Simultaneous Surface Modification and Defect Passivation on Tin Oxide–Perovskite Interfaces using Pseudohalide Salt of Sodium Tetrafluoroborate
Kay Thi Soe, Somya Thansamai, Non Thongprong, Waranchit Ruengsrisang, Ibrahim Adam Muhammad, Ekkaphop Ketsombun, Ratchadaporn Supruangnet, Anusit Kaewprajak, Pisist Kumnorkaew, Viboon Saetang, Thidarat Supasai, Nopporn Rujisamphan
Abstract
Passivating electron‐transporting layers (ETLs) with alkali salts have demonstrated a facial approach that is essential in healing defective surfaces, consequently improving the functionality and stability of perovskite‐based solar cells (PSCs). Herein, the pseudohalide salt of sodium tetrafluoroborate, whose anions have a higher electronegativity than other halide salts (i.e., iodide and chloride), with the potential to passivate the surface of tin oxide while enhancing the optoelectronic properties of a perovskite film, is presented. Meanwhile, the density functional theory calculations show that BF 4 − /F − ions exhibit a robust ionic interaction with an uncoordinated Sn 4+ site. In contrast, the Na ion is bound to an oxygen atom of the OH − group, which helps reduce surface defect states and improves charge transfer properties. Thus, the best PSC exhibits a current density of 23.51 mA cm −2 , an open‐circuit voltage of 1.10 V, and an excellent fill factor of 80.48, providing an efficiency of 20.82%, which exceeds that of a control device (18.38%). Importantly, the retention of the power conversion efficiency on NaBF 4 ‐based PSCs without encapsulation is 18.44% after 1000 h of aging under ambient conditions, whereas the retention of a control device is only 16.08%.