Theoretical Study of the Electronic Properties of Silicon Nanocrystals Partially Passivated with Cl and F

Density functional theory calculations and theoretical representations of the density of states (DOS) were undertaken in order to understand the electronic properties of silicon nanocrystals (Si-nc), when partially passivated with Cl and F. Effects relating to cluster size (Si-29, Si-35, and Si-87), type, and percentages of halogen surface passivant, concerning both the cluster gap and electron-donor-acceptor capabilities, were analyzed. These calculations indicate that as the percentage of Cl and F substitution increases, the energy of the LUMO decreases, and consequently, the HOMO-LUMO gap decreases. Correspondingly, we found that the high-electronegativity substituent Cl and F atoms produce the appearance of shoulders in the DOS band edges, thus reducing the band gap. These results explain the photoluminescent experimental data reported for Si-nc. The evaluation of the electrodonating and electroaccepting powers of Si-nc partially passivated with Cl and F indicates that Si-nc have potential applications for bulk heterojunction solar cells and electroluminescent devices.