Effects of triplet energies and transporting properties of carrier transporting materials on blue phosphorescent organic light emitting devices

Abstract

We have studied the effects of the hole transporting layers and electron transporting layers on the device efficiencies of iridium(III) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) doped 3,5′−N,N′-dicarbazole-benzene (mCP) host blue phosphorescent organic light emitting diodes. We found that the device efficiency is very sensitive to the hole transporting materials used and both the triplet energy and carrier transport properties affect the device efficiency. On the other hand, there is no apparent correlation between the device efficiency and the triplet energy of the electron transporting material used. Instead, the device efficiency is affected by the electron mobility of the electron transporting layer only.

High‐Efficiency Solution‐Processed Small Molecule Electrophosphorescent Organic Light‐Emitting Diodes

“…Second, its high E T1 and deep HOMO level ( − 6.4 eV) confi ne holes and excitons within the EML, resulting in high effi ciencies. [ 42 ] The spin-coated EML of Device A consists of CBP only. The EL spectrum, which peaked at ∼ 409 nm, is apparently due to bulk emission from CBP.…”

A Bipolar Host Material Containing Triphenylamine and Diphenylphosphoryl‐Substituted Fluorene Units for Highly Efficient Blue Electrophosphorescence

“…The values of E T of BPAF (2.87 eV, estimated from the phosphorescent spectra measured in 2-methyltetrahydrofuran at 77 K) and TAZ (2.70 eV) [47] were sufficiently high to prevent any possible luminescence quenching by the carrier-transporting layers and to confine the triplet excitons in the EML. [48,49] For comparison, we also fabricated the corresponding devices incorporating APF, PODPF, and the conventional material N,Ń -dicarbazolyl-3,5-benzene (mCP), respectively, as hosts. Figure 9 displays the current density-voltage-luminance (I-V-L) characteristics of these blue-light-emitting devices.…”

“…These values are much higher than that of the device based on the conventionally used material mCP and are among the highest ever reported for FIrpic-doped devices. [28,33,[47][48][49][50] Table 3 lists the key characteristics of the blue electrophosphorescence obtained using the various host materials. In addition to the efficient carrier-injection in the POAPF-based device, we also attribute the high efficiencies to the effective carrier/exciton confinement within the EML.…”

A Highly Efficient Universal Bipolar Host for Blue, Green, and Red Phosphorescent OLEDs

“…Device B1 using FIrpic as the dopant with device structure ITO/NPB (30 nm)/mCP (20 nm)/BCPO: FIrpic (8%) (25 nm)/TAZ (50 nm)/LiF(1 nm)/Al (100 nm) was thus fabricated. In this device, NPB acts as hole-transporting material, mCP as a hole-transporting material and also as an exciton blocker (E T , 2.9 eV) to prevent diffusion of exciton to the NPB layer [20,21] and TAZ as the electron-transporting and hole blocking layer. [10] The device performance, as summarized in Table 1, Figure 2 and S. I.…”