The DFT study on the electronic structures of polytitasilanes: Several new classes of narrow band gap polymers

The exploring theoretical investigation on Ti-substituted polysilane model, (Si5TiH12)n, (Si3TiH8)n and (SiTiH4)n, has been performed by using density functional theory (DFT). Ti substitutions have little effect on geometrical structures. The characteristic IR band of Ti substitutions is at 1710-1760 cm−1. TDDFT calculations on excited states illuminate that electronic spectrum absorption of polytitasilanes locates at visible light area (400-750 nm). Periodic density functional theory (PDFT) calculation on polymers shows the gap of polytitasilanes is lower greatly than the parent polysilane. Compared with the same size polysilane, with an increase of the Ti/Si ratio, the band gap is lowed by 2.0 eV for (Si5TiH12)n, 2.1 eV for (Si3TiH8)n eV and 2.2 eV for (SiTiH4)nd, that is to say, the higher the doping level of Ti atom is, the lower the gap is. Ti's 3d orbital in LUCB of Ti substitutions plays a significant role in the decrease of band gap.