MBE-grown InGaAsP solar cells with 1.0 eV bandgap on InP(001) substrates for application to multijunction solar cells

Abstract

In this study, we have developed the first ever solid-source molecular beam epitaxy (SS-MBE)-grown In0.81Ga0.19As0.43P0.57/In0.47Ga0.53As dual-junction solar cells grown on InP substrates with a 1.0/0.7 eV bandgap for use in mechanically stacked multijunction solar cells. We studied the adsorption efficiencies of As2 and P2 to determine the optimal parameters for the growth of lattice-matched In0.81Ga0.19As0.43P0.57 by SS-MBE. The adsorption efficiency of As2 was found to be seven times greater than that of P2, and lattice-matched In0.81Ga0.19AsyP1−y (y = 0.43) can be achieved at a PAs/(PP + PAs) ratio of ∼0.10. Then, we studied the effect of growth temperature on the characteristics of lattice-matched In0.81Ga0.19As0.43P0.57 single-junction solar cells. The open-circuit voltage (VOC) was found to be greatly affected by the growth temperature, and the highest VOC = 0.47 V (efficiency η = 10.5%) was obtained for cells grown at 440 °C. On the other hand, photoluminescence intensity measured for these cells at room temperature monotonically increased with an increase in the growth temperature, which implies that the reduction in VOC for the cells grown at 400 and 420 °C was due to the increase in the intrinsic defects and unexpected contaminations. By contrast, the reduction in VOC for the cell grown at 450 °C is presumably attributed to an increase in local compositional fluctuations. We integrated the abovementioned In0.81Ga0.19As0.43P0.57 top cell with the In0.47Ga0.53As bottom cell and an η of 3.7% was obtained using an 880-nm-long pass filter.