Indium-Free Transparent Conductive Oxide Interconnection Layer for Achieving Over 30%-Efficiency Perovskite/Silicon Tandem Solar Cells
Perovskite/silicon tandem solar cells (TSCs) have achieved power conversion efficiencies (PCE) up to 34.9%, surpassing the Shockley-Queisser limit of single-junction devices. The interconnection layer (ICL) critically bridges top and bottom subcells, enabling charge carrier recombination. Conventional indium oxide (In2O3)-based TCOs suffer from high-energy ion bombardment during sputtering, damaging amorphous silicon subcells and reducing open-circuit voltage (VOC) and fill factor (FF). Additionally, indium scarcity and cost necessitate indium-free alternatives. Here, we introduce a highly degenerate indium-free samarium-doped cadmium oxide (CdO:Sm) TCO as the ICL for perovskite/SHJ TSCs, deposited via low-damage reactive plasma deposition (RPD). The ultrathin CdO:Sm film (~3 nm) exhibits average transmittance of 85% (400–1200 nm) and 90% (800–1200 nm), enabling efficient near-infrared absorption in the bottom subcell. High doping concentration and mobility ensure excellent electrical conductivity. The low work function (4.04 eV) of CdO:Sm facilitates carrier tunneling and efficient recombination. Devices employing CdO:Sm ICL achieved approximately 1% higher efficiency compared to those with indium-based TCO ICLs. Detailed characterization including contact resistivity (1.68 mΩ cm2), conductive atomic force microscopy, Kelvin probe force microscopy, and photoluminescence quenching confirm enhanced carrier transport and extraction. This work demonstrates a viable indium-free ICL for high-efficiency perovskite/SHJ TSCs, addressing both performance and sustainability challenges.