Thermal treatment on vertical morphology of PffBT4T-2OD: ITIC non-fullerene bulk heterojunction thin films

Full text: Solution-processable organic solar cells are extensively attractive in academic and industrial fields with the advantages of roll-to-roll processing and flexible and lightweight large area devices. Bulk- heterojunction (BHJ) is a device architecture comprising electron donors and acceptors in the mixtures. The donor-acceptor mixed phases in the BHJ morphology aid in dissociating the photogenerated excitons and transporting the charges to the respective electrodes through the individual phase segregation. Therefore, optimizing BHJ nanomorphology for efficient exciton dissociation and charge extraction highly determines the device performance. Neutron reflectivity is conducive to probing the vertical morphology in a blend film. In this work, PffBT4T-2OD and ITIC are used as donor and acceptor materials in a BHJ layer. The study aims to (1) profile the vertical distribution of donor and acceptor phases in the blend film. Reveal the effect of donor-acceptor composition and solvents on the morphology change of the BHJ layer. (2) understand the changes in vertical morphology through thermal annealing. The elevated temperature possibly initiated the preferred molecular interaction to generate a morphology change in the BHJ layer. These results will complement the other characterization techniques, such as AFM, GIWAXS, and molecular dynamics simulation, assisting in developing high efficient non-fullerene organic solar cells. (Author)