Dual-spectrum CQD-CCTS/CNTS bilayer photovoltaics: bridging high-efficiency solar energy harvesting and indoor IoT powering

Abstract The novel chalcogenide carbon quantum dot-based Cu 2 CoSnS 4 (CQD-CCTS), featuring a direct bandgap of 1.26 eV, emerges as a highly promising absorber for large-area and cost-effective solar cells. This study employs a systematic computational framework to optimize single-absorber (CQD-CCTS) and bilayer (CQD-CCTS/CNTS) photovoltaic cells under AM1.5G and indoor LED illumination. Through rigorous device engineering, including layer thickness tuning, carrier concentration optimization, buffer layer selection, and back-contact modification, high efficiencies were reached. The single-absorber cell attains an efficiency of 20.80%, marking a 297-fold improvement over prior experimental reports (0.07%). Introducing a bilayer architecture with a 1.74 eV bandgap CNTS absorber enhances efficiency to 22.86% with AM1.5G illumination and 26.11% with LED illumination, enabled by reduced thermalization losses and interfacial electric field amplification at the CNTS/CQD-CCTS heterojunction. Further analysis reveals sufficient power output under varying LED intensities for low-light IoT applications. This work establishes CQD-CCTS/CNTS heterostructures as a dual-spectrum energy harvesting platform, bridging high-efficiency outdoor and indoor photovoltaics.