Solution-Processed Efficient Blue Phosphorescent Organic Light-Emitting Diodes (PHOLEDs) Enabled by Hole-Transport Material Incorporated Single Emission Layer

Abstract

Solution-processed blue phosphorescent organic light-emitting diodes (PHOLEDs) based on a single emission layer with small-molecule hole-transport materials (HTMs) are demonstrated. Various HTMs have been readily incorporated by solution-processing to enhance hole-transport properties of the polymer-based emission layer. Poly(N-vinylcarbazole) (PVK)-based blue emission layer with iridium(III) bis(4,6-(di-fluorophenyl)pyridinato-N,C2′)picolinate (FIrpic) triplet emitter blended with solution-processed 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) gave luminous efficiency of 21.1 cd/A at a brightness of 6220 cd/m2 with an external quantum efficiency (EQE) of 10.6%. Blue PHOLEDs with solution-incorporated HTMs turned out to be 50% more efficient compared to the reference device without HTMs. The high hole mobility, high triplet energy of HTM, and favorable energy transfer between HTM blended PVK host and FIrpic blue dopant were found to be important factors for achieving high device performance. The results are instructive to design and/or select proper hole-transport materials in solution-processed single emission layer.

Impact of Peripheral Functionalities around a Pyridine Core on Molecular Arrangement: Potential Hole Transport Materials

“…So far, much attention has been focused on the development of emission layer (EML) materials to achieve highly efficient and operationally stable OLEDs. − Moreover, efforts have been directed also toward developing HTMs to advance overall device efficiencies. − In particular, high triplet HTMs play an important role in obtaining high device performance by blocking triplet excitons and reinforcing recombination in the emission layer. − It is well-known that only a few HTMs are reported with high E T suitable for confining triplet emitters. ,, To achieve high triplet energy, the design process utilizes the concept of molecules with twisted geometry which might affect the carrier mobility. ,− As a solution, we find that the high triplet energy materials could be obtained with the inclusion of a weak electron-deficient core into the molecular structure. − …”

Highly Efficient and Stable Green Phosphorescent Light‐Emitting Diodes Based on Solution‐Processable Ir(III) Complexes with Electron‐Transporting Ancillary Ligands

“…In this regard, the fabrication of PHOLEDs through solution-process is desirable for the near future due to its cost-effectiveness and applicability to large-area devices. [6][7][8][9][10][11] To realize high-performance solutionprocessed PHOLEDs, phosphorescent dopants of metal complexes should be carefully designed. Recently, many research groups reported efficient green emitters with electron-transporting ancillary ligands, such as phosphine oxide (P = O), 1,3,4-oxadiazole (OXD), triazole, and N-heterocyclic derivatives because the electron transport property of triplet emitters is a key in improving the performance of PHOLEDs.…”

“…In this regard, the fabrication of PHOLEDs through solution‐process is desirable for the near future due to its cost‐effectiveness and applicability to large‐area devices. [ 6–11 ]…”

2,7(3,6)-Diaryl(arylamino)-substituted Carbazoles as Components of OLEDs: A Review of the Last Decade

“…Since the first discovery of organic electroluminescent compounds, huge attention has been devoted to the creation of new materials and optimized multilayer device architectures for viable and practical organic light emitting diodes (OLEDs), which would demonstrate low-driving voltage, high brightness, full-color emission, a long lifetime, and the easy formation of flexible thin-film devices. The commercial benefit of OLED devices is seen in the emergence of digital cameras, mobile cell phones as well as display technologies; however, there is still a strong demand to considerably improve the performance and lifetime of the devices for lighting technologies [1][2][3][4][5].…”