Prof. Gitti Frey
Department of Materials Science and Engineering, Technion
The performance and stability of organic electronic devices are intimately linked to the microstructure of their active layers, particularly in systems based on material blends. These systems exhibit complex phase morphologies that strongly influence key processes such as charge transport, recombination, and extraction processes. The morphologies are often metastable, featuring a mixture of pure and mixed phases with varying degrees of crystallinity. Therefore, understanding the thermodynamic and kinetic factors governing phase evolution is essential to improving device functionality, performance and longevity. One example is organic solar cells (OSCs), where the active layer—typically a donor:acceptor bulk heterojunction (BHJ) blend—features a heterogeneous microstructure that strongly influences charge generation and transport. We developed a selective staining method for electron microscopy to visualize BHJ domains and track morphology changes during annealing. This allowed us to propose a thermodynamic and kinetic model correlating microstructural evolution with performance. In parallel, we employed a blend-based strategy in organic electrochemical transistors (OECTs), combining p-type and n-type mixed ionic-electronic conductors (OMIECs). By tuning composition and thermal processing, we controlled phase separation and crystallinity to optimize ionic and electronic transport. This approach yielded ambipolar OECTs and dual-mode devices that function as both Electrolyte-Gated Organic Field-Effect Transistors (EGOFETs) and OECTs, with distinct domains supporting different operational modes. Together, these case studies demonstrate how engineered blend microstructures can be leveraged to enhance performance, stability, and functionality in organic electronic devices.