A laminar MAPbBr3/MAPbBr3-xIx graded heterojunction single crystal for enhancing charge extraction and optoelectronic performance

Halide perovskite single crystals (SCs) have recently been regarded as a promising candidate in optoelectronic devices by virtue of their remarkable intrinsic properties. Herein, a laminar MAPbBr(3)/MAPbBr(3-x)I(x) (MA = CH3NH3+) graded heterojunction single crystal (GHSC) with a thickness of about 11 m and an area of 4 x 5 mm has been synthesized via a space-limited inverse temperature crystallization growth method and a gaseous halide exchange process in sequence. Compared to the pristine MAPbBr(3) SC, such a MAPbBr(3)/MAPbBr(3-x)I(x) GHSC possesses graded valence band alignment via a halide gradient distribution, which significantly enhances the hole extraction and accelerates carrier transport, leading to a high-performance perovskite SC photodetector with an improved external quantum efficiency of approximate to 170% at -2 V and an impressively rapid response speed of 0.56 s. Our results provide a promising strategy to solve the carrier extraction obstacle and suppress recombination loss, which opens potential optoelectronic applications of laminar heterojunction SCs.