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.

Electroluminescence explored internal behavior of carriers in InGaAsP single-junction solar cell

“…Since Dimroth et al reported the wafer bonded four-junction GaInP/GaAs//GaInAsP/InGaAs solar cell with a highest efficiency of 46.0% at approximately 500 suns, [5] the InGaAsP solar cell has received more and more attention motivated by achieving higher conversion efficiency. [6][7][8][9][10][11][12] In this regard, a better understanding of the internal behaviors of carriers in InGaAsP solar cell should be desired. On the other hand, as is well known, quaternary alloy with different ionic radii is difficult to grow [13] because the miscibility gap inhibits the mixing of constituents within the alloy, different kinds of clustering (atomic ordering, quantumdots-like formations, and atomic content fluctuation, etc.)…”

Effects of buffer layer and back-surface field on MBE-grown InGaAsP/InGaAs solar cells

“…Considering the low growth temperature and phase separation that result in deep centers and=or defect states, the quaternary compound of InGaAsP with a band gap of 1.05 eV is difficult to grow by MBE. 7) Very recently, an InGaAsP SC with an efficiency of 10.5% and an InGaAs= InGaAsP dual-junction SC with an efficiency of 3.7% were reported; 8) such a report indicates a great potential to improve the device performance. An efficient back-surface-field (BSF) layer can confine the photogenerated minority carriers and keep them within reach of the p-n junction and, at the same time, ensure the transport of majority carriers to be efficiently collected.…”