this research aims to study and discuss the theoretical models and simulation of optoelectronic properties of a-Si-H PIN photosensors based on Shockley-Read-Hall assumptions. The variation of carrier life time, recombination and generation rates as a function of the intrinsic layer (I-layer) thickness will be simulated using MATLAB program. The effects of intrinsic layer thickness on electrons and holes concentration, collection efficiency and short circuit current density have been studied and analyzed. It has been found that as the thickness increased, the parameters: recombination rate, generation rate, internal electric field, electrons and holes concentration, carriers' life times, and short circuit current density, were subjected to some variations.