利用電泳法製備奈米二氧化鈦薄膜應用於可撓式染料敏化太陽能電池之研究

染料敏化太陽電池是由1991年瑞士 M. Grätzel 實驗室發展出一種高效率、低成本的太陽能電池。這是利用奈米級結晶 TiO2多孔膜製作電極，以釕錯化合物之染料敏化處理後，再使用碘/碘離子溶液作為電解質，對電極為鍍上鉑金屬的導電玻璃。一個有效率的染料敏化太陽能電池，首先即是扮演最重要角色的工作電極，也就是TiO2電極，它必需要能提供染料吸附的表面積、電流的路徑，還必需要具有多孔性的結構來幫助電解質的擴散。光敏染料分子吸附在奈米級半導體TiO2表面，將提高光電陽極吸收太陽光的能力。這是因為奈米級TiO2粒子所組成的多孔結構，體積小、粗糙度夠大、比表面積也大，能夠提供染料分子很充足的吸附面積，故即使粒徑表面的染料只有一層，所表現出來的吸收效率還是很好。本研究選擇電泳沉積法去製作TiO2薄膜電極，主要是因為電泳沉積法之優點包括製程設備簡單、便宜、沉積速率快、製程溫度低、適用於材料鍍膜上。利用電泳法製備TiO2薄膜，並改善TiO2奈米薄膜結構，以及製備TiO2奈米管於電極材料上的使用，在使用不同染料去比較染料的差異性，和製備膠態電解液來取代液態電解液不易封裝的缺點而去改善常見的封裝問題，藉由這些方法去製作高效率的可撓式染料敏化太陽能電池。首先將商業用TiO2奈米粒子放置在高溫爐鍛燒450℃維持30分鐘，然後取經過鍛燒後的TiO2奈米粒子加入100ml 異丙醇中，粒子濃度約0.35g/l。然後添加硝酸鎂其濃度為1x10-4 M 作為製備TiO2懸浮液之電解質，即完成所需的TiO2 懸浮液。而工作電極以Pt 方片為陽極，塑膠基材為陰極，兩極間距固定為15mm，將兩電極置入於TiO2 懸浮液中，利用直流電源供應器施予固定外加電壓，其電壓值為40 V、電流值為0.005 mA、沉積時間為3分鐘，則完成所需要的TiO2薄膜。而電泳過程中，同時以磁攪拌持續進行懸浮液之攪拌，以避免粒子凝聚及沉降。在電泳法沉積完成的TiO2薄膜，再利用自動壓縮機去壓縮薄膜，其壓力為200 bar、時間為2分鐘，即完成壓縮製程。 TiO2奈米管的備製，一樣取鍛燒後的TiO2 奈米粒子與NaOH 固體，兩者的重量比(克)分別為1：80，再加入去離子水使其為200 毫升的溶液，將此溶液放置於血清瓶中，利用油浴加熱的方式維持在110℃左右進行迴流60 小時。當反應完成後，先進行靜置冷卻，接著將冷卻完的溶液倒出至燒杯中進行清洗的步驟，不斷加入1M HCl 水溶液進行酸洗步驟，直到水溶液呈現酸性(pH=1)以及有固體粉末沉澱於杯底，將此杯溶液浸泡24小時，之後再用去離子水不斷清洗固體粉末至水溶液pH 值接近7。將接近中性的固體粉末經由過濾後在80℃下進行烘乾，再經研磨收集，即可獲得具有高產率及均一性較高的TiO2奈米管。然後取適量的TiO2奈米管調配成TiO2 懸浮液，再利用電泳法沉積所需要的TiO2奈米管薄膜。接著將沉積完成的TiO2奈米薄膜浸泡在濃度為1x10-3 M的染料分子EY和N3溶液中進行吸附。接著利用蒸鍍法來製備白金(Pt)背電極。液態電解質的製備為調配濃度含0.5M的碘化鉀(KI)與0.05M的碘(I2)之乙腈溶液作為電解質。膠態電解液是先調配好的液態電解液為7g EC混 3g的PC並加入1.1g的碘化鉀(KI)和0.1g的碘(I2)和膠態溶液為3g 的PEG 加入6g 的丙烯胺單體中加熱70℃維持30分鐘，並把0.06g 的過硫酸銨加入1g的PEG中，加以混合即為膠態溶液。最後在把液態電解液和膠態溶液加以混合即完成膠態電解液。最後將浸泡與吸附染料完成的TiO2電極，和Pt電極形成三明治結構的太陽能電池元件，並在兩電極中使用厚度為3mm 之塑膠夾片凹槽來進行封裝，即完成染料敏化太陽能電池元件的組裝。我們將組裝好的染料敏化太陽能電池元件以”Newport Oriel lnstriments”之模擬太陽光光源當作入射光的來源來做量測，使用PL = 100mW/cm2 (AM 1.5) 並量測元件之電壓、電流值及其效率之計算。本論文研究以電泳沉積法的方式來製備奈米TiO2薄膜。由XRD分析發現，商業用TiO2奈米粒子在經過鍛燒溫度450℃後，電泳法沉積出來的薄膜為所需的Anatase 結晶相。從SEM表面分析可觀察到壓縮製程後薄膜表面變為緊密，有助於電子傳遞並提高與染料接觸的面積。染料是選用具有釕錯化合物的N3染料，能夠幫助TiO2的光激發波段提升至可見區。而由吸收光譜圖來看，吸附染料後的TiO2會有較強的吸收光能力。二氧化鈦奈米管其高比表面積與孔徑度較大的特性，有利於電解液的擴散與染料分子的吸附。從以上的改善方式可以證實對染料敏化太陽能電池的效率提升都有幫助。

