緻密層用於提升染料敏化太陽能電池特性的研究曾被Petra J. Cameron等人發表過。本研究針對透明導電膜與電解液之間的逆反應情況，以二氧化鈦緻密層沉積於透明導電膜表面，減少電荷複合所造成的轉換效率下降。二氧化鈦緻密層成長方式為磁控濺鍍法以及熱氧化法，而非噴霧熱解法。 在本研究的染料敏化太陽能電池製程方面，元件光電轉換效率為2%~4%之間，藉此製程觀察二氧化鈦緻密層對電池特性的影響。在本研究設計三種厚度的二氧化鈦薄膜，分別為20nm、50nm和100nm，以及兩種晶體結構即銳鈦礦(Anatase)與金紅石(Rutile)。 未加入緻密層前，元件的短路電流密度與轉換效率為5.30±0.35 mA/cm2、2.1±0.2%；加入二氧化鈦緻密層後，在短路電流密度部份，以金紅石型50nm與銳鈦礦型20nm兩者提升程度最佳，分別為8.98±0.57 mA/cm2與7.95±0.35 mA/cm2。在轉換效率部份，銳鈦礦型二氧化鈦在20nm厚度其轉換效率3.7±0.2%；金紅石型二氧化鈦在50nm厚度其轉換效率3.8±0.2%。隨著緻密層厚度增加至100nm，轉換效率下降，推測原因為光穿透率在100nm下僅有50% (參考端為FTO導電玻璃基板)。 由交流阻抗實驗所得到的Nyquist plot可知，電池的Rh與R1因為加入二氧化鈦緻密層而有下降的現象，無論二氧化鈦緻密層晶體結構為銳鈦礦或是金紅石結構。其中，Rh為FTO導電玻璃之接觸電阻，R1為二氧化鈦緻密層與二氧化鈦光電極之間的電荷傳遞電阻。 在外加偏壓0.4V下，未加入緻密層元件之暗電流密度為625 μA/cm2，而加入銳鈦礦型緻密層元件之暗電流密度為68 μA/cm2 (20nm)、88 μA/cm2 (50nm)、97 μA/cm2 (100nm)；加入金紅石型緻密層元件之暗電流密度為75 μA/cm2 (20nm)、79 μA/cm2 (50nm)、97 μA/cm2 (100nm)。 二氧化鈦緻密層有效隔絕透明導電膜與電解液介面間的逆反應(back reaction)發生。 The compact layers used to improve the performance of dye-sensitized solar cells have been reported by Petra J. Cameron et al.. In our study, we applied a new TiO2 compact layer in the interface between the transparent fluorine doped SnO2 (FTO) anode and the electrolyte in order to reduce charge recombination losses. TiO2 compact layers were prepared by the sputtering and thermal oxidations instead of spray pyrolysis. The dye-sensitized solar cells with a TiO2 compact layer fabricated in this study, the solar energy conversion efficiency is about 2%~4%.According to this result, we prepared the compact layer with crystal structures as Anatase and Rutile. The thicknesses were varied from 20nm, 50nm, to 100nm. Solar cells without the compact layer, their short circuit current and the solar energy conversion efficiency were 5.3±0.35mA/cm2 and 2.1±0.2% respectively. After adding the compact layer, the short circuit current and the solar energy conversion efficiency were both increased, especially for those solar cells with compact layer thinner than 50nm. For the device with 20nm thickness Anatase type TiO2 compact layer, the short circuit current and the solar energy conversion efficiency of the cells were 7.95±0.35mA/cm2 and 3.7±0.2% respectively. For the device with 50nm thickness Rutile type TiO2 compact layer, the short circuit current and the solar energy conversion efficiency of the cells were 8.98±0.57mA/cm2 and 3.8±0.2% respectively. When the compact layer about 100nm thick, the solar energy conversion efficiency of the cell was lower than the thinner compact layer cells. Measurements of AC impedance in the Nyquist polt were found that the Rh and R1 in the dye-sensitized solar cell could be reduced by applying the TiO2 compact layer, no matter if the TiO2 compact layer is Anatase type or Rutile type. That is, the contact resistance of the FTO substrate and the charge transfer resistance of the interface between TiO2 compact layer and the TiO2 phtoelectrode were both reduced. By comparing the electrical properties of the dye-sensitized solar cells with and without TiO2 compact layer, we also found that the dark current was greatly reduced (68μA/cm2) in the device with TiO2 compact layer with 0.4V forward bias voltage. The dark current density of the cell without compact layer was 625μA/cm2. In conclusion, the TiO2 compact layer does prevent the back reaction between the interface of FTO substrate and electrolyte.
