Modeling and Simulation of GaTlAs Quantum Well Solar Cells

Multiple Quantum Wells (MQW) have been an ongoing topic of research and discussion for the scientific community with structures like InGaAs/GaAs and InGaP/GaAs quantum wells producing promising results that could potentially improve overall solar energy conversion. Here, we use WEIN2K, a commercial density functional theory package, to study the ternary compound Ga_1-xTl_xAs and determine its electronic properties. Using these results combined with experimental confirmation we extend these properties to simulate a MQW GaAs/ Ga_1-xTl_xAs solar cell. Ga_1-xTl_xAs is a tunable compound, with its bandgap being strongly dependent on the concentration of Tl present. Concentrations of Tl as low as 7% can reduce the bandgap of Ga_1-xTl_xAs to roughly 1.30 eV at room temperature with as little as a 1.7% increase in lattice constant. The change in bandgap, accompanied by the relatively small change in lattice constant makes Ga_1-xTl_xAs a strong candidate for a MQW cell with little to no strain balancing required within the structure to minimize unwanted defects that impede charge collection within the device. Our GaAs photodiode with TlGaAs MQWs shows an expanded absorption band and improved conversion efficiency over the standard GaAs photovoltaic cell.