Activity: Talk or presentation › Talk or presentation at a conference
The intermolecular charge transfer (CT) state formed at the interface between the donor (D) and the acceptor (A) is crucial for the device performance of organic cavity-based near-infrared (NIR) photodetectors. In such a device, a high interfacial contact area between D:A is required because it significantly promotes the CT absorption . PBTTT:PC61BM, a well-known benchmark system, is selected because the intercalation of the fullerene acceptor between the side chains of the polymer donor maximizes the D:A contact . Two novel PBTTT derivatives were developed to further lower the energy gap between the HOMO of the donor and the LUMO of PC61BM, and thus extend the CT absorption of the device more into the NIR .
In this research, Rapid Heat-Cool DSC (RHC) and temperature-resolved synchrotron XRD are combined for the construction of state diagrams. As the phase behavior and morphology of the D:A mixtures directly affect the device performance, it is important to construct state diagram which reveal the composition-temperature-phase behavior relationships of the blends . RHC has been proven to be a well-suited technique for the construction of the state diagram, as it allows a relatively wide range of heating and cooling rates up to 2000 K/min . Temperature-resolved synchrotron XRD allows to study the structural changes accompanied by thermal transitions as a function of temperature. With the help of synchrotron XRD results, the complex phase behavior, including formation of cocrystals and eutectics, of the PBTTT:PC61BM benchmark system is revisited, and compared to the systems based on the novel derivatives. Furthermore, it is also found that homocoupling, a common defect arising from the synthesis of these donor materials, plays a crucial role in the intercalation behavior.