First Principle calculations of the internal conversion and intersystem crossing rates of IDIC, Y6, and PC$_{70}$BM.

Abstract

The efficiency of OSCs is controlled by elementary processes occurring within the donor and acceptor domains and at their interface. Herein, we introduce a fully quantum mechanical, first-principles framework for quantitatively predicting the rates of these elementary processes with high accuracy and at an affordable computational cost. The approach integrates Fermi’s Golden Rule with density functional theory (DFT), enabling direct evaluation of both radiative and non-radiative transition rates from the knowledge of equilibrium nuclear configurations and vibrational frequencies and normal modes. It has been shown that the method yields excellent agreement with experiments and provides new insights into the role of electronic coupling and vibronic interactions in voltage losses. Here we apply it for evaluating the internal conversion and intersystem crossing rates of IDIC, Y6, and PC$_{70}$BM.