Study On Growth Of Organic Polycrystalline Thin Films

In recent years, the performance of organic electronic devices is similar to theperformance of inorganic with the rapid development of electronic technology, and alsobecause organic semiconductor material have many unique advantages, such as, easilyto process and deposited on any kinds of substrates include the flexible substrates,large-area, good photoelectricity properties, synthesizable, a wide range of materials,light weight, low cost and so on, organic semiconductor materials have gainedtremendous attention and display a extensive potential in the applications of organicdevices including organic light emitting diode, photovoltaic, and organic thin filmtransistor. The key of device fabrication is the growth of the organic semiconductorsthin films, and the thin films morphology plays a crucial role in the performance ofthese devices especially organic thin film transistors, so the research on the growth oforganic thin film is of significance for the technical control of organic thin film growthto realize better device performance.Firstly, we deposited the different thickness pentacene thin films on the heavilydoped silicon substrates covered with the thermal oxide layers and coated with aself-assembling monolayer by vacuum thermal evaporation, the surface morphology ofthe pentacene thin film was measured in air by atomic force microscopy(AFM), thegrowth of pentacene thin film exceed the certain thickness is the island growth mode,the surface roughness of the thin films is rapidly roughening with the film thicknessincreases, in the range from10nm to about30nm, the evolution of the roughness versusthickness (γ)is about0.07,the value of γ is about0.03when the thickness of thin film is30nm,but the γ value is nearly zero and the surface is almost not change with thethickness increasing when the thickness is beyond60nm, the γ value suggest the extentof the interlayer mass transport for organic multilayer surfaces. For comparison, anotherseries of pentacene films on the non treated substrates were prepared under the sameconditions, the similar behavior is clearly present in spite of the very largely differentpentacene grain size, this demonstrates that the grain size may have a little or no influence on the roughening not agreeing with the ESB mode, and the surfaceroughening of pentacene is arise from the gradual phase change during the thin filmgrowth.Secondly, we research the growth of the new synthetic N type(naphthalenediimides) thin films, we get the surface morphology of the different thickness thin filmsby AFM, the roughness of the thin films demonstrated an oscillatory behavior between0.4nm and1.3nm, as a clear evidence of the layer-by-layer growth. Meanwhile, westudy the isomeride material, and analysis their crystal structure by AFM and XRD, andusing them as the organic semiconductor active device layer prepared OTFTs, and getthe performance of the devices.Finally, we discuss surface morphology of the double active layer structure, andstudy the new synthetic N type thin films deposited on the pentacene thin films withdifferent thickness and different roughness, we found that the surface roughness of newsynthetic N type thin films is more and more rough with the thickness of pentaceneincreasing, and we fabricated different bipolar OTFTs by change the order ofdeposition.To summarize, this thesis provides insights on the organic thin film growth, andstudy the two different growth modes of two layer-by-lay growth and the island layergrowth, analyzing the growth mechanism of organic thin film for the higher order andcontinuous thin films are the most important methods to improve the mobility oforganic semiconductor layer and device performance.