Ligand Control of the Work Function of CdSe Semiconductor Nanosurfaces

Surface passivation tunes the work function of semiconductor nanomaterials to optimize charge transport and optoelectronic performance. Using first-principles simulations, we investigate how ligand structure and surface coverage influence the work function of the wurtzite CdSe (100) surface. We consider ligands varying in chain length, electronegativity, conjugation, halogenation, binding site, and surface coverage. Work function shifts scale linearly with ligand coverage for a given ligand but exhibit complex correlations with the ligand's electrostatic dipole moment. Calculations show that surface passivation enables programmable work function tuning through interfacial charge transfer and electronic delocalization by inducing an interfacial dipole and stabilizing or destabilizing the valence-band maximum, while intrinsic ligand polarity plays a secondary role. We further show that ligand binding energy cannot be used to predict either the interfacial dipole or the work function trends, indicating that the strength of passivation is not a reliable measure of ligand-induced redistribution of electron density.