Anion-controlled passivation effect of the atomic layer deposited ZnO films by F substitution to O-related defects on the electronic band structure for transparent contact layer of solar cell applications

Anion-controlled chemistry in ZnO films is essential to obtain stable charge-carrier transport and to prevent degradation in the performance of the transparent contact layer in solar cells through passivation of O-related defects by F substitution. Therefore, in this work, the passivation effect of F doping in ZnO was confirmed by analysis for the chemical state of O in ZnO films using XPS surface analysis in the O 1s region. Furthermore, we investigated the effect of F doping in a ZnO matrix on the electronic structure of the resulting films as a function of electron concentration by optical band gap shift (Burstein-Moss theory) and near-band-edge transition (photoluminescence with Stokes shift theory) measurements in ZnO films with different F doping concentrations. The band gap narrowing effect was not significant in the F-doped ZnO films due to valence band perturbation from anion doping rather than conduction band perturbation. Finally, the band structure could be approximated by the relationship between experimental analysis and the formation of valence and conduction bands in ZnO orbitals.