Characteristic improvements of vertically aligned columnar quantum dot solar cell with a GaAsSb capping layer

This study demonstrates the feasibility of improving the optical properties of a vertically aligned quantum dot (QD) structure and the performance of a quantum dot intermediate band solar cell (QD-IBSC) by capping a GaAsSb layer on the InAs QD. Experimental results indicate that this capping process significantly improves dot-size uniformity because of the strain modification in vertically aligned dot layer growth. A solar cell device with an InAs/GaAsSb columnar dot structure increases the short-circuit current density (Jsc) by 8.8%, compared to a GaAs reference cell. This dot structure also increases quantum efficiency by up to 1200 nm through the absorption of lower-energy photons. The InAs/GaAsSb QD-IBSC also improves the open-circuit voltage (Voc), indicating a reduction in misfit defect density and recombination current density. Power dependent photoluminescence (PL) and time resolved photoluminescence (TRPL) measurement are employed to characterize the optical properties of typical InAs/GaAs type-I and InAs/GaAsSb type-II vertically aligned quantum dot structure. Extended carrier lifetime is demonstrated in the columnar InAs/GaAsSb type-II band structure. The results of this study confirm the ability and thermal stability of a columnar InAs/GaAsSb QD structure to enhance device performance.