Solution processed small molecule-based green phosphorescent organic light-emitting diodes using polymer binder.

The authors have demonstrated efficient green organic light-emitting diodes (OLEDs) by using polymer binder. We fabricated small molecular green OLEDs and mixed polymer as a binder such as polystyrene (PS) or poly(N-vinylcarbazole) (PVK). The 4,4'-N,N'-dicarbazole-biphenyl (CBP) is a small molecular material with excellent electrical properties however it become crystalline at high temperature. Polymer binder prevents crystallization of CBP and lead to high efficiency. Therefore, we added PS or PVK into CBP as a polymer binder. As a result, we obtained maximum luminous efficiency, power efficiency and quantum efficiency of 22.8 cd/A, 11.6 Im/W and 6.61% at 23% PS added device.

Luminance mechanisms in green organic light-emitting devices fabricated utilizing tris(8-hydroxyquinoline)aluminum/4,7-diphenyl-1, 10-phenanthroline multiple heterostructures acting as an electron transport layer.

The electrical and the optical properties in green organic light-emitting devices (OLEDs) fabricated utilizing tris(8-hydroxyquinoline)aluminum (Alq3)/4,7-diphenyl-1,10-phenanthroline (BPhen) multiple heterostructures acting as an electron transport layer (ETL) were investigated. The operating voltage of the OLEDs with a multiple heterostructure ETL increased with increasing the number of the Alq3/BPhen heterostructures because more electrons were accumulated at the Alq3/BPhen heterointerfaces. The number of the leakage holes existing in the multiple heterostructure ETL of the OLEDs at a low voltage range slightly increased due to an increase of the internal electric field generated from the accumulated electrons at the Alq3/BPhen heterointerface. The luminance efficiency of the OLEDs with a multiple heterostructure ETL at a high voltage range became stabilized because the increase of the number of the heterointerface decreased the quantity of electrons accumulated at each heterointerface.

Luminance efficiency enhancement in green organic light-emitting devices fabricated utilizing a cesium fluoride/fullerene heterostructure electron injection layer.

Enhancement mechanisms of the luminance efficiency in green organic light-emitting devices (OLEDs) fabricated utilizing a cesium fluoride (CsF)/fullerene (C60) heterostructure acting as an electron injection layer (EIL) were investigated. The luminance efficiencies as functions of the current density showed that the luminance efficiency in the green OLEDs fabricated utilizing a CsF/C60 heterostructure acting as an EIL was higher than that in the green OLEDs fabricated utilizing a CsF, a Liq, or a C60 single EIL. The interfacial dipole existing at the CsF layer decreased the electron injection barrier, and the stability of the OLEDs with a CsF EIL was enhanced due to the lower diffusion rate of Cs atoms in comparison with Li atoms. The enhancement of the luminance efficiency of the OLEDs with a heterostructure EIL was attributed to the increase in the electron injection. These results can help improve understanding of the enhancement mechanisms of the luminance efficiency in green OLEDs utilizing a CsF/C60 heterostructure acting as an EIL.

A study on the phosphorescent blue organic light-emitting diodes using triplet exciton blocking layer.

We studied the use of N,N'-dicarbazolyl-3,5-benzene (mCP) of the triplet energy level 2.90 eV and p-bis(triphenylsilyly)benzene (UGH2) of the wide triplet energy band gap 3.50 eV as triplet exciton blocking layer (TEBL) to get high efficiency in phosphorescent blue organic light-emitting diodes. Five devices (Devices I-V) with different structures were fabricated to investigate the effect of mCP and UGH2 TEBLs on device performances. The maximum quantum efficiencies of devices I, II, III, IV and V were 5.10%, 1.41%, 5.90%, 4.98% and 0.61%, respectively.