Impact of heterogeneous passivation of trimethylphosphine oxide and di-methylphosphine oxide surface ligands on the electronic structure of CdnSen (n=6, 15) quantum dots: A DFT study

• Structural distortion is removed in CdSe QDs using impurity DMPO ligands.
• Non-polar surface 112¯0 is active for impurity binding in CdSe QDs.
• Heterogeneous passivation of ligands blue shifts absorption spectra of CdSe QDs.

We report the significant influence of multiple capping ligands such as tri-methylphosphine oxide (TMPO) and di-methylphosphine oxide (DMPO) on the surface morphology and electronic structure of CdnSen (n=6, 15) quantum dots (QDs) using density functional theory (DFT). From the structural parameters the TMPO passivated structures shows strong structural distortion along non-polar 112¯0 surface. Besides, the binding energy values indicate that the TMPO ligands are weakly bound to 112¯0 surface. On introducing DMPO at 112¯0 non-polar surface from binding energy values, we observe significant surface reconstruction and stabilization of the structure due to the Se-H dative bond in addition to strong Cd–O bond. The NBO analysis indicates that charge transfer is maximum between metal and ligand in 112¯0 surface. The results of PDOS and molecular orbital (MO) analyses show that DMPO ligands significantly contribute to the occupied molecular orbitals near HOMO, which is not case in QDs with pure TMPO ligand. Further, the absorption spectra of CdSe QDs indicate that optical gaps are blue shifted by DMPOs. Hence, the multiple ligands can be employed in tuning the desired structural and optoelectronic properties of colloidal QDs (CQDs).

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