An efficient organic–inorganic hybrid hole injection layer for organic light-emitting diodes by aqueous solution doping
The authors develop an aqueous solution-processed hole injection layer, MoO3 doped copper phthalocyanine-3,4′,4′′,4′′′-tetra-sulfonated acid tetra sodium salt (TS-CuPc), in organic light-emitting diodes (OLEDs) via an environmentally-friendly and easy fabrication process. The generation of a charge transfer complex in TS-CuPc:MoO3 composite films is confirmed by absorption spectra and X-ray photoemission spectroscopy (XPS) measurements. Enhanced hole injection in OLEDs is attributed to the decreased hole barrier at the ITO side, which is in agreement with the Schottky thermal emission evaluation. The efficient modification of ITO by TS-CuPc:MoO3 is further confirmed by ultraviolet photoemission spectroscopy (UPS) measurements.