溶液法製備鈮凝膠應用摻混二氧化鈦作為染料敏化太陽能電池光電極研究

Solution-Based Synthesis of Nb Sol-Gel and Its Application in Doping Tio_2 For Photoanode of Dye Sensitized Solar Cells

黃榆婷(Yu-Ting Huang) ； 馮憲平(Shien-Ping Feng)

《興大工程學刊》 26卷2期 (2015/10) Pp. 47-54

https://doi.org/10.6287/JENCHU.2015.2602.02

摘要

染料敏化太陽能電池因具備可轉換太陽能源為電力，被視有潛力發展再生能源之裝置而受到關注，而染敏電池中，提供染料吸附、電子傳遞且有著大比表面積之多孔性二氧化鈦光電極，為影響染敏電池光電轉化效率之關鍵因素，然而在電子傳遞過程中，液態電解液包含之氧化還原對物質會捕捉傳遞電子，稱為逆反應或者電子再結合因而降低整體效能，常發生於多孔性二氧化鈦薄膜與電解液之固－液界面，雖提供染料吸附但也同時增加電子再結合之機率。因此文獻中提到多孔性二氧化鈦顆粒之形貌、尺寸、接附性、多孔性以及電性影響著整體效能。為了有效改善逆反應，如改變吸附染料、異質結構以及離子摻混等方式皆被提出，少數研究提到由摻混金屬至二氧化鈦作為光電極不僅可增進染敏電池效率、加強電子傳遞以及有效抑制電子逆反應發生，其中鈮元素的摻混具備優異的電子導電性、與鈦元素原子大小相近、易形成價態可提高載子濃度以及結構穩定等特點。本研究利用市售二氧化鈦粉末進行球磨使其縮小尺寸後製備成漿料，再以一具有鈮金屬氧化物凝膠與之混合形成具有鈮摻混之漿料製備成光電極，此簡易方式適用於量產且經過最適化之摻混條件，鈮摻混之光電極可增加電子導電度進而增加整體效能。

關鍵字

二氧化鈦 ； 摻雜 ； 染料敏化太陽能電池

並列摘要

Dye sensitized solar cells (DSSCs) have received attention as a potential alternative for converting solar energy into electricity. The performance of energy conversion efficiency in DSSCs is mainly determined by the mesoporous TiO2 photoanode, which provides not only an enormous surface area for dye chemisorption but also electrons transportation. However, the electrons transport in DSSCs is greatly influenced by the electron recombination from the electrolyte of redox couple, especially triiodide (I3 -). The most happened route for the I3 - to capture the electrons, so called back reaction or charge recombination, particularly for the liquid-electrolyte system of DSSC is happened at the liquid-solid interfaces of electrolyte and mesoporous TiO2 film, which provides the great area for dye adsorption but meanwhile also increases the interfaces for charge recombination. The electrons at LUMO state from dye and those injected into ECB of TiO2 could be trapped by I3 - or release florescence. According to the literature, the characteristics of the porous TiO2 nanoparticles (NPs) including the morphology and size, inter-particle connectivity, pore structure, and electric structure are greatly vital in determining the final photovoltaic performance of DSSCs. In order to address these problems, several strategies, such as dye sensitizing, heterostructure, ion doping, etc., have been developed. Among them, the ion doping is believed to be the most economical and facile method to optimize the performance of TiO2 NPs by simply modifying its structure, which has been widely used in the photocatalysis, biological engineering and gas sensors fields, but there are relatively few studies applied in DSSCs. Several methods have been tried to modify nanostructured TiO2 NPs by metal ions in order to further improve the efficiency of DSSCs, enhance electron transportation and suppress charge recombination. Of these doping elements, the Nb element stands out to show great potential in improving DSSCs performance due to the synergistic advantages of superior electrical conductivity, similar atom radii with Ti, high valence favorably enhancing free carriers and excellent ability in stabilizing the phase structure and tailoring the optical properties. However, one determined and important limitation for the practical application of the presently reported Nb-doped TiO2 NPs applied in DSSCs is that the starting materials either use expensive niobium ethoxide or the method to prepare such materials commonly adopts the hydrothermal technique which includes multi steps and long time procedure, thereby leading to high preparation cost and low production efficiency. To further improve the performance of TiO2 electrode, we firstly develop a scalable synthesis of TiO2 slurry from commercial and low-lost powder by ball-milling to make the particles down to 30nm. The Nb-doped TiO2 NPs was then made by simply mixing TiO2 paste with sol gel contained of niobium oxide used as the DSSC photoanode. This facile method is suitable for mass production. By optimizing the doping amount of Nb into TiO2 NPs, the adjustment of conduction band minimum (CBM) to a positive-shift and Fermi level closer CBM enhance the electron injection and the improved electron conductivity facilitates the electron transport, leading to 12% improvement of photo conversion efficiency of Nb-TiO2 NPs compared with the standard TiO2 NPs DSSCs.

並列關鍵字

TiO_2 nanoparticles ； doping ； dye-sensitized solar cell