Development of high-efficiency white OLEDs using thermally activated delayed fluorescence(TADF)emitters

The current commercial OLED (organic light-emitting diode) lighting involves the use of phosphorescent emitters since nearly 100% internal quantum efficiencies are achievable. Excellent stability for red and green phosphorescent OLEDs has been observed, but performance of blue phosphors remains inadequate. OLEDs with fluorescent emitters have advantages in terms of lower cost, longevity, and the ability to use earth-abundant materials, but their internal efficiency has been limited by the physics of charge recombination to around 25%. Recent work has shown that OLEDs based on fluorescent materials with small singlet-triplet energy gaps can achieve nearly 100% quantum efficiency by enabling thermal activation of the triplet leading to delayed fluorescence from the excited singlet state (TADF). Use of blue TADF materials has significant potential advantages over the current blue phosphorescent emitters in reducing the triplet energy by 0.2-0.4 eV thereby decreasing the energy available for degradation processes. During Phase I, OLEDWorks will investigate commercially-available TADF materials to develop highly efficient and stable blue devices and incorporate these materials into tandem white OLEDs. This work will be a collaborative effort between OLEDWorks and the University of Rochester (UOR). The key properties of the blue TADF materials will be measured spectroscopically at UOR to identify promising device candidates. Advanced device design, fabrication, encapsulation and testing will be used to incorporate blue TADF materials into devices by OLEDWorks. Phase I goals are to quantify photophysical performance of TADF emitters, find promising materials and develop OLEDs demonstrating high efficiencies. In Phase II, OLEDWorks will do lifetime testing and systematic analysis of degradation routes of the successful Phase I materials that will enable us to address chemical instabilities by synthetic modification. The proposed research could lead to development and commercialization of OLED lighting products that would greatly benefit the lighting market. Incorporation of efficient and stable blue component(s) into white OLEDs will help to minimize the effects of blue stack degradation such as, for example, device color change during operation, and enable a wider selection of OLED lighting products, such as 4000K CCT lighting panels, to penetrate the market. Development and commercialization of US manufactured OLED lighting panels will reduce energy consumption and create US manufacturing jobs. Investigation of novel blue emitting OLED materials is critical to reduce the cost and improve the performance of OLED lighting panels, thereby enabling this key portion of the solid state lighting revolution.