Theoretical investigation of lattice-matched III-N-V/Si double-junction solar cells

Abstract

The lattice-matched III-N-V/Si double-junction (DJ) solar cells are designed with GaNAsP and GaInNP top cells, respectively. Under AM1.5G condition, the efficiencies of III-N-V/Si DJ cells are calculated with variable electron lifetime (τe) and electron surface recombination velocity (Se) in top cell. When Se is 100 cm/s and τe rises from 1 to 1000 ns, the optimal efficiency of GaNAsP/Si cell increases from 31.12% to 36.13% due to the increasing short-circuit current and open-circuit voltage. With τe of 100 ns, the optimal efficiency keeps at a high value of ~35% when Se changes from 10 to 1000 cm/s, but drops obviously with Se of 10000 cm/s. In comparison, the optimal efficiency of GaNAsP/Si cell is less sensitive to Se than to τe. With fixed Se of 100 cm/s, GaNAsP/Si cell shifts the optimal top-cell bandgap from 1.716 to 1.787 eV with adjustable top-base thickness when raising τe from 1 to 1000 ns. However, the effect of Se on optimal top-cell bandgap is negligible. For III-N-V/Si cell with 100-ns τe and 100-cm/s Se, an optimal efficiency is obtained as ~35.1%, which would be closer to the experimental limit owing to the expectable values of τe and Se. Furthermore, the optimal efficiency of GaNAsP/Si cell drops slightly when thinning Si substrate from 300 to 150 μm, but has a maximum of 35.95% with substrate doping of 1 × 1016 cm-3 when the doping concentration varies from 1 × 1015 cm-3 to 1 × 1018 cm-3. The results and discussion in this work may act as a guidance for studying III-N-V/Si DJ cell.