Exciton diffusion in poly(3-hexylthiophene) by first-principles molecular dynamics

Poly(3-hexylthiophene) (P3HT) is a polymer used in organic solar cells as a light absorber and an electron donor. Photogenerated excitons diffuse and dissociate into free charge carriers provided they reach the absorber boundaries. The device efficiency is therefore dependent on the exciton diffusion. Although measurements can be performed for example by time-resolved photoluminescence, a quantitative modeling is highly desirable to get an insight into the relationship between the atomic structure at finite temperature and the diffusion coefficient of the exciton. This is the objective of the present work, achieved by resorting to first-principles molecular dynamics in combination with the restricted open-shell approach to model the singlet excited state. The maximally localized Wannier functions and their centers are used to monitor and localize the electron and the hole along the dynamics. The resulting diffusion coefficient is in close agreement with available measurements.

Automated summary

P3HT is a polymer used in organic solar cells as a light absorber and an electron donor. The efficiency of the solar cell depends on the diffusion of photogenerated excitons, which can be measured using time-resolved photoluminescence. This study used first-principles molecular dynamics and the restricted open-shell approach to model the singlet excited state of P3HT and found that the resulting diffusion coefficient agrees with experimental measurements.