在本篇研究中採用兩種替代的方式合成硫化鉛膠體量子點，以取代傳統由高毒性前驅物六甲基二矽硫烷的使用。適合作為太陽能元件中吸收層、能隙介於1至1.45電子伏特的硫化鉛量子點皆可以透過調整反應參數從兩種途徑中合成。藉由改善表面配體置換流程及元件設計，已製備出能量轉換效率高於5%的量子點太陽能元件。其中我們採用了液相配體置換流程製備量子點墨水，並以一次性塗佈製程形成太陽能元件吸收層，此置換流程能使量子點表面由較多的鹵素鈍化且能提升太陽能元件的電流密度至25 mA/cm2。在本篇研究中，由於使用較低價格的前驅物合成硫化鉛量子點並採取簡易的一次性塗佈製程，進而能大幅降低元件製造成本，於未來大規模量子點光伏應用中深具潛力。

In this work, two alternative synthetic routes are employed to obtain lead sulfide (PbS) colloidal quantum dots (CQDs) for avoiding the usage of highly toxic sulfur precursor bis(trimethylsilyl) sulfide (TMS2S). The PbS CQDs with bandgap from 1.45 to 1 eV which are adaptable as absorber materials for photovoltaics can be obtained from both routes by tuning the reaction parameters. Through the improvements of ligand-exchange process and the architectural design, PbS CQD-based devices with PCE exceeding 5% under one sun illumination have been fabricated. Herein, we adopt the single-step active layer fabrication via solution-phase ligand-exchange process to increase the halide substitution ratio and achieve a high current density of 25 mA/cm2. The lower material cost as well as facile fabrication provide potential in large-scale manufacture and enhance the feasibility for PbS CQD-based photovoltaic applications.

中文摘要 i
Abstract ii
致謝 iii
Contents iv
Chapter 1 Introduction 1
Chapter 2 Literature reviews 3
2.1 Size‑dependent physical properties of colloidal quantum dots (CQDs) 3
2.2 Synthesis of PbS quantum dots 7
2.3 Architecture design of PbS quantum dot photovoltaic (QDPV) devices 13
2.4 Surface modification and characteristics control of CQDs based solar cells 16
2.5 Motivation of this study 21
Chapter 3 Experimental Methods 22
3.1 Materials 22
3.2 Nanocrystal synthesis 22
3.2.1 PbS CQDs via elemental sulfur synthesis 22
3.2.2 PbS CQDs via substituted thiourea synthesis 23
3.3 Photovoltaics device fabrication 24
3.3.1 Layer-by-Layer (LBL) spin-casting technique 24
3.3.2 Single-step active layer fabrication based on n-type PbS ink 24
3.4 Characterization 25
3.4.1 J-V characterization 25
3.4.2 Ultraviolet-visible absorption spectroscopy (UV-Vis) 25
3.4.3 X-ray diffraction (XRD) 26
3.4.4 Atomic force microscope (AFM) 26
3.4.5 X-ray Photoelectron Spectroscopy (XPS) 26
3.4.6 Fourier-Transform Infrared (FTIR) Spectrometer 27
Chapter 4 Results and discussion 28
4.1 PbS CQD via elemental sulfur synthesis 28
4.1.1 Characterization of PbS CQD via elemental sulfur synthesis 28
4.1.2 Surface chemistry of PbS CQD via elemental synthesis 31
4.1.3 Purification issues and PbS CQD photovoltaic device 35
4.2 PbS CQD via substituted thiourea synthesis 40
4.2.1 Characterization of PbS CQD via substituted thiourea synthesis 40
4.2.1 PbS layer formation based on layer-by-layer (LBL) deposition 43
4.2.2 Single-step active layer fabrication based on n-type PbS ink 59
Chapter 5 Conclusions 70
References 71
Appendix I

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