Degradation free SiO2 passivation layer oxidized by TCA process

Degradation of the Si/SiO₂ interface in solar cells induced by sunlight irradiation can be eliminated by controlling the concentration of 1.1.1. trichloroethane (TCA) in the oxidation ambient. Despite the higher carbon concentration, the oxide which was grown 48 hours after the TCA cleaning showed no evident light degradation. A low interface trap density, D_it, was obtained for this Si/SiO₂ interface. Bias light dependence of the surface recombination velocity for such degradation-free SiO₂ layers was intensively analyzed by measuring effective lifetimes. The mechanism that limits fill factors in recent high-efficiency one-sun solar cells is discussed quantitatively in terms of the dependence of the surface recombination velocities on excess carrier concentration. It was clarified that even with such a small D_it, a high surface recombination velocity will result at the SiO₂/Si interface with the excess carrier concentration under Vop condition