Linearly Tailored Work Function of Orthorhombic CsSnI₃ Perovskites

Currently, the green tin halide perovskites are emerging as one of alternatives to their toxic lead halide counterparts. However, the recognized big problem hindering their application in photovoltaic devices is their inferior open-circuit voltage, which could be effectively addressed by tuning work function (Φ). Herein, we propose a strategy for tailoring the Φ of γ-CsSnI3 via surface passivation with phenylethylammonium (PEA+) and its halogen derivatives (XPEA+) by first-principles calculations. The Φ of γ-CsSnI3 is tightly correlated with the surface dipole, while the contributions from surface structure relaxation and charge exchange are negligible. Accordingly, the Φ can be linearly aligned with a slope of −1.435 and Adj. R2 of 0.995 from 1.74 to 5.28 eV as a function of surface dipole and ligand layer coverage. Consequently, the reduced Φ causes a downward band bending to facilitate electron transfer with enhanced VOC, underscoring their potential in efficient environmentally friendly solar cells.