Ultraviolet photodetectors (UVPDs) based on SZTO thin-film transistors (TFTs) with a different carrier concentration of double channel layer (DCL) structure and NiO capping layer (CL) are reported. Experimental results indicate that proposed SZTO TFT UVPD with a 30-nm-thick upper layer stacked on a 50-nm-thick bottom layer and a patterned NiO CL has excellent detection performance in photoresponsivity and photosensitivity up to 1672 A/W and 1.03×10^7 A/A under illuminated at 275 nm, which increased by about 272 and 137 times than the conventional SZTO TFT with Tch of 30 nm. These improvements are due to the use of DCL increase the space for UV illumination and the use of NiO CL lowers the dark current and causes a considerable negative threshold voltage shift under UV irradiation to significantly boost the photocurrent.