Contribution to the study of sub-bandgap photon absorption in quantum dot InAs/AlGaAs intermediate band solar cells

Abstract: Intermediate band solar cells (IBSCs) pursue the increase in efficiency by absorbing below-bandgap energy photons while preserving the output voltage. Experimental IBSCs based on quantum dots have already demonstrated that both below-bandgap photon absorption and the output voltage preservation, are possible. However, the experimental work has also revealed that the below-bandgap absorption of light is weak and insufficient to boost the efficiency of the solar cells. The objective of this work is to contribute to the study of this absorption by manufacturing and characterizing a quantum dot intermediate band solar cell with a single quantum dot layer with and without light trapping elements. Using one-dimensional substrate texturing, our results show a three-fold increase in the absorption of below bandgap energy photons in the lowest energy region of the spectrum, a region not previously explored using this approach. Furthermore, we also measure, at 9K, a distinguished split of quasi-Fermi levels between the conduction and intermediate bands, which is a necessary condition to preserve the output voltage of the cell.