Enhancing Crystallization and Optimizing the Buried Interface via Hydrophobic Trifluoromethyl Molecules for Efficient Sn–Pb Perovskite and All‐Perovskite Tandem Solar Cells

ABSTRACT Hybrid tin‐lead (Sn–Pb) perovskites, with bandgaps tunable down to 1.25 eV, hold great promise for high‐efficiency photovoltaics. However, their performance is often hampered by the buried interface defects and instability induced by the commonly used hole‐transport layer (HTL), Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), which suffers from intrinsic hygroscopicity and non‐uniformity. Here, we introduce a multifunctional molecule, (S)‐methyl 2‐amino‐2‐(3‐fluoro‐4‐(trifluoromethyl)phenyl)acetate hydrochloride (MTFP), into PEDOT:PSS to address these issues. MTFP mitigates the hygroscopicity and improves the uniformity of PEDOT:PSS while concurrently modifying the buried interface. It regulates the quinoid structure proportion in PEDOT, optimizes the work function of the HTL, and passivates interfacial defects. These actions collectively enhance charge extraction and promote the crystallization of the overlying perovskite film. Furthermore, the hydrophobic trifluoromethyl group in MTFP significantly boosts the environmental stability of the device. Consequently, the optimized Sn–Pb perovskite solar cells achieve a champion power conversion efficiency of 23.36%, with a high open‐circuit voltage of 0.88 V. This strategy also enables a two‐terminal all‐perovskite tandem solar cell with a remarkable PCE of 28.67%.