Dual-functional TFSI additive engineering for (100)-oriented wide-bandgap perovskite solar cells with enhanced efficiency and stability

Controlling crystal orientation in wide-bandgap (WBG) perovskite solar cells (PSCs) is pivotal for optimizing performance and stability, yet achieving this remains a significant challenge. Herein, bis(trifluoromethanesulfonyl)imide (TFSI) was employed as an in-situ additive to modulate the crystallization of WBG films. TFSI molecule induced (100)-preferred orientation through strong interactions with the perovskite lattice, resulting in enhanced film homogeneity in terms of vertical and horizontal scale. Meanwhile, the multifunctional groups of fluoride, amino, and sulfonate effectively passivation both positive and negative defects, reducing the defect state density and carrier non-radiative recombination. This dual functionality mitigates phase segregation and lattice mismatch, significantly improving film stability. The resultant 1.77 eV WBG PSCs achieve a champion efficiency of 18.88% with a high open-circuit voltage of 1.322 V. Additionally, TFSI-treated films exhibit suppressed halide segregation under illumination and retain perovskite phase for over 120 days in ambient conditions. This work highlights the importance of oriented crystallization and defect passivation in enhancing the efficient perovskite photovoltaics.