Aqueous Phase Exfoliating Quasi-2D CsPbBr Nanosheets with Ultrahigh Intrinsic Water Stability.

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have emerged as attractive optoelectronic materials due to the excellent optical and electronic properties. However, their environmental stability, especially in the presence of water, is still a significant challenge for their further commercialization. Here, ultrahigh intrinsically water-stable all-inorganic quasi-2D CsPbBr nanosheets (NSs) via aqueous phase exfoliation method are reported. Compared to conventional perovskite NCs, these unique quasi-2D CsPbBr nanosheets present an outstanding long-term water stability with 87% photoluminescence (PL) intensity remaining after 168 h under water conditions. Moreover, the photoluminescence quantum yields (PLQY) of quasi-2D CsPbBr NSs is up to 82.3%, and these quasi-2D CsPbBr NSs also present good photostability of keeping 85% PL intensity after 2 h under 365 nm UV light. Evidently, such quasi-2D perovskite NSs will open up a new way to investigate the intrinsic stability of all-inorganic perovskites and further promote the commercial development of perovskite-based optoelectronic and photovoltaic devices.