Strain-Balanced InGaAsP/GaInP Multiple Quantum Well Solar Cells With a Tunable Bandgap (1.65-1.82 eV)

Currently available materials for III-V multijunction solar cells lattice matched to GaAs covering the spectral range from 1.65 to 1.82 eV are composed of either immiscible quaternary alloys or contain aluminum. We report the fabrication of a novel aluminum-free In_x Ga_{1-x}As _{1-z}P_z /Ga_{1-y}In _yP ( x > y ) strain-balanced multiple quantum-well (SBMQW) p-i-n solar cell structure lattice matched to GaAs, grown by metal-organic chemical vapor deposition. SBMQWs consist of alternating layers of In _xGa_{1-x} As_{1-z}P _z wells and Ga _{1-y}In_y P barriers ( x > y ) under compressive and tensile strain, respectively. When compared with standard GaInP devices, SBMQW structures exhibit longer photoluminescence wavelength (680-780 nm) emission and enhanced light absorption with improved short-circuit current density. In this study, the SBMQW emission and absorption wavelength is controlled by adjusting the layer thickness of InGaAsP wells, while the arsenic and indium compositions are fixed. We show that carriers generated in QWs are extracted via thermionic emission. The proposed SBMQWs allow more flexibility in the design of current multijunction solar cells and future cells with more than four junctions. InGaAsP/GaInP SBMQWs may also be used in applications other than solar cells, such as light-emitting diodes (LEDs) and lasers, with the advantages of tuning the emission and absorption processes.