Amplifying the photovoltaic properties of tetrathiafulvalenes based materials by incorporation of small acceptors: a density functional theory approach

Currently, polycyclic aromatic compounds in organic solar cells (OSCs) have gained substantial consideration in research communities due to their promising characteristics. Herein, polycyclic aromatic hydrocarbons (PAHs) core-based chromophores (TTFD1-TTFD6) were designed by structural modifications of peripheral acceptor groups into TTFR. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were carried out at B3LYP/6-311G (d, p) functional to explore insights for their structural, electronic, and photonic characteristics. The structural modulation unveiled notable electronic impact on the HOMO and LUMO levels across all derivatives, leading to decreased band gaps. All the designed compounds exhibited band gap ranging from 2.246 to 1.957 eV, along with wide absorption spectra of 897.071-492.274 nm. An elevated exciton dissociation rate was observed due to the lower binding energy values (E_b = 0.381 to 0.365 eV) calculated in the derivatives compared to the reference (E_b = 0.394 eV). Furthermore, data from the transition density matrix (TDM) and density of states (DOS) also corroborated the effective charge transfer process. Comparable results of V_oc for reference and designed chromophores were obtained via HOMO_donor-LUMO_PC71BM. The declining V_oc order values was noted as TTFD5 > TTFD6 > TTFD4 > TTFD3 > TTFD2 > TTFD1 > TTFR. Interestingly, TTFD5 was found with the smallest energy gap and highest absorption value, resulting in better charge transference among all the derivatives. The results illustrated that the modification in indenofluorene based chromophores with end-capped small acceptors proved to be a significant approach in achieving favorable photovoltaic properties.