本研究著墨於一高效能且低毒性的鈣鈦礦太陽能電池新製程技術開發。在此製程中，吾人選用水搭配銷酸鉛做為鈣鈦礦薄膜製備的前驅物，相較於傳統所使用的碘化鉛搭配二甲基甲醯氨，硝酸鉛水溶液系統完全避免了有毒溶劑的使用，對人體及環境危害較低，但在製程中也有較多困難需要被克服。
將硝酸鉛水溶液前驅物用於連續沉積法(sequential deposition)製備鈣鈦礦薄膜時發現，基板的潤濕性對於選轉塗布後的硝酸鉛薄膜形貌有顯著的影響，且發現硝酸鉛/水系統中的鈣鈦礦晶體生成速度明顯緩慢，此現象造成長時間浸泡步驟的必要性，但也由於晶體的熟化(ripening)過程使鈣鈦礦薄膜呈現不均勻分布。吾人在深入了解晶體的成長機制後發現，此長時間浸泡所導致的晶體熟化過程包含了溶解及再結晶兩步驟，其不僅會破壞薄膜的連續性，過度成長的晶體也造成表面過於粗糙，兩者皆會大幅降低元件的光電表現行為。
此外，吾人也對硝酸鉛/水系統中鈣鈦礦晶體生成緩慢的原因進行探討，發現其中硝酸根離子的去除為主要控制薄膜品質及晶體生成速率的關鍵。對此，吾人於原先的硝酸鉛/水系統製程進行相關優化：加入甲基碘化銨於浸泡溶液及導入多次循環浸泡法，此優化製程不僅成功避免了溶解-再結晶步驟所造成的不良影響，也能夠加速硝酸根離子的去除，使吾人成功製備出15.11%的高效率元件。
最後吾人使用瞬態雷射技術對元件進行光電行為探討，結果發現硝酸鉛/水系統製備之電池雖然有較長的再結合壽命(recombination lifetime)，但也同時具有較高的缺陷密度，此現象顯示硝酸鉛/水系統製程中獨特的晶體生長行為可能有效降低缺陷的活性，減少再結合反應的發生，其也說明了使用硝酸鉛/水系統適用於製備高效率鈣鈦礦太陽能電池的原因。

This study aim for developing a low-toxicity process to prepared perovskite solar cells (PSC), where lead nitrate aqueous precursor instead of conventional PbI2/DMF precursor is selected. It involves four parts to progressively achieve a promising result. First, a process using Pb(NO3)2/water system to fabricate perovskite film is pioneeringly developed. Second, the perovskite crystal formation mechanism in sequential deposition is scrutinized to provide routes for further device optimization. Third, a process engineering tailored to the unique perovskite crystal formation is conducted. Finally, transient laser analysis is applied to take insight into device photoelectronic properties.
Chapter 2 describes the pioneering work on Pb(NO3)2/water-based perovskite preparation. We find that to obtain a uniform Pb(NO3)2, an additional surface modification before spin coating Pb(NO3)2 aqueous precursor was crucial to create a hydrophilic surface. A special two-step crystal conversion is discovered by time-trajectory XRD and UV-Vis analysis, which results in a slow crystal transformation from Pb(NO3)2 to CH3NH3PbI3, accompanying a film deterioration with generating coarsened crystals. In spite of the imperfect CH3NH3PbI3 morphology, efficient device of 12.58% power conversion efficiency is achieved.
Next in chapter 3, the formation of coarsened CH3NH3PbI3 crystals is investigated in traditional PbI2/DMF system. By tuning the dipping time of PbI2 substrate in CH3NH3I/2-propanol solution, the results of morphological, structural and optical changes indicate that the simple interfacial reaction is not the only mechanism controlling perovskite crystal formation and growth. The dissolution-recrystallization process dominates over simple interfacial reaction as dipping time prolonged. Moreover, the element mapping images evidences the thermodynamic preference of reducing surface energy, showing a material migration from inner TiO2 layer to outer surface by dissolution and recrystallization reaction.
With sufficient knowledge gained in chapter 3, we come back to pay attention to the root that caused the slow crystal conversion dynamics from Pb(NO3)2 to CH3NH3PbI3. By in-situ UV-vis investigations and a series of XRD measurements, the removal of NO3- is confirmed to be main role in slow process and perovskite crystal formation. Taking into account NO3- removal and dissolution-recrystallization mechanism, we modify previous process on preparing perovskite layer by adding two innovations: applying CH3NH3Cl in dipping bath and multiple-cycle dipping step. Consequently, the resultant perovskite film becomes a uniform and flawless, which boosts the device efficiency to 15.11%. The stability of full device was excellent over 55 days long-term test.
In the last chapter, a series of transient techniques are first used to scrutinize the relation between charge carrier recombination kinetics and energetic trap distribution in a device fabricated by using a low-toxicity Pb(NO3)2/water system. The results reveal a controversial photoelectronic property of long recombination lifetime in spite of a high trap density still presented. Based on this, we are able to propose a trap inactivation benefit from the unique material contribution in Pb(NO3)2/water system.

