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

Singlet fission (SF) may potentially increase solar cell efficiency by generating two triplet-state excitons from one high-energy 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 (GW+BSE) to study the excitonic properties of pyrene-stabilized acenes. We propose a criterion to define 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 may be a possible candidate for triplet-triplet annihilation (TTA). Ref: JPCM 32, 184001 (2020);