Band gap design of thiophene polymers based on density functional theory

Hybrid density functional theory calculations are carried out to investigate the band gaps of thiophene derivatives. We carry out density functional theory (DFT) calculations for finite-length oligomers and estimate the band gaps of infinite-length polymers using an extrapolation scheme. The calculated band gaps of polythiophene, poly(3-hexylthiophene) (P3HT), poly(2-ethenylthiophene), and polyisothianaphthene (PITN) are close to experimental values. We predict the band gap of poly(2-ethenyl-3-hexylthiophene). The calculated band gaps of various thiophene derivatives in this study are 1.10-1.81 eV; therefore, we have demonstrated that the band gaps can be controlled using thiophene derivatives. We discuss the mechanism of band gap decrease in derivatives, which is useful for the band gap design of thiophene derivatives.