The Effects of Grain Boundary and Interface Recombination on the Performance of Thin-Film Solar Cells

The effects of grain boundary and interface minority carrier recombination on polycrystalline thin-film photovoltaic heterojunctions are presented. The grain boundary is modeled accounting for interface states, due to low-, medium- and high-angle grain boundaries. The dark and illuminated diffusion potentials are calculated as functions of interface state densities and carrier concentrations. These are used to estimate the recombination velocities and minority carrier lifetimes. These parameters are, in turn, correlated with the short-circuit currents and open-circuit voltages. The dependence of V_oc upon grain diameter is predicted. Junction interface states are discussed in terms of a dislocation model. The dependence of V_oc, affected primarily through dark reverse current, on the recombination velocity is indicated. The combined effects of grain boundary and interface recombination mechanisms on J_sc is discussed. Data are presented to verify the model based upon the CdS/CuInSe₂ photovoltaic heterojunction.