Recent advances in organic optoelectronics, particularly in efficient organic light-emitting devices (OLEDs), have called for new electro-active organic materials as well as for new device technologies. Small OLED-based displays already generate hundreds of millions of dollars. Larger OLED displays will penetrate the television market in the not-too-distant future. Nowadays white displays play important role in lightening. Further advances of these devices substantially rely on development and studying of high-performance organic charge-transport and emitting materials, theoretical understanding of charge and energy transport in the organic systems and their well-balanced application in OLED devices. About one third world’s electric energy is used for lightning technologies. Until a half of the electric energy would be saved after development of efficient organic light emitting diodes-based lightning. The project is contributed with energy saving technologies – lightning by organic light emitting diodes and respectively with factor of economic benefit as well as with new scientific information for scientific community.
Project funding:
KTU Research and Innovation Fund
Project results:
Several groups of new organic compounds, that were used in OLED devices as a positive charge transporting host, were synthesized. New carbazole and quinoxaline based low molar mass bipolar derivative was synthesized, characterized and tested as hole transporting host derivative in phosphorescent OLED. The material could form homogeneous amorphous materials (layers) with very high glass transition temperature of 136 oC and also with very high initial thermal decomposition temperature of about 387 oC. The electron photoemission spectra of the layers of the synthesized compound showed ionization potentials of about 5.85 eV. The compound was tested as host material for green Ir(ppy)3, blue FIrpic and yellow PO-01 triplet phosphorescent guests. The device with the yellow PO-01 triplet emitter exhibited the best overall performance. The most efficient yellow OLED demonstrated turn-on voltage of 4.9 V, a maximum brightness exceeding 4050 cd/m2 and current efficiency of 10.8 cd/A with power efficiency of 6.9 lm/W at 100 cd/m2.
New electroactive derivative: 2,7-di(4-biphenyl)-9,9-dihexylfluorene was synthesized and characterized as charge transporting host for electroluminescent devices. The compound is thermally stable and forms solution processed homogeneous electro-active amorphous layers with glass transition temperature of 47 ?C. The derivative has been tested as hole transporting material in multilayer organic light emitting diodes with Alq3 as the emitter and electron transporting layer. A device with hole injecting layer of PEDOT and with the hole transporting layer of 2,7-di(4-biphenyl)-9,9-dihexylfluorene exhibited good overall performance with low turn on voltage of 3.2 V, maximum brightness exceeding 15600 cd/m2 and photometric efficiency of about 4.5 cd/A. The device was highly stable in the observed luminance window up to high brightness of about 2000 cd/m2.
A series of novel fluorene-based hole transporting hosts, 9,9-diethyl-2,7-bis(2-(trifluoromethyl)phenyl)-9H-fluorene, 9,9-diethyl-2,7-bis(3-(trifluoromethyl)phenyl)-9H-fluorene and 9,9- diethyl-2,7-bis(4-(trifluoromethyl)phenyl)-9H-fluorene containing symmetrical and asymmetrical substitution of trifluoromethyl pendants at different positions were synthesized. The synthesized materials have an exceptional solubility in common organic solvents and possess good thermal stability to form morphologically stable films. The relevant molecular energy level alignment (HOMO-LUMO), adequate ionization potential and high triplet energies promote materials performance as a good hole transporting host. Solution-processed yellow phosphorescent OLEDs fabricated with a conventional yellow emitter Iridium(III)bis(4-phenylthieno[3,2-c]pyridinato-N,C2′)acetylacetonate (PO-01) doped in 4,4?-bis(N-carbazolyl)-1,1?-biphenyl (CBP) host. The best device with 9,9-diethyl-2,7-bis(3-(trifluoromethyl)phenyl)-9H-fluorene showed an improvement of 54% in CE from 23.3 to 35.8 cd/A and 14% in EQE from 11.3 to 12.9%, compared to reference device containing N, N?-Bis(naphthalen-1-yl)-N,N?-bis(phenyl)benzidine (NPB) as HTL.
Period of project implementation: 2020-04-14 - 2020-12-31
Project coordinator: Kaunas University of Technology
