Mobility and optical gaps in different a-Si:H based materials and their impact on cell performance

This work investigates the correlation between the “mobility gaps” (E_μ) and the “optical gaps” (E_OPT) of a-Si:H materials and the open circuit voltages (V _oc) of their standard solar cell structures. The study was carried on both RF and DC glow discharge materials using p-i-metal Schottky barrier and p-i-n cell structures having abrupt junctions formed with p-a-Si:C,H layers. Because the correlation between E_OPT and E_μ in amorphous materials has not been established, a self-consistent approach is presented here which can be applied to both a-Si:H and a-Si:C,H materials. The self-consistency of the E_μ results obtained using internal photoemission with the activation energies of the dark reverse currents in the p-i-metal structures is also presented. It is found that hydrogen dilution has a large effect on “displacing” E_μ further away from E_OPT, which is consistent with higher V_oc observed with such materials