The influence of growth temperature on the microstructure of hydrogenated amorphous silicon (a-Si:H) layers deposited on glass substrates at different temperature has been examined by means of X-ray diffraction and positron annihilation techniques in order to relate the initial configuration of the defect and the degree of ordering in the material to the growth temperature and the effects of light-soaking. The effect of light soaking, using a simulated day light spectrum, on the crystallinity, defect structure and total hydrogen concentration is being investigated in an ongoing project.