A novel luminophore based on [1,2,4]triazolo[1,5-a]pyridine has been utilized as an emitter and host for high-efficiency deep-blue fluorescence and orange phosphorescence OLEDs, respectively.
Twon ovel bipolar deep-bluef luorescent emitters, IP-PPI and IP-DPPI, featuring different lengths of the phenyl bridge,w ere designed and synthesized, in which imidazo[1,2-a]pyridine (IP) andp henanthroimidazole (PI) were proposed as an electron acceptor and an electron donor,r espectively.Both of them exhibit outstanding thermal stability and high emission quantumy ields. All the devices based on these two materials showedn egligible efficiency roll-off with increasing current density.I mpressively,n on-doped organic light-emitting diodes (OLEDs) based on IP-PPI and IP-DPPI exhibited externalq uantum efficiencies(EQEs) of 4.85 %a nd 4.74 %w ith CIE coordinates of (0.153, 0.097) and (0.154, 0.114) at 10000cdm À2 ,r espectively.I na ddition, the 40 wt % IP-PPI doped device maintained ah igh EQE of 5.23 %w ith CIE coordinates of (0.154, 0.077) at 10000 cd m À2 .T he doped deviceb ased on 20 wt %I P-DPPIe xhibited ah igher deepblue electroluminescence (EL) performance with am aximum EQE of up to 6.13 %a tC IE of (0.153,0 .078) and maintained an EQE of 5.07 %a t1 0000 cd m À2 .T ot he best of our knowledge,t hese performances are among the state-of-thea rt devices with CIE y 0.08 at ah igh brightness of 10000cdm À2. Furthermore, by doping ar ed phosphorescent dye Ir(MDQ) 2 (MDQ = 2-methyldibenzo[f,h]quinoxaline) into the IP-PPI and IP-DPPI hosts, high-performance red phosphorescentO LEDs with EQEs of 20.8 %a nd 19.1 %w ere achieved, respectively. This work may provide an ew approach for designinghighly efficient deep-blue emitters with negligible roll-off for OLED applications.
To build up efficient host materials, two novel organic small molecules ICz‐PPI and 2ICz‐PPI were designed and synthesized, in which phenanthro[9,10‐d]imidazole (PI) is proposed as a potential luminophore with high stability, while the indolo[3,2,1‐jk]carbazole (ICz) has a high triplet energy and excellent thermal stability. Both exhibited weak intramolecular charge transfer, high decomposition temperature (Td) and high quantum yield. ICz‐PPI and 2ICz‐PPI can act as the emitting layer in non‐doped organic light‐emitting diodes (OLEDs), which achieved an external quantum efficiency (EQE) of 2.47 and 1.94 % with CIE coordinates of (0.153, 0.121) and (0.161, 0.102), respectively. In addition, the high triplet energy allows them to be used as hosts for phosphorescent OLEDs (PhOLEDs). Accordingly, high performance for green (62.5 cd A−1, 70.9 lm W−1, 17.8 %) and red (25.7 cd A−1, 26.9 lm W−1, 19.4 %) had been achieved from the ICz‐PPI‐based PhOLED. Particularly, the ICz‐PPI‐based red PhOLED showed surprisingly low roll‐off and maintained an EQE of 14.9 % at 10 000 cd m−2. Furthermore, an ICz‐PPI‐based white OLED (WOLED) exhibited warm white light (CIEx,y=(0.427, 0.468)) and high efficiencies with a CEmax of 31.8cd A−1, PEmax of 37.0lm W−1 and EQEmax of 14.4 %.
Acquiring desirable device performance with deepblue color purity that fulfills practical application requirements is still a challenge. Bipolar fluorescent emitters with hybrid local and charge transfer (HLCT) state may serve to address this issue. Herein, by inserting anthracene core in the deep-blue building blocks, the authors successfully developed two highly twisted D-π-A fluorescent emitters, ICz-An-PPI and IP-An-PPI, featuring different acceptor groups. Both exhibited superb thermal stabilities, high photo luminescent quantum yields and excellent bipolar transport capabilities. The nondoped OLEDs using ICz-An-PPI and IP-An-PPI as the emitting layers showed efficient blue emission with an external quantum efficiency (EQE max ) of 4.32 % and 5.41 %, and the CIE coordinates of (0.147, 0.180) and (0.149, 0.150), respectively. In addition, the deep blue doped device based on ICz-An-PPI was achieved with an excellent CE max of 5.83 cd A À 1 , EQE max of 4.6 % and the CIE coordinate of (0.148, 0.078), which is extremely close to the National Television Standards Committee (NTSC) standard. Particularly, IP-An-PPI-based doped device had better performance, with an EQE max of 7.51 % and the CIE coordinate of (0.150, 0.118), which was very impressive among the recently reported deep-blue OLEDs with the CIE y < 0.12. Such high performance may be attributed to the hot exciton HLCT mechanism via T 7 to S 2 . Our work may provide a new approach for designing high-efficiency deepblue materials.
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