| Summary: | Summary: Formamidinium lead iodide (FAPbI3) perovskite is a front-runner material for efficient perovskite solar cells (PSCs) due to its high light-absorption coefficient, narrow band gap, and superior photostability and thermostability. High-quality FAPbI3 perovskite formation typically requires an >160°C annealing process to induce phase transition from the photoinactive yellow phase (δ-FAPbI3) to the photoactive black phase (α-FAPbI3). 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 α-FAPbI3 perovskite films at room temperature, without thermal annealing or vacuum-assisted processes. Combined computational and experimental results reveal the crystallization mechanism of α-FAPbI3 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.
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