Recombination velocity at grain boundaries in polycrystalline Si under optical illumination

Calculations have been performed of recombination currents at grain boundaries in polycrystalline silicon for three different energy distributions of recombination centers. These results show that the relationship between the recombination current density and the minority carrier concentration at the grain boundary, under conditions of optically induced separation of the electron and hole quasi-Fermi levels, is highly nonlinear. It is further shown that the recombination velocity is an increasing function of the minority carrier concentration at the grain boundary. In this calculation, it is necessary to relax the earlier assumptions [1] of equal capture cross sections for electrons and holes of the grain boundary recombination centers and [2] of a flat minority-carrier quasi-Fermi level in the space-charge region, since these assumptions prove to be unjustified in the general case.