Halogenation of the Side Chains in Donor-Acceptor Based Small Molecules for Photovoltaic Applications: Energetics and Charge-Transfer Properties from DFT/TDDFT Studies

摘要

Incorporation of halogen atoms in conjugated polymer and small molecule (SM) based donors has been a practical approach to improve the efficiency of devices. In this report, we present a comprehensive study on the effects of halogenation of the side chains of three SM donors on the structural, optoelectronic, and charge-transfer properties of donors and donor/PC61BM blends. Starting with experimentally prepared three novel SM donors with three different lateral side chains, we have computationally designed three halogenated donor SMs for each of those three SMs. Properties such as HOMO/LUMO energies, open-circuit voltages, and charge transfer/recombination rates are calculated. Halogenated systems have deeper HOMO values than parent systems, and as a result, larger open-circuit voltages are obtained for these new systems. In the halogenated systems, rates of charge-transfer and charge-recombination are larger and smaller, respectively, than in the parent systems. All these indicate better photovoltaic performances of these halogenated SM-based devices.