Compensation of the dangling-bond space charge in amorphous silicon solar cells by graded low-level doping in the intrinsic layer

The compensation of the dangling-bond space charge in amorphous silicon <i>p-i-n</i> solar cells by graded, low-level doping in the intrinsic layer is discussed and demonstrated experimentally. Carrier collection in <i>p-i-n</i> cells without doping indicates that the degraded state space charge is largely positive, and thus that boron doping should be beneficial. Solar cells with linearly decreasing boron doping profiles are shown to yield a homogeneous collection in the intrinsic layer, and a red light conversion efficiency superior to that of undoped cells after light soaking. Also, the optimal doping concentration is shown to be a direct measure of the degraded state defect density.