Dopamine Hydrochloride-Assisted Synergistic Modulation of Perovskite Crystallization and Sn²⁺ Oxidation for Efficient and Stable Lead-free Solar Cells

Tin perovskites have received great concern in solar cell research owing to their favorable optoelectronic performance and environmental friendliness. However, due to their poor crystallization and easy oxidation, the performance improvement for tin-based perovskite solar cells (TPSCs) is rather challenging. Herein, reductive 3-hydroxytyramine hydrochloride (DACl) with NH2·HCl and phenol groups as co-additives with SnF2 is added into the precursor to modulate perovskite crystallization and inhibit Sn2+ oxidation for high-performance TPSCs. The Lewis base group of NH2 HCl in DACl could bind to perovskite lattices to modulate the crystallization with suppressed defects in the bulk and grain boundary, whereas reductive phenol groups effectively constrain the Sn2+ oxidation. Moreover, the undissociated DACl decreases the supersaturated concentration of tin perovskite solution and creates a pre-nucleation site for rapid nucleation to further regulate crystallization. Consequently, the DACl-derived TPSCs achieve a high power-conversion efficiency (PCE) that reaches up to 11%. More impressively, the device remains at 84% of the initial PCE after full-sun illumination in N2 over 600 h without being encapsulated. This DACl-based synergistic modulation of a lead-free perovskite demonstrates a feasible approach using one molecule with different functional groups to manipulate crystallization, Sn2+ oxidation, and defect reparation of tin perovskite films, providing a critical guideline for constructing high-quality perovskites by multifunctional additives with high photovoltaic performance.