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

Abstract The iodide precursor oxidation has persistently plagued solution grown iodine‐based perovskite single crystals (IPSCs) that inevitably introduce undesirable triiodide ion (I 3 − ) 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 I 3 − defects. Typically, the as‐fabricated MAPbI 3 single crystal possesses an extremely low trap density of 3.57 × 10 8 cm −3 and a high carrier mobility‐lifetime ( µτ ) product of 2.74 × 10 −3 cm 2 V −1 , which enables its photodetection capabilities to be on a par with the state‐of‐art MAPbI 3 single crystal photodetectors. This work paves an efficacious and green pathway for high‐quality IPSC fabrication toward advanced optoelectronic utilizations.