Attaining Long-Term Stability, Pure Phase and High Efficiency Beyond 23% in FAPbI₃ Perovskite Solar Cells via CsSCN Additives

Perovskite solar cells (PSCs) have garnered substantial attention due to their exceptional power conversion efficiency (PCE) and cost-effective fabrication. Among the semiconductors, the cubic α-phase of formamidinium lead triiodide (FAPbI₃) has emerged as the most promising choice for creating highly efficient and stable perovskite solar cells. Maximizing the performance of this material is of paramount importance to the perovskite research community. However, thin FAPbI₃ films tend to undergo a phase transition from the photoactive black α-phase to an inactive yellow δ-phase when the temperature drops below 150°C. In this study, we explored the impact of introducing cesium thiocyanate (CsSCN) into the perovskite precursor solution. This addition facilitated the creation of a stable perovskite film with a larger grain size, even at a lower temperature of 100°C. The role of SCN^– anions proved critical in promoting the formation and stabilization of α-FAPbI₃ below its thermodynamic phase transition temperature. Notably, the inclusion of the CsSCN additive resulted in a remarkable enhancement of the power conversion efficiency (PCE) of the devices, exceeding 23%. This performance improvement can be attributed to several factors, including the formation of a stable perovskite film with larger grains, a film that is more uniform and compact, reduced defects, and improved charge transport properties. Furthermore, X-ray diffraction analysis verified that the CsSCN additive facilitated the formation of pure α-phase perovskite crystals, eliminating undesirable secondary phases. These findings underscore the effectiveness of CsSCN as an additive in achieving stable and high-performance α-FAPbI₃ perovskite solar cells with a pure phase composition.<br/>Keywords: Perovskite solar Cells, Formamidinium lead triiodide, Cesium thiocyanate.