Simulation of double junction In_0.46Ga_0.54N/Si tandem solar cell

A comprehensive study of high efficiency In${}_{0.46}$Ga${}_{0.54}$N/Si tandem solar cell is presented. A tunnel junction (TJ) was needed to interconnect the top and bottom sub-cells. Two TJ designs, integrated within this tandem: GaAs($n^{+}$)/GaAs($p^{+}$) and In${}_{0.5}$Ga${}_{0.5}$N($n^{+}$)/Si($p^{+}$) were considered. Simulations of GaAs(n${}^{+}$)/GaAs(p${}^{+}$) and In${}_{0.5}$Ga${}_{0.5}$N (n${}^{+}$)/Si(p${}^{+}$) TJ I–V characteristics were studied for integration into the proposed tandem solar cell. A comparison of the simulated solar cell I–V characteristics under 1 sun AM1.5 spectrum was discussed in terms of short circuit current density ($J_{sc}$), open circuit voltage ($V_{OC}$), fill factor (FF) and efficiency ($\eta$) for both tunnel junction designs. Using GaAs(n${}^{+}$)/GaAs(p${}^{+}$) tunnel junction, the obtained values of $J_{sc}=21.74$ mA/cm${}^2$, $V_{OC}=1.81$ V, FF = 0.87 and $\eta =34.28\%$, whereas the solar cell with the In${}_{0.5}$Ga${}_{0.5}$N/Si tunnel junction reported values of $J_{sc}=21.92$ mA/cm${}^2$, $V_{OC}=1.81$ V, FF = 0.88 and $\eta =35.01\%$. The results found that required thicknesses for GaAs(n${}^{+}$)/GaAs(p${}^{+}$) and In${}_{0.5}$Ga${}_{0.5}$N (n${}^{+}$)/Si(p${}^{+}$) tunnel junctions are around 20 nm, the total thickness of the top InGaN can be very small due to its high optical absorption coefficient and the use of a relatively thick bottom cell is necessary to increase the conversion efficiency. (paper)