TiO2/SnO2 branched heterojunction nanostructure with TiO2 branches on electrospun SnO2 nanofiber (B-SnO2 NF) networks serves as a model architecture for efficient self-powered UV photodetector based on a photoelectrochemical cell (PECC). The nanostructure simultaneously offers a low degree of charge recombination and a direct pathway for electron transport. Without correcting 64.5% loss of incident photons through light absorption and scattering by the F-doped tin oxide (FTO) glass, the incident power conversion efficiency reaches 14.7% at 330 nm, more than twice as large as the nanocrystalline TiO2 (TiO2 NC, 6.4%)-film based PECC. By connecting a PECC to an ammeter, the intensity of UV light is quantified using the output short-circuit photocurrent density (Jsc) without a power source. Under UV irradiation, the self-powered UV photodetector exhibits a high responsivity of 0.6 A/W, a high on/off ratio of 4550, a rise time of 0.03 s and a decay time of 0.01 s for Jsc signal. The excellent performance of the B-SnO2 NF-based PECC type self-powered photodetector will enable significant advancements for next-generation photodetection and photosensing applications.