We report highly transparent and low resistive new cathode structures, which basically consist of nano-composite layer/Ag/WO3 for transparent organic light-emitting diode (TOLED) applications. Our new cathode structure exhibits an extremely high transmittance of 91.2% at 550 nm, a low sheet resistance of 5.4 Ω □(-1), and excellent electron injection properties. Such a high transmittance along with a low resistivity of the fabricated new cathode could be explained by surface-modifying behavior with the generation of a nano-composite thin silver oxide layer during Ag deposition. Chemical interaction at the interface between the electron injection layer and the electron transport layer results in good electron injection properties in TOLEDs. The fabricated TOLEDs with our new cathode structures have a full device transmittance of 85-87% at 550 nm.
The aim of this study is to analyze and mitigate the voltage drift phenomenon observed in top-emitting organic light emitting diodes (OLED) when driven at constant current. An operating device may experience voltage increase over time due to factors such as interface or bulk material degradation, charge accumulation and formation of trap states. Single-carrier devices were fabricated to understand the contribution to voltage drift from each of these causes. Doping in electron injection layer (4, 7-diphenyl-1,10-phenanthroline or Bphen) and hole injection layer (2,2',7,7'-tetra(N,N-di-tolyl)amino-spiro-bifluorene or Spiro-TTB) were optimized to obtain ohmic injection contacts. Devices with tris(8-hydroxy-quinoline) aluminium (Alq3) degrade significantly with holes injection and undergo high voltage increase in lifetime test measurements. On the contrary, devices with N,N'-di(naphtalen-1-y1)-N,N'-diphenyl-benzidine (NPB) exhibit an ambipolar charge transport behavior and low voltage drift under both hole and electron injection.
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