| Abstract [eng] |
The aim of this work is to produce red thermally activated delayed fluorescence OLED featuring high efficiency and to study the electrical and electroluminescence properties of the device. Two series of organic light-emitting diodes named R and Pi have been manufactured. The emissive layer matrix for the R series OLEDs is TPBi and for Pi series devices – newly synthesized phenanthroimidazole compounds. If the emissive layer of the OLED is a pure emitter layer, due to strong concentration quenching and aggregation, the OLED exhibit 1.2% external quantum efficiency and emit light at 710 nm. OLED exhibits high, up to 7.2% external quantum yield when the emitter molecules are dispersed in the matrix. Due to reduced aggregation of the emitter molecules, the OLED emission blue shifts as compared to the emission of a pure emission layer OLED. New phenanthroimidazole compounds synthesized at Kaunas University of Technology were employed to produce Pi series OLEDs. The compounds show a good energy transfer to the emitter, according to a study made by the scientists of Institute of Photonics and Nanotechnology at the Vilnius University Faculty of Physics. The analysis of electrical and optical characteristics showed that matrix 2PiPt is not suitable due to triplet exciton back transfer caused by similar matrix and emitter triplet levels. The structure of OLED fabricated using phenanthroimidazole-carbazole matrix was optimized by hole injection layer, electron injection layer and emitter concentration in the emissive layer optimization stages and eventually a new optimized orange–red thermally activated delayed fluorescence OLED structure was created: ITO/TAPC(50nm) / PiCz:TPA-DCPP(4 %)(20 nm) / DPEPO(5 nm) / TPBi(50 nm) / LiF(0,8 nm) / Al(100 nm). |
