我們嘗試以添加良好導體：石墨，與染料敏化太陽能電池中的二氧化鈦奈米粒子形成複合材料，藉以研究它對染料敏化太陽能電池光電轉換效率的影響。
我們利用了改良式 Hummer’s 方法合成氧化石墨，再用化學還原方法將氧化石墨還原；此二步驟的產物皆以紫外-可見光光譜儀和傅立葉紅外光光譜儀鑑定產物。
另外，實驗中發現，在製做二氧化鈦光陽極的時候加入少許的乙醇，能夠提高染料敏化太陽能電池的光電轉換效率，開路電壓 0.68 V，斷路電流 16.36 mA/cm2 ，填充因子 0.49，光電轉換效率達到 7.11%，比起未加入乙醇的二氧化鈦電極所製做的太陽能電池開路電壓 0.66 V，斷路電流 11.24 mA/cm2 ，填充因子 0.48，光電轉換效率4.50%，整體表現都要來的好。
而在二氧化鈦中加入還原的氧化石墨的複合材料製做成的染料敏化太陽能電池，開路電壓 0.68 V，斷路電流 18.48 mA/cm2 ，填充因子 0.51，光電轉換效率達到 7.83%。此結果顯示添加了還原的氧化石墨確實可以提升電子轉移的效率，產生較大的光電流。

In my study, I attempted to use the high electrical conductivity of graphite modified TiO2 nanoparticles to study the effect of graphite modification to the performance of dye-sensitized solar cell.
Graphite oxide (GO) was successfully prepared by the improved Hummer’s method. Graphenes that from the as-prepared GO reduced with hydrazine hydrate and sodium borohydride were characterized by Fourier transform infrared spectroscopy (FT-IR) and UV-visible spectroscopy.
The performance of TiO2 based DSSC revealed a short-circuit photocurrent density of 11.24 mA/cm2, an open-circuit voltage of 0.66 V, and a fill factor of 0.48, yielding an overall conversion efficiency of 4.50%. The TiO2 / r-GO composite based DSSC showed higher efficiency than those standard DSSC, revealed a short-circuit photocurrent density of 18.48 mA/cm2, an open-circuit voltage of 0.68 V, and a fill factor of 0.51, yielding an overall conversion efficiency of 7.83%. On the other hand, we found the DSSC that treated with small amount of alcohol in making the TiO2 paste showed superior performance to that with untreated photoanode, the ratio of energy conversion efficiency being 7.11% to 4.50%.

Abstract in Chinese………………………………………………………. vi
Abstract in English…………………………………………………..........vii

INTRODUCTION
1.1 Energy crisis………………………………………………………1
1.2 Development of Solar Cells………………………………………2
1.3 Dye-Sensitized Solar Cells (DSSC)………………………………4
1.4 Structure and working principle of DSSC………………………...5
1.5 Characterization of dye-sensitized solar cell……………………...8
1.6 Objective and motivation………………………………………..13

EXPERIMENTAL SECTION
2.1 Preparation graphite oxide and reduced graphite oxide……..…..16
2.2 Chemicals…………………………………………………..……22
2.3 Conductive glass…………………………………………………24
2.4 Substrate cleaning process……………………………………….25
2.5 Preparation of titanium dioxide thin films………………………26
2.6 Sintering stages for TiO2 photoanode…………………………...28
2.7 Preparation of counter electrodes……………………………......29
2.8 Liquid electrolyte (Z300)………………………………………..30
2.9 Preparation of dye-adsorbed TiO2 photoanodes…………………30
2.10 Device assembling……………………………………………...31
2.11 Measurement methods………………………………………….32

RESULTS &DISCUSSION
3.1 Diffuse reflectance UV-Vis spectra of TiO2 composite……….....39
3.2 The morphology of TiO2 composite……………………...……...45
3.3 The impedance spectrum of TiO2 composite on DSSC……...….53
3.4 Performance of DSSC…………………………………………...63

CONCLUSIONS……………………………………………………...…..72

REFERENCES……………………..……………………………...……...74

LIST OF TABLES
Table 1. Resistance of TCO glass………………………………………...25
Table 2. Parameters of the elements fitted in equivalent circuit……….…56
Table 3. Performance of the DSSCs built with various amounts of additives…………………………………………………………...………63
Table 4. Performance of the differently built DSSCs………………..…...64

