We fabricated a yellow organic light-emitting diode (OLED) based on the star-shaped donor compound tri(9-hexylcarbazol-3-yl)amine, which provides formation of the interface exciplexes with the iridium(III) bis[4,6-difluorophenyl]-pyridinato-N,C2']picolinate (FIrpic). The exciplex emission is characterized by a broad band and provides a condition to realize the highly effective white OLED. It consists of a combination of the blue phosphorescent emission from the FIrpic complex and a broad efficient delayed fluorescence induced by thermal activation with additional direct phosphorescence from the triplet exciplex formed at the interface. The fabricated exciplex-type device exhibits a high brightness of 38 000 cd/m(2) and a high external quantum efficiency.

The starburst carbazole derivative and phosphorescent bis-cyclometalated iridium(III) complex (IC2) were used for the preparation of multilayered “warm-white” organic light-emitting diodes (OLEDs), the emission spectra of which are modulated by the thickness of the phosphorescent layer. It was shown that the electroluminescence spectra of the fabricated devices are more extended into the visible region compared with the photoluminescence spectra of both component materials. The observed extension of the electroluminescence spectra can be assigned to the phosphorescent emission of the low-energy exciplex formed at the interface of the emissive layers. The quantum-chemical calculations performed by the DFT and (TD) DFT methods support the formation of the low-energy triplet exciplex at the interface of the IC2 layer and the neighboring layer of the starshaped carbazole-based compound, (4,4′,4″-tris[3-methylphenyl­(phenyl)amino] triphenylamine, tri(9-hexylcarbazol-3-yl)amine (THCA). Indeed, the triplet excited state of such bimolecular complex corresponds to intermolecular charge transfer between IC2 and THCA. The experimentally observed electrophosphorescence of these exciplexes is induced by strong spin–orbit coupling in the THCA:IC2 complexes due to the Ir(III) heavy atom effect. With dependence on the iridium(III)-complex film thickness (5–9 nm), the CIE coordinates changed from (0.41, 0.41) to (0.52, 0.47), corresponding to the warm white and orange color. The brightness of the fabricated OLEDs at the 15 V bias was in the range from 500 to 6000 cd/m2.

The single-layer and bilayer devices showed blue monomer, electromer or interface exciplex emission.

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Development of emissive materials for utilization in organic light-emitting diodes (OLEDs) remains a highly relevant research field. One of the most important aspects in the development of efficient emitters for OLEDs is the efficiency of triplet-to-singlet exciton conversion. There are many concepts proposed for the transformation of triplet excitons to singlet excitons, among which thermally activated delayed fluorescence (TADF) is the most efficient and widespread. One of the variations of the TADF concept is the hot exciton approach according to which the process of exciton relaxation into the lowest energy electronic state (internal conversion as usual) is slower than intersystem crossing between high-lying singlets and triplets. In this paper, we present the donor–acceptor materials based on 2-pyridone acceptor coupled to the different donor moieties through the phenyl linker demonstrating good performance as components of sky-blue, green-yellow, and white OLEDs. Despite relatively low photoluminescence quantum yields, the compound containing 9,9-dimethyl-9,10-dihydroacridine donor demonstrated very good efficiency in sky-blue OLED with the single emissive layer, which showed an external quantum efficiency (EQE) of 3.7%. It also forms a green-yellow-emitting exciplex with 4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine. The corresponding OLED showed an EQE of 6.9%. The white OLED combining both exciplex and single emitter layers demonstrated an EQE of 9.8% together with excellent current and power efficiencies of 16.1 cd A–1 and 6.9 lm W–1, respectively. Quantum-chemical calculations together with the analysis of photoluminescence decay curves confirm the ability of all of the studied compounds to exhibit TADF through the hot exciton pathway, but the limiting factor reducing the efficiency of OLEDs is the low photoluminescence quantum yields caused mainly by nonradiative intersystem crossing dominating over the radiative fluorescence pathway.

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The work is dealing with the problem of developing an embedded system for supply voltage converter of Organic Light-Emitting Diode (OLED) with advanced built-in ability to measure the volt-ampere (I – V) characteristics of structures directly during their operation. This feature is crucial in the development of a new generation of intelligent OLED controllers, which in relation to known solutions, are characterized by reduced power consumption and increased speed of periodic or continuous measurement of the I – V characteristics of OLED structures. On the basis of such measurement the drift of characteristics of OLED structures in the course of their operation is carried out, and therefore, the possibility of operative correction of their power modes is provided. The measurement of I – V characteristics of OLED structures is performed on the transients of voltage generation in the boost circuits of the drivers. To meet the requirements for such measurements, the parameters of the transient pulses must meet certain criteria. The pulse amplitude should be sufficient to scan the I – V characteristics of OLED structures in the whole range of their possible operation, and the shape and rise time should be optimal from the point of view of further detection of these I – V patterns, in particular, regarding their drift in temperature modulation or OLED structure degradation. In a number of tasks scanning and measurement of I – V characteristics should be fast enough to prevent heating, but acceptable for high-precision analog-to-digital conversion. The parameters of the pulses provide the ability to measure the thermal parameters of thermal resistance and its dependence on the duration of heating. The controller is implemented on the basis of programmable systems on the chip, namely on the PSoC 5LP.