Abstract: In order to solve the problem of dark current increase caused by disordered interface state in two dimensional (2D)/ three dimensional (3D) heterojunction photodetectors, an interface performance optimization strategy was proposed for in-situ oxidation of MXene to TiO₂. Treating MXene with oxygen plasma, MXene/TiO₂/Si vertical heterostructures were prepared, in which MXene was arranged as a transparent electrode to form a Schottky contact with n-type Si, to promote the extraction and separation of photogenerated carriers within the formed electric field. To analyze the heterostructure, the cross-sectional element token and energy band alignment theory were used to prove the TiO₂ barrier layer introduced by in-situ oxidation of optimizing the interface properties between MXene and Si. The test results show that the dark current of the optimized photodetector can be reduced by one order of magnitude, and the response time of the photodetector can reach up to 0.72 ms and the photoresponse can achieve as high as 524.8 mA/W under illuminating of 470 nm wavelength.