Room temperature photoluminescence studies of a-Si:H/c-Si heterodiodes in open circuit, short circuit, and maximum power point operation

We have quantitatively analyzed the splitting of the quasi-Fermi levels in a-Si:H/c-Si heterojunctions, and in corresponding c-Si absorber wafers at AM1-equivalent photon fluxes by room temperature photoluminescence. For the determination of bulk and surface properties of the (p)-c-Si absorbers we have studied photoluminescence yields from c-Si wafers with different treatments of the originally optimally SiO₂-passivated crystalline Si surface, such as etching, and metallization. Furthermore we have monitored photoluminescence from a-Si:H/c-Si-heterojunctions under identical conditions with varying carrier extraction rates, which means differing modes of operation between open (v_oc), and short circuit (i_sc). From ratios of luminescence-yields Y_pl(0,v_oc)Y_pl(i,v) emitted from the illuminated diodes we see additional recombination undoubtedly introduced by defect states at the a-Si:H/c-Si interface. We estimate their densities to about 10¹³ cm^-2.