For effectively reducing the off-state signal loss resulting from the a-Si:H thin film transistors' (TFTs) photo leakage current, the a-Si:H TFTs with the use of indium tin oxide as source-drain metal have been fabricated for this study. A remarkable transformation in photo leakage current has been observed under the 3300 cd m2 cold cathode fluorescent lamp (CCFL) backlight illumination. The source-drain barrier height engineering has been proposed for this study. According to the energy band diagram, the barrier height for hole is estimated to be about 3 eV. As a result, the photogeneration holes blocked in the Schottky barrier could effectively result in the different characteristic of photo leakage current.