Accurate prediction of the energies of the lowest excited states, S ₁ , T ₁ , and T ₂ , of chromophores for improving solar cell applications

The lowest singlet excited state and triplet states of acene and polyaromatic hydrocarbon derivatives are calculated using a screened range separated hybrid functional within a polarizable continuum model (SRSH-PCM). Excited state energies are obtained at the time-dependent density functional theory (TDDFT) and the Tamm-Dancoff approximation (TDA) levels. The SRSH-PCM electronic structure protocol successfully incorporates the effect of the electrostatic environment of an active molecule. SRSH-PCM TDDFT excitation energies present a significantly decreased averaged deviation from relevant experimental benchmark energies in comparison to TDA energies. In particular, the energies of the two lowest lying excited triplet states, T₁ and T₂, are predicted with an average error of 0.06 eV and that of the lowest singlet state, S₁, with an average error of 0.11 eV for a molecular test set following a linear fit correction based on a benchmark set. The predictive description of the excited states can be achieved only by properly incorporating effects of the dielectric medium as accomplished by the SRSH-PCM approach. The results highlight the prospect of using SRSH-PCM to uncover molecules bearing optimal properties for singlet fission or triplet-triplet annihilation upconversion applications, where the conditions addressing the energies of these states must be satisfied.