2 Quantitative Estimation of Exciton Binding Energy of Polythiophene-Derived Polymers Using Polarizable Continuum Model Tuned Range-Separated Density Functional

Exciton binding energies of six polythiophene-derived polymers were studied through using a nonempirical, optimally tuned range-separated (RS) functional combining with the polarizable continuum model (PCM). We demonstrate that this approach predicts ionization energies (IE), electron affinities (EA), transport gaps, optical gaps, and exciton binding energies of six different polymer chains in both vacuum and solid (dielectric medium) with accuracy comparable to many-body perturbation theory within the GW approximation and Bethe-Salpeter equation (BSE). Furthermore, the behavior of exciton binding energy versus dielectric constant was also reasonably described by the PCM-tuned RS functional, whereas the conventional functionals such as PBE, B3LYP, M062X, and nontuned LC-omega PBE completely fail. We believe our method provides for a reliable and computationally efficient tool for future investigation of efficiency-enhancing mechanism and molecular design in organic solar cells.