Search

Organic light-emitting diodes (OLEDs) have emerged as one of the dominant technologies in displays due to their high emission efficiency and low power consumption. However, the development of blue color emitters has fallen behind that of red and green emitters, posing challenges in achieving optimal efficiency, stability, and accessibility. In this context, thermally activated delayed fluorescence (TADF) emitters hold promise as a potential solution for cost-effective, exceptionally efficient, and stable blue OLEDs due to their potential high efficiency and stability. TADF is a principle where certain organic materials can efficiently convert both singlet and triplet excitons, theoretically achieving up to 100% internal quantum efficiency. This research focused on diphenyl sulfone derivatives with carbazole groups as TADF compounds. Quantum chemical calculations and photoluminescence properties show the potential TADF properties of the molecules. New materials exhibit glass transition temperatures that would classify them as molecular glasses. Depending on the structure of the molecule, the photoluminescence emission is in the blue or green spectral region. Organic light-emitting diodes were fabricated from neat thin films of emitters by the wet casting method. The best performance in the deep blue emission region was achieved by a device with a turn-on voltage of 4 V and a maximum brightness of 178 cd/m2. In the blue-green emission region, the best performance was observed by an OLED with a turn-on voltage of 3.5 V, reaching a maximum brightness of 660 cd/m2. [ABSTRACT FROM AUTHOR]

Over the past few decades, organic light-emitting diodes (OLEDs) find applications in smartphones, televisions, and the automotive sector. However, this technology is still not perfect, and its application for lighting purposes has been slow. For further development of the OLEDs, we designed twisted donor-acceptor-type electroactive bipolar derivatives using benzophenone and bicarbazole as building blocks. Derivatives were synthesized through the reaction of 4-fluorobenzophenone with various mono-alkylated 3,3′-bicarbazoles. We have provided a comprehensive structural characterization of these compounds. The new materials are amorphous and exhibit suitable glass transition temperatures ranging from 57 to 102 °C. They also demonstrate high thermal stability, with decomposition temperatures reaching 400 °C. The developed compounds exhibit elevated photoluminescence quantum yields (PLQY) of up to 75.5% and favourable HOMO-LUMO levels, along with suitable triplet-singlet state energy values. Due to their good solubility and suitable film-forming properties, all the compounds were evaluated as blue TADF emitters dispersed in commercial 4,4′-bis(N-carbazolyl)-1,10-biphenyl (CBP) host material and used for the formation of emissive layer of organic light-emitting diodes (OLEDs) in concentration-dependent experiments. Out of these experiments, the OLED with 15 wt% of the emitting derivative 4-(9′-{2-ethylhexyl}-[3,3′]-bicarbazol-9-yl)benzophenone exhibited superior performance. It attained a maximum brightness of 3581 cd/m2, a current efficacy of 5.7 cd/A, a power efficacy of 4.1 lm/W, and an external quantum efficacy of 2.7%. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes (OLEDs) have played a vital role in showing tremendous technological advancements for a better lifestyle, due to their display and lighting technologies in smartphones, tablets, television, and automotive industries. Undoubtedly, OLED is a mainstream technology and, inspired by its advancements, we have designed and synthesized the bicarbazole-benzophenone-based twisted donor–acceptor–donor (D-A-D) derivatives, namely DB13, DB24, DB34, and DB43, as bi-functional materials. These materials possess high decomposition temperatures (>360 °C) and glass transition temperatures (~125 °C), a high photoluminescence quantum yield (>60%), wide bandgap (>3.2 eV), and short decay time. Owing to their properties, the materials were utilized as blue emitters as well as host materials for deep-blue and green OLEDs, respectively. In terms of the blue OLEDs, the emitter DB13-based device outperformed others by showing a maximum EQE of 4.0%, which is close to the theoretical limit of fluorescent materials for a deep-blue emission (CIEy = 0.09). The same material also displayed a maximum power efficacy of 45 lm/W as a host material doped with a phosphorescent emitter Ir(ppy)3. Furthermore, the materials were also utilized as hosts with a TADF green emitter (4CzIPN) and the device based on DB34 displayed a maximum EQE of 11%, which may be attributed to the high quantum yield (69%) of the host DB34. Therefore, the bi-functional materials that are easily synthesized, economical, and possess excellent characteristics are expected to be useful in various cost-effective and high-performance OLED applications, especially in displays. [ABSTRACT FROM AUTHOR]

Well-defined electroactive bipolar derivatives of new structure have been synthesized from 3-(N,N-diphenylamino)-9H-carbazole and bis(4-fluorophenyl)sulfone, 4-fluorophenylsulfone or 4,4′-difluorobenzophenone, respectively. The full characterization of their structure is described. The amorphous materials with very high glass transition temperatures of 111–173 °C also possess high thermal stability, with onset decomposition temperatures of 351–398 °C. Some of the compounds having the best solubility were tested as the emitters dispersed in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host for preparation of organic light emitting diodes (OLEDs). A device containing 15 wt% of the guest bis[4-{3-(N,N-diphenylamino)carbazol-9-yl}phenyl] sulfone demonstrated the best overall characteristics with maximum brightness exceeding 2630 cd/m2, current efficiency of 3.2 cd/A, power efficiency of 2.2 lm/W, and external quantum efficiency exceeding 1.7% at 100 cd/m2. [ABSTRACT FROM AUTHOR]

The N-alkylcarbazoles with different aromatic fragments at the carbazole core's 3, 6 and 8 positions were synthesized and characterized as potential compounds for optoelectronics. Their thermal, electrochemical and optical properties were determined by considering the effect of their chemical structure. The experimental results were supported by the theoretical calculations (DFT). The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results showed high thermal stability in the range of 346 – 410 °C of the investigated N-alkylcarbazoles and the possibility of forming molecular glasses with the highest glass transition temperature (T g = 123 °C) registered for the 1,3,6-tri[(4-diphenylamino)phenyl]− 9-(2-ethylhexyl)carbazole compound. The electrochemical activity was examined by the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The electrodonating character of the investigated compounds was revealed with the E HOMO below − 5.66 eV. Only for the compound 1,3,6-tri[(4-diphenylamino)phenyl]− 9-(2-ethylhexyl)carbazole the oxidation process was registered at 0.39 V. The optical investigationsin the solutions (the five solvents with different polarity) and in the solid state (as the thin film and powder) were carried out. The quantum yield (Φ) was also registered and in the non-polar solvents the Φ was lower than in polar solvents. The 3,6-bis[(fluoren-9-ylidene)methyl]− 9-hexylcarbazole as the only was non-emissive in the solution. The xerographic discharge method was utilized to confirm the possibility of the hole charge mobility of the 1,3,6-tri[(4-diphenylamino)phenyl]− 9-(2-ethylhexyl)carbazole compound. This same compound was tested in the perovskite solar cell as the hole-transporting material (HTM) doped with the lithiumbis-(trifluoromethanesulfonyl)imide salt. • Seven carbazole derivatives were synthesized and investigated. • Compounds exhibited good solubility in the common organic solvents. • Carbazole derivatives are the blue emitters with thermal stability up to 340 °C. • The xerographic discharge method was used to investigated the semiconductor behavior. • The compound with triphenylamine units exhibited a p-type photoconductor character. [ABSTRACT FROM AUTHOR]