High-performance all-inorganic perovskite-based metal/semiconductor/metal (MSM) photodetectors with a bilayer composite film of mesoporous TiO2 and CsPbBr3 quantum dots as a photosensitizer were prepared. The photodetectors demonstrated significantly improved on/off ratios of nearly three orders of magnitude compared to those of pure bromine-based perovskite nanocrystal photodetectors with an MSM structure.