Highly Efficient Solution-Processed Organic Light-Emitting Diodes Containing a New Cross-linkable Hole Transport Material Blended with Commercial Hole Transport Materials

Abstract

A new small-molecular thermally cross-linkable material {[4-(9-phenyl-9H-carbazol-4-yl)phenyl]-bis-(4′-vinylbiphenyl-4-yl)-amine} (PCP-bis-VBPA, PbV) containing the styrene moiety was synthesized for hole transport layers in wet processed organic light-emitting diodes (OLEDs). It was found that PbV exhibited relatively high glass temperatures above 154 °C and a triplet energy (T 1 ) greater than 2.81 eV. This new synthetic hole transport material (HTM) forms very uniform films after crosslinking reaction with little pin-holes, although it was smallmolecule-based cross-linkable HTM. However, to solve the certain minor non-uniformity caused by pinholes with various sizes, a semi-interpenetrating network was formed with well-known polymeric HTM with high mobility [e.g., poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenyl amine), TFB, or poly(N,N′-bis-4-butylphenyl-N,N′-bisphenyl)benzidine, poly-TPD]. As a result, we successfully fabricated red phosphorescent OLED showing an efficiency of about 16.7 cd/A and 12.4% (external quantum efficiency) if we applied PbV blended with 20% of TFB or poly-TPD. In particular, the efficiency and lifetime are significantly improved by 1.5 and 4.5 times, respectively, compared to those of the control device without using blended HTM.

52.4: Suppression of Initial Degradation for High‐Efficiency Solution‐Processed Organic Light Emitting Diodes

“…It has been shown that the mobility of this x-HTL (μh~10 -5 cm -2 V -1 s -1 ) [4] is much lower compared to that of ETL1:Liq (1:1) (μh~10 -3 cm -2 V -1 s -1 ) [5] . This large difference in mobility of x-HTL and s-ETL can cause the exciton formation region to occur at the mixing interface between x-HTL and EML, resulting in low performance and short lifetime.…”

P‐135: New Hole‐Transport Materials Composed of Indenocarbazole‐Based Copolymer for Ultra‐High‐Efficiency Solution‐Processed OLED

“…Thus, we modified the devices with the following structures: interface of HTL/EML causing reduction of efficiency. [7] This low mixing ratio of NH helps to pull the exciton recombination region away from the EML/TPBi interface. As a result, we could obtain much higher efficiency and lower Von.…”

Construction of a fully conjugated cross-linked hole-transport film based on ethynyl to enable high mobility for efficient solution-processed OLEDs

“…17,18 In the preparation of multilayer OLEDs, a cross-linked hole transport layer (HTL) provides a platform to prepare the emitting layer (EML) by the solution method. A series of cross-linkable hole transport materials (HTMs) based on unsaturated acid esters, [19][20][21] oxetane, [22][23][24] benzocyclobutene 25 and vinyl [26][27][28] cross-linking groups have been successfully applied in solution-processed OLEDs. However, the cross-linked HTMs generally exhibited low hole mobility (m) compared with small molecules or conjugated polymers, leading to carrier imbalance in the EML and weakened the device performance.…”