Periodic Reporting for period 1 - TADFsolutions (- addressing the challenges of high-performance solution-processed OLEDs using sustainable materials)
Reporting period: 2022-10-01 to 2024-09-30
In the 21st century, displays play a central role. They are embedded in almost every type of electronic device and it is difficult to imagine a world without mobile phones, monitors and televisions. Driving the pervasiveness of displays is the disruptive organic light-emitting diode (OLED) technology. There are, however, some structural weaknesses in state-of-the-art vacuum-deposited OLEDs. These include the use of scarce metals within the materials of the device and the reliance on energy-intensive and expensive vacuum deposition fabrication methods. Solutions are required to make these devices more sustainable from choice of materials to manufacturing processes. The European Doctoral Training Network TADFsolutions will train a cohort of dynamic researchers to devise, develop and implement sustainable solutions for improving the device performance of solution-processed OLEDs. The 10 PhD scientists will undertake multidisciplinary research to meet this design challenge. Despite being cheaper, the current best solution-processed OLEDs (SP-OLEDs) still rely on scarce noble-metal based phosphorescent emitters and underperform compared to vacuum-deposited OLEDs. Starting from bespoke organic thermally activated delayed fluorescence emitter materials, the performance of SP-OLEDs will be maximized based on improved predictive models of charge transport, film processing techniques, and device structures. A strongly interconnected approach is required not only to effectively train the DFs but to meet the objectives. The TADFsolutions network consists of 8 leading European academics, 4 companies and 6 international partners that are equipped and experienced to not only confront the materials and device design challenges but to provide a robust multidisciplinary and intersectoral training environment to ensure that the DFs have the requisite skills, both soft and technical, to enter the employment market and contribute to securing Europe’s leading role in OLED materials.
Hence, the goal of TADFsolutions is to develop highly efficient OLED emitters that can be processed using solutions. The materials should become more efficient, have higher colour purity, and be more stable. We structured our efforts into two research lines. One line focusses on the development of suitable materials, the other line was concerned with advancing the technology of OLED design. Regarding the materials, we aimed for compounds that simultaneously fulfil the requirement of giving efficient electroluminescence, a narrow linewidth of emission and that result in a long lifetime of the OLED, i.e. that do not degrade notably over time. To this aim, we have developed novel emitters that do not use scarce metals. These emitters are based on different material classes. They comprise of dendrimer, liquid crystals and chiral polymer emitters with high luminescence efficiency. Furthermore, we made significant progress with OLED designs where energy is transferred from abundantly formed non-emissive triplet states to narrow linewidth emitters (hyperfluorescent OLEDs). The OLED efficiency could also be enhanced by developing new materials for efficient charge injection and transport, notably for positive charges, which greatly enhances charge balance in the OLED and hence the external quantum efficiency in solution-processed devices. We also made progress in integrating the hybrid semiconductor material perovskites in the OLED structure, both as a layer for charge injection and as an efficient material for light emission. These experimental advances were complemented by theory and simulation. We developed models to simulate light and charge propagation in OLEDs, taking care to include the effect of the structural inhomogeneities associated with solution processed layers. Finally, simulations to control the internal temperature in the OLED were performed. They serve as basis for further optimization of device architecture.
This project focuses on improving OLED technology using solution-based processing instead of traditional vacuum methods. The goal is to match or exceed current performance levels while making the process more sustainable and cost-effective. At this mid-term stage, a number of scientific publications have highlighted our progress on solution-processed OLED's, with improved emitter materials, and with our new developments regarding new processing techniques that can also benefit solar cells, sensors, and other applications. From an industrial perspective, the project promotes environmentally friendly manufacturing by reducing energy use and material waste. It also moves away from using rare and unsustainable metals in displays. The research has broader implications for organic electronics, including flexible displays, memory devices, and solar cells. Additionally, advancements in modeling and simulation, particularly in OLED efficiency and electro-thermal modeling, will contribute to the next generation of commercial software. On a societal level, the project has provided valuable training and career opportunities for students, enhancing their skills through workshops, conferences, and international collaborations. It also strengthens Europe's role in scientific research while involving key partners from Asia and industry leaders. Economically, patents and commercialization of research findings are expected in the later stages of the project, further driving innovation and industry adoption.