Inorganic materials-based light sources have been widely used throughout the last century, ranging from extremely low-efficiency incandescent bulbs to reasonably-efficient light-emitting diodes (LEDs), which are still widely used today regardless of the heavy metals (mercury, gallium, indium) or compounds thereof that they contain, mechanical fragility of the structure, and the cost of disposal. However, organic light-emitting diodes (OLEDs) with higher luminance and efficiency are gaining ground alongside LED-type sources. Devices such as flexible TVs, phones with employed flexible light-emitting and image-generating OLED matrices were already been presented at world exhibitions (CES, CEATEC) and can be purchased on the market. Still the most important issues related with short lifetime of devices remain. Together with materials optical properties OLED efficiency and lifetime is also strongly related with thermal and electrochemical stability of all materials. Around 40-50% of the OLED structures, published in scientific review journals, are formed using commercially available hole transporting materials – TCTA, NPB, TAPC – although their stability has long been called into question. Therefore, our aim is related with the tuning of commercially available hole transporting materials (TCTA, MTDATA, NPB, TAPC) by inserting alkoxy or N,N-dialkylamine substituents into their structures, in order to:
-increase the morphological stability of the HTL layers and to enhance the transportation of holes towards the emission layer;
-increase the electrochemical stability of compounds;
-ensure that compounds are capable of forming stable molecular glasses;
-increase compounds HOMO values in order to improve the efficiency of the hole injection from the side of the anode.
Project funding:
This research project is funded by the European Social Fund according to the 2014–2020 Operational Programme for the European Union Funds’ Investments, under measure’s No. 09.3.3-LMT-K-712 activity “Promotion of postdoctoral fellowships studies”.
Project results:
New hole transporting materials which have triphenylamine, carbazole, naphthyl and biphenyl moieties were synthesized and identified. Every target structure possess methoxy, ethoxy and dimethylamine electrondonating groups. During the project thermal, electrochemical, photophysical, photoelectrical, charge transporting and optoelectrical properties of all new derivatives were investigated and compared with the results of commercial counterparts. Additionally, effect of methoxy-substitutions on the hole transport properties of carbazole-based compounds was studied using computational approaches. Results were presented in two international conferences (GSELOP2021 ir IPOE2022) and published in the following high rated journals: Journal of Materials Chemistry C (DOI: 10.1039/d1tc02000e), Physical Chemistry Chemical Physics (DOI: 10.1039/d2cp03811k).
Period of project implementation: 2020-08-14 - 2022-08-13
Project coordinator: Kaunas University of Technology
