Epitaxial Growth of Lead-Free 2D Cs 3 Cu 2 I 5 Perovskites for High-Performance UV Photodetectors.

The all-inorganic lead-free Cu-based halide perovskites represented by the Cs-Cu-I system, have sparked extensive interest recently due to their impressive photophysical characteristics. However, successive works on their potential application in light emission diodes and photodetectors rely on tiny polycrystals, in which the grain boundaries and defects may lead to the performance degradation of their embodied devices. Here, 2D all-inorganic perovskite Cs 3 Cu 2 I 5 single crystals are epitaxially grown on mica substrates, with a thickness down to 10 nm. The strong blue emission of the Cs 3 Cu 2 I 5 flakes may originate from the radiative transition of self-trapped excitons associated with a large Stocks shift and long (microsecond) decay time. Ultravioelt (UV) photodetectors based on individual Cs 3 Cu 2 I 5 nanosheets are fabricated via a swift and etching-free dry transfer approach, which reveal a high responsivity of 3.78 A W -1 (270 nm, 5 V bias), as well as a fast response speed (τ rise  ≈163 ms, τ decay  ≈203 ms), outperforming congeneric UV sensors based on other 2D metal halide perovskites. This work therefore sheds light on the fabrication of green optoelectronic devices based on lead-free 2D perovskites, vital for the sustainable development of photoelectric technology.