Efficient Thermally Evaporated γ-CsPbI3 Perovskite Solar Cells

Thin-film deposition by thermal evaporation offers many advantages, yet in the field of perovskite photovoltaics solution-processed devices significantly outperform those fabricated by thermal evaporation. Here, high-quality gamma-CsPbI3 perovskite layers by coevaporation of PbI2 and CsI with a small amount of phenylethylammonium iodide (PEAI) are deposited. It is demonstrated that the addition of PEAI into the perovskite layers leads to a preferred crystal orientation and a far improved microstructure, with columnar domains that protrude throughout the film's thickness. This is accompanied by a reduced density of defects as evidenced by the increase in photoluminescence and decrease in Urbach energy as compared to reference CsPbI3 films. Photovoltaic devices based on the PEAI containing perovskite layers reach up to 15% in power conversion efficiency, thus surpassing not only the performance of reference CsPbI3 devices, but also that of most solution-processed PEAI containing inorganic CsPbX3 (X = Cl, Br, I) perovskite solar cells. Importantly, encapsulated thermally evaporated perovskite devices maintain their performance for over 215 days, demonstrating the stabilizing effect of PEAI on thermally evaporated CsPbI3.