Browsing by Author "Choi, S."
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Item Recent Advances in the Science and Engineering of Organic Light-Emitting Diodes(SPIE) Kippelen, B.; Gaj, M. P.; Zhang, X.; Choi, S.; Fuentes-Hernandez, C.; Zhang, Y. D.; Barlow, S.; Marder, S. R.; Voit, Walter E.; Wei, Andrew; So, F.; Adachi, C.; Kim, J. J.; Voit, Walter E.; Wei, AndrewIn this talk, we will discuss recent advances in the science and engineering of organic light-emitting diodes (OLEDs). First, we will focus on materials in which light emission involves the process of thermally activated delayed fluorescence (TADF). In these materials, triplet excited states can convert into optically emissive singlet excited states by reverse intersystem crossing, allowing for nearly 100% internal quantum efficiency. This process can be used to design a new class of materials that are all organic, offering a lower cost alternative to conventional electrophosphorescent materials that contain heavy and expensive elements such as Pt and Ir. We will discuss molecular design strategies and present examples of materials that can be used as emitters or hosts in the emissive layer. In a second part of this talk, we will review recent progress in fabricating OLEDs on shape memory polymer substrates (SMPs). SMPs are mechanically active, smart materials that can exhibit a significant drop in modulus once an external stimulus such as temperature is applied. In their rubbery state upon heating, the SMP can be easily deformed by external stresses into a temporary geometric configuration that can be retained even after the stress is removed by cooling the SMP to below the glass transition temperature. Reheating the SMP causes strain relaxation within the polymer network and induces recovery of its original shape. We will discuss how these unique mechanical properties can also be extended to a new class of OLEDs. ©2016 SPIEItem ZnO Composite Nanolayer with Mobility Edge Quantization for Multi-Value Logic Transistors(Nature Publishing Group, 2019-04-30) Lee, L.; Hwang, Jeongwoon; Jung, J. W.; Kim, J.; Lee, H. -I; Heo, S.; Yoon, M.; Choi, S.; Van Long, N.; Park, J.; Jeong, J. W.; Kim, Jiyoung; Kim, K. R.; Kim, D. H.; Im, S.; Lee, B. H.; Cho, Kyeongjae; Sung, M. M.; 0000-0003-2781-5149 (Kim, J); 0000-0003-2698-7774 (Cho, K); 70133685 (Kim, J); 369148996084659752200 (Cho, K); Hwang, Jeongwoon; Kim, Jiyoung; Cho, KyeongjaeA quantum confined transport based on a zinc oxide composite nanolayer that has conducting states with mobility edge quantization is proposed and was applied to develop multi-value logic transistors with stable intermediate states. A composite nanolayer with zinc oxide quantum dots embedded in amorphous zinc oxide domains generated quantized conducting states at the mobility edge, which we refer to as “mobility edge quantization”. The unique quantized conducting state effectively restricted the occupied number of carriers due to its low density of states, which enable current saturation. Multi-value logic transistors were realized by applying a hybrid superlattice consisting of zinc oxide composite nanolayers and organic barriers as channels in the transistor. The superlattice channels produced multiple states due to current saturation of the quantized conducting state in the composite nanolayers. Our multi-value transistors exhibited excellent performance characteristics, stable and reliable operation with no current fluctuation, and adjustable multi-level states. ©2019, The Author(s).