Monolithic two-terminal hybrid a-Si:H/CIGS tandem cells

Abstract

Copper-indium-gallium-di-selenide (CIGS) is the present record holder in lab-scale thin-film photovoltaics (TF-PV). One of the problems of this PV technology is the scarcity of indium. Multi-junction solar cells allow better spectral utilization of the light spectrum, while the required current generation per layer is much lower, allowing much thinner absorber layers of CIGS. In this contribution we demonstrate working fabricated devices of CIGS bottom cells that are monolithically integrated with a hydrogenated amorphous silicon (a-Si:H) top cell. The proposed structures are a unique fusion of two distinct fabrication methods, being co-evaporation and plasma enhanced chemical vapor deposition (PE-CVD). In addition, devices without any ZnO have been processed. In those cells a nc-SiO_x:H n-layer acted as an electron recipient and lateral insulator for the CIGS p-layer, and a highly p- and n-doped nc-SiO_x:H layer served as the tunnel recombination junction. The top TCO on the a-Si:H cell was varied with ZnO:Al (AZO) and In₂O₃/Sn₂O₃ (ITO). Efficiencies of the not yet optimized devices have reached 7.9% active area efficiency (with V_oc=1.23V, FF=64%, J_sc= 9.95 mA/cm²).