Balanced-Strength Additive for High-Efficiency Stable Perovskite Solar Cells

Perovskite films prepared using the low-temperature solution method show plentiful defects, especially at grain boundaries and on the surface. A few additives have been exploited to fabricate high-quality perovskite films made up of larger grains with smaller boundaries and surfaces, and hence fewer defects, by slowing down the crystallization process. However, when the grain size becomes too large, the uniformity of the perovskite film is compromised. Herein, an additive, 1-hexanethiol (HA), is developed not only to appropriately enlarge grain size but also to form uniform perovskite films; meanwhile, most bulk defects are effectively passivated, leading to improved perovskite solar cell performance. As predicted by the density functional theory, the HA effectively forms a complex with the PbI2 in the precursor solution, which slowly releases free Pb2+ for controlled crystallization to form optimized perovskite film. The photoluminescence and trap density measurements demonstrate that the defects within perovskite film are significantly reduced owing to fewer grain boundaries, better crystallinity, and more effective passivation by HA. As a result, the efficiency of devices reaches 22.43% with negligible hysteresis. The unencapsulation device retains about 90% of its initial value when exposed to the ambient for 90 days, demonstrating its good stability. This development paves an effective avenue toward high-quality perovskite films for general optoelectronic applications, in particular for high-efficiency solar cells.