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Studies On Application Of Dip Coating Process In Organic Light Emitting Diodes And Polymer Solar Cells

Posted on:2016-04-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y W ChenFull Text:PDF
GTID:1108330479993460Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
Due to its wide viewing angle, self-emitting, low power consumption, simple processing and flexibility, organic light-emitting diodes(OLEDs) have great application prospects in the field of display and lighting. After decades of development, OLEDs have gained their applications in the commercial nowadays, but all of these products are basically prepared using vacuum evaporation. Due to the higher equipment expense and lower material utilization efficiency, the cost of this method is relatively high. Whereas the solution process is simpler and cheaper in fabricating OLEDs. At present, the spin-coating is the most widely used solution process. However, due to the low material utilization and limitations in the large-area manufacturing, the spin-coating is not suitable for the preparation of large-area OLEDs. Dip-coating is a simple and historic film coating technology, which is widely used in the industry. Compared to spin-coating, dip-coating has a higher material utilization and suitable for large-area substrates. In the thesis, we investigated the effect of solution concentration, pulling speed and structure of the substrate on the film thickness and uniformity during dip-coating process. By optimizing the process parameters, we finally successfully prepared a five-inch OLED which has the same performance with spin-coated devices and better luminous uniformity.With the advent of the global energy crisis, the research and development of renewable energy, such as solar energy, received more and more attention. Among them, the polymer solar cells have been widely favored due to their advantages in the low-cost and mass production. Currently, spin-coating is the most commonly used method for the preparation of the active layer in the polymer solar cells research. But spin-coating process is difficult to achieve mass production in the industry due to its own limitation. Dip-coating is a simple and effective method for film preparation, and it has a great advantage in material utilization and large volume production. We fabricated the polymer solar cells using the dip-coating process, and studied the effect of the solvent system and the drying conditions of the active layer on the morphology and phase separation of the active layer and device performance. Compared with the spin-coated device, we found that the active layer has a more dispersed phase due to the different conditions of solvent evaporation in the dip-coating process. The dispersed phases are not conductive for the transmission and collection of photo-generated carriers reducing the performance of the device.The inverted structure of polymer solar cell becomes the focus of research at home and abroad due to its advantage in terms of stability. In the inverted device structure, n-type metal oxides such as Ti Ox and Zn O are usually utilized as the electron transport layer to facilitate the electron extraction. Due to its low work function, high electron mobility, excellent optical transparency, and environmental friendliness nature, Zn O becomes the most widely used ETL in the inverted PSCs. Commonly, the preparation method of Zn O is not compatible with inexpensive and temperature sensitive flexible substrates, because the conversion temperature is often higher than 200 °C. In our study, we used an aqueous solution processed Zn O ETL with extremely low conversion temperature based on zinc oxide hydrate(Zn O·x H2O) in inverted PSCs. Due to the low energy metal-ammine dissociation and hydroxide condensation/dehydration chemistry, a conversion temperature(TA) as low as 80 °C is achieved. With the photoactive layer of poly(N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-3′,2′,1′-benzothiadiazole)):[6,6]-phenyl C71 butyric acid methyl ester(PCDTBT:PC71BM), an average PCE up to 6.48% is realized. In comparison, at a conversion temperature of 200 °C, the device with Zn O ETL deposited by sol-gel process based on zinc acetate has an average PCE of 5.53%. The device performance enhancement is attributed to the smoother ETL surface and better charge transportation of the Zn O ETL prepared by the aqueous solution. The low conversion temperature and the simple solution process make the aqueous Zn O·x H2 O suitable in the inverted PSCs fabricated on low cost, flexible substrates.
Keywords/Search Tags:dip-coating, large area, organic light-emitting diodes, polymer solar cells, ZnO
PDF Full Text Request
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