Study On The Application Of Patterning Graphene Electrode Reduced By Femtosecond Laser In Organic Light-emitting Devices

As one of flat panel display technologies, organic light-emitting devices（OLEDs） haveattracted much attention in recent years due to its advantages such as light-weight, lowdrive-voltage, high brightness, good flexibility, etc. Indium-tin-oxide （ITO） is tradtionaltransparent electrode of OLED. It is very necessary now to find an alternative electrode,because of the brittle drawback of ITO and the sacrcity of indium on the earth.Graphene has brilliant properties such as excellent conductivity, high transparency,good flexibility, etc, and is one of the most promising alternative electrode for ITO. On theother hand, the fabrication of graphene and making patterns on graphene through the wayof micro-nano processsing have attracted more and more attention.Through the research of the fabrication and patterning work of graphene, we realizedthat we can reduce graphene oxide to graphene by means of femtosecond laserdirect-writing process. Huge quantity of heat produced by the laser beam focusing canwipe out the oxygen molecule in graphene oxide. Meanwhile, since the precision offemtosecond laser micro-nano fabrication is very high（about1nm）, high resolution3Dpattern can be obtained. Therefore, we can employ the femtosecond laser micro-nanofabrication technology to make the patterned graphene electrode, and apply the electrodeinto OLED.The main work of this thesis includes fabrication micro and patterned graphenereduced by femtosecond laser as electrode, and application of the patterned graphene intoOLEDs. The main works are as follows:1. Design and fabrication of electrical connection between graphene electrode andlead. Since the reduced graphene electrode is in micrometer size, it is difficult to applyvoltage to device directly. We evaporated Au film onto glass substrate as the electricalconnection between the graphene electrode and lead. A channel was left at the middle of it,where is the reduced area of the graphene electrode.2. Fabrication of the patterned graphene electrode. First of all, we used graphite as theraw material to prepare the graphene oxide suspension by the oxidization method, andspin-coated it onto the lead electrode; then we made us of the laser to complete the reduction work, take the graphene electrode on both ends of the channel. According to thepreviously designed program, at the meantime of the reduction work is done, the laserpoint finished the patterning work. We had made patterns of square, ladder and bow tiewith graphene at microndimension in our experiment successfully, and through the testwork of resistance, we proved the graphene electrode with a good conductivity.3. Fabrication and characterization of OLEDs with patterned graphene electrode. Atfirst, we fabricated the standard bottom-emitting device structure based on the grapheneelectrode: Graphene/m-MTDATA （30nm）/NPB （20nm）/Alq3（50nm）/LiF （1nm）/Al（100nm）. We observed the luminous phenomenon of device with different patterning electrodeby fluorescent microscope successfully, and found two important factors which affect theluminous uniformity of the device: the thickness of electrode and the bubbles that emergedin the reduction of graphene. We obtained the device with improved luminous uniformityby optimizing the fabrication process.4. Characterization of the reduced graphene electrode. We observed the surfacetopography, roughness and thickness of the electrode by atomic force microscope. Theroughness of graphene is5.45nm, which is increased after reduction. The thickness ofreduced graphene is21nm, which is decreased compared to that of the graphene oxide.Through the investigation of the D peak at1354cm^-1and G peak at1590cm^-1and theintensity ratio between them in Raman spectrum, we confirmed that the graphene is wellreduced. At last, we estimated the resistivity and conductivity of the graphene electrode.The resistivity of the reduced graphene electrode is9.19×10^-4·m, and the conductivity is1.09×10³S/m, when the laser power is controlled between6～8mW.We have employed femtosecond laser micro-nano fabrication technique to fabricatepatterned graphene and applied it into OLEDs as its electrode. It proposes a newdevelopment direction for OLED, at the same time it also has some reference significancefor the application of graphene in other microelectronic devices.