Morphological and electro-optical characterization of an ultrasonic spray coated electron injection and transport layer for organic light emitting diodes
Diphenylamine and thiophene compounds are promising materials for organic light-emitting diodes (OLEDs). We report here, the synthesis and optical property of a novel small molecular weight derivative,N4.N4,N4'.N4'-tetrakis (4- (thiophen-2-yl) phenyl)-[1,1'-bipheny-4,4'-diamine (TPPA). The target molecule was synthesized using 4,4'-dibromobiphenyl as the starting material, and the proceeding reactions included bromination, Buchwald and Suzuki coupling reactions. According to the optical characterization of it, the absorption peak and excitation peak is at 351nm and 412 nm, respectively. The luminescence quantum yields (LQY) of TPPA is measured at 61.3%.
AbstractAlthough significant progress has been made in the development of light-emitting materials for organic light-emitting diodes along with the elucidation of emission mechanisms, the electron injection/transport mechanism remains unclear, and the materials used for electron injection/transport have been basically unchanged for more than 20 years. Here, we unravelled the electron injection/transport mechanism by tuning the work function near the cathode to about 2.0 eV using a superbase. This extremely low-work function cathode allows direct electron injection into various materials, and it was found that organic materials can transport electrons independently of their molecular structure. On the basis of these findings, we have realised a simply structured blue organic light-emitting diode with an operational lifetime of more than 1,000,000 hours. Unravelling the electron injection/transport mechanism, as reported in this paper, not only greatly increases the choice of materials to be used for devices, but also allows simple device structures.
Polymeric nanocomposite films from PEDOT and MEH-PPV embedded with surface modified TiO2nanoparticles for the hole transport layer and emission layer were prepared, respectively, for organic emitting diodes (OLEDs). The composite of MEH-PPV+nc-TiO2was used for organic solar cells (OSCs). The characterization of these nanocomposites and devices showed that electrical (I-Vcharacteristics) and spectroscopic (photoluminescent) properties of conjugate polymers were enhanced by the incorporation of nc-TiO2in the polymers. The organic light emitting diodes made from the nanocomposite films would exhibit a larger photonic efficiency and a longer lasting life. For the organic solar cells made from MEH-PPV+nc-TiO2composite, a fill factor reached a value of about 0.34. Under illumination by light with a power density of 50 mW/cm2, the photoelectrical conversion efficiency was about 0.15% corresponding to an open circuit voltageVoc= 0.126 V and a shortcut circuit current densityJsc= 1.18 mA/cm2.
Ultrasonic spray coating of polyethylenimine (ethoxylated) as electron injection and transport layer for organic light emitting diodes: The influence of layer morphology and thickness on the interface physics between polyethylenimine (ethoxylated) and the Al cathode
