In-sensor broadband convolutional processing (BCP) holds great significance to the advancement of high-precision image recognition for remote sensing and environmental monitoring. Two-dimensional (2D) heterostructures offer abundant band alignment configurations with electrical tunability, which is promising to implement the in-sensor BCP at hardware level. Huge efforts have been devoted to developing 2D heterostructures based intelligent edge devices for BCP, which however either lack the potential for scalability and reproducibility, or require high processing temperature. Here, we demonstrate a PtSe₂/WSe₂ heterostructure based Schottky diode fabricated by using thermal-assisted conversion (TAC) technique, which converts the pre-deposited Pt films into PtSe₂ via the controllable selenization process with complementary metal-oxide-semiconductor (CMOS) back-end-of-line (BEOL) compatible thermal budget. The TAC-PtSe₂ in various thicknesses demonstrate high crystalline nature and low contact resistance (425 Ω·μm), facilitating an atomically sharp interface and gate-tunable band alignment. Such characteristics give rise to polarity-changeable built-in electric field, resulting in a remarkable rectification ratio approaching ~ 10⁵. Moreover, the positive–negative switching of the photoresponse with linear intensity dependence is achieved across a wide spectrum from ultraviolet to near-infrared light, which is desirable in constructing various convolution kernels for BCP tasks. A hyperspectral remote sensing image is adopted to demonstrate the BCP operations including edge detection and sharpness, where the outputs are of comparable quality with the simulated results. Our work envisions a CMOS-compatible approach for fabricating 2D Schottky diodes with tunable band alignment, offering a viable route for the scalable hardware implementation of broadband image processing units.