Perovskite Seeding Approach of Two-Step Sequential Deposition for Efficient Solar Cells

High-quality perovskite film is critical for efficient perovskite solar cells. However, it is still challenging to obtain high-quality perovskites processed with the sequential deposition method since the intercalation between the lead diiodide and formamidinium-iodide-rich salts is always hampered by unfavorable formation pathways. Herein, we report a perovskite seeding approach to tailor the formation pathway by making biguanide-hydrochloride-containing two-dimensional perovskites before formamidinium-iodide-rich salt deposition, which renders the perovskite films exhibiting improved crystallinities and surface morphologies. Specifically, the crystallization of perovskite films is greatly enhanced, and the average grain size is increased by 2.5 times. Meanwhile, this tailored sequential deposition with biguanide-hydrochloride agents has led to the formation of two-dimensional perovskites present at the grain boundaries of the resultant perovskite, serving as a passivation agent. Our results show a good energy level alignment for the resultant perovskite absorbers. As a result, a champion power conversion efficiency of 22.12% is obtained. The nonencapsulated device retains 94.69% of the initial efficiency after 600 h of storage in the air (relative humidity <30% at 25 °C). Hence, our finding opens an avenue for fabricating high-performance perovskite solar cells.