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2D p–n homojunctions exhibit distinctive structural properties, including continuous energy band structure and perfect lattice matching, making them promising for the design of optoelectronic and electronic devices. Herein, we present a straightforward approach to fabricate a highly sensitive, self-driven photodetector based on a WS2 homojunction. The p-doping on the WS2 interface is easily achieved through water treatment, eliminating the need for chemical dopants. There is an evident reversal of polarity in the WS2 devices treated as compared to the intrinsic WS2. Particularly, the mobility of the weak p-doping WS2 field-effect transistor is 0.65 cm2 V−1 s−1, and the on/off ratio can reach 103 after water treatment. The WS2 p–n homojunction can be prepared by local boron nitride covering on n-type WS2. Moreover, the lateral p–n homojunction demonstrates remarkable photovoltaic properties, including a maximum short-circuit current of 7.55 nA and an open-circuit voltage of 0.15 V. Additionally, due to the effective in-plane built-in field, the device achieves a high Ilight/Idark ratio of nearly 105, a high specific detectivity of 5.8 × 1011 Jones, and a large linear dynamic range of 60 dB. This investigation offers a promising facile and soft avenue for the design of high-performance self-driven homojunction photodetectors with potential applications in low-consumption optoelectronics. [ABSTRACT FROM AUTHOR]