The Role of Charged Gap States in Light-Induced Degradation of Single-Junction a-Si:H Solar Cells

Computer simulations of single-junction hydrogenated amorphous silicon (a-Si:H) solar cells with different thickness of the intrinsic layer were carried out in order to study the role of charge gap states in their light-induced degradation. It is demonstrated that it is the decrease of positively charged states above midgap, Dh, and the increase of neutral states around midgap,Dz, and negatively charged states below midgap, De in the intrinsic layer that result in a drop of performance of the solar cells due to light soaking. These changes in the gap states are in accordance with our recent experimental results from the charge deep-level transient spectroscopy on undoped a-Si:H. The experimentally observed changes in the dark and illuminated J-V curves and spectral response could not be simulated with the same set of input parameters by only increasing the defect-state density in the intrinsic layer.