The fabrication of perovskite films with high crystallization quality, less defects, and fewer grain boundaries (uncoordinated ions) is one critical step to obtain excellent power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In this work, we develop a novel method to control the perovskite growth toward better crystallinity and less defects using iodide ions (I-) and thiourea as additives for the first time (we define ITU for I- and thiourea). Grain boundaries in the perovskite films are significantly reduced compared to the traditional method. Moreover, concentration of the defects in perovskite films is decreased by nearly one-half. Based on high-quality films, the PSCs with a champion PCE of 20.39% present a stabilized output efficiency of 19.26% under one sun illumination compared to that of the control devices (17.75%). The devices also exhibit small hysteresis and excellent long-term and light stability. The devices can retain 80% of the initial PCE after 100 h of light soaking or 30 days of aging in ambient atmosphere. This work not only demonstrates a novel approach to passivate the defects by balancing iodide ions but also offers a strategy to control the perovskite film growth, which can be widely used in photoelectric devices.
Keywords: crystallinity; defect states; iodide ions; light stability; perovskite solar cells.