NOVELTY - The method (200) involves forming an absorber layer comprising an absorber material above a substrate. A buffer layer is formed (206) over the absorber layer. A front transparent layer is formed (208) over the buffer layer. The photovoltaic device is exposed (210) to heat or radiation at a temperature from about 80 degrees C to about 500 degrees C for a period of time, subsequent to forming a buffer layer over the absorber layer. A back contact layer is formed (202) above a substrate before forming the absorber layer above the substrate.    USE - Method for fabricating photovoltaic device (claimed) e.g. solar cells.    ADVANTAGE - The internal quantum efficiency of the photovoltaic device is improved through passivation of the junction and an increase in the depletion region in the p-n or n-p junction formed between the absorber layer and the buffer layer. Thermal energy or radiation excitation is used to provide controlled ion diffusion from the buffer layer to the absorber layer to decrease or eliminate defects and resulting recombination. Intrinsic zinc oxide (ZnO) having high electrical resistance mitigates the shunt current and reduces formation of the shunt paths. Both high electrical conductivity and high optical transmittance of the transparent conductive layer improve photovoltaic efficiency. An improvement of 5% in internal quantum efficiency (IQE) resulting from the thermal annealing results in significant improvement in the photo-carrier collection, the effective short circuit current and the conversion efficiency.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a photovoltaic device.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating the method for fabricating photovoltaic device.    Method for fabricating photovoltaic device (200)    Step for forming back contact layer (202)    Step for forming buffer layer over absorber layer (206)    Step for forming front transparent layer over the buffer layer (208)    Step for exposing photovoltaic device to heat or radiation at specific temperature (210)