In this study, indium gallium zinc oxide (InGaZnO [IGZO]) active layer capped with an ultrathin p-type stannous oxide (SnO) is demonstrated to be a thin film transistor (TFT) for color scanning and photosensing device applications. Typically, the sole IGZO-based TFT is blind to visible light and hard to be developed for visible light sensing. The combination of IGZO and SnO layers can extend the light detection spectrum into visible light wavelengths and ameliorate the photosensing characteristics. The optical responsivity and signal to noise ratio can even be enhanced from 1.05 × 10 −2 to 398.02 A W −1 and from 2.1 × 10 1 to 6.8 × 10 5 with at least four orders of magnitude, respectively. With the detailed material analysis and physical model discussed, it suggests that the large amount of additional light-excited carrier generated in the capping layer is the key factor for the significant improvement. Furthermore, the phenomenon of persistent photoconductivity can be effectively suppressed by its natural recombination under the heterojunction structure without applying charge-pumping method. The electrical uniformity of the sensor device is also highly potential for the next-generation displays integrating the photosensing functions.