The Binding Energy of Triplet Excitons in Non-Fullerene Acceptors: The Effects of Fluorination and Chlorination

Abstract

One strategy to improve the photovoltaic properties of non-fullerene acceptors (NFAs) is the rational fluorination or chlorination of those molecules. Although this modification improves important acceptor properties, little is known about the effects on the triplet states. Here, we combine the polarizable continuum model with optimally tuned range-separated hybrid functional to investigate this issue. We find that fluorination or chlorination of NFAs decreases the degree of HOMO-LUMO overlap along these molecules. Consequently, the energy gap between $T_1$ and $S_1$ states, $\Delta E_{ST}=E_{S_1}-E_{T_1}$, also decreases. This effect simultaneously enhances the generation of triplet excitons and reduce the binding energy of the triplet excitons ($E_{b,T}$) which favor their dissociation into free charges. Interestingly, although Cl has a lower electronegativity than F, the chlorination is more effective to reduce $\Delta E_{ST}$. Since chlorination of NFAs is easier than fluorination, Cl substitution can be a useful approach to enhance solar energy harvesting using triplet excitons.

26 pages, 6 figures, 1 table

References in corpus (1)

• Conditions for efficient charge generation preceded by energy transfer process in non-fullerene organic solar cells

Cited by in corpus (4)

• Enhancing Chemical Stability and Photovoltaic Properties of Highly Efficient Nonfullerene Acceptors by Chalcogen Substitution: Insights from Quantum Chemical Calculations
• TMM$-$Sim: A Versatile Tool for Optical Simulation of Thin$-$Film Solar Cells
• Exploring the Electronic Potential of Effective Tight$-$Binding Hamiltonians
• RI$-$Calc: A User Friendly Software and Web Server for Refractive Index Calculation