Study On Optimization And Performance Of Organic Optoelectronic Devices

Organic functional materials in organic light-emitting diodes (OLEDs) orpolymer light-emitting diodes (PLEDs) and organic photovoltaic (OPV) devicesapplictions have been attracting considerable attention. OLEDs have thecharacteristics such as the low driving voltage, high brightness, wide viewing angleand fast response. Since2003, OLEDs have been widely used in MP3players and cellphone, but the large-area OLED display has not yet into the wide range of applicationstage because the issues of the life and stability. Since1986, the organic photovoltaiccells’ efficiency significantly has been improved and become to the hot-spot inresearch now.In this thesis, we introduced the OLEDs and OPVs’ recent progress at first, andthen illustrated the devices’ structures, the general fabricated process and the workingprinciples of the OLEDs and OPVs. The materials, such as electrode materials,luminescent materials, hole-transporting materials, electron-transporting materials andbuffer materials which are used in OLEDs were also introduced. Then, the whiteOLEDs were prepared using a polymer, PVK, as the host material and a newphosphorescent material, platinum/iridium (Pt/Ir) metal-organic complexe doped in asguest material. The working mechanism of the white OLEDs was also studied. Finally,amounts of works were done in organic photovotaic devices’structure optimized andstudied on its’ performance.There are some conclusions are obtained as follows.1. The thermal, photophysical, and electrochemical properties of dinuclearplatinum-iridium complexes were studied. Electroluminescent properties ofcomplexes were studied by fabricating a serial of PLEDs with a single-emitting layerdoped with the complexs. We obtained expectant near-white emissions at low dopedconcentrations of multi-nuclear Pt/Ir metal-organic complexes and lowdriving-voltages. The wihte PLEDs have the CIE coordinate of (0.33,0.34) which isnear the CIE coordinate of pure white light,(0.33,0.33). The efficiencies can beimproved obviously by controlling the distance appropriately between the twophosphors. The investigation has laid a well foundation for further study on thedinuclear or multi-nuclear complexes of white-emitting materials. Moreover, it may promote the development of white polymeric single dopant light-emitting diodes withhigh stability and efficiency.2. The photovoltaic cells based on a fluorene, thiophene and triphenylaminecopolymer (PFO-3ThPz-Tpa) as donor and PCBM as accepter were fabricated withthe structure of ITO/PEDOT:PSS/Donor:PCBM/LiF(0.5nm)/Al.The effect of solvent on the performance of polymer solar cell was studied. Thedevices based on PFO-3ThPz-Tpa:PCBM fabricated in chlorobenzene (CB) as solventhas a higher power conversion efficiency (PCE). However, it is found that highershort circuit current (Jsc) was obtained in the devices from1,2-dichlorobenzene (DCB)as solvent.With the different ratios of the Donor/Accepter, it is found that the open circuitvoltage (Voc) of the devices has a greater change with the increasing amount ofPCBM.We use solvent additives as a simple method to tune the photovoltaicperformance of PFO-3ThPz-Tpa and PCBM bulk heterojuncton solar cells. When CBwas used as the solvent and1,8-diiodooctane (DIO) was used as additives to influencefilm formation, an increase in Jsc and PCE of the solar cells was observed.The effects of Ca, LiF or CsF inter layer on the photovoltaic characteristics ofthe device also have been investigated. The modified devices show an increase in theopen circuit voltage (Voc), but a decline in the Jsc. These changes of photovoltaicproperties are attributed to the dipole layer between composite film and Al cathodedue to the introduction of LiF/CsF layers. This dipole layer equivalently lowers thework function of the cathode, which enhance the build-in potential and the Voc.