Extending The Absorption Threshold Of Ingap Solar Cells To 1.60 Ev Using Quantum Wells: Experimental And Modeling Results

Strain balanced multiple quantum wells (SBMQWs) lattice matched to GaAs consisting of InGaAsP wells balanced with InGaP barriers have been used to extend the absorption of In0.49Ga0.51P subcells to longer wavelengths for use in five and six junction photovoltaic devices. Thin layers of InGaAsP quantum wells that absorb beyond 760 nm, have been grown with compositions within the miscibility gap of InGaAsP while maintaining thermodynamic stability. External quantum efficiency and current-voltage measurements reveal that InGaAsP/InGaP SBMQWs extend absorption beyond the InGaP band-edge and improve the short circuit current with minimal degradation of open circuit voltage. We study the effect of barrier height on the carrier transport through altering the Indium percentage in the InGaP barrier. Three samples of different barrier heights are fabricated and compared with each other. Results indicate that with proper design of the layers thicknesses and compositions, the absorption threshold of InGaP can be extended up to 780 nm (similar to 1.59 eV). The promising results of InGaAsP/InGaP SBMQWs in this work offer tremendous potential to alleviate current matching restrictions in next generation and current photovoltaic devices.