Accurate prediction of the energies of the lowest excited states, S1, T1, and T2, of chromophores for improving solar cell applications

Abstract

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.