Computer simulation of the a-Si:H p-i-n solar cell performance sensitivity to the free carrier's mobilities, the capture cross sections and the density of gap states

This paper deals with the effects of some material properties on the J-V characteristic of hydrogenated amorphous silicon (a-Si:H)-based p-i-n solar cell. The factors considered are the free carrier's mobilities, the capture cross sections of the gap states and the bulk density of states (i-layer DOS). Accurate investigation of the cell photo-parameters' sensitivity to these factors is carried out using a simulation program, previously developed by our group. The model is based on a complete set of Poisson and carrier continuity equations taking into account the defect pool model for the a-Si:H gap density of states. Ours results reveal the important role of the hole mobility when it takes low values, as given frequently in the literature, on the recombination rate at interface regions as well as in the bulk. This considerably affects the short-circuit current density (Jsc), the open-circuit voltage (Voc), the fill factor (FF) and the conversion efficiency (η). Moreover, by changing separately the capture cross sections of the band's tails and those of dangling bonds we found more precisely that Jsc, Voc, and η are more sensitive to the interface recombination while the FF seems to depend more on the bulk recombination. Ultimately, when the i-layer DOS is higher than 1016 cm-3, the recombination rate, which was first limited by the valence band tail's states, becomes limited by the dangling bond's states. Then, any further increase significantly deteriorates the solar cell performance