Effects of Nuclear Vibrations on the Energetics of Polythiophene: Quantized Energy Molecular Dynamics

TL;DR

This study investigates how nuclear vibrations influence the electronic properties of polythiophene, introducing a quantum-aware molecular dynamics method that captures temperature and isotope effects, impacting organic solar cell performance.

Contribution

A novel quantum vibrational molecular dynamics algorithm is developed, revealing significant effects of nuclear motions on polythiophene's electronic energetics relevant for solar cells.

Findings

Nuclear motions alter frontier orbital energies by ~0.1 eV.

Quantized vibrations broaden energy levels by about 20% at 300K.

Temperature and deuteration further increase spectral broadening by over 20%.

Abstract

Effects of nuclear dynamics on the energetics of polythiophene relevant for the performance of organic solar cells are studied for the first time. Nuclear motions change the expectation values of frontier orbital energies and the band gap by about 0.1 eV vs. values at the equilibrium geometry, which is expected to have a significant effect on light absorption, charge separation, and donor regeneration. A new molecular dynamics (MD) algorithm, which accounts for the quantum nature of vibrations, is introduced. It reproduces effects of temperature and deuteration which are lost in the standard MD. Inclusion of quantized vibrations leads to a broadening of the band gap and of energy levels by about 20% at 300K, while having little effect on their expectation values (which change by up to 0.03 eV). Increase in temperature from 300K to 400K and deuteration cause an additional broadening of the spectrum by about 26% and 21%, respectively.