Unlocking Quantum Confinement in Two-/Three-Dimensional Tin-Based Perovskites for High-Efficiency Photovoltaics

Two-dimensional/three-dimensional (2D/3D) mixed tin halide perovskites are promising lead-free photovoltaic absorbers, but uncontrolled crystallization produces excessive low-n phases that impede charge extraction due to a quantum confinement effect. Here, we employ 1,4-benzenediammonium iodide (1,4-BDI2) as a multifunctional additive to regulate crystallization, phase distribution, and defects. The additive modulates precursor colloid assembly and retards low-dimensional crystal growth, yielding dense films dominated by highly oriented three-dimensional perovskites with suppressed n = 1 and reduced n = 2 phases. Meanwhile, 1,4-BD2+ cations and unincorporated organic ligands accumulate at grain boundaries to form a passivating complex that passivates deep-trap states and forms favorable interfacial energy-level alignment to promote charge transfer. Consequently, inverted tin perovskite solar cells achieve a power conversion efficiency of 15.94% and an open-circuit voltage of 0.91 V, together with improved operational and storage stability. This work establishes an integrated molecular strategy for phase regulation and defect passivation in efficient lead-free photovoltaics.