Crystallization Control via Sulfonic Zwitterions for Inverted CsPbI₃ Perovskite Solar Cells with Efficiency over 22%

The inverted inorganic CsPbI 3 perovskite solar cells (pero-SCs) show lower efficiency compared to the organic–inorganic hybrid pero-SCs, mainly due to its wide bandgap and poor fill factor (FF). Here, by doping a multifunctional additive, 4-(1,3,5-Triaza-7-phosphaadamantan-1-ium-1-yl)butane-1-sulfonate (PTABS), the compact perovskite film forms and grows into large grains during thermal annealing through the ripening process. Moreover, the evaporation of DMAI is accelerated owing to the hydrogen bond formed between DMAI and PTABS, which limits the invasion of moisture during annealing. After the evaporation of DMAI, the remaining PTABS coordinates with the Pb 2+ ions and reduces the defects. Consequently, a high FF of 86.17% is reached, and the power conversion efficiency of the inverted CsPbI 3 pero-SCs is improved to 22.09%. The stability is also improved, owing to the decreasing defects. This work emphasizes the significance of controlling the crystallization process in improving the efficiency of inorganic CsPbI 3 pero-SCs.