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A novel hot exciton blue fluorophores and white organic light-emitting diodes with simplified configuration
摘要： The two efficient non-doped blue emitters with hybridized local and charge transfer state namely, NDBNPIN and DBTPIN have been synthesised and characterised. These materials are employed as a host for green and red phosphorescent OLEDs. The white device based on DBTPIN:Ir(MDQ)2(acac) (4%) exhibit maximum external quantum efficiency (ηex) ?24.8%; current efficiency (ηc) ?57.1 cdA?1; power efficiency (ηp) ?64.8 lmW?1 with Commission Internationale de l’Eclairage (CIE:0.49, 0.40) than NDBNPIN:Ir(MDQ)2acac (4%) device [ηex ? 23.1%; ηc ?54.6 cd A?1; ηp? 60.0 lm W?1 with CIE (0.47, 0.42)]. Development of blue emitter is crucial in organic light emitting devices (OLEDs) to reduce power consumption effectively1. For an OLED with stable emission the current efficiency (CE) is proportional to external quantum efficiency (?ex): power efficiency (PE) is determined by CE and operating voltage (V) [PE = π CE/V]2–4. Iridium and platinum based phosphorescent complexes and TADF (thermally activated delayed fluorescent materials) exhibit high ?ex, however, suffered with short lifetime and roll-off efficiency and also the production cost of phosphorescent materials are unfavourable for practical applications5. Therefore, low driving voltage with high brightness become the major issue to achieve efficient OLEDs6. In OLEDs, balanced hole: electron recombination leads to formation of CT exciton (charge-transfer) which undergo decay directly or relaxes to LE (local exciton), thus, utilization of both CT exciton and LE provides efficient EL (electroluminescence). From 4-(dicyanomethylene)-2-methyl-6-[4-(dimethylaminostyryl)-4H-pyran] with CT state maximum efficiency have been harvested7–9. Donor–acceptor (D–A) compounds with low % CT leads to RISC (reverse intersystem crossing) process which results high singlet utilisation efficiency(?s), however, colour-purity is still poor due to broadened PL (photoluminescence) and EL (electroluminescence) spectra10–13. D-A architecture with high % LE state leads to higher efficiency because of maximum orbital overlap whereas high % CT provides low efficiency due to partial hole and electron overlap. However, because of small energy splitting (ΔES-T ≈ 0) CT state undergo RISC process 11,12. These issues are overcome, by employing D–A configured emissive materials with results in enhanced ηs HLCT emissive state: stabilised LE and CT states results in ηPL(photoluminance efficiency) and high ηs.. Thus, construction of D–A emitters with HLCT emissive state is novel strategy to design efficient blue emitters.
关键词： hybridized local and charge transfer state,blue emitters,OLEDs,electroluminescence,phosphorescent
更新于2025-09-23 15:19:57
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Blue thermally activated delayed fluorescence emitters incorporating acridan analogues with heavy group 14 elements for high-efficiency doped and non-doped OLEDs
摘要： Deep-blue thermally activated delayed fluorescence (TADF) emitters are promising alternatives for conventional fluorescence and phosphorescence materials for practical application in organic light-emitting diodes (OLEDs). However, as appropriate bipolar hosts for deep-blue TADF-OLEDs are scarce, the development of efficient deep-blue TADF emitters that are applicable to both doped and non-doped systems is an urgent task. In this study, we developed a new family of blue TADF emitters that demonstrated high photoluminescence (PL) and electroluminescence (EL) quantum efficiencies in both doped and non-doped (neat) systems. Four new donor–acceptor (D–A)-type TADF molecules incorporating phenazasiline, phenazagermine, and tetramethylcarbazole as weak D units and phenothiaborin as a weak A unit were designed and synthesized. By varying the structural rigidity/flexibility as well as the electron-donating ability of the D units, the resulting photophysical and TADF properties of the D–A molecules could be systematically regulated. A comprehensive photophysical investigation revealed that phenazasiline and phenazagermine-based emitters concurrently exhibit blue TADF emissions (464–483 nm), high PL quantum efficiencies (≈100%), extremely fast spin-converting reverse intersystem crossing rates (>107 s?1), and suppressed concentration quenching. These fascinating features in conjunction produced high-performance doped and non-doped blue TADF-OLEDs. The doped and non-doped TADF-OLEDs using the phenazasiline-based emitter demonstrated extremely high maximum external EL quantum efficiencies (ηext) of 27.6% and 20.9%, with CIE chromaticity coordinates of (0.14, 0.26) and (0.14, 0.20), respectively. Further, ultra-low efficiency roll-off behavior for both the doped and non-doped devices was demonstrated by their ηext as high as 26.1% and 18.2%, respectively, measured at a practically high luminance of 1000 cd m?2.
