Pyrene-Stabilized Acenes as Intermolecular Singlet Fission Candidates: Importance of Exciton Wave-Function Convergence

Singlet fission (SF) is the conversion of a singlet exciton into two triplet excitons. SF could increase the efficiency of organic solar cells by harvesting two carriers from one photon. Polyacene crystals, such as tetracene and pentacene, have shown outstanding SF performance. However, their instability prevents them from being utilized in SF-based photovoltaic devices. In search of practical SF chromophores, we use many-body perturbation theory with the GW approximation and Bethe-Salpeter equation to study the excitonic properties of pyrene-stabilized acenes. We propose a criterion to determine the convergence of exciton wave-functions with respect to the fine k-point grid used in the BerkeleyGW code. An open-source Python code is presented to perform exciton wave-function convergence checks and streamline the double-Bader analysis of exciton character. We find that the singlet excitons in pyrene-stabilized acenes have a higher degree of charge transfer character than in the corresponding acenes. The pyrene-fused tetracene and pentacene derivatives exhibit comparable excitation energies to their corresponding acenes, making them potential SF candidates. The pyrene-stabilized anthracene derivative is considered as a possible candidate for triplet-triplet annihilation (TTA).