Periodic Reporting for period 1 - TSFP (Thermally activated delayed fluorescence (TADF) sensitized fluorescent emitting polymers for low cost solution-processing organic light emitting diodes (OLEDs))
Berichtszeitraum: 2019-09-16 bis 2021-11-15
Organic light-emitting diode (OLED) displays are currently used extensively in small displays such as smart phones, watches and automotive displays due to their excellent colour reproduction, high contrast ratio and low power consumption relative to alternative technologies, such as LCDs (liquid crystal displays). There is strong demand for the excellent picture quality of OLED displays in larger displays such as laptops, computer monitors and TVs. However, the cost to manufacture OLED displays through the current, vacuum deposition, manufacturing techniques is extremely high and OLED displays are only available in very expensive, premium displays. Vacuum deposition (VD) fabrication techniques are energy intensive, wasteful of materials and scale poorly to large display areas. As a result, it is only suited to small OLED display panels and is cost-prohibitive in comparison to other display technologies like LCDs for large displays. In contrast, solution-processing (SP) technology such as ink-jet printing provides a lower-cost alternative that uses less energy and materials to fabricate OLED displays and easily scales to large area panels. Despite the lower production cost, the adoption of SP-OLEDs has been slower due to poorer display quality, with SP-OLEDs exhibiting poorer colour reproduction, brightness, and efficiency in comparison to VD-OLEDs. Recent improvements in the materials available for use in SP-OLEDs has improved display performance to the point where it is suitable for commercial fabrication. Like VD-OLEDS, current SP-OLEDs use emitters that are based on the scarce, expensive heavy metal Iridium (cost – US$5400/Oz, global production 3 tonnes per annum). Replacing these emitters with more economical and sustainable materials is essential to large scale, cost effective manufacturing of large area OLED displays. Solution-processed OLEDs must address two technical challenges to become a viable alternative. First, the performance of solution-processed devices must improve to compete with vacuum-deposited OLEDs. Secondly, the emitter materials must be synthesized from more sustainable sources, which is particularly relevant for medium to large size OLED panels where the volume of emitter material used is significantly larger.
A sustainable solution to this issue is to develop purely organic emitters that can harvest 100% exciton in OLEDs. Thermally activated delayed fluorescent compounds (TADF) can harvest dark triplets via thermal back population of singlets from triplets. However, only a handful of TADF emitters have been developed for solution-processed OLEDs which also show moderate performance that cannot compete with vacuum deposited OLEDs. We have developed organic, sustainable emitters that are ideally suited for SP-OLEDs and address the two main issues with adoption of this technology. By improving the performance of SP-OLEDs, our materials ensure that solution processing is a viable manufacturing method to produce high quality OLED displays. Our emitters are also free of scarce, expensive heavy metals that have previously been an integral part of all OLED emitters. Combining the change in manufacturing method with the lower cost, our developed metal-free emitters will significantly reduce OLED fabrication costs. The outcome of this project will strengthen EU’s leading role as material supplier for OLED displays.
A sustainable solution to this issue is to develop purely organic emitters that can harvest 100% exciton in OLEDs. Thermally activated delayed fluorescent compounds (TADF) can harvest dark triplets via thermal back population of singlets from triplets. However, only a handful of TADF emitters have been developed for solution-processed OLEDs which also show moderate performance that cannot compete with vacuum deposited OLEDs. We have developed organic, sustainable emitters that are ideally suited for SP-OLEDs and address the two main issues with adoption of this technology. By improving the performance of SP-OLEDs, our materials ensure that solution processing is a viable manufacturing method to produce high quality OLED displays. Our emitters are also free of scarce, expensive heavy metals that have previously been an integral part of all OLED emitters. Combining the change in manufacturing method with the lower cost, our developed metal-free emitters will significantly reduce OLED fabrication costs. The outcome of this project will strengthen EU’s leading role as material supplier for OLED displays.
Each WP consists of designing materials, computational screening, designing synthetic routes, successful synthesis with high purity, optoelectronic characterization and finally investigating their EL performance.
Work Package 1
Regiochemistry of Donor Dendrons Controls the Performance of Thermally Activated Delayed Fluorescence Dendrimer Emitters Translating in Their Use in High Efficiency Solution-Processed Organic Light-Emitting Diodes: We have developed a series of TADF dendrimers by adjusting the donor dendron substitution pattern about the central triazine acceptor. Our study reveals that the reorganization energies and thus the reverse intersystem crossing (RISC) rate can be controlled by the regiochemistry of the donor dendrons. We demonstrate a two-fold improved EQE in solution-processed OLEDs using meta-connected versus a para-connected TADF dendrimers as emitters. This work is going to be submitted to a peer-reviewed journal.
