A crystal-growth boundary-fusion strategy to prepare high-quality MAPbI3 films for excellent Vis-NIR photodetectors

Rendering high-quality perovskite films is integral for excellent performance of optoelectronic devices and highly challenging as well. Here, we establish a two-round pressure-assisted solvent-engineering (TPS) strategy to achieve remarkable enhancement in grain size (~400 μm 2 ), crystallinity , orientation and, especially, boundary fusion. Crystal growth and boundary welding of MAPbI 3 grains are mainly attributed to pressure-enhanced ion diffusion and defect elimination, which facilitates lateral enlargement of grains and formation of ultra-smooth film. Dramatic diminution of trap density determines long carrier lifetime and improved lateral charge transport, as demonstrated by the superior performance of MAPbI 3 -based photodetectors , e.g. ultrahigh on/off ratio (~10 6 ), good stability, fast response, high responsivity and high detectivity (1.3 × 10 14 Jones). When upconversion nanoparticles are uniformly assembled on the high-quality MAPbI 3 films, interestingly, the hybrid device exhibits dominantly elevated photoelectric capability in near infrared range (NIR, 980 nm) with long-term stability in ambient air. The results and method pave a novel way for ongoing fabrication of efficient and stable optoelectronic devices based on high-quality perovskite films.