Improving efficiency in RGB phosphorescent and white organic light emitting diodes via donor-spiro-boron acceptor host materials

Abstract

The universal host material with boron acceptor core structure is exceptionally sparse to be designed for red, green, and blue in efficient phosphorescent organic light emitting diodes (PhOLEDs) accompanying white OLEDs, possessing indistinguishable device feature. Herein, two boron acceptors spiro-host materials namely 1'-(4-(dimesitylboranyl)phenyl)-10-phenyl-10H-spiro[acridine-9,9′-fluorene] (TPA-PBM) and 1-(4-(dimesitylboranyl)phenyl)-3′,6′-dimethylspiro[fluorene-9,8′-indolo[3,2,1-de]acridine] (2MeCz-PBM) were designed and synthesized. The designed rigid donor strategy exhibited good device performance among the reported boron donor-spiro-acceptor (D-spiro-A) skeleton for organic light emitting diodes (OLEDs). In particular, we fabricate RGB three-color phosphorescent OLEDs based on TPA-PBM and 2MeCz-PBM. The red devices exhibit a maximum external quantum efficiency (EQE) of nearly 28 % (26.8 % for TPA-PBM and 27.5 % for 2MeCz-PBM), with an electroluminescence spectrum at 608 nm. The green/blue devices obtain maximum EQEs of 21.2 %/15.3 % and 21.8 % 17.3 %, for TPA-PBM and 2MeCz-PBM, respectively. Furthermore, green devices display an extremely low efficiency roll-off with decreasing 1 % and 3 % at luminance of 5000 cd m⁻². Additionally, the two-color white OLED using 2MeCz-PBM exhibits EQE_max and PE_max are 24.5 % and 62.9 lm W⁻¹ respectively, the EQE remain 23.8 % at commercial lighting brightness of 1000 cd m⁻². The WOLED also shows a stable white spectrum with CIE varying range of (0.41, 0.47) to (0.39, 0.46) at 100 cd m⁻² to 15000 cd m⁻². All obtained results confirmed that our targeted molecules have advantage of carrier balance and efficient charge recombination, which might replace many other commercial host materials.