Engineering Cu₃AsS₄-CuInS₂ nano-heterostructures for improved photocarrier dynamics and high-efficiency solar energy...

The wide bandgap and rapid charge carrier recombination of CuInS₂ limit its photovoltaic performance. In this work, a Cu₃AsS₄-CuInS₂ nano-heterostructure absorber was developed to improve light absorption and charge transport. X-ray diffraction confirmed the coexistence of crystalline CuInS₂ and Cu₃AsS₄ phases with a decreased average crystallite size of 33.3-19.1 nm, while Raman spectroscopy verified the phase purity. SEM and HR-TEM analyses revealed a compact nanograined morphology and well-defined lattice fringes with increased interplanar spacing of 3.192-3.213 Å, confirming successful heterostructure formation. Optical studies showed a reduced bandgap from 1.73 eV (CuInS₂) to 1.65 eV for the Cu₃AsS₄-CuInS₂, indicating enhanced visible-light absorption. Energy-band alignment demonstrated a favorable type-II band alignment that promotes efficient charge separation and carrier transport. The heterostructure-based solar cell exhibited improved photovoltaic performance with FF of 0.633, and PCE of 7.09%, outperforming the pristine CuInS₂ and Cu₃AsS₄ devices. The enhanced performance was further supported by electrochemical impedance spectroscopy and external quantum efficiency measurements, which indicated reduced charge recombination and improved charge collection efficiency.