γ-Valerolactone Enabling Spontaneously Inhibited Iodide Oxidation for High-Quality Perovskite Single Crystal Fabrication

The iodide precursor oxidation has persistently plagued solution grown iodine-based perovskite single crystals (IPSCs) that inevitably introduce undesirable triiodide ion (I₃⁻) defects and severely hindering crystal quality, despite IPSCs having garnered remarkable progress in multifarious photoelectronic applications. In this work, the spontaneously inhibited iodide oxidation is discovered in an eco-friendly solvent, γ-Valerolactone (GVL), and demonstrates a universal solution approach for fabricating high-quality IPSCs. Compared to the routine γ-Butyrolactone (GBL) system, GVL provides a lowered growth temperature and a significantly broadened inverse temperature operation window, thereby improving the theoretical utilization rate of perovskite precursors up to 88.6%. More importantly, due to its higher open-ring hydrolysis energy, GVL can spontaneously inhibit the iodide precursors oxidation without any additional reductant and therefore effectively prevent the forming I₃⁻ defects. Typically, the as-fabricated MAPbI₃ single crystal possesses an extremely low trap density of 3.57 × 10⁸ cm⁻³ and a high carrier mobility-lifetime (µτ) product of 2.74 × 10⁻³ cm² V⁻¹, which enables its photodetection capabilities to be on a par with the state-of-art MAPbI₃ single crystal photodetectors. This work paves an efficacious and green pathway for high-quality IPSC fabrication toward advanced optoelectronic utilizations.