High-efficiency cadmium-free Cu(In,Ga)Se2 flexible thin-film solar cells on ultra-thin glass as an emerging substrate

Cu(In,Ga)Se 2 (CIGSe) solar cells have significantly progressed in associated flexible photovoltaic technologies. Recently, ultra-thin glass (UTG) has been recognized as an emerging novel flexible substrate that is compatible with conventional thick glass-based methodology. In this work, the flexible CIGSe solar cell on UTG using a well-known three-stage process yielded 18.1 % with CdS buffer, which is higher than that of conventional solar cells on thick glass. However, UTG becomes brittle at high temperatures (>600 °C) due to thermal reorganization of potassium. To address the issue, a thin Ag precursor layer was introduced, enabling effective grain growth at reduced temperatures (<500 °C). Optimized Ag alloying (∼1 at%) enhanced grain structure and device efficiency, reaching up to 17.45 % at lower temperatures. Additionally, (Zn,Mg)O as a cadmium-free buffer was explored to address environmental concerns. With the inclusion of an intrinsic zinc oxide (i-ZnO) layer, the CIGSe/(Zn,Mg)O heterojunction was protected from transparent conductive oxide (TCO) sputtering damage, showing increased open circuit voltage and efficiency. Overall, we have successfully demonstrated a flexible and environmentally friendly cadmium-free CIGSe solar cell with an efficiency of approximately 17.81 %. Moreover, scaling up the fabrication process for a large-area cell with 60 cm² achieved a device efficiency of 10.11 % with a lamination process. This study advances the potential of high-efficiency CIGSe solar cells on flexible UTG substrates for various practical applications, including building integration on curved surfaces, portable devices, and automobiles. • Demonstrated flexible, Cd‐free Cu(In,Ga)Se₂ solar cells on emerging ultrathin glass substrates. • Achieved a record efficiency of 17.81 % for flexible, Cd‐free Cu(In,Ga)Se₂ solar cells on ultrathin glass substrates. • Achieved an efficiency of 10.11 % for 60 cm² large-area Cd-free CIGSe cells. • Established a platform for controlling microstructure and defect properties through low-melting-point Ag doping.