| Summary: | 碩士 === 國立臺灣海洋大學 === 光電科學研究所 === 103 === In this thesis, we study about the thermally activated delayed fluorescence (TADF) light emitting devices. TADF enables triplet excitons to up-convert to emissive singlet excitons through effective reverse intersystem crossing (RISC) to reach 100 % exciton harvesting ability. As a result, TADF has evolved to be the most feasible EL mechanism for the next-generation OLED in replace of the high-cost PhOLEDs. In first part, we reported two TADF host materials (pCNCz and pCNCz-PH) to evaluated the performance of OLEDs containing the dopants 4CzIPN (green emission), 4CzTPN (yellow emission) and 4CzTPN-Ph (orange emission) as emitters. In order to estimate the theoretical enhancement of EL efficiency, we setup a time-resolved spectrometer system and absolute photoluminescence quantum yield measurement system to measure transient PL and PL Q.Y. By employing pCNCz-PH : 4CzIPN as an emitter, we have achieved high-performance TADF-based green OLEDs, exhibiting EQE as high as 15.4 %. The yellow and orange OLEDs had EQE of 9.1 % and 8.2 %, respectively, which are also higher than those of conventional fluorescence-based OLEDs.
In the second part, we study of NPCz and NPDa with different linking topology as host materials to evaluate the performance of OLEDs. The different linking-topology and effective π-conjugation length comprehensively tune the energy levels and their bipolar transport abilities allowing to the unexpected high device performance. Notably, p-NPCz, employed as a TADF host doped with 4CzIPN, exhibited the remarkable maxima EQE of 18.5 % (60.8 cd/A and 53.8 lm/W). At rather high current densities, a high EQE of 17.7 % was obtained at 1000 cd/m2. From transient PL and PL Q.Y. analysis, the theoretical maximum EQE is thus estimated to be 18.5 % (assuming a light outcoupling efficiency of 20 %), which are close to experimental data. Therefore, near-complete carrier recombination and exciton confinement in the EML were realized in the device.
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