Work package 2
Thermally Activated Delayed Fluorescent Dendrimers that Underpin High-efficiency Host-Free Solution-Processed Organic Light Emitting Diodes: We developed a rational design of a donor-acceptor dendrimer emitter that shows remarkable photophysical properties, including efficient TADF and high photoluminescence quantum yield. We demonstrate its use in a host-free solution-processed OLED that shows record-high external quantum efficiencies. This work is going to be submitted to a peer-reviewed journal.
Work package 3
Star-Shape Thermally Activated Delayed Fluorescence Emitters for High Efficiency Non-Doping Solution-Processed Organic Light-Emitting Diodes: We designed and synthesised a solution-processable TADF emitter by encapsulating the core unit with closely packed multiple donors. We observed less concentration quenching by this design and the non-doped OLEDs can maintain the performance as in the doped devices, which simply the device configurations. This work is under preparation and will be submitted to a peer-reviewed journal.
Work Package 1
Regiochemistry of Donor Dendrons Controls the Performance of Thermally Activated Delayed Fluorescence Dendrimer Emitters Translating in Their Use in High Efficiency Solution-Processed Organic Light-Emitting Diodes: We have developed a series of TADF dendrimers by adjusting the donor dendron substitution pattern about the central triazine acceptor. Our study reveals that the reorganization energies and thus the reverse intersystem crossing (RISC) rate can be controlled by the regiochemistry of the donor dendrons. We demonstrate a two-fold improved EQE in solution-processed OLEDs using meta-connected versus a para-connected TADF dendrimers as emitters. This work is going to be submitted to a peer-reviewed journal.
Work package 2
Thermally Activated Delayed Fluorescent Dendrimers that Underpin High-efficiency Host-Free Solution-Processed Organic Light Emitting Diodes: We developed a rational design of a donor-acceptor dendrimer emitter that shows remarkable photophysical properties, including efficient TADF and high photoluminescence quantum yield. We demonstrate its use in a host-free solution-processed OLED that shows record-high external quantum efficiencies. This work is going to be submitted to a peer-reviewed journal.
Work package 3
Star-Shape Thermally Activated Delayed Fluorescence Emitters for High Efficiency Non-Doping Solution-Processed Organic Light-Emitting Diodes: We designed and synthesised a solution-processable TADF emitter by encapsulating the core unit with closely packed multiple donors. We observed less concentration quenching by this design and the non-doped OLEDs can maintain the performance as in the doped devices, which simply the device configurations. This work is under preparation and will be submitted to a peer-reviewed journal.
We developed a series of highly efficient TADF dendrimers with a simple strategy which affords an extremely efficient utilization of triplet excitons because of a vanishing singlet-triplet splitting energy, that is critical to determine the efficiency of TADF materials. From our thorough investigation of the photophysical properties in toluene solution, we were able to reveal the origin and nature of the lowest excited states. Systematic investigations demonstrated the validity of this design strategy for a highly efficient TADF dendrimer. These outcomes further inspired us to improve the photophysical properties and device performance through the synergistic effects of different connections. Importantly, the reverse intersystem crossing is significantly increased, and the distribution of donor dendrons can effectively suppress concentration quenching. The extremely small EST and large oscillator strength in both solution and neat film are evidence of the qualities that make our TADF dendrimers high-performance emitters in efficient solution-processed OLEDs. The outcome of this project about the dendrimer design strategy provides a route to high-performance solution-processed TADF OLEDs and evidences the full potential of dendrimers as emissive materials.
All the work carried out during this project is aimed at developing cost-effective, easy to access and sustainable solution-processable emitters for display applications. The work carried out in this project is of potential impact to the OLED manufacturers who seek emitter solutions for next-generation solution-processed OLEDs. The outcomes underpin the spin-out of a company in which I am a co-founder. I have been awarded a prestigious RAEng Enterprise fellowship recently. I will continue to drive the innovation, lead the research and commercialization.
All the work carried out during this project is aimed at developing cost-effective, easy to access and sustainable solution-processable emitters for display applications. The work carried out in this project is of potential impact to the OLED manufacturers who seek emitter solutions for next-generation solution-processed OLEDs. The outcomes underpin the spin-out of a company in which I am a co-founder. I have been awarded a prestigious RAEng Enterprise fellowship recently. I will continue to drive the innovation, lead the research and commercialization.