EXCITON BINDING ENERGY OF ELECTRONIC POLYMERS: A FIRST PRINCIPLES STUDY

Abstract

Exciton binding energy (E b ) is a key factor for the polymer electronics as well as for the fundamental polymer physics, which has been controversial since long time. Light-emitting polymer requires a large E b so that the charge recombination dominates. But, the photovoltaic polymers need small E b to allow efficient charge separation. First-principles Density Functional Theory (DFT) is employed to calculate E b for polydiacetylene (PDA), trans-polyacetylene (PA), polythiophene (PT), poly(2,5-thienylenevinylene) (PTV), and poly(p-phenylene vinylene) (PPV). We find that the hybrid B3LYP, B972, PBE1PBE, and B1B95 functionals with 20–25% amount of exact HF exchange can give reasonable results and predict E b is around 0.1–0.6 eV for these π-conjugated polymers.