Highly efficient solution‐processible phosphorescent dendrimers for organic light‐emitting diodes

Abstract— Currently, most research into organic light‐emitting diodes (OLEDs) has focused on two main classes of materials: small organic molecules and conjugated polymers. An alternative approach is to use conjugated dendrimers. We show that conjugated dendrimers are a promising new class of solution‐processible materials for use as the active layer in highly efficient organic LEDs. By optimizing the choice of device structure, host material, and electron transport layer, we can obtain efficiencies of 55 cd/A and power efficiencies of 40 lm/W. This is an excellent result for a spin‐coated emissive layer.     

Improved performances in organic and polymer light‐emitting diodes using solution‐processed vanadium pentoxide as a hole injection layer

We report that a solution‐processed vanadium pentoxide (V₂O₅) layer can be utilized as an effective and stable hole injection layer in organic light‐emitting diodes and polymer light‐emitting diodes instead of polyethylene dioxythiophene : polystyrenesulfonate (PEDOT : PSS). The organic light‐emitting diode and polymer light‐emitting diode with the V₂O₅ layer have driving voltages that are 2.2 and 0.3 V lower for 1000 cd/m², respectively, than the devices with PEDOT : PSS. In addition, the devices with the V₂O₅ layer show improved operational stability compared with the devices with PEDOT : PSS. Therefore, a solution‐processed V₂O₅ layer can be utilized as an effective and stable hole injection layer instead of PEDOT : PSS.     

Optoelectronic properties of poly(fluorene) co‐polymer light‐emitting devices on a plastic substrate*

Abstract— The optoelectronic properties of red, green, and blue poly(fluorene) co‐polymer light‐emitting devices (PLEDs) on a plastic substrate having a multi‐layered structure with water vapor and oxygen transmission rates of less than 10^?5 g/cm²‐day‐atm and 10^?7 cc/cm²‐day‐atm, respectively, is reported. A semitransparent thin metal multi‐layer (i.e., Au/Ag/Au or Ag/Au/Ag) is placed between the plastic substrate and the ITO coating, achieving a low sheet resistance of 12–13 Ω/□ and an adequate optical transmission greater than 75%. A wider color gamut and a maximum emission efficiency of 0.7, 10, and 1.7 cd/A for red, green, and blue PLEDs, respectively, was obtained. Finally, a simple equivalent‐circuit model was used to simulate the current‐density—voltage characteristics of PLEDs.     

Highly efficient blue organic light‐emitting diode with high color purity using 4,4′‐N,N′‐dicarbazole‐biphyenyl (CBP) doped with 1,4‐bis[2‐(3‐N‐ethylcarbazoryl) vinyl]benzene (BCzVB)

Abstract— An efficient pure blue multilayer organic light‐emitting diode employing 1,4‐bis[2‐(3‐N‐ethylcarbazoryl)vinyl]benzene (BCzVB) doped into 4,4′‐N,N′‐dicarbazole‐biphyenyl (CBP) is reported. The device structure is ITO (indium tin oxide)/TPD (N,N′‐diphenyl‐N,N′‐bis (3‐methylphenyl)‐1,1′biphenyl‐4,4′diamine)/CBP:BCzVB/Alq₃ (tris‐(8‐hydroxy‐quinolinato) aluminum)/Liq (8‐hydroxy‐quinolinato lithium)/Al; here TPD was used as the hole‐transporting layer, CBP as the blue‐emitting host, BCzVB as the blue dopant, Alq₃ as the electron‐transporting layer, Liq as the electron‐injection layer, and Al as the cathode, respectively. A maximum luminance of 8500 cd/m² and a device efficiency of 3.5 cd/A were achieved. The CIE co‐ordinates were x = 0.15, y = 0.16. The electroluminescent spectra reveal a dominant peak at 448 nm and additional peaks at 476 nm with a full width at half maximum of 60 nm. The Föster energy transfer and, especially, carrier trapping models were considered to be the main mechanism for exciton formation on BCzVB molecules under electrical excitation.