Preparation of π-Conjugated Polymer Ultrathin Films and their Application to Organic Nanodevices

π共轭聚合物因其具有多用途的电子和光子特性、结构柔韧性和易于加工等优点，在电致发光器件、场效应晶体管和分子电器件中得到了广泛的应用。这些聚合物薄膜一般通过浇铸、浸渍、旋涂和喷墨方法形成。然而，很难在分子水平和分子取向上控制薄膜厚度。在制备有机纳米器件的过程中，必须控制超薄膜的厚度。Langmuir-Blodgett （LB）技术具有在分子水平上制备具有分子取向和有序的超薄膜的优势。然而，由于芳香族主链之间的π-π相互作用较强，π共轭聚合物在水表面形成单层的能力较弱。为了克服这一问题，我们尝试制备π共轭聚合物和两亲性聚合物的混合LB膜。我们发现聚（N-d…More odecylacrylamide） （pDDA）能够在水面形成稳定的单层膜，并制备出优良的LB膜。在本研究中，研究了pDDA与聚（3-己基噻吩）（PHT）或聚[2-[2',5'-双[2 " -乙基己氧基苯基]-1,4-苯基乙烯基乙烯基（BEHP-PPV）的混合物在水面上的单层行为，并利用互指阵列（IDA）电极测量其混合LB膜的电导率。我们发现π共轭聚合物可以很好地与pDDA相混，通过LB技术可以在水面上形成稳定的单层，在底物上形成LB膜。以pDDA和π共轭聚合物为原料，采用LB法制备了π共轭聚合物超薄导电膜。掺杂后混合PHT LB膜的电导率达到3 S/cm，比未掺杂时提高了约3个数量级。期望利用混合LB膜制备分子电子器件。研究了混合PHT LB薄膜在有机电致发光（EL）器件上的空穴注入性能。需要ITO阳极的功函数与注孔材料的HOMO能级之间的能势匹配，而理想的注孔层不需要注孔层的厚度。由于从氧化铟锡（ITO）阳极到PHT薄膜的空穴注入能量势垒降低，使用PHT LB薄膜的EL器件的起始电压随着层数的增加而降低。在单层PHT LB薄膜EL器件上，量子效率得到了提高。我们证明了混合PHT LB薄膜可以作为电致发光器件的空穴注入层。少

π-Conjugated polymers have received much attention for the application to electroluminescent devices, field-effect transistors and molecular electric devices because of their versatile electronic and photonic properties, structural flexibility and easy processability. These polymer films are generally formed by casting, dipping, spin-coating and ink-jet method. However, it is difficult to control film thickness at a molecular level and molecular orientation. It is necessary to control the thickness of ultrathin films for preparation of organic nano-devices. The Langmuir-Blodgett (LB) technique has attractive features to fabricate ultrathin films at a molecular level with molecular orientation and ordering. However, π-conjugated polymers have less ability to form monolayer on a water surface due to strong π-π interaction between aromatic main chains.To overcome the problem, we try to fabricate mixed LB films of π-conjugated polymer and an amphiphilic polymer. We have found that poly(N-d … More odecylacrylamide) (pDDA) has an ability to form a stable monolayer on the water surface and to fabricate an excellent LB film. In this study, the monolayer behavior of the mixtures of pDDA and poly(3-hexylthiophene) (PHT) or poly[2-[2',5'-bis[2''-ethylhexyloxyl]phenyl]-1,4-phenylene vinylenel (BEHP-PPV) on the water surface was investigated and conductivity of their mixed LB films was evaluated by conductivity measurement using interdigitated array (IDA) electrodes. We have found that π-conjugated polymers are well miscible with pDDA and the mixtures can form a stable monolayer on a water surface and LB film on substrates by the LB technique. The π-conjugated polymer ultrathin conducting film was fabricated by LB method using the mixture of pDDA and π-conjugated polymers. The conductivity of the mixed PHT LB film becomes 3 S/cm with doping, which is about three orders of magnitude higher than that of the undoping. It is expected to fabricate molecular electronic devices using the mixed LB films.Performance of the mixed PHT LB films on hole-injection for organic electroluminescent (EL) devices was also investigated. The matching of the energy potential between the work function of the ITO anode and HOMO energy level of the hole-injection materials is needed whereas the thickness of the hole-injection layer would not be needed as an ideal hole-injection layer. Onset voltage of EL devices using PHT LB films decreased with increasing number of layers due to reduction of energy barrier of hole injection from indium-tin-oxide (ITO) anode to PHT films. Quantum efficiency was improved at the monolayer PHT LB film EL devices. We demonstrated that the mixed PHT LB films could function as a hole-injection layer for EL devices. Less