- 學位論文
TiO2奈米粒子應用於染料敏化太陽能電池光電極之研究
Investigation of Applying TiO2 Nanoparticles in Photoelectrode of Dye Sensitized Solar Cell
摘要
本文是研究以三種奈米級氧化鈦材料；放電式奈米流體製程(EDNP)產出二氧化鈦(TiO2)奈米粒子、商用P25(TiO2)粒子以及利用水熱式化學反應改質P25而成的氧化鈦(TiO)奈米管，分別應用於染料敏化太陽能電池的光電極材料。藉由旋轉加熱塗佈平台裝置與電泳沉積技術，將奈米粒子均勻的塗佈沉積在ITO導電玻璃上形成薄膜，再浸泡入N719 染料中12小時以上作為DSSC的光電極元件。EDNP產出的TiO2奈米粒子具有優質的銳鈦礦晶相性質，粒徑尺寸可控制在20~50nm之間。奈米流體的表面電位約為-22 to -28.8mV，所以粒子是穩定懸浮於去離子水內。添加微量的介面活性劑Triton X-100在導電玻璃表面上，可以輔助製成均勻與緻密的TiO2薄膜，然後持續加熱旋轉平台達200℃以上就能去除混入的介面活性劑。ED(TiO2)薄膜也展現較佳的染料吸附成效，甚至不必藉由熱處理程序來提升本質特性。經過DSSC能量轉換分析結果呈現，比較厚的薄膜結構將提升Jsc而導致較高的光電轉換效率(η)5.37%。但是，當薄膜結構太厚(超過20μm)，Voc與FF兩者都會逐漸下降而導致DSSC效率變差。P25(TiO2)搭配異丙醇(IPA)之膠體添加1x10-4的電解質Mg(NO3)2．6H2O可維持膠體的穩定；電泳沉積薄膜的最佳電場強度在40V/cm時之薄膜堆積效率最佳，並且呈現高平整特性的薄膜表面粗糙度(Ra=1005.725Å)。以400℃高溫熱處理持續30分鐘有助於P25(TiO2)薄膜的銳鈦礦晶相轉強並且提高薄膜緻密性，多層電泳沉積不僅可以防止薄膜因內部應力的破壞，並且能夠降低裂縫缺陷的存在，使得TiO2薄膜的粒子增加染料分子吸附量，進而提升DSSC之光電流密度至12.2mA/cm2(η=5.29%)。TiO奈米管(Tnt)是無晶相的鈦酸鹽結構[H2Ti3O7]，雖然奈米管擁有較大的比表面積能吸附較多的染料，但是因為材料性質無法像銳鈦礦或是金紅石一樣具有良好的半導體特性，其能量轉換效率最高也只有3.16% (9μm)。因此，從P25改質後所得到初形成的Tnt不適合直接作為光電極材料的應用。
並列摘要
The investigation is to apply three kind of oxide titanium nanomaterials, TiO2 nanoparticles by electrical-discharge-nanofluids-process (EDNP), commercial P25 nanopowders (TiO2) and TiO nanotube which made by hydrothermal chemistry reaction to be photoelectrode material of dye sensitized solar cell. Through spreading nanoparticles evenly onto the ITO glass by spin-heat platform coats a TiO2 thin film and then soaks it in the dye N719 more than 12 hours to prepare for the photoelectrode device. The TiO2 nanoparticles produced by EDNP has premium anatase crystal property, and its diameter can be controlled within a range between 20-50 nm. The surface energy zeta potential of nanofluid is about -22 to -28.8 mV, it is a stable particles suspension in the DI water. Using a trace of surfactant Triton X-100 upon the surface of ITO glass can helpful produce a uniform and dense TiO2 thin film, heating up the spin platform to over 200℃ is able to eliminate mixed surfactant. The ED(TiO2) film presents excellent dye absorption performance as well and even doesn’t through heat treatment procedure to enhance essential property. Results of energy analysis show the thicker film structure will increase the Jsc generation that causes higher conversion efficiency (η) 5.37%. But, as the film structure is large thick condition (over 20μm), both Voc and FF will decline gradually to lead bad of DSSC efficiency. The P25(TiO2)/IPA colloid could well suspend when it mixed with electrolyte 10-4M of Mg(NO3)2．6H2O. The optimal electric field intensity of EPD indicates at 40V/cm, which produce well thin film roughness about 1005.725Å. Through 400℃ heat treatment to keep 30 minutes for P25(TiO2) film is able to reinforce helpfully the anatase crystalline property improvement and density consolidation. Multilayers EPD could not only prevent inner stress to breack film structure but also decrease vacancy and crack defect in the film, and absorb more quantity of dye molecule on the P25(TiO2) particle surface to increase photocurrent density of DSSC at 12.2mA/cm2(η=5.29%). TiO nanotube (Tnt) belongs amorphous H2Ti3O7 phase, even though the Tnt has higher specific surface area to absorb huge dye molecule, but its material property is not like anatase or ruitle phase to present great semiconductor feature as well, its best η result is 3.16% at 9μm thickness. Consequently, the initial phase changed of Tnt, which made by chemical reaction from P25, is not best suitable for photoelectrode material application directly.