二氧化鈦 (TiO2) 由於其合適的能階、高耐熱性、低成本和無毒，通常用作鈣鈦礦太陽能電池 (PSC) 中的電子傳輸層 (ETL)。 TiO2薄膜的沉積方法有旋塗（SC）、噴塗、原子層沉積和電沉積（ED）等多種方法；其中，ED 因其易於控制、可擴展性和成本效益而被認為是一種可行的生產方法。我們的實驗室先前研究了來由TiCl3 水溶液的 TiO2 薄膜的 ED，並將其用作 PSC 的緻密層。之後，我們實驗室還嘗試了多孔 TiO2 薄膜的 ED，並探索了將其用作 PSC 支架的可能性。
在這項研究中，我們進一步改進了用於 PSC 的 電沉積TiO2 技術。在第一部分中，研究了 ED 參數，如外加電位、電解液溫度、循環次數對對薄膜的形貌和性能的影響。可以觀察到，當在-0.50 V 下電沉積並在 ED 期間施加更多熱量時，尤其是在 70 oC 時，TiO2 薄膜的形態被完全覆蓋且多孔。此外，循環次數的增加導致成核和生長速率的變化，從而改善了薄膜的多孔形貌。最後，我們獲得了一個最佳方案，即 ED 在 -0.50 V、70 oC、180 秒、6 個循環。所得薄膜完全覆蓋，多孔，結晶度高，電子提取能力好。相對於在-0.50 V、常溫、單循環的條件，可以觀察到效率由12.6 % 上升至16.8 %。
在本論文的第二部分，我們的目標是將上述的參數應用於共電沉積 Sn摻雜的 TiO2。我們首先進行了實驗，分別了解 Ti3+ 和 Sn2+ 離子的電化學行為，以推測兩種離子共電沉積過程的可能性和機制。之後，製備了Sn摻雜的ED TiO2薄膜，從形貌、光學和電學性能方面研究了不同Sn2+濃度對ED電解質中的影響。結果表明Sn元素成功摻雜到TiO2晶格中。所得的摻雜 Sn 的氧化物層比純 TiO2 的導電性更好。此外，通過摻雜 Sn 的 ETL 製造的 PSC 顯示出 JSC、VOC 和 FF 的改善。最佳元件由 Sn-5 ETL（ED 電解液中 Sn2+ 的摩爾比為 5%）製備而成，PCE 為 19.3%，與由純 ED TiO2 ETL 製造的電池的16.8%相比，PCE 高出許多。

Titanium dioxide (TiO2) is commonly used as the electron transport layer (ETL) in perovskite solar cells (PSC) due to its suitable energy level, low cost and low toxicity. There are many methods used to deposit TiO2 thin film such as spin-coating (SC), spray-coating, atomic layer deposition and electrodeposition (ED); in which, ED is considered a feasible method for production in large scale because of its controllability, scalability and cost effectiveness. Our laboratory previously studied ED of TiO2 film from an aqueous TiCl3 bath and applied it to deposit the compact layer for PSC. After that, our laboratory also tried ED of porous TiO2 film and explored the possibility to use it as the scaffold in a PSC.
In this study, we further improve ED of mesoporous TiO2 film for PSC. In the first part, the effects of ED parameters such as applied potential, electrolyte temperature, number of cycles on the morphology and properties of the resultant films are studied. It is observed that the morphology of TiO2 films is fully-covered and more porous when electrodeposited at -0.50 V and applied more heat during ED, especially ED at 70 oC. Moreover, the increase in number of cycles leads to the change of nucleation and growth rates, thus improving the porous morphology of the films. Finally, we obtain an optimal condition which is ED at -0.50 V, 70 oC in 180 s with 6 cycles. The resultant film is fully-covered, porous with highly crystallinity and good electron extraction ability. Compared with ED TiO2 film at -0.50 V, room temperature and single cycle, the conversion efficiency of PSC improved from 12.6 % to 16.8 %.
In the second part of this thesis, we aim to apply the above protocol to co-electrodeposit Sn-doped TiO2 film. We first conducted the experiments to understand the electrochemical behavior of Ti3+ and Sn2+ ions individually to figure the possibility and the mechanism of co-electrodeposition process of both ions. After that, the Sn-doped ED TiO2 films were prepared, in which the effect of various Sn2+ concentrations in the ED electrolyte is studied in terms of morphology, optical and electrical properties. The results show that Sn element is successfully doped into TiO2 lattice. The resultant Sn-doped oxide layers are more conductive than that of the pure TiO2. Furthermore, PSCs fabricated by Sn-doped ETL show an improvement in JSC, VOC, and FF. The champion device was produced by Sn-5 ETL (5% molar ratio of Sn2+ in ED electrolyte) with the PCE of 19.3% which is higher than that of 16.8 % recorded from PSC using pure ED TiO2 ETL.

Abstract i
摘要 iii
Acknowledgement iv
Table of Contents v
Content of Figures viii
Content of Tables xii
Chapter 1: General introduction 1
1-1 Energy situation 1
1-2 Perovskite solar cells 3
1-2.1 Different device architectures of n-i-p-type PSCs 7
1-2.2 Working principle of a PSC 8
1-3 TiO2 as an electron-transporting layers in PSCs 9
1-1.1 TiO2 compact layer (CL) 11
1-1.2 TiO2 mesoporous scaffold layer (MS) 15
1-4 The mechanism of TiO2 anodic electrodeposition 22
1-5 Motivation of this study 24
Chapter 2: Experiment 26
2-1 Materials and chemicals 26
2-2 Equipment and methodology 28
2-2.1 Equipment 28
2-2.2 Characterization Methods 28
2-3 Experimental section 40
2-3.1 Preparation of cleaned FTO substrates 40
2-3.2 Preparation of TiO2 CL and MS by SC method 41
2-3.3 Preparation of TiO2 CL and MS by ED method 41
2-3.4 Perovskite solar cell fabrication 43
Chapter 3: Electrodeposition of mesoporous TiO2 film for PSC application 44
3-1 Electrochemical study of ED TiO2 44
3-2 Effect of deposition potential on the morphology of the electrodeposited TiO2 47
3-3 Effect of deposition temperature during ED TiO2 49
3-3.1 Morphology of ED TiO2 49
3-3.2 Characterization of TiO2 films 52
3-4 Effect of cycle number during ED TiO2 57
3-4.1 Morphology 57
3-4.2 Characterization of ED TiO2 films 58
Chapter 4: Co-electrodeposition of Sn-doped mesoporous TiO2 film for PSC application 63
4-1 The mechanism of co-electrodeposition of Sn-doped TiO2 63
4-2 The morphology of electrodeposited Sn-TiO2 films 65
4-3 Characterization of electrodeposited Sn-TiO2 films 67
4-3.1 XPS study 67
4-3.2 XRD pattern 71
4-3.3 Conductivity, optical band gap study 72
4-4 J-V characteristics of devices using Sn-doped TiO2 as the ETLs 74
Chapter 5: Conclusion & Future work 77
5-1 Conclusion 77
5-2 Future work 77
References 78

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