Saijun Huang

Highly conductive and uniform graphene oxide modified PEDOT:PSS electrodes for ITO-Free organic light emitting diodes

We have successfully obtained a highly transparent and conductive film by doping poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with graphene oxide (GO) and sodium dodecyl benzene sulfonate (SDBS). The PEDOT:PSS hybrid film mixed with 0.02% GO:SDBS by weight exhibits a sheet resistance of 85 ohm per square and a transmittance of 87% at 550 nm. The improvement of conductivity is mainly attributed to the weakening of coulombic attraction between PEDOT and PSS by the functional groups on GO nanosheets, and forming an extended conductive network by connecting PEDOT chains with GO nanosheets. Using the optimized PEDOT:PSS hybrid film as an anode, indium tin oxide (ITO)-free organic light emitting diodes (OLEDs) have been demonstrated on glass and polyethylene naphthalate (PEN) substrates, showing better performance than that with ITO as the anode. This proves that such PEDOT:PSS and GO:SDBS hybrid films are promising alternatives to ITO for low cost flexible OLEDs.

Low-temperature MoO3 film from a facile synthetic route for an efficient anode interfacial layer in organic optoelectronic devices

A low temperature solution-processed MoO3 (sMoO3) thin film with a facile method for organic optoelectronic devices is developed. The film is extremely smooth with a root mean square (RMS) roughness of 0.318 nm, which is a significant advance for fabricating devices. An X-ray photoelectron spectroscopy (XPS) measurement shows that the sMoO3 possesses few Mo5+ states with a Mo : O stoichiometry of 2.99, demonstrating a nearly ideal MoO3 stoichiometry at a low annealing temperature. The sMoO3 film exhibits a superior hole injection ability in both an organic light-emitting diode (OLED) and organic photovoltaic cell (OPV), compared to conventional hole injection material poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). It is proved that the sMoO3 fabricated by the simple and low-cost method is an excellent alternative to a PEDOT:PSS anode buffer layer for solution-processed organic optoelectronic devices.

Enhancing the Hole Injection and Transporting of Organic Light-Emitting Diodes by Utilizing Gradient Doping

We demonstrate significant improvement of hole injection and transporting in organic light-emitting diodes (OLEDs) by utilizing gradient doping in hole transporting layer (HTL). An ultrahigh doping concentration at the anode side to enhance the hole injection, whereas low doping concentration close to emission layer to avoid possible quenching of excitons. A plural HTL with concentration step are introduced in between to smooth the hole transporting. Compared to conventional hole injection technologies, the gradient doping significantly enhances the current density and luminance of the OLED.