TSFP · Thermally activated delayed fluorescence (TADF) sensitized fluorescent emitting polymers for low cost solution-processing organic light emitting diodes (OLEDs)

Thermally activated delayed fluorescence (TADF) sensitized fluorescent emitting polymers for low cost solution-processing organic light emitting diodes (OLEDs)

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.

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