LIST OF FIGURES
Figure 1. The role of renewable energy in the worldwide energy supply….1
Figure 2. Types of solar cells……………………………………………....2
Figure 3. The structure of DSSC device…………….………………….......5
Figure 4. Schematic diagram of working principle of DSSC…………...….6
Figure 5. The airmass at small angles between a normal surface and the rays of sun……………………………………………………………….....9
Figure 6. The standard AM-1.5 global solar spectrum………………..…..10
Figure 7. I-V curve of dye-sensitized solar cell………………………..…11
Figure 8. Schematic diagram of the TiO2-based DSSC……………..……13
Figure 9. Graphite oxide from oxidation of graphite..…………….…..….14
Figure 10. Preparation of reduced graphite oxide by reducing agent...…..15
Figure 11. The UV-visible spectrum of graphite oxide absorb in ethanol..17
Figure 12. The FT-IR spectrum of graphite oxide……………………..…18
Figure 13. The UV-visible spectrum of reduced graphite oxide dispersed in ethanol…………………………………………….………………………20
Figure 14. The FT-IR spectrum of reducted graphite oxide…………....…21
Figure 15. Dependence of resistance and sintering temperature………….24
Figure 16. Sintering processes of TiO2…………………………………...29
Figure 17. Assembling of solar cell device…………………………….....31
Figure 18. Schematic circuit representation of the RC-model…………....33
Figure 19. Schematic circuit representation of the double RC-model…....33
Figure 20. Nyquist plot of double RC-model……………………….....….34
Figure 21. Schematic circuit representation of the CPE-model…………..34
Figure 22. Layout of the measuring device and data processing………....36
Figure 23. Zenith angle at the moment of measurement……………….....38
Figure 24. Diffused UV-Visible reflectance spectra of TiO2 powder compared with TiO2 composite (reduced graphite oxide by NaBH4)….…39
Figure 25. Diffused UV-Visible reflectance spectra of TiO2 powder compared with TiO2 composite (reduced graphite oxide by N2H4)……....40
Figure 26. Diffused UV-Visible reflectance spectra of TiO2 powder compared with TiO2 composite (reduced graphite oxide by heat)……..…41
Figure 27. Diffused UV-Visible reflectance spectra of TiO2 powder compared with TiO2 composite (mixed with carbon nanotube)…………..42
Figure 28. Diffused UV-Visible reflectance spectra of TiO2 powder compared with TiO2 composite (mixed with graphite)…………………...43
Figure 29. SEM morphology of TiO2 composite. Top view…………...…46
Figure 30. EDS of carbon………………………………..……….……….46
Figure 31. EDS of oxygen………………………………………...………47
Figure 32. EDS of titanium……………………………...……………......47
Figure 33. EDS Quantitative Results………………...…………………...48
Figure 34. Cross section of SEM morphology of TiO2 composite.…........49
Figure 35. EDS of carbon…………………………………………...…….50
Figure 36. EDS of oxygen………………………………………………...50
Figure 37. EDS of titanium……………………………………………….51
Figure 38. EDS of indium………………………………………………...51
Figure 39. EDS Quantitative Results………………………………......…52
Figure 40. EIS plot with fitted line (green) of TiO2 powder electrode in DSSC………………………………………………………………...…....55
Figure 41. Equivalent circuit for the ESI plots of TiO2 powder electrode..55
Figure 42. EIS plot with fitted line (green) of TiO2 / r-GO (NaBH4) composite in DSSC……………………………………………………….58
Figure 43. Equivalent circuit for the ESI plots of TiO2 composite….........58
Figure 44. EIS plot with fitted line (green) of TiO2 / r-GO (N2H4) composite in DSSC……………………………………………..………...59
Figure 45. EIS plot with fitted line (green) of TiO2 / r-GO (heat) composite in DSSC.......................................................................................................59
Figure 46. EIS plot with fitted line (green) of TiO2 / CNT composite in DSSC……………………………………………….…………………......60
Figure 47. ESI plot with fitted line (green) of TiO2 / graphite composite in DSSC………………………………………………………………….......62
Figure 48. The open-circuit voltage of pure TiO2 powder and TiO2 composite made solar cells……………………………………………….64
Figure 49. The short-circuit photocurrent density of pure TiO2 powder and TiO2 composite made solar cells…………………………………..…......65
Figure 50. The fill factor of pure TiO2 powder and TiO2 composite made solar cells………………………………………………………………….66
Figure 51. The conversion efficiency of pure TiO2 powder and TiO2 composite made solar cells………………………………………………..67

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