Effect of thienyl group on absorption spectra and excitation energy transfer of eco-friendly organic heterojunction from theoretical methods

Recently, more and more researchers have committed to designing higher-performance materials to improve the power conversion efficiencies (PCEs) of OSCs. However, the inherent laws of synthesising high-quality organic materials are still ambiguous. It is important to explore the structural effect on the photoelectric properties of the synthesised organic. In 2023, the Zou group designed two electron donors, 2DTBDT and 2DTBDT-2T, which are respectively without and with bithiophene in the molecular skeleton. The introduction of bithiophene into 2DTBDT-2T made the PCE of 2DTBDT-2T:Y6 heterojunction triple the 2DTBDT counterpart. Based on this, we selected eco-friendly electron acceptors, CBM, FBR, O-IDFBR and O-IDTBR, to compose the heterojunction with 2DTBDT and 2DTBDT-2T. The ionisation energies (IEs) and absorption spectra of all independent molecules and the excitation energy transfer (EET) couplings of heterojunction are accurately investigated from many-body Green's function theory (MBGFT). We found that the electronic structure and excitation are sensitive to the resonance-antiresonance transitions and the electron–hole interactions. The thienyl group makes the molecule lower CT energy and the stronger EET coupling of heterojunctions, to promote the efficiency of relevant OSCs. The Dexter and overlap types couplings are very important to the study on the EET of organic heterojunctions.