Effect of the compositional distribution on the photovoltaic power conversion of SiGe solar cells

Theoretical investigation on the photovoltaic power conversion of SiGe solar cells was carried out focusing on the impact of the compositional distribution. The absorption coefficient and the intrinsic carrier concentration were assumed to be macroscopically uniform parameters controlled by the compositional distribution. Under an assumption with finite minority carrier diffusion length, solar cell based on SiGe was revealed to have power conversion superior to that based on Si in a limited compositional window on the Si-rich side. In the window, the increase in the photocurrent density overcompensates the decrease in the voltage, and controls the overall conversion efficiency. The width of the window was greatly affected by the compositional distribution in SiGe. A comparison was made with experiments to support the existence of such a compositional window.