Highly Efficient Solution-Processed Thermally Activated Delayed Fluorescence Bluish-Green and Hybrid White Organic Light-Emitting Diodes Using Novel Bipolar Host Materials

Abstract

Two pyridine-containing bipolar host materials with high triplet energy, 9,10-dihydro-9,9-dimethyl-10-(3-(6-(3-(9,9-dimethylacridin-10­(9H)-yl)­phenyl)­pyridin-2-yl)­phenyl acridin (DDMACPy) and N-(3-(6-(3-(diphenyl amino)­phenyl)­pyridin-2-yl)­phenyl)-N-phenylbenzenamine (DTPAPy), are synthesized from the modification of the commonly adapted host material 2,6-bis­(3-(9H-carbazol-9-yl)­phenyl)­pyridine (DCzPPy). The highest occupied molecular orbital levels of DDMACPy (5.50 eV) and DTPAPy (5.60 eV) are found to be shallower than that of DCzPPy (5.90 eV) that leads to the improvement in hole injection from the hole transport layer PEDOT:PSS (WF = 5.10 eV). These host materials are used in the emitting layer of bluish-green organic light-emitting diode (OLED) with the thermally activated delayed fluorescence (TADF) emitter, 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine, as the guest. The DDMACPy-based device shows the highest performance among them, with the maximum external quantum efficiency (EQEmax), current efficiency (CEmax), and power efficiency (PEmax) of 21.0%, 53.1 cd A–1, and 44.0 lm W–1 at CIE (0.17, 0.42), respectively. By further doping with the red-emitting phosphor iridium­(III) bis­(2-phenylquinoline)­(2,2,6,6-tetramethylheptane-3,5-ionate) [Ir­(dpm)­PQ2] and yellow-emitting phosphor iridium­(III) bis­(4-(4-t-butylphenyl)­thieno­[3,2-c]­pyridinato-N,C20)­acetylacetonate (PO-01-TB) emitters into the bluish-green emitting layer, a TADF–phosphor hybrid white OLED (T–P WOLED) is obtained with excellent EQEmax, CEmax, and PEmax of 17.4%, 48.7 cd A–1, and 44.5 lm W–1 at CIE (0.35, 0.44), respectively. Moreover, both the bluish-green and WOLED show a low efficiency roll-off with external quantum efficiencies at the brightness of 1000 cd m–2 (EQE1000) of 18.7 and 16.2%, respectively, which are the highest performance records among the solution-processed TADF bluish-green and T–P WOLEDs.

Highly efficient solution-processed white organic light-emitting diodes based on a co-host system by controlling energy transfer among different emitters

“…The hole mobilities of TcTa and CzSi as determined are 3.52 × 10 −6 and 4.33 × 10 −6 cm 2 V −1 s −1 , respectively, whereas TcTa : CzSi (1 : 1) exhibited about a twofold higher hole mobility of 8.67 × 10 −6 cm 2 V −1 s −1 compared with that of TcTa or CzSi. 31–33 The improved hole mobility may be attributed to the improved stability of the co-host film, which is helpful in increasing the hole-transport efficiency.…”

“…Up to the present, solution-processed white organic lightemitting diodes (s-WOLEDs) have drawn considerable attention from the perspective of next-generation solid-state lighting and flat-panel displays owing to their outstanding merits of being physiologically friendly, showing high resolution and flexible capabilities. [1][2][3][4][5] To achieve high-efficiency s-WOLEDs, phosphor materials containing noble metals, which achieve efficient spin-orbital coupling, can harvest both singlet and triplet electrically generated excitons for emission through an efficient intersystem crossing (ISC) process, and realize 100% internal quantum efficiency, both of which are imperative to boosting the high performance of WOLEDs. [6][7][8] Generally, with regard to most high-performance OLEDs fabricated using traditional vacuum-deposition techniques, the basic requirement is strict technological conditions, which will undoubtedly increase the fabrication cost.…”

Recent advances in thermally activated delayed fluorescence for white OLEDs applications

“…Because both TADF materials and phosphorescence materials can harvest all excitons, co-doping of TADF and phosphorescence has always been an important method for enhancing WOLEDs performance, and it is also the mostly reported strategy to develop WOLEDs in recent years [64][65][66][67][68]. Therefore, the efficient and color stable hybrid WOLEDs can be fabricated by adjusting the exciton distribution reasonably.…”

Hybrid white organic light‐emitting diodes based on platinum complex

“…Due to their superior stability as compared with all phosphorescent white organic light‐emitting diodes (WOLEDs), hybrid WOLEDs have attracted much research interest in recent years 1–7 . Since the issue of photochemical instability, high efficiency blue fluorescence emitters substitute the blue phosphorescence emitters in the construction of hybrid WOLEDs 8–26 . To reach a minimum color rendering index (CRI) of the WOLED, which is 80 for the application in lighting industry, at least two phosphorescent dopant materials, one with green or bluish green emission and the other with orange or red emission, to be incorporated in the hybrid WOLEDs.…”

“…[1][2][3][4][5][6][7] Since the issue of photochemical instability, high efficiency blue fluorescence emitters substitute the blue phosphorescence emitters in the construction of hybrid WOLEDs. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] To reach a minimum color rendering index (CRI) of the WOLED, which is 80 for the application in lighting industry, at least two phosphorescent dopant materials, one with green or bluish green emission and the other with orange or red emission, to be incorporated in the hybrid WOLEDs. For a high efficiency electroluminescence (EL) concern, emitters based on iridium complexes are the ideal choice.…”