對於電化學沉積的氧化亞銅/二氧化鈦塊材異質接面特性的研究

Abstract

由於染料敏化太陽能電池的低製造成本以及較短的能源償還期特性，對於能源的應用來講它是一種很吸引人的選擇。但是封裝膜的劣化所造成的電解液漏液的問題是很難避免的。為了要進一步改善染料敏化電池長期使用的穩定性，固態材料或許可以用來替代液態的電解液層。在這篇論文中，氧化亞銅被用來當作電洞傳輸層而且很成功的形成氧化亞銅/二氧化鈦塊材異質接面。 首先，用電化學沉積法將氧化亞銅沉積在奈米多孔狀的二氧化鈦膜中。由於沉積條件是和我們所要沉積上去的物質的表面特性息息相關，所以不容易找到最佳的沉積條件。因此，材料分析扮演了一個很重要的角色。藉由X-光光電子儀以及X-射線繞射光譜儀，我們可以從各種沉積條件中去找出最佳的條件。此外，藉由掃描電子顯微鏡我們可以觀察到沉積的速率。我們相信所有的材料分析技術可以幫助我們成功地去行形成氧化亞銅/二氧化鈦塊材異質接面。 接著，藉由光電量測以及電阻抗儀，我們研究了這個塊材異質接面的基本特性。由我們得到的結果中，復合機制被認為是限制這個接面表現的主要原因。在運用到染料敏化太陽能電池之前，對於復合中心數量的抑制是很重要的。因此，我們測試了很多條件以進一步的減少復合電流。藉由電阻抗儀的量測，我們從復合機制對於頻率的響應去研究復合機制的變化，並試著找到最好的方法來改善接面的表現。 對於氧化亞銅/二氧化鈦塊材異質接面有了初步的了解後，我們做了一些進階的量測來研究這個接面的其他特性。首先，藉由提高溫度來檢驗這個接面對於溫度的相依性。接著，用不同的衰減片來調整光的強度，並研究這個接面在不同照光強度下的影響。最後，我們分析接面對於電壓的響應，並由電阻抗儀的結果來得到我們所要的莫特-蕭特基圖。藉由莫特-蕭特基的結果，我們可以得到平帶電壓並且構建出完整的能帶模型。 在本論文中，我們藉由電化學沉積法以及適當的沉積條件，成功地形成了氧化亞銅/二氧化鈦塊材異質接面。並且由直流的電流-電壓量測和交流的電阻抗儀量測來觀察這個接面的特性。儘管將氧化亞銅沉積在吸附染料的二氧化鈦上還未完成，現在對於氧化亞銅/二氧化鈦塊材異質接面的研究仍對我們未來研究有很大的幫助。基於這篇研究的結果，我們相信只要能夠將氧化亞銅應用在染料敏化太陽能電池上，有著較佳長期使用穩定性的固態染料敏化太陽能電池就可以實現。

Dye-sensitized solar cell (DSSC) is an attractive candidate for solar application owing to its properties of low cost and shorter payback time. But the leakage of electrolyte caused by the degradation of sealant is hard to avoid. To further improve the long term stability of DSSC, solid-state material may be a good substitute for liquid electrolyte layer. In this thesis, Cu2O was used as a hole conductor and the Cu2O/TiO2 bulk hetero-junction is successfully formed. In the beginning, the electrochemical deposition method is used to deposit the Cu2O layer onto the nano-porous TiO2 film. Since the deposition conditions are dependent on the surface properties of matter on which we deposited, it is not easy to find the best condition of deposition. As a result, material analysis plays an important role in the experiment. With the help of XPS and XRD analyses, we can find the best condition from variety of conditions. Besides, with the SEM technique, the deposition rate of material can be investigated. It is believed that all of the techniques of material analysis can help us to form the Cu2O/TiO2 bulk hetero-junction successfully. Next, characteristics of the bulk hetero-junction are investigated with photo-electrical measurements and electrical impedance spectroscopy (EIS). With the results we obtained, it is though that the recombination mechanism limits the performance of junctions. It is critical to inhibit the number of recombination centers before applying to DSSC. As a result, many conditions are tested in order to further eliminate the recombination current. With the EIS measurement, we can investigate the variation of recombination mechanism form its frequency response and then find the better way to improve the junction performance. With the basic understanding of the bulk hetero-junction, some advanced measurements are performed to investigate the other characteristics of the junction. First, temperature dependence of junction is examined with the elevated temperatures. Second, optical condition of junctions is observed with different neutral density filters. Finally, the voltage response of junction is analyzed and the Mott-Schottky plot is obtained with the EIS results. With the Mott-Schottky result, the flat-band voltage is obtained and the complete model of band energy can be constructed. In this thesis, the Cu2O/TiO2 bulk hetero-junction is form successfully with electrochemical deposition method and suitable deposition conditions. And the characteristics of the junction are investigated by the measurement of DC IV and AC EIS techniques. Although deposition of Cu2O on dyed-TiO2 is not accomplished, the research of Cu2O/TiO2 bulk hetero-junction now will be a good help in the future study. Based on this research, it is believed that solid-state DSSC with better long term stability can be achieved with application of Cu2O material to DSSC.