關鍵字

染料敏化太陽能電池；二氧化鈦；可撓式

並列摘要

The dye-sensitization solar cell is a kind of low-cost solar cell with high efficiency developed by Swiss M. Gratzel laboratory in 1991. The electrode is made by utilizing nano-grade crystallization of TiO2 porous thin film. After processing by Ru-complex of day-sensitization and using the iodine/ the iodine ion solution as the electrolyte to the conductive ITO glass on the metal of platinum of electrode plate, the dye-sensitization solar cell is made. Basically, TiO2 electrode plays a most important role on an efficient dye-sensitization solar cell. It must offer the route of electric and surface area that dye absorption, and also need porous structure to help diffusion of electrolyte. It will improve the ability of absorbing the sunlight of photoelectric positive pole that the photosensitive dye molecule adhere the TiO2 surface of nano-grade semiconductor. As the small area, heavy roughness, big surface area composed by nano-grade TiO2 porous structure, it can offer sufficient area of absorbing dye molecule even only one stratum dye on the surface. It shows high absorption efficiency in UV light regions. In this study, we choose the electrophoresis depositing method to make the thin film electrode of TiO2 is due to electrophoresis depositing method has the advantages of simple and cheap production equipment, high-speed depositing, low-temperature production suitable for material plating membrane. Utilizing electrophoresis to manufacture TiO2 thin film can improve TiO2 nano thin film structure and producing the usage that TiO2 nanotubes applied on electrode material. We also use various dye to compare the differences of efficiency and produce colloidal electrolytic liquid to replace electrolytic liquid to improve the assembling of solar cell. These methods are applied to produce high-efficiency dye-sensitization solar cells. TiO2 nanoparticles were calcined 450 oC in high-temperature stove for 30 minutes and put the calcined TiO2 nanoparticles in 100ml isopropyl alcohol, the concentration of particle was about 0.35g/l. Then add nitric acid magnesium which the concentration was 1x10-4 M as electrolyte of producing TiO2 suspension, then TiO2 suspension liquid was finished. And the working electrode regarded Pt side as the positive pole, the plastic sill as the negative pole, the regular interval between two poles was 15mm. Put two electrodes into TiO2 suspension and utilized the galvanic power supplying device to bestow the regular applied voltage. The voltage value was 40V, electric current value was 0.005 mA. As depositing for 3 minutes, the TiO2 thin film was finished. In the electrophoresis process, we stirred the suspension continuously with the magnetism at the same time in order to prevent the particle from condensing and subsiding. TiO2 membrane was compressed by the automatic compressor for 2 minutes. The pressure was 200 bar. In order to produce TiO2 nanotubes, we put the calcined TiO2 nanoparticles and NaOH solid with the weight ratio 1/ 80 in deionized water to prepare 200 milliliters of solution. Then put this solution in the serum bottle, and made it maintain 110 oC by utilizing oil bath heat for 60 hours. After the reaction was finished, we proceeded the cooling still first, and poured the cooled solution to the beaker for the washing procedure, and then put 1M HCl aqueous solution constantly in the acid washing process until the aqueous solution presented acid (pH =1) and the solid powder precipitated at the bottom of the cup. Then put this cup of solution in air for 24 hours and washed the solid powder with iron water constantly until the solution pH value was close to 7. While filtering the solid powder close to neutral, then baked it under 80 oC and collected by grinding. Thus we could get TiO2 nanotubes with high production rate and higher consistence. Finally, we fetched appropriate amount TiO2 nanotubes to mix TiO2 suspension, and utilized TiO2 nanotubes thin film that electrophoresis method depositing needed. We soaked the finished TiO2 nano thin film on EY and N3 dye which the concentration were 1x10-3 M to proceed the absorption. Then utilized the steam and plate method to prepare platinum side electrodes. Mixed the acetonitrile which contains KI of 0.5M and I2 of 0.05M to produce the liquid electrolyte. The colloidal electrolyte was regarded as the liquid electrolyte and it’s 7g EC mixed PC of 3g and join KI of 1.1g and PEG of 3g, then heated by 70 oC for 30 minutes by adding 6g acrylamide monomer then blended the 0.06g ammonium persulfate and PEG of 1g to be colloidal electrolyte. Mixed the liquid electrolytic colloidal solution finally and the colloidal electrolytic was finished. For assembling the TiO2 electrode, we soaked and absorbed the dye and the sandwich-structure solar cell component formed by Pt electrode in the 3mm-thickness fillister of plastic slice between two poles. And the equipment of the solar cell component of day sensitization was finished. We used the "Newport Oriel Instruments" simulated sunlight as source that streams in through our build-up sensitization solar cell component to measure its voltages, currents and efficiency by utilizing PL = 100mW/cm2 (AM 1.5) According to XRD analysis, the membrane deposited by electrophoresis after calcined commercially TiO2 nanoparticle by 450 oC is the anatase phase as we required. From the results of SEM, we can observe that the membrane surface gets compact thru compress process, and that it’s helpful for electron transmit and enhancing the contact area with dye. The dye is selected from N3 dye with Ru-complex, it can help enhance light exciting wave band of TiO2 to visible area. And observing from absorbing spectrogram, TiO2 after absorbing the dye will have stronger ability of light absorption. TiO2 nanotube has the character of bigger surface area and bigger pore diameter is useful for diffusion of the electrolytic liquid and the absorption of dyes molecule. It is provided an improvement way to enhance the efficiency of the dye-sensitization solar cell.