Decoupling Nucleation and Growth of Crystal for DMSO-Free Self-Assembly Tin Perovskite Films and Their Optoelectronic Application

Tin (Sn)-based perovskites show significant potential in lead-free perovskite optoelectronics. Currently, the spin-coating method combining DMSO co-solvent and antisolvent-dropping has been adopted to produce Sn-based perovskite films. However, DMSO intrinsically oxidizes Sn²⁺ while fast antisolvent-dropping causes serious coupling between crystal nucleation and growth, leading to the easy formation of defects and poor stability of Sn-based perovskite films. Herein, hydrazine acetate (HAAc) ionic salt, possessing strong coordination ability with Sn²⁺, is developed to stabilize Sn²⁺ and decouple the crystallization by promoting pre-formed crystals (PFCs) in precursor solution and enabling the self-assembly of PFCs during spin-coating. The HA_xFA_1-xSnI₃ films fabricated by this PFCs self-assembly technique show tunable bandgap, low defect density, and oriented crystals, producing optoelectronic devices with decent photovoltaic and electroluminescence performance. The DMSO-free one-step film-forming enabled by HAAc-assisted crystallization decoupling can open up new avenues for facile and low-cost manufacturing of efficient and stable optoelectronic devices adopting Sn-based perovskite films.