Anti-Site Defect-Induced Cascaded Sub-Band Transition in CuInS₂ Enables Infrared Light-Driven CO₂ Reduction

Photocatalytic CO₂ conversion is a promising approach to simultaneously mitigate climate change and alleviate the energy crisis. However, infrared light, which constitutes nearly half of the solar energy, has not been effectively utilized yet. In this work, we discover a photogenerated charge transition mechanism in CuInS₂ with intrinsic In_Cu antisite defects for synergistic utilization of full-spectrum photons. Femtosecond transient absorption spectroscopy and DFT calculation unveil an intermediate band induced by the intrinsic antisite defects, where cascaded sub-band transition could be realized by high-energy photons (UV-vis) and low-energy (IR), thus improving the absorption range of infrared light as well as the utilization efficiency of photogenerated carriers. <i>In situ</i> Kelvin probe force microscopy demonstrates that the generation of photoexcited electrons could be greatly enhanced through this synergistic utilization of full spectrum light. Moreover, <i>in situ</i> X-ray photoelectron spectroscopy and <i>in situ</i> diffuse reflectance infrared Fourier transform spectroscopy reveal that infrared photons could also enhance the adsorption and activation of CO₂ and H₂O on the catalyst surface. As a result, the CO production rate under full spectrum light reaches 19.9 μmol g^-1 h^-1, which is more than a 7-fold increase over that under UV-vis irradiation.