Developing of dual junction GaInP/GaAs solar cell devices: effects of different metal contacts
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DJ GaInP/GaAs SC structure was designed by using analytical solar cell model. The electrical parameters (J(sc), V-oc, FF and eta) were calculated by determining optimum conditions for improving the performance of the SCs. Considering the optimization conditions in design of SC, lattice and current matched DJ GaInP/GaAs SC structure was grown using MBE technique. Alloy composition and lattice constants of each layers in the structure were estimated from measured XRD data. To evaluate of effects on conversion efficiency of different metal contact materials, SC devices were fabricated by photolithographic technique. Two types of front-side electrodes, which included Au and Au/Ti metals, were separately fabricated on devices and denoted as S1 and S2, respectively. Performance of the S1 and S2 were determined using I-V measurements under the AM1.5 illuminations. S2 possesses 4.16% enhancement in conversion efficiency compared to that of S1. The better performance of the S2 can be attributed to having higher I-sc and V-oc due to higher conductivity of titanium as well as good adhesion on GaAs. In addition, Al2O3/TiO2 anti-reflective coating effect on performance of the S1 and S2 was also investigated. Sputtered anti-reflective layer increased the efficiencies from 14.65 to 15.72% and 15.26 to 16.90% for S1 and S2, respectively.