Towards Multi-Layer Polymer Electronics through Tailored Thermal Treatments

• Applicant: Dr.-Ing. Katherina Haase
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Polymer Materials
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555553457

Recent efforts in conjugated polymer (CP) chemical design and processing methodologies have yielded distinctly enhanced polymer-based electronic devices. However, the often-limited sequential solution-coating ability, which arises from similar solubilities of many successful CPs, has essentially hampered their use in many novel and promising device architectures. Therefore, a multitude of strategies, ranging from the targeted chemical synthesis of cross-linkable polymers to innovative process engineering such as protective solvent coatings, have been developed. While those results are already very promising, many strategies are limited to specific CPs, require dedicated synthesis, or could lead to unintended doping or degradation of devices. Hence, the development of immobilization strategies with low chemical, thermal, and radiative loads, but wide compatibility is highly desirable. This project investigates the use of thermal physical cross-linking (TPC) for sequential solution-coating. The TPC effect was recently observed and reported for several conjugated polymers. It is characterized by a change in the polymer thin films’ resistance against its original solvent upon the morphological changes occurring during post-deposition annealing. TPC adds a novel element to the pool of available multilayer processing strategies and stands out due to its simplicity, close to zero added process complexity, elimination of cross-linking additives and prevention of possible reaction residues. However, so far there has not been any dedicated study on the mechanism and its potential use for the fabrication of multilayer polymer electronics. This is where the focus of this project lies. The aim is to understand how TPC can be utilized in the fabrication of multilayer devices by essentially mapping out its limitations and determining the material properties that are a prerequisite for TPC to occur. These findings are then applied to the sequential solution-based fabrication of novel multilayer structures with a focus on organic transistors. Whilst organic transistors might not constitute devices that are instantaneously associated with multilayer sequential coating, they can benefit in a multitude of ways from vertically stacked layer architectures, such as in the context of anti-ambipolar transistors (AATs) and hetero-structured OFET memory. Yet, their respective device layouts are comparably simple (e.g., in contrast to OLEDs), and both, lateral and vertical device designs can be adopted - factors which render them suitable templates for this device study. Furthermore, the anticipated devices - if successfully realized - have high novelty and would therefore constitute a significant contribution in the area of polymer-based electronics. Beyond these devices, the project will provide new insights and inspiration for the further development of physical cross-linking strategies and their use for even more complex device designs.

• DFG Programme: Research Grants