Effect of tunnel junction grown at different growth rates on the optical properties and improved efficiency of InGaP/GaAs double-junction solar cells

Abstract

Abstract The optical properties of InGaP/GaAs double-junction solar cells (DJSCs) grown by metalorganic chemical vapor deposition were investigated using temperature- and excitation power-dependent photoluminescence (PL) measurements. The InGaP/GaAs DJSC samples studied were the same structures; however, the corresponding tunnel junctions were grown at different growth rates (1.0 and 1.5 A/s). The PL spectrum measured at 10 K for both samples exhibited a strong main peak at ∼1.97 eV with a weak shoulder peak at ∼1.94 eV, which could be attributed to the emissions of disordered and ordered InGaP, respectively. A PL peak located at ∼1.91 eV was observed under a low excitation power, originating from the donor–acceptor pair (DAP) transition. With the increase in the temperature, the emission related to the DAP of the sample grown at a growth rate of 1.0 A/s was found to be less dominant compared with the sample grown at a growth rate of 1.5 A/s. The power-conversion efficiency of the sample grown at a growth rate of 1.0 A/s was improved compared to that of the sample grown at a growth rate of 1.5 A/s, owing to fewer defect states. Our results help understand the luminescence properties of InGaP/GaAs DJSCs, which could be a crucial factor in fabricating high-efficiency solar cells.