染料敏化及以施受體發光團為染料之太陽能電池研究

A Study on the Dye-Sensitized Solar Cells and Donor Acceptor Chromophores as a Novel Sensitizer

黃中奕(Chung-Yi Huang)

指導教授 ： 何國川

國立臺灣大學/工學院/化學工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.10049

摘要

染料敏化太陽能電池近幾年已逐漸受到各界重視，主要原因是其效率已可與無晶系之矽太陽能電池相比，可達10~11%，且其製備價格與環境相較於矽太陽能電池要來得便宜且方便，因此才會持續不斷地被探討其機制與表現。雖然此效率表現尚無法運用至功率較大之儀器上，但卻已可操作於功率較低之設備上，如小型風扇等。本研究主要目的是在探討染料敏化太陽能電池中二氧化鈦薄膜電極與白金對電極其不同製備方式以及導電基材和反應面積之影響，同時也以不同染料來作探討與比較。

在二氧化鈦薄膜電極上，本研究嘗試改變不同之水熱溫度與薄膜電極厚度來觀察其所帶來之影響。二氧化鈦之孔徑與比表面積大小影響元件表現甚鉅，當比表面積越大時，電極就能吸附足夠之染料；而在此系統中，孔徑也須要有足夠之空間使電解質中的I-/I3-較易擴散至薄膜深處來還原處於氧化態之染料。當水熱溫度從180 ℃提升至260 ℃，孔徑大小會由原先的7.1 nm增加至15.7 nm，而其比表面積則由111.3 m2/g降至63.8 m2/g。經由元件測試之結果，當水熱溫度操控在240 ℃以及薄膜電極厚度大於10 mm以上時，對元件會有一較佳之表現。本研究也利用交流阻抗法來佐證上述之結果。

白金對電極最後則選定濺鍍時間為30分鐘之電極，此電極經由交流阻抗分析後發現有一較小之電阻值。反應面積與導電基材方面，經由測試之結果發現，當反應面積越小以及導電玻璃之導電度越佳時，元件所表現出之FF也會相對地較好。最後選用反應面積為0.25 cm2，導電基材頁阻抗值為7 ohm/sq.，所組成之元件於光強度100 mW/cm2下，其效率表現可以達到7.97%，開環電壓為0.69 V，短路電流為4.53 mA而FF值為0.64。

元件長期穩定性測試中，則持續觀察200天以上。開環電壓由起初之0.61 V降至0.56 V，短路電流由1.30 mA降至0.93 mA，而效率由原先的5.0%下降至3.0%。造成元件表現降低之因素，在此則是推測元件內含有些許之不純物或是水分，當元件操作時，不純物或是水分會與染料反應使染料失去活性，因此才造成元件表現逐漸降低之現象。

於具有能量轉移之施體-受體發光團作為染料之方面，經光譜與電化學系統量測後得知，此系統確實可以運用在染料敏化太陽能電池上，其效率可達1.26%；雖此表現尚無法與現今較常見之染料N3相比，但卻提供另一種染料之型態，使光敏染料擁有其他更多之合成結構與吸收波長方式。

關鍵字

染料敏化太陽能電池 ； 水熱溫度 ； 交流阻抗法 ； 導電玻璃 ； 能量轉移 ； 施體-受體發光團

並列摘要

The research work on dye-sensitized solar cells (DSSCs) has been progressed rapidly since 1991 by Prof. Grätzel’s group. DSSC, a novel type of solar cell, can harvest visible light energy for the generation of electricity by a dye sensitizer, which is adsorbed on TiO2 particles, and the efficiency of DSSCs can reach about 10~11%. Their efficiency is very comparable with that of the amorphous silicon solar cell. In order to optimize the performance of DSSCs, various hydrothermal temperatures and thicknesses of TiO2 were investigated in this study. Further, the effects of counter electrode, active area, and substrates’ conductivity on the efficiency were also explored. In addition, electrochemical impedance spectroscopy (EIS) was used to analyze internal resistances of the DSSCs. Finally, few novel sensitizers such as hybrid choromophores were synthesized and fabricated in photovoltaic devices for improving their efficiency.

The effects of hydrothermal temperature in preparing TiO2 and film thickness on the performance of DSSCs were investigated. The pore diameter and surface area of TiO2 played important roles in determining the cell efficiency. The TiO2 film in the DSSC must provide enough surface area to adsorb sufficient dyes, while an adequate pore size is required to facilitate the transport of the redox couple. When autoclaving temperature was increased from 180 ℃to 260 ℃, it was found that the pore diameters increased from 7.1 nm to 15.7 nm, and surface area decreased from 111.3 m2/g to 63.8 m2/g.

The results revealed that DSSCs made with TiO2 films prepared under hydrothermal temperature of 240 ℃, and film thickness of larger than 10 mm possessed the optimal performance. This result can be explained by the reported lifetime of photo-injected electrons. EIS was also used to analyze internal resistance, which was affected by the thickness of the TiO2 thin film. EIS results also support an earlier observation that the thickness of the TiO2 film would be greater than 10 mm.

When the sputtering time of Pt (counter electrode) was 30 min, the resistance of the device had been decreased. The sheet resistance of FTO also had some influences on fill factor (FF). On other hand, when the active area was 0.25 cm2, the cell would have less IR drop and a better value on FF. By using 0.25 cm2 as the active area with the FTO sheet resistance of 7 ohm/sq., the cell efficiency would reach to 7.97%, and the value of VOC, Isc, and FF were 0.69 V, 4.53 mA and 0.64, respectively.

The at-rest stability of the DSSC for over 200 days was monitored; At the end of this peroid, the value of VOC varied from 0.61 V to 0.56 V, JSC decreased from 1.30 mA/cm2 to 0.93 mA/cm2, and the efficiency reduced from 5.0% initially to 3.0% This may be due to the sealing imperfection and impurity, such as water and oxygen, which may react with the sensitizer.

Hybrid donor-acceptor choromophores can also work as the sensitizers, where the efficiency could reach about 1.26% Even though this efficiency is not comparable with N3 dye, it provides an alternative for the organic dyes in harvesting the light energy using DSSCs.

並列關鍵字

DSSC ； Hydrothermal temperature ； Electrochemical impedance spectroscopy ； Conductive glass ； Energy transfer ； Hybrid choromophores

參考文獻

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