Hybrid surface passivation of PbS/CdS quantum dots for efficient photoelectrochemical hydrogen generation

Abstract

Surface ligands facilitate the high dispersibility of colloidal quantum dots (QDs) during synthesis and storage, and also play a key role in passivating surface traps. The most commonly used ligands [oleic acid (OA) or oleylamine (OLA)] are insulating long organic linkers, which prevent efficient charge transfer between QDs and exhibit limited surface passivation, thus significantly reducing the overall performance of QDs based optoelectronic devices. Here we develop a solid-state ligands exchange process for PbS/CdS QDs sensitized TiO2 photoanode with hybrid inorganic ligands (I− and SCN−) to replace the original insulating OA ligands and passivate the surface traps. The hybrid surface passivation of PbS/CdS QDs removes ~75% of insulating OA ligands. The saturated photocurrent density of the photoelectrochemical (PEC) cells improves significantly through the hybrid ligand exchange process, reaching a value of 4.0 mA cm−2 which is more than two times higher compared to the control PEC cells. In addition, the long-term stability of PEC cells is better for the hybrid ligand exchange process (only 15% loss of its initial photocurrent density) than the control PEC cells (38% loss). Our results indicate that hybrid ligands engineering is a promising pathway to achieve high performance and stable PEC cells for hydrogen generation.