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Role of charged defects in the light-induced degradation of single junction a-Si:H solar cells

Our experimental results from the charge deep-level transient spectroscopy on undoped hydrogenated amorphous silicon (a-Si:H) reveal that during light soaking positively charged states above midgap, D/sub h/, are annihilated while neutral states around midgap, D/sub z/, are created. Using computer simulations we demonstrate that it is the annihilation of the positively-charged D/sub h/ states that causes a drop in the spectral response of a-Si:H solar cells in the short wavelength region (/spl lambda/<550 nm) and the change in the slope of the dark J-V curve under light exposure, as observed experimentally. Only increasing the defect-state density in the intrinsic layer, which reflects the creation of additional defects, could not simulate these changes.