Numerical simulation of the impurity photovoltaic effect in silicon solar cells doped with thallium

Many attempts have been made to increase the efficiency of solar cells by introducing a deep impurity level in the semiconductor band gap. Since Tl may be the most suitable impurity for crystalline Si solar cells, the impurity photovoltaic (IPV) effect in silicon solar cell doped with thallium as impurity was investigated by the numerical solar cell simulator SCAPS. Results show that the IPV effect of thallium extends the spectral sensitivity in the sub-band gap range from 1000 to about 1400 nm. When the Tl concentration (Nt) is lower than the base doping density (ND), the short-circuit current density and efficiency increase with increasing Nt. But they decrease rapidly as the impurity density exceeds the shallow base doping density (Nt>ND). The optimum Tl concentration is about equal to the base doping density. For the Si solar cells with high internal reflection coefficients, the IPV effect becomes appreciable (ΔJsc≈9 mA/cm2 and Δη≈2%).