Optimizing Reorganization Energies of Small Conjugated Molecules Using an Inverse-Design Approach

During the past years, organic solar cells (OSCs) have been at the center of a significant scientific interest. However, it is still a big challenge to identify organic molecules with the best performances due to the almost inexhaustible chemical space. We recently proposed an inverse-design approach, i.e.. poor man's materials optimization (PooMa), which combines global optimization based on genetic algorithms (GA) and a fast, efficient parametrized density-functional tight-binding (DFTB) method for the calculation of the electronic structure for each individual structure. Here, we applied this method to identify conjugated systems with low reorganization energies for charge-transfer processes. We have considered benzene and pyridine as two different simple test systems and selected 20 different functional groups for the construction of organic molecules. The results showed that our approach (PooMa) is able to construct numerous new structures and successfully identify molecules with good performance at a low computational cost. Furthermore, we present a simple theory that can capture the main results of our study.