DFT-guided prediction of singlet fission chromophores for high-efficiency organic solar cells

Theoretical design and DFT calculations were performed to find new SF chromophores to be used in high efficiency organic solar cells. These included 6 new compounds containing boron, nitrogen, selenium, TIPS and phenyl groups. All of these molecules demonstrated near-planar geometries with extended π-conjugation and had HOMO–LUMO gaps between 3.04 and 3.32 eV. The excitation energies for the singlet and triplet states were in the ranges of 2.11–2.25 eV and 1.00–1.10 eV, leading to singlet–triplet energy gaps ranging from 1.11– –1.16 eV. All compounds met the critical energetic requirement for efficient singlet fission whereby \mathrm{E_{S1}} > 2 \mathrm{E_{T1}} for all chromophores. Some selected derivatives, such as N1 and N4 were found to have Δ \mathrm{E_{ST}} values of 1.15 and 1.14 eV, respectively, which are equal to or greater than the benchmark value of pentacene which is 1.02 eV and diketopyrrolopyrrole which is 1.18 eV. Moreover, the new chromophores are expected to have greater absorption and thermal stability spectrum making them better suited for next-generation organic solar cells. This study highlights the promise of rational heteroatom and functional group design for SF-active materials with advanced optoelectronic and device-engineering properties.