Light Induced Degradation in Silicon Heterojunction Solar Cells

We report on our study of the effects of light/excited carriers on the degradation of silicon heterojunction solar cells. We used a unique combination of molecular dynamics, machine learning, density functional theory, stochastic and analytical modeling to perform a comprehensive study on the effects of photo-excited carriers on the degradation of the c-Si/a-Si:H interface in silicon heterojunction solar cells. Previously we have shown that the main mechanism of cell degradation in the dark was the thermally activated breaking of the Si-H bonds at the interface, and the subsequent H drift away from the interface, leaving behind a Si dangling bond, thereby de-passivating it. The de-passivation rate was determined by the competing processes of bond breaking and the recapture of hydrogen. Here we report that the main new degradation process in the presence of light is the temporary occupation of the dangling bond by a photo-excited electron. This suppresses the recapture rate of the hydrogen atoms, and thus enhances degradation. Our simulations provide an approximate explanation of experimental degradation data.