p-CuInS₂ /n-Polymer Semiconductor Heterojunction for Photoelectrochemical Hydrogen Evolution

An inorganic p-type CuInS₂ semiconductor was combined with the semiconducting polymer of PNDI3OT-Se1 and PNDI3OT-Se2 with different HOMO/LUMO levels for photoelectrochemical hydrogen production. Charge transfer behaviors at polymer/CuInS₂ junctions were investigated by electrochemical impedance spectroscopy. The heterojunction of p-CuInS₂ and n-type polymer (both PNDI3OT-Se1 and Se2) successfully made p-n junctions and showed improved charge transfer. However, we found that higher HOMO levels of polymer than valence band maximum (VBM) of CuInS₂ spurred charge recombination at interfaces. As a result, CuInS₂ /PNDI3OT-Se1/TiO₂ /Pt, which has suitable energy levels matched between PNDI3OT-Se1 and CuInS₂ , shows photocurrent (-15.67 mA cm^-2 ) improved concretely when compared to a CuInS₂ /TiO₂ /Pt photoelectrode (-7.11 mA cm^-2 ) at 0.0 V vs. RHE applied potential. Additionally, the photoelectrochemical stability of CuInS₂ /PNDI3OT-Se1/TiO₂ /Pt photoelectrode was also investigated.