釕金屬錯合物元件在碘液與溴液電解質中的電子轉移與染料再生動力學研究

Abstract

本論文將討論四個具有不同推拉電子基修飾之聯吡啶釕錯合物染料(Ru-1~Ru-4)作為染料敏化太陽能電池之敏化劑，藉由光致吸收光譜 (Photoinducted Absorption) 、瞬態吸收光譜 (Transient Absorption) 與瞬態光電壓/光電流衰減光譜 (Transient Photovoltage/ Photocurrent decay) 的量測來討論不同電解液環境對染料之電子傳遞速率以及電池效率的影響。由瞬態光電壓衰減結果可得知，在聯吡啶上修飾拉電子基之染料吸附於二氧化鈦時，會導致二氧化鈦半導體之費米能階下降，此結果可能是修飾拉電子基之染料吸附於二氧化鈦半導體上之分子偶極穩定二氧化鈦導帶上的電子。利用瞬態吸收光譜量測電解液與染料陽離子反應的再生生命期可以得知，其染料再生速率與短路電流值有相當的關聯性，且發現溴液電池之短路電流會較碘液電池之短路電流低，這是由於染料陽離子與 I3- 的反應速率比其與 Br3- 的反應速率大了約 10 倍，藉由 Marcus Theory 來模擬本實驗中所得到之染料陽離子與電解液反應的速率式關係，進而得知除了 Ru-3 與電解液的反應速率位於 normal-region 外，其他染料則位於inverted-region。此外我們也對於本實驗中最佳的染料 (Ru-1) 進行元件優化，其溴液電池的最佳光電轉換效率可達 5.09%，JSC 為 6.307 mA/cm-2、VOC 為 1.02V、FF 為 0.79。

Photo-induced Absorption (PIA), Transient Absorption decay measurements (TAD), Charge Extraction (CE) and transient Photovoltage decay measurement (TVD) were carried out to investigate the electron transfer kinetics and the photovoltaic performance of the four Ru-based dye-sensitized solar cell (DSSC) in iodide-based electrolyte or bromide-based electrolytes. With CE measurement, we observed a specific down shift of the conduction band edge of titanium dioxide sensitiged with the ruthenium complex containing the electron-withdrawing group on the bipyridine ligand. Is result indicated that the direction of dipole moment of the Ru complexes modified with electron-withdrawing group favors better interaction with the conduction band electrons than the others. The regeneration rate of dye cations obtained by the TAD measurement using were much slower with Br3- than with I3-, consistent with the trend of photocurrents of the devices. We found that the regeneration rate constant of the Ru-3 device was located on the Marcus normal-region, but the others were on the Marcus inverted-region. The DSSC using Ru-1 as a sensitizer and 3Br-/Br3- as electrolyte exhibited the best performance with overall power conversion efficiency 5.09 % with a short-circuit current density (JSC) 6.307 mAcm-2, an open-circuit voltage (VOC) 1.02 V, and a fill factor of 0.79. The VOC value of 3Br-/Br3- (1.02 V)was significantly greater than that of 3I-/I3- (0.655 V) due to the more positive Fermi level of 3Br-/Br3- Than that of 3I-/I3-.