A CBP derivative as bipolar host for performance enhancement in phosphorescent organic light-emitting diodes

Abstract

4,4 0 -biphenyl (CBP) is one of the most successful uni-polar host materials for phosphorescent organic light-emitting diodes (PhOLEDs). We report the synthesis and properties of one novel CBP derivative, CBP-CN, with two cyano groups (CN) at the 3-site of carbazole rings. The strong electron-withdrawing CN group was introduced with the expectation to promote electron-injecting/transporting abilities and to achieve bipolar features for CBP-CN. In comparison with the parent CBP, CBP-CN possesses lowered HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels and dramatically increased T g (glass transition temperature, 162 C), but unaltered HOMO-LUMO band gap and triplet energy (2.69 eV). Green and red PhOLEDs were fabricated with CBP-CN as hosts for traditional iridium phosphors. The maximum luminance efficiency (h L ) of 80.61 cd A À1 (23.13%) was achieved for the green PhOLED, and 10.67 cd A À1 (15.54%) for the red one, which represent efficiency increases of 25-33% compared with those of the best devices with CBP host and are even among the best data for phosphorescent OLEDs reported so far. The theoretical calculation and the carrier-only devices investigation confirmed that the electron-injecting/-transporting character and the bipolar nature of CBP-CN should be responsible for the performance enhancements.

Effects of side groups on the kinetics of charge carrier recombination in dye molecule-doped multilayer organic light-emitting diodes

“…The device structure is shown in Figure 2 and the related energy levels are collected from the references. [34][35][36] As shown in Figure 3a, four devices have almost the same EL spectra peaked at around 500 nm. This peak is significantly different from the peak at ~ 550 nm from pure Alq 3 , [37] meaning that the carrier recombination is mainly confined in the molecule doping layer.…”

Solution-processed blue phosphorescent OLEDs with carbazole-based polymeric host materials

“…Despites the significant decrease of the glass transition temperature of PEPEK compared to that of PEPK, no morphological change upon heating during device operation is attended, the device temperature being not expected to exceed 50°C during operation. Especially, the glass transition temperature of PEPEK is comparable to that reported for benchmark carbazole-based host materials such as 1,3-bis(9-carbazolyl)benzene (mCP) (65°C) or N,N 0 -dicarbazolyl-4,4 0 -biphenyl (CBP) (62°C) [62,63] and much higher than that of silane-based ultrahigh energy gap hosts (UGHs) (26-53°C) [64,65]. Besides, to Scheme 1.…”

Exploring the Limiting Open‐Circuit Voltage and the Voltage Loss Mechanism in Planar CH3NH3PbBr3 Perovskite Solar Cells

“…A series of HTLs including carbon nanotubes, [2] spiro-MeOTAD, [5,7] PIF8-TAA, [3,4] and CBP [6] already were utilized for CH 3 NH 3 PbBr 3 solar cells, and the corresponding V oc was typically in the regime between 1.4 and 1.5 V. However, all these HTLs had totally different HOMO levels (carbon nanotubes −5.0 V, [2] spiroMeOTAD −5.2 V, [2] PIF8-TAA −5.5 V, [4] CBP −5.7 V. [27] ). This finding demonstrates that the V oc is probably not dominated by the HOMO level of the HTL.…”