In Situ Ionic Liquid Oligomer Encapsulation Enabled Robust Perovskite Single Crystals toward High-Efficiency X-ray Detection

Because of the susceptibility of perovskite single crystals (PerSCs) to moisture- and oxygen-induced degradation, the simultaneous improvement of their environmental durability and optoelectronic properties remains an intractable challenge. Herein, we develop an in situ encapsulation approach for PerSCs using a polymerizable ionic liquid, named 1-vinyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide (Bvim-TFSI), as an additive. Bvim-TFSI addition can facilitate the thermokinetic growth process and eliminate the need for intricate post-treatments owing to its self-cleaning property. More importantly, the in situ radical polymerization of Bvim-TFSI on the crystal surface leads to the formation of an oligomeric encapsulation layer, imparting an enhanced environmental robustness to the as-fabricated PerSC, with no observable degradation after 10 months of air exposure. The resulting MAPbI₃ single crystal exhibits an X-ray detection sensitivity of 1.80 × 10⁵ μC Gy_air^–1 cm^–2 with a low limit of detection of 10.37 nGy_air s^–1. Moreover, the PerSC-based device demonstrates nearly 100% performance retention after 30 days of storage in ambient air without additional protection. This study provides a facile route for the fabrication of high-quality and durable PerSCs toward optoelectronic applications.