Fine structural tuning of diketopyrrolopyrrole-cored donor materials for small molecule-fullerene organic solar cells: A theoretical study

Two novel strategies to tune diketopyrrolopyrrole and its derivatives by lactam-lactim and alkoxy-thioalkoxy exchange were theoretically presented for improving the efficiency of bulk heterojunction solar cells. The structural tunings could synergistically reduce the HOMO level and the energy gap of donors due to the disrupted aromaticity of the linked pyrrole derivatives. Compared with the parent molecule, the new designed donors not only create a more red-shift of absorption spectrum but also show better hole transport rates, larger fill factor, higher open circuit voltage and more favorable solar cell efficiency. Moreover, the arrangements at the interface and the optical properties of the donor-PCBM complexes were computationally investigated to get insight into the absorption of charge transfer states. Consequently, the strategies are judicious approaches to enhance their intrinsic properties of donors and can be used for further improving the performance of other DPP-based molecules in bulk heterojunction solar cells. (C) 2016 Elsevier B.V. All rights reserved.