Temperature effect on the internal conversion dynamics following different stimulated absorptions in a conjugated polymer

Abstract By applying a femtosecond electric pump pulse to a conjugated polymer, we theoretically study the temperature effect on the internal conversion dynamics following different stimulated absorptions. The simulations are performed within the framework of an extended version of the tight-binding Su-Schrieffer-Heeger model modified to include temperature effect. Firstly, temperature effect on different stimulated absorptions is focused, by which we speculate that the absorption spectra of a single polymer should be nearly temperature independent. However, following stimulated absorptions, the internal conversion (IC) from a higher-lying excited state to the lowest-lying exciton state will be remarkably accelerated by increasing temperature. From this point of view, temperature effect is not favorable for charge separation in polymer solar cells (PSCs), since charge separation from a higher-lying excited state can be effectively suppressed by its IC relaxation. In addition, considering that these IC relaxations are lattice vibration assisted, effects of the vibrational damping and the electron-lattice interaction on them are separately discussed. These findings are crucial for further understanding the primary photovoltaic process in PSCs, especially the role of a higher-lying excited state in charge separation.