Modification of surface conduction band minimum in Cu(In1-x,Gax)Se2 photoelectrodes under CO2-saturated conditions

Abstract

In this study, two strategies to modulate the conduction band minimum (CBM) of Cu(In,Ga)Se₂ (CIGS) photoelectrodes were investigated to enhance their photoelectrochemical (PEC) performance for CO₂ reduction. First, the surface Ga composition of CIGS film was systematically varied, demonstrating that increasing the Ga content elevates the CBM above the CO₂ reduction potential, thereby enhancing the driving force for reduction reactions and increasing photocurrent density. Second, the effect of CsF post-deposition treatment (CsF-PDT) was evaluated, revealing that CsF-PDT modifies the band structure through the formation of Cs-containing compounds (e.g., CsInSe₂), which reduce grain boundary recombination and improve carrier lifetime, as evidenced by time-resolved photoluminescence. Electrochemical impedance spectroscopy confirmed that the interfacial charge transfer resistance was reduced after CsF-PDT. These combined modifications increased the photocurrent density and onset potential, improving PEC performance. This work highlights the importance of CBM tuning and interface engineering in CIGS photoelectrodes, and will provide insights for future optimizations in solar-driven CO₂ reduction efficiency.