Facile Solution Processed Alumina Thin Films For Organic Optoelectronics Devices

Generally，a high performance of organic optoelectronic device (such as, organicsoalr cells and organic light-emitting diodes) can be achieved by utilizing a highquality organic semiconductor, and by reducing the energy barrier at the interfacebetween the organic layer and electrodes, and facilitating/balancing the hole andelectron transport, collection or injection. In order to achieve excellent performanceOFETs, besides an organic semiconductor with high carrier mobility, ahigh-capacitance gate dielectric is also desired to achieve low operating-voltage toreduce the device power consumption. This has made the research of the high qualityorganic semiconductors and interfacial layers materials a very attract research filed inrecent years.In this thesis, we demonstrated a new method to prepare alumina thin films foroptoelectronic devices, through by a facile solution-processed synthesis route. Weinvestigated the formation of alumina and the atomic ratio of Al:O by TGA, XRD,XPS and EDS respectively. Also, the morphology of ultra thin alumina-coated ITOsubstrates and alumina-coated Si substrates were investigated by AFM and SEM，andthe work function of the ultra thin alumina-coated ITO were examined by UPS. Andthen, we investigated the performance of such facile solution processed alumina filmsused as interfacial layers for OPVs, OLEDs and OFETs.(1). The reaearch of ultra thin alumina films used as electron-selecting layers forP3HT:PCBM-based OPVs, and the detailed device structure isITO/alumina/P3HT:PCBM/MoO3/Al. we found that these OPVs using Al2O3thin filmas the electron-extraction layer demonstrated improved diode characteristics and achieved (PCE=3.66%) a20%higher power conversion efficiency than devices usingthe conventional ZnO buffer layer (PCE=3.05%).(2). The reaearch of ultra thin alumina films used as electron injection layers forOLEDs, and the detailed device structure is ITO/alumina/ETL/EML/HTL/HIL/Al. Weachieved a high current efficiency of5.12cd A-1at10mA cm-2and the best currentefficiency approaching5.5cd A-1at40mA cm-2without doping of an emission layer(EML) for a single Alq3-based greenfluorescent IOLED, and a high current efficiencyfor a green phosphorescent IOLED as well. Furthermore, the extrapolated50%decaylifetime (t50) shows that our Alq3-based green fluorescent IOLED is about5timesmore stable than the conventional OLED.(3). The reaearch of alumina thin films used as insulating layers forpentacene-based OFETs. We found that the pentacene-based OFETs using alumina thinfilms gate dielectric achieved comparable on-off drain current ratio (over105), fivetimes high field-effect mobility (~2.7cm2/Vs), threshold voltage of-1.4V and agreatly reduced operating voltage. Meanwhile, we also investigated the performance ofalumina used as gate dielectric for PET/ITO-based OFETs, and found that the effectivemobility, μ, was calculated to be~1.8cm2/Vs with a threshold voltage of~-0.7V and acomparable on/off current ratio (over105).