Fabrication and Characterization of Titanium Oxide Nanotube-based Dye Sensitized Solar Cells
|摘要:||二氧化鈦奈米管薄膜由於具有一維傳導特性，使得一維方向的電子傳導速率較快、電子電洞分離率也較高，電子-電洞再結合率也因此下降，因此，相當適合應用於染料敏化太陽能電池(Dye-sensitized solar cell)之光陽極，並可應用於氣體感應器、光催化，鋰電池等其他領域。本論文即是以陽極處理方法製備一維二氧化鈦奈米管(TiO2 nanotube, TNT)光陽極結構結合本實驗室開發之新穎釕金屬染料RD16-RD18，製備高效能之TNT-DSSC元件，並量測其光電轉換效率、入射光子－光電流轉換效率、瞬態衰減光譜來探討染料分子結構對於染料敏化太陽能電池(DSSC)元件之電子傳遞及電荷重組過程所造成的影響。
由所製備之奈米管元件，RD16導入苯並咪唑以及帶有陰電性的氟，並在聯吡啶上加入噻吩官能基團，有效提昇了元件的短路電流，讓電池元件的效率達到7.18%。修飾RD16結構中接上長碳鏈基團的RD17與具有雙噻吩及長碳鏈基團的RD18染料，則因有明顯的團聚現象而造成染料吸附量的低下與電流下降，尤其以RD18團聚現象最為嚴重。配合瞬態衰減光譜與電荷萃取技術的分析，得知二氧化鈦在RD系統中導帶位置為：RD16 < RD17 < RD18；電子生命期(□R)之趨勢為：RD17 □ RD16 ＞ RD18。將RD系列染料搭配上DINHOP以及CDCA共吸附劑，經過元件效率最佳化，在35μm的奈米管元件中，RD16染料搭配上適當比例之CDCA共吸附劑，可得到14.983 mAcm-2的光電流，VOC = 0.714V，FF = 67.05，效率也高達7.18%。|
Self-organized 1-D titania nanotube (TNT) arrays have a great potential as materials for photocatalysis, self-cleaning, gas sensing, lithium batteries and dye-sensitized solar cells (DSSC) due to their excellent charge collection efficiency and slow charge recombination. In this work we fabricated highly efficient TiO2 nanotubes-based dye-sensitized solar cells sensitized by novel heteroleptic ruthenium dyes, RD16-RD18, and studied electron transport and charge recombination kinetics of the relative devices using transient photocurrent/photovoltage decay and charge extraction techniques. A series of heteroleptic ruthenium complexes RD16-RD18 containing fluoro- substituted and thiophene-based benzimidazole ligands were developed by Professor Diau’s group. The RD16-sensitized TNT-DSSC reveals an enhanced short-circuit current density (JSC) and efficiency (□) of power conversion compared to N719 due to the increasing light-harvesting and the broadened spectral features with thiophene-based ligands. However, the devices made of RD17 and RD18 were confronted by the poor adsorption of dyes on TNT surface resulting in a decreased short-circuit current density especially in RD18. Instead of retarding charge recombination, the substitution of thiophene and long alkyl chain in RD17 and RD18 caused an aggregation of sensitizers. Investigating using the photovoltage decay and charge extraction measurements, we found that the TiO2 potential shift downward in a systematic trend of Ecb : RD16 < RD17 < RD18 and the electron lifetimes show the order of RD17 □ RD16 ＞ RD18. In order to preventing the aggregation, co-absorber, DINHOP and CDCA, were introduced in RD sensitizers. Upon optimization, the device made of RD16 yielded JSC/mA cm-2 = 14.98, VOC/mV = 714, FF = 0.67 and the efficiency reaches 7.18 %.
|Appears in Collections:||Thesis|