Contents
致謝 I
ABSTRACT II
摘要 IV
CONTENTS V
CONTENTS OF FIGURES IX
CONTENTS OF TABLES XIII
CHAPTER 1 INTRODUCTION 1
1.1 Evolution of Photovoltaic 1
1.2 Introduction of Perovskite Solar Cell 4
1.2.1 Historical Background 4
1.2.2 Development of Perovskite Solar Cells 6
1.2.2.1 Device Architectures 8
1.2.2.1.1 Mesoscopic cell structure 8
1.2.2.1.2 HTM (hole transport material)-free cell structure 10
1.2.2.1.3 Meso-superstructured cell 11
1.2.2.1.4 Planar cell structure 12
1.2.2.1.5 ETL (electron transport layer)-free cell structure 14
1.2.2.1.6 Inverted cell structure 15
1.2.2.2 Deposition process 16
1.2.2.2.1 One-step processes 17
Chloride inclusion and coordination engineering 18
Additives addition 19
Antisolvent-solvent extraction 20
1.2.2.2.2 Two-step processes 22
Sequential deposition 22
Two-step spin-coating process 24
Vacuum process 24
1.3 Motivation of this study 26
CHAPTER 2 EFFICIENT PEROVSKITE SOLAR CELL FABRICATED USING AN AQUEOUS LEAD NITRATE PRECURSOR 28
2.1 Introduction 29
2.2 Experimental 30
2.2.1 Synthesis of CH3NH3I 30
2.2.2 PSC fabrication 31
2.2.3 Characterization 33
2.3 Results and discussions 34
2.3.1 Preparation and characterization of perovskite film 34
2.3.2 Optimization of Pb(NO3)2 film 36
2.3.3 Evolution of crystal conversion 38
2.3.4 Device performances 44
2.4 Conclusion 46
CHAPTER 3 CRYSTAL GROWTH AND DISSOLUTION OF METHYLAMMONIUM LEAD IODIDE PEROVSKITE IN SEQUENTIAL DEPOSITION 47
3.1 Introduction 48
3.2 Experimental 50
3.2.1 Synthesis of CH3NH3I 50
3.2.2 Preparation of FTO/meso-TiO2/CH3NH3PbI3 Film 51
3.2.3 Fabrication of perovskite solar cells 52
3.2.4 Characterization of morphological, structural and spectroscopic properties 52
3.2.5 Current-voltage characterization of perovskite solar cells 53
3.3 Results and discussions 54
3.3.1 Evolution of CH3NH3PbI3 morphology 54
3.3.2 Evolution of CH3NH3PbI3 structure 59
3.3.3 Evolution of CH3NH3PbI3 optical properties 61
3.3.4 Evolution of device performance 62
3.3.5 Elemental mapping 66
3.3.6 Development of coarsening mechanism 68
3.4 Conclusion 71
CHAPTER 4 STABLE AND EFFICIENT PEROVSKITE SOLAR CELLS FABRICATED USING AQUEOUS LEAD NITRATE PRECURSOR: INTERPRETATION OF THE CONVERSION MECHANISM AND RENOVATION OF THE SEQUENTIAL DEPOSITION 72
4.1 Introduction 73
4.2 Experimental 76
4.2.2 Synthesis of MAI and MACl 76
4.2.3 Device fabrication 77
4.2.4 Characterisation 79
FE-SEM measurement 79
XRD measurement 79
UV-Vis spectroscopy 79
IPCE measurement 79
Time-resolved photoluminescence (TRPL) measurement 79
Current-voltage (JV) characterization 79
4.3 Results and discussions 81
4.3.1 Challenges on morphological flaws 81
4.3.2 Scrutiny of crystal growth mechanism 86
4.3.3 Process engineering 95
4.3.4 Device performance 99
4.3.5 Long-term stability 104
4.4 Conclusion 107
CHAPTER 5 STABLE AND EFFICIENT PEROVSKITE SOLAR CELLS FABRICATED USING AQUEOUS LEAD NITRATE PRECURSOR: INTERPRETATION OF THE CONVERSION MECHANISM AND RENOVATION OF THE SEQUENTIAL DEPOSITION 108
5.1 Introduction 109
5.2 Experiment 111
5.2.2 Perovskite solar cells fabrication 111
5.2.3 Characterization 113
Current-voltage (JV) measurement 113
Transient photovoltage (TPV) analysis 114
Transient photocurrent (TPC) analysis 115
5.2 Result and discussion 117
5.3.1 Device configuration and perovskite preparation 117
5.3.2 Device Current-voltage (JV) performance 118
5.3.3 Transient Photovoltage (TPV) analysis 121
5.3.4 Time-resolved photoluminescence (TRPL) 124
5.3.5 Differential capacitance 126
5.3.6 Photo-induced differential charging 129
5.3.7 Discussion 131
5.4 Conclusion 134
6. CONCLUSION AND OUTLOOK 135
7. BIBLIOGRAPHY 138
8. CV AND PUBLICATIONS 153

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