关键词： phenazasiline,phenothiaborin,tetramethylcarbazole,thermally activated delayed fluorescence,OLEDs,phenazagermine,blue emitters
更新于2025-09-16 10:30:52
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Synthesis of Alloyed ZnSeTe Quantum Dots as Bright, Color-Pure Blue Emitters
摘要： Considering a strict global environmental regulation, fluorescent quantum dots (QDs) as key visible emitters in the next-generation display field should be compositionally non-Cd. When compared to green and red emitters obtainable from size-controlled InP QDs, development of non-Cd blue QDs remains stagnant. Herein, we explore synthesis of non-Cd, ZnSe-based QDs with binary and ternary compositions toward blue photoluminescence (PL). First, size increment of binary ZnSe QDs is attempted by a multiply repeated growth until blue PL is attained. Although this approach offers a relevant blue color, excessively large-sized ZnSe QDs inevitably entail a low PL quantum yield (QY). As an alternative strategy to the above size enlargement the alloying of high-band gap ZnSe with lower-band gap ZnTe in QD synthesis is carried out. These alloyed ternary ZnSeTe QDs after ZnS shelling exhibit systematically tunable PL of 422?500 nm as a function of Te/Se ratio. Analogous to state-of-the-art heterostructure of InP QDs with a double-shelling scheme, an inner shell of ZnSe is newly inserted with different thicknesses prior to an outer shell of ZnS, where the effects of the thickness of ZnSe inner shell on PL properties are examined. Double-shelled ZnSeTe/ZnSe/ZnS QDs with an optimal thickness of ZnSe inner shell are then employed for all-solution-processed fabrication of blue QD-light-emitting diode (QLED). The present blue QLED as the first ZnSeTe QD-based device yields a peak luminance of 1195 cd/m2, current efficiency of 2.4 cd/A, and external quantum efficiency of 4.2%, corresponding to the record values reported from non-Cd blue devices.
关键词： external quantum efficiency,alloyed ZnSeTe quantum dots,Non-Cd blue emitters,ZnSe inner shell,quantum dot-light-emitting diode
更新于2025-09-11 14:15:04
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Importance of Chromophore Rigidity on the Efficiency of Blue Thermally Activated Delayed Fluorescence Emitters
摘要： Four new symmetrical donor?acceptor?donor (D?A?D)-type molecules are reported with diphenylamine (DPA) or 10,11-dihydro-5H-dibenz[b,f ]azepine (Az) as electron donors and 9,9-dimethylthioxanthene-S,S-dioxide (TXO2) as the electron acceptor. The donors are attached at different positions on the acceptor core: either para or meta to the sulfone unit. This series provides new insights into the effects of chromophore rigidity/flexibility on the efficiency of thermally activated delayed fluorescence (TADF). The molecules have been characterized by X-ray crystallography, by in-depth photophysical studies, and by theoretical calculations. The clear differences observed in the photophysical properties when using DPA or Az as a donor are shown to originate from different geometries of the donor unit which, in turn, influence the geometry of the nitrogen lone pair and the donating strength of the corresponding fragment. Thus, a para-substituted Az derivative demonstrated blue TADF in polar media, while the compounds with more flexible DPA units did not show delayed fluorescence. To obtain deep-blue emitters, weaker donating units are needed. A more flexible donor unit leads to increased local excited state (donor) LE emission and reduced TADF. However, a certain amount of flexibility has to be present to ensure deep-blue TADF.
关键词： chromophore rigidity,blue emitters,donor-acceptor-donor,photophysical properties,thermally activated delayed fluorescence
更新于2025-09-04 15:30:14