address this issue. When the top layer of the hole‐transport material (HTM) is deposited from the dimethylsulfoxide (DMSO) cosolvent, the HTM penetrates a predeposited bottom layer of perovskite (the light‐absorption layer) during the spin‐coating process, resulting in an interdiffusion structure with layer‐evolved nanomorphology. In addition, the cosolvent DMSO captures vacant perovskite CH3NH3+ groups at the boundaries of perovskite grains, resulting in the growth of large‐sized grains. Compared to a conventional device, this new design realizes enhanced optical absorption, reduced crystal defects in perovskite film, tight contact, and well‐matched energy‐level alignment between the perovskite film and the hole‐transport layer (HTL). This strategy enables the fabrication of PSCs with enhanced short‐circuit current density (Jsc), fill factor (FF), and open circuit voltage (Voc), resulting in an enhanced power conversion efficiency (PCE) of 19.40% from 15.29% under standard testing conditions. This sequential deposition represents a feasible route for the preparation of high‐performance PSCs with spontaneous improvements in film quality and interfacial engineering for photovoltaic applications.