Study of the light-induced degradation of tandem $\alpha$-Si : H/$\mu c$-Si : H photovoltaic converters

The photo-induced degradation of tandem $\alpha$-Si : H/$\mu c$-Si:H photovoltaic converters with an initial efficiency of 10.4% under light flux densities of 1 and 10 kW m$^{-2}$ (AM1.5G) is studied. It is shown that the stabilized state is reached after 500 h of exposure to the standard light-flux density and after 300 min at a flux 10 times higher in density. In both cases, the efficiency decreases by 1.2–1.4 abs.%. The experimentally measured spectral and current-voltage characteristics of the photovoltaic converters are used to determine the nonequilibrium carrier lifetimes and to calculate variation dependences of the dangling-bond concentration in $i$-$\alpha$-Si : H и $i$-$\mu c$-Si:H layers. The dependences are approximated in terms of the floating-bond model. The calculated dangling-bond concentrations after various exposure times are used to simulate the dependences of the photovoltaic-converter parameters on light exposure. The results obtained show good coincidence between the simulated degradation rates of the current and efficiency of a tandem photovoltaic cell and the experimental data.