Polarity Engineering to Optimize the Crystallization Process of Tin Halide Perovskites for Photovoltaic Applications

Abstract

Tin-based perovskites usher in a promising avenue for eco-friendly photovoltaics. However, their further development is hindered by the intrinsic issues of easy Sn²⁺ oxidation and the difficulty in controlling crystallization. In tin-based perovskite solar cells (TPSCs), zwitterionic additives can ameliorate perovskite films through hydrogen bonding and coordination with components of perovskite. Yet, the role of additive dipole moments remains underexplored. Herein, the critical role of zwitterionic additive polarity in modulating the performance of TPSCs is systematically investigated through polarity engineering. Polarities of zwitterionic additives (β-alanine (β-Ala), 2-aminoethylsulfonic acid (ACES), and 2-aminoethylphosphate (2-AEP)) are regulated by introducing distinct acid groups. Among them, β-Ala, with an optimal dipole moment of 5.35 D, forms optimal hydrogen bonds and moderate coordination interaction with Sn²⁺, resulting in a lower absolute zeta potential of the solution colloid. Attributed to more uniform colloid size and larger colloid particles, the β-Ala-Sn perovskite exhibits faster uniform nucleation and delayed crystallization kinetics. The optimized perovskite film demonstrates excellent crystallinity, prolonged carrier lifetime, and reduced defect density, along with improved energy level matching. Consequently, the optimized device achieves an enhanced power conversion efficiency of 8.75% and maintains 85% of its initial efficiency after 2000 h of storage in a nitrogen environment.