Surface Energy Regulated Growth of α-phase Cs 0.03 FA 0.97 PbI 3 for Highly Efficient and Stable Inverted Perovskite Solar Cells.

Methylammonium (MA) free formamidine (FA) dominated Cs x FA (1-x) PbI 3 is rising as the most promising candidate for highly efficient and stable perovskite solar cells. However, the growth of high quality Cs x FA (1-x) PbI 3 black phase perovskite structure without ion doping in lattice remains to be a challenge. Herein, we synthesized a propeller-shaped halogenated tertiary ammonium showing high binding energy on perovskite surface and large steric hindrance. This molecule can significantly reduce the barrier of high surface energy that suppress the growth of α-phase Cs x FA (1-x) PbI 3 structure. As a result, α-phase structure can be formed at room temperature, which can further act as seed for the growth of high-quality film. Solar cells based on the film show a record efficiency up to 23.6% for MA free Cs x FA 1-x PbI 3 solar cells with inverted structure, and excellent stability at 85°C over 200 hours. This article is protected by copyright. All rights reserved.