An investigation of spin dependent recombination processes in p+in+ a-Si:H solar cell by photovoltaic detection of magnetic resonance (PDMR) is reported. The study indicates that the PDMR signals for various solar cells made by different technology have different g-values and line shapes, so the dominant recombination processes are different. The influence of the speed of growth, substrate temperature and intrinsic thickness of a-Si:H film on solar cell properties is discussed in terms of the PDMR results.