Room Temperature Formation of Semiconductor Grade α-FAPbI3 Films for Efficient Perovskite Solar Cells

Formamidinium lead iodide (FAPbI(3)) perovskite is a front-runner material for efficient perovskite solar cells (PSCs) due to its high light-absorption coefficient, narrow band gap, and superior photo. stability and thermostability. High-quality FAPbI(3) perovskite formation typically requires an >160 degrees C annealing process to induce phase transition from the photoinactive yellow phase (alpha-FAPbI(3)) to the photoactive black phase (alpha-FAPbI(3)). However, this high-temperature annealing can induce defects in the films and hinders application in flexible solar cells. Here, we report a facile method to fabricate high-quality alpha-FAPbI(3) perovskite films at room temperature, without thermal annealing or vacuum-assisted processes. Combined computational and experimental results reveal the crystallization mechanism of alpha-FAPbI(3) formation at room temperature. We demonstrate PSCs with a power-conversion efficiency of 19.09%, which is the highest efficiency for room temperature PSCs to the best of our knowledge. This study may offer a cost-effective way to fabricate highly efficient PSCs at room temperature.