Purely organic electroluminescent material realizing 100% conversion from electricity to light

Abstract

Efficient organic light-emitting diodes have been developed using emitters containing rare metals, such as platinum and iridium complexes. However, there is an urgent need to develop emitters composed of more abundant materials. Here we show a thermally activated delayed fluorescence material for organic light-emitting diodes, which realizes both approximately 100% photoluminescence quantum yield and approximately 100% up-conversion of the triplet to singlet excited state. The material contains electron-donating diphenylaminocarbazole and electron-accepting triphenyltriazine moieties. The typical trade-off between effective emission and triplet-to-singlet up-conversion is overcome by fine-tuning the highest occupied molecular orbital and lowest unoccupied molecular orbital distributions. The nearly zero singlet–triplet energy gap, smaller than the thermal energy at room temperature, results in an organic light-emitting diode with external quantum efficiency of 29.6%. An external quantum efficiency of 41.5% is obtained when using an out-coupling sheet. The external quantum efficiency is 30.7% even at a high luminance of 3,000 cd m−2.

Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts

“…35 They found that the PLQYs of the polymer neat films decreased with increasing Ir(ppy) 3 phosphor concentrations (0.5-29 mol.%), suggesting the presence of undesirable interchromophore interactions in the film when the phosphor content became more concentrated, which is consistent with the observations reported in the aforementioned studies. 27,29,31 Although the copolymer with 0.5 mol.% Ir(ppy) 3 phosphor exhibited the best PLQY of 81% among the series, a minimum of 3 mol.% phosphor was required to complete the energy transfer from the host to the dopant. Thanks to the bipolar characteristics of the host to facilitate both hole and electron injections and transport, a single-layered PLED [ITO/AQ1200/Poly(M6-MAco-Ir-2C-MA) ($30 nm)/LiQ (2 nm)/Al (100 nm)] was fabricated, where a 6 mol.% phosphor was found to show the best compromise between PLQY and charge transport in the polymeric emitting layer.…”

“…Page et al very recently reported a library of random copolymers consisting of a carbazole-pyrimidine bipolar host and a pendant Ir(ppy) 3 phosphor for PLED applications (the best performing copolymer among the series, Poly(M6-MA-co-Ir-2C-MA), is shown in Fig. 9).…”

“…123 Under certain circumstances, a high-molecularweight polymer is not necessarily superior to a low-molecular-weight one, but workers can make a wise use of their different physical properties. For instance, Al-Attar and Monkman fabricated an allsolution processed OLED device, in which a lowmolecular-weight poly(N-vinylcarbazole) doped with Ir(ppy) 3 as the emitting layer, was spun-coated on a high-molecular-weight poly(N-vinylcarbazole) which functioned as the hole transport electron blocking layer. 125 Undesirable interlayer mixing during the fabrication of the low-molecular-weight poly(N-vinylcarbazole) was prevented because the dissolution of the high-molecular-weight poly(Nvinylcarbazole) in toluene (spin-coating solvent) was very slow.…”

Red Organic Light‐Emitting Diode with External Quantum Efficiency beyond 20% Based on a Novel Thermally Activated Delayed Fluorescence Emitter

“…Generally, efficient reverse intersystem crossing (RISC) process and high fluorescence quantum yield ( Φ F ) are two essential requirements for efficient TADF emitters 1, 5. For the former one, an extremely small singlet‐triplet energy split (Δ E ST ) between lowest singlet excited state (S 1 ) and lowest triplet excited state (T 1 ) is highly desired to up‐convert triplet excitons to singlet excitons through thermal excitation 4, 6, 7, 8, 9, 10. Thus, electron‐donor (D)–electron‐acceptor (A) frameworks with a highly twisted way are generally employed to construct TADF emitters, as they can well isolate highest occupied molecular orbitals (HOMOs) in D moieties and lowest unoccupied molecular orbitals (LUMOs) in A moieties, respectively, resulting in small Δ E ST s and thus effective RISC process 11, 12, 13, 14, 15.…”

Recent progress of green thermally activated delayed fluorescent emitters

“…Other than the compounds explained above, 5,10-bis(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5,10-dihydrophenazine (DHPZ-2TRZ) was known [31], and the solution-processed 2,4,6-tris(4-(9 H-[9,3 :6 , 9 -tercarbazol]-9 -yl)phenyl)-1,3,5-triazine (G2TAZ), 2, 4,6-tris(4-(6 ,6 -di(9H-carbazol-9-yl)-9 H-[9,3 :9 ,3 : 6 ,9 :3 ,9 -quinquecarbazol]-9 -yl)phenyl)-1,3,5-triazine (G3TAZ), and G4TAZ emitters were also described [50]. In spite of the various design approaches, the EQE of the triazine compounds could not reach 20%, but the development of 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-N3,N3,N6,N6-tetraphenyl-9H-carbazole-3,6-diamine (DACT-II) compound resolved the low EQE issue of the triazine compounds [51]. A diphenylaminocarbazole donor was the key to solving the problem by enabling 100% PLQY and 100% up-conversion efficiency with the help of the close to 0 eV E ST and the dipole orientation of the emitter.…”