Sub-band gap photocurrent in reverse biased p-i-n a-Si:H solar cells

The spectra of the primary photocurrent excited by subband-gap radiation in p-i-n solar cells were simulated by solving the full set of transport equations. The expressions of the distribution function and of the recombination rate were modified to take into account the effects of subband-gap generation. The relationship between these spectra and the absorption coefficient was analyzed for different sets of the parameters involved in the simulation. It was concluded that the absorption coefficient as derived from the primary photocurrent is a good estimate of the absorption coefficient in the i-layer. In order to verify these concepts, measurements of the primary photocurrent on different kinds of p-i-n solar cells were performed