EXCITON BINDING ENERGY OF ELECTRONIC POLYMERS: A FIRST PRINCIPLES STUDY

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 pi-conjugated polymers.