Effect of ligand exchange on photocurrent enhancement in cadmium selenide (CdSe) quantum dot water splitting cells

We report photocurrent enhancement through ligand exchange in cadmium selenide (CdSe) photoelectrochemical (PEC) cells. CdSe quantum dot (QD) layers were used as a light absorption layer in combination with titanium dioxide (TiO2) layers. For a shorter ligand exchange, pristine CdSe QDs with oleic acid (OA) ligands were treated with 1,2-ethanedithiol (EDT) and CdSe QD PEC cells exhibited enhanced photocatalytic properties in comparison with pristine CdSe PEC cells. To articulate the origin of enhanced photocurrent, ligand dependent energy band bending at the CdSe/TiO2 interface was probed from thickness dependent highest occupied molecular orbital level measurements using photoelectron spectroscopy in air. Increase in the photocurrent also originates from enhancement in charge transport through ligand exchange to shorter EDT ligands in the bulk CdSe film with OA ligands suppressing back diffusion of carriers from TiO2 to CdSe.