Flexible InGaP/GaAs Double-Junction Solar Cells Transferred onto Thin Metal Film

InGaP/GaAs 이중접합 기반의 고효율 플렉시블 태양전지 제조기술 연구

III-V compound semiconductor based thin film solar cells promise relatively higher power conversion efficiencies and better device reliability. In general, the thin film III-V solar cells are fabricated by an epitaxial lift-off process, which requires an $Al_xGa_{1-x}As$ ($x{\geq}0.8$) sacrificial layer and an inverted solar cell structure. However, the device performance of the inversely grown solar cell could be degraded due to the different internal diffusion conditions. In this study, InGaP/GaAs double-junction solar cells are inversely grown by MOCVD on GaAs (100) substrates. The thickness of the GaAs base layer is reduced to minimize the thermal budget during the growth. A wide band gap p-AlGaAs/n-InGaP tunnel junction structure is employed to connect the two subcells with minimal electrical loss. The solar cell structures are transferred on to thin metal films formed by Au electroplating. An AlAs layer with a thickness of 20 nm is used as a sacrificial layer, which is removed by a HF:Acetone (1:1) solution during the epitaxial lift-off process. As a result, the flexible InGaP/GaAs solar cell was fabricated successfully with an efficiency of 27.79% under AM1.5G illumination. The efficiency was kept at almost the same value after bending tests of 1,000 cycles with a radius of curvature of 10 mm.