Theoretical Study of p- and n‑Doping of Polythiophene- and Polypyrrole-Based Conjugated Polymers

Density functional theory (DFT) calculations were carried out to investigate the tunable nature of band gaps of polythiophene (PTh)- and polypyrrole (PPy)-based conjugated polymers. Two series of conjugated polymers were studied as S is replaced in PTh with O, Se, and Te, and N is replaced in PPy with P, As, and Sb in the presence of Li and Cl atomic dopants. Li and Cl atoms facilitate n-type and p-type doping, respectively. Molecular and periodic calculations were carried out with a GGA functional (PBE) incorporating dispersion corrections. Narrowing band gaps or HOMO–LUMO gaps were obtained when going from O to Te in PTh analogs and P to Sb in PPy analogs. Further reduction in band gaps was observed upon doping especially in the series of PTh and analogs. A slight increase in band gaps was observed with doping in PPy analogs but the band gap is very narrow. Overall, the electronic structure of conjugated polymers can be tuned with Li and Cl atomic dopants, and this is useful in electronic device applications of conjugated polymers. Similar trends are observed for the band gaps in molecular calculations when other functionals (PBE0, B3LYP, M06) are used.