The impact of effective mass mismatch and quantum dot size on the interband absorption and sub-bandgap photocurrent of box-shaped InAs/GaAs quantum dot-intermediate band solar cells

Abstract

The InAs/GaAs quantum dot intermediate band solar cells (QD-IBSCs) have the potential for high conversion efficiency. In practice, their efficiencies have not reached 20%. In this study, the confined energy levels, interband absorption coefficients, and absorbed sub-bandgap photocurrent densities are calculated with QD size using equal effective mass and effective mass mismatch for the box-shaped InAs/GaAs QD system. The four-band k\(\cdot \)p model was applied to the InAs/GaAs QD system. The energy of IB levels with the effective mass mismatch decreased compared with the equal effective mass. The interband photocurrent density increased with effective mass mismatch since more confined energy states contributed to interband absorption. If the in-plane QD density raised from \(4\times 10^{10}\) \(\hbox {cm}^{-2}\) to \(4\times 10^{11} \,\hbox {cm}^{-2}\), the interband photocurrent density increased from 0.58 to 5.19 \(\hbox {mA/cm}^{2}\) for equal effective mass and 0.99 to 8.38 \(\hbox {mA/cm}^{2}\) for the effective mass mismatch with 16 nm \(\times \) 16 nm \(\times \) 6 nm of QD size, under one sun concentration. Increasing the QD size also allows additional IB states within the forbidden band; thus, the interband photocurrent increases with QD size. The interband photocurrent density for 10 nm and 16 nm QD widths is 0.39 \(\hbox {mA/cm}^{2}\) and 0.99 \(\hbox {mA/cm}^{2}\), respectively.