Study on Electron Injection of Phosphorescent Polymer Light-Emitting Diodes Utilizing CsF/Metal Cathode

Abstract

The effect of electron injection in polymer light-emitting diodes based on the phosphorescent material of fac-tris(2-phenylpyridine) iridium (Ir(ppy) 3 ) devices with CsF=MgAg=Ag cathodes were investigated. The device with MgAg (1 nm)=CsF (3 nm)=Ag cathode showed almost similar current density-voltage-luminance characteristics to that with CsF (3 nm)=MgAg (1 nm)=Ag cathode. The existence of interface between the organic layer and Cs or CsF results in low turn on voltage. To achieve the efficient electron injection and the low turn on voltage, it is necessary to exist MgAg and CsF interface at the position of about 1 nm from organic layer. To achieve the efficient electron injection, it is necessary to exist Cs layer just on the organic layer. The electron injection effects between devices with CsF and Cs are different. It is suggested that the dipole of CsF affect the efficient electron injection.

Doping of the Metal Oxide Nanostructure and its Influence in Organic Electronics

“…Early prominent examples of functional interfacial layers used in the development of OLEDs and OPVs include: i) introduction of LiF, CsF, AlO x , etc. as an electron buffer layer in OLEDs, [10][11][12] ii) application of polyaniline (PANI) [13] and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport/buffer layer, [14] iii) insertion of a TiO x layer as an optical spacer/hole blocking layer, [15,16] and iv) combination of an n-and p-type transport layer for tandem OLEDs (e.g., LiF-V 2 O 5 ). [17] The role of cesium as an effective interfacial material has been proven.…”

Mechanism study on highly efficient polymer light-emitting diodes utilizing double-layered alkali halide electron injection layer

“…One was the combined effect of low-work-function metal such as Ba, Ca and alkali metal Cs or Li from evaporated CsF 30 or LiF 32 . The second possible mechanism was the formation of interface dipole layer because of the molecular dipole properties of CsF or LiF 33 . The last possible mechanism was the diffusion of alkali halide 34 or alkali atom 35,36 .…”