| Abstract [eng] |
In the recent years organic light-emitting diodes and organic semiconductors are getting a lot of attention in the industry. These devices have a number of distinct advantages, including a low cost, quick and easy manufacturing process, durability, optical clarity, and light weight. Despite OLEDs' recent commercialization, primarily in smartphone and television displays, their external quantum efficiencies still remain below the theoretical limit. It is primarily concerned with the properties of organic semiconductors (OLED emitters). Solid state photoluminescence quantum yield close to the 100 percent, good stability under electrical excitations, ability to harvest both singlet and triplet excitons, sufficient energy levels for hole and electron injections, and so on are all characteristics of a good emitter. However, achieving a perfect combination of the aforementioned properties is extremely difficult, particularly when dealing with heavy-atom-free compounds. The aim of this research was to look at new group of organic semiconductors and show their potential to be used in OLED applications as emitters. The main object of the study were four heavy-atom-free compounds based on mono and tetra phenothiazine substituted tetraphenylethylenes containing cyano groups. UV-Vis spectrometry, photoelectron emission spectrometry, and time of flight measurements were used in order to investigate the photophysical, electrooptical, and charge transporting properties of the studied compounds prior to OLED fabrication. All studied compounds were characterized by prompt fluorescence with aggregation-induced emission enhancement properties. The investigated compounds emit efficiently in the solid state, with intensity of photoluminescence maxima ranging from 464 to 575 nm and photoluminescence quantum yields ranging between 19-28 percent, while optical band gaps were calculated to be in the range of 2.32 – 2.88 eV. Aggregation-induced emission enhancement for studied phenothiazine substituted tetraphenylethylenes derivatives was proved by testing them in THF/water solutions. Photoelectron emission spectrometry revealed that ionization potentials of the studied compounds ranged from 5.48 to 5.63 eV, while time-on-flight measurements showed that all compounds only capable to transport holes with maximum holes mobility of 1.67 × 10-4 cm2 /Vs. Based on obtained results three different OLEDs’ structures were fabricated using various fabrication techniques. The best OLED which had pure emission layer maximum brightness of 4070 cd/m2 , maximum current efficiency of 5.70 cd/A and external quantum efficiency of 1.73 %. The best hyperfluorescence based device was characterized by maximum external quantum efficiency of 8.2 %, current efficiency of 21.58 cd/A and maximum brightness of 3400 cd/m2 . |
