大氣硒化製程於銅銦鎵硒太陽能電池特性之研究

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研究生：	楊鎮華 Yang, Chen-Hua
論文名稱：	大氣硒化製程於銅銦鎵硒太陽能電池特性之研究 Investigation of Atmospheric Selenization Process on Cu(In,Ga)Se2 Thin Film Solar Cells
指導教授：	闕郁倫 Chueh, Yu-Lun 沈昌宏 Shen, Chang-Hong
口試委員:	楊智超 Yang, Chin-Chao 謝東坡 Hsieh, Tung-Po
學位類別：	碩士 Master
系所名稱：	工學院 - 材料科學工程學系 Materials Science and Engineering
論文出版年：	2018
畢業學年度：	106
語文別：	英文
論文頁數：	58
中文關鍵詞：	大氣硒化、銅銦鎵硒、太陽能電池
外文關鍵詞：	Atmospheric selenization
相關次數：	點閱：4 下載：0
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為因應世界能源短缺，可重複使用、乾淨的能源為下一代考量的重點。CIGS為第二代薄膜太陽能電池，具有諸多特點如高吸收係數、高穩定性、能源回收期短、成本低廉等競爭優勢，至今為止，德國ZSW研究機構已發展出效率達22.6%之CIGS太陽能電池，其未來應用於市場之潛力十分龐大。
許多研究著重於硒化製程溫度對於CIGS之性質的影響，然而，很少有團隊在研究硒化製程壓力對於CIGS吸收層之性質的影響，目前已證實隨著壓力增加，可以觀察到能隙隨之增大的現象，因為硒可以更好的被併入吸收層裡。但是壓力對於電池表現以及CIGS成長卻還未被討論，在本研究裡，我們將探討此項議題。
從電池表現來看，開路電壓會隨著壓力增加而增加，印證了能隙增加的現象，因為在高壓下製成的CIGS表面可以發現到比較高含量的和較平均分布的鎵，但是根據TRPL結果發現隨著壓力增高，表面離子再復合的情況也隨之上升，導致高壓製程下的電池效率並不會比低壓高。另外，在探討高壓和低壓對於CIGS成長的結果裡，我們發現到，由於在高壓下硒可以較快速的擴散進去並反應，所以能夠在較低溫的時候形成CIGS，導致產生較少的相分離和較均勻的鎵分布情況，另外，透過XPS結果得知，在低壓下，由於較多的硒空缺產生，導致氧氣能夠佔據硒空缺，形成了表面鈍化效應，此效應也造成表面銅缺乏的現象。此一銅缺乏的現象因此引起在後續CdS 沉積後，鎘離子能夠擴散進去CIGS吸收層並且佔據銅空缺，進而抑制表面離子再復合和同質接面增大的情況，進一步提升電池表現。
此研究展示了壓力對於電池表現以及CIGS成長的情形，目前在硒化壓力為150 torr下可以得到效率超過10%的電池表現，另外，在高壓600 torr下製成的電池效率能夠超過9%，展現出未來低成本大氣硒化的潛力。

For the sake of energy shortage, renewable and clean energy substitution is a considerable point for the next generation. CIGS is the best thin film solar cell among the second generation solar cells owing to its plenty outstanding behaviors such as high absorption coefficient, excellent outdoor stability, the easiest integration with Si-based technology and the highest efficiency in thin film solar cells. Therefore, it has already attracted tremendous attention in academic and industrial fields. Up to date, the highest efficiency of 22.6% has been demonstrated by ZSW in Germany.
Many researches focus on the investigation of temperature effect during selenization on the properties of CIGS. Only few studies demonstrated the influence of selenization pressure on properties of CIGS absorber. It is verified that energy band gap increases with increasing pressure due to better incorporation of Se into CIGS absorber. However, pressure effect on cell performance and CIGS growth mechanism is still needed to figure out.
Cell performance shows an enhanced Voc with increasing pressure due to higher band gap. This can be related to higher contents of Ga at the surface and more uniform Ga distribution, resulting in higher band gap. On the contrary, Jsc and FF of cell fabricated under high pressure are lower than that of low pressure which is resulted from surface recombination based on TRPL results. To shed light on growth mechanism, XRD results of phase evolution indicate that formation of CIGS under high pressure happens earlier than that of low pressure owing to higher amount of Se incorporated into CIGS thin film. According to XPS results, Cu-poor at the surface was observed in the case of low pressure which is mainly related to Se vacancies. As a result, Cu-poor triggers CdCu substitutions based on TEM-EDS results, leading to widened buried homo-junction and improvement in cell performance.
In this study, we have demonstrated pressure effect on cell performance and growth mechanism under low pressure and high pressure. The optimized pressure for selenization is 150 torr with conversion efficiency of 10.12% owing to better film quality, suppressed interface recombination and less defects. Furthermore, the conversion efficiency of over 9% of cells fabricated under 600 torr can be achieved, revealing the potential for the low-cost atmospheric selenization.

摘要    I
ABSTRACT    III
致謝    V
CONTENTS    VI
LIST OF FIGURES    IX
LIST OF TABLES    XII
Chapter 1    Introduction    1
1.    Preface    1
1.    Different type of solar cell    2
2.    Basic principle and characteristic of solar cell    3
3.    CIGS solar cell introduction    8
3.1.    CIGS introduction and development potential    8
3.2.    CIGS device structure    9
4.    Motivation    13
5.    Paper review    13
Chapter 2    Experiment and Analysis    15
1.    Fabrication instrument    15
1.1.    In-line sputtering system    15
1.2.    Atmospheric selenization furnace    15
2.    Analysis instrument    16
2.1.    Solar cell simulator system    16
2.2.    Scanning electron microscope, SEM    19
2.3.    X-ray diffraction analysis, XRD    20
2.4.    Raman scattering analysis, Raman    21
2.5.    Photoluminescence system, PL    22
2.6.    Time-Resolved Photoluminescence, TRPL    23
2.7.    Electron spectroscopy for chemical analysis, ESCA    24
2.8.    Energy dispersive spectrometers, EDS    25
2.9.    IPCE (Incident photon to current efficiency) / EQE (external quantum efficiency) System    26
Chapter 3    Experimental    27
1.    CIGS solar cell fabrication    27
1.1.    Soda-lime glass cleaning    27
1.2.    Mo electrode deposition    28
1.3.    CIG precursor sputtering    29
1.4.    CIGS selenization process    30
1.5.    CdS buffer layer deposition    31
1.6.    ZnO/ITO window layer and Al electrode fabrication    33
Chapter 4    Results and Discussion    34
1.    CIGS thin film analysis    34
1.1.    SEM analysis of microstructural and morphology    34
1.2.    X-ray diffraction & Raman scattering spectrum analysis    36
1.3.    SEM/EDS analysis of composition profile    38
2.    CIGS solar cell analysis    39
2.1.    PL & TRPL analyses    39
2.2.    Efficiency measurements of CIGS solar cell    41
2.3.    EQE analysis    43
3.    Pressure effect on CIGS Growth    44
3.1.    X-ray diffraction analysis    45
3.2.    XPS analysis of surface composition    47
3.3.    TEM/EDS analysis of CIGS/CdS interface    50
Chapter 5    Conclusion    52
Chapter 6    Future work    53
Chapter 7    References    55


                                

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