臺灣博碩士論文加值系統

由於石油將於本世紀內用磬，尋找新的替代能源已是當務之急。太陽能乾淨且幾乎無限，所以許多科學家都在努力研發高效率低成本太陽電池。目前太陽電池多為單晶矽或多晶矽之p-n接面，這種傳統結構之轉換較率已逼近理論上限。因此在本論文中，我們將探討過去提高矽太陽電池效率的手段，使用這些方法在MEDICI中模擬出傳統結構多晶矽太陽電池，藉此找出電池各部分對效率的影響，嘗試將傳統結構矽太陽電池最佳化。
除此之外，我們也試驗了新結構電池。這種新結構利用了能帶穿遂效應(Band to band tunneling)來產生額外的載子，我們發現穿遂產生的載子甚至比光激發的載子更多。雖然這種結構因為載子多而有較高的短路電流，但是由於高電流區的輸出電壓太低，導致它的效率仍然比不上傳統電池。我們也在它通道上方加了一個閘極，閘極電壓會稍稍改變通道區的能帶，也會對能帶穿遂效應有影響。為了更進一步增強它內部的穿遂效應，我們使用能帶較低的矽鍺合金(SiGe)來取代矽。一如預料，矽鍺穿遂電池有更明顯的穿遂效應，所以它擁有更高的短路電流。雖然如此，由於它的能帶小，開路電壓較矽穿遂電池更大，因此效率比不上矽穿遂電池，遑論傳統結構。對於穿遂電池，我們將會討論摻雜濃度、莫耳分率(mole fraction)、淺接面以及閘極電壓的影響。
最後，我們模擬了水平結構的電池。這種結構雖無助於提升效率，但是卻方便和IC製程整合，同時也方便製成串聯電路來提高輸出電壓。對於這種結構，我們也對它測試了通道長度、電池厚度以及淺接面對效率的影響。

Because petroleum will be used up in this century, it is urgent to find new substitute energy. Because solar energy is clean and almost unlimited, many scientists are working on developing high efficiency and low cost solar cells. Until now, practical solar cells are silicon p-n junction structure. However, efficiency of this structure approaches theoretical limit. In this work, we will first introduce strategies used to improve cells’ performance. We will discuss effect of each part of this cell and expect to optimize it.
We also developed a new cell structure using band to band tunneling. Band to band tunneling in this structure generates many carriers even more than photo-generated carriers. Those additional carriers enlarge short circuit current very much. However, the efficiency of the above band-to-band tunneling structure is still smaller than that of conventional structure because output voltage at high output current region is too low. A gate electrode is put upon channel region. This gate voltage can change band in channel region and thus affect band to band tunneling. To cause more band to band tunneling, SiGe which has smaller bandgap is used instead of silicon. As expected, band to band tunneling in SiGe tunneling structure is more prominent and short circuit current becomes larger. However, open circuit voltage is smaller in SiGe tunneling structure. So the resultant efficiency is lower than that for the Si tunneling and the conventional structures. We will discuss effects of doping concentration, mole fraction, shallow junction and gate voltage in tunneling structure.
Finally, we will discuss lateral structure. This structure doesn’t help to improve cell performance but this structure is easy to be integrated with IC process. It is also easy for this structure to be connected in series to enlarge output voltage. We will discuss effects of channel length, thickness, and shallow junction.

Abstract (Chinese) I
Abstract (English) III
Acknowledgement V
Contents VI
Figure Captions IX
Chapter 1 1
1.1 Brief history of solar cell 1
1.1.1 First solar cell 1
1.1.2 Schottky barrier solar cell 1
1.1.3 Silicon solar cell 1
1.1.4 Modern age solar cells 2
1.2 Basic characteristics of silicon solar cell 3
1.2.1 p-n junction solar cell 3
1.2.2 I-V Characteristics of solar cell under illumination 3
Chapter 2 15
2.1 Monocrystalline silicon solar cells 15
2.1.1 Typical silicon solar cell 15
2.1.2 Performance improvement of monocrystalline silicon cell 15
2.1.3 Examples of modern silicon solar cells 16
2.2 Thin film silicon solar cells 17
2.2.1 Amorphous silicon (a-Si) properties 17
2.2.2 p-i-n structure 18
2.2.3 Typical a-Si solar cell 18
2.2.4 Performance improvement of a-Si solar cells 18
2.2.5 Polycrystalline silicon (poly-Si) cells 20
Chapter 3 34
3.1 Cell structure and parameters 34
3.1.1 Cell structure 34
3.1.2 Simulation parameters 34
3.2 Effect of base thickness 34
3.2.1 Base thickness effects on JSC 35
3.2.2 Base thickness effects on VOC 35
3.2.3 Base thickness effects on efficiency 35
3.3 Effects of emitter 35
3.3.1 Emitter thickness effects on output current 36
3.3.2 Emitter thickness effects on output voltage 36
3.3.3 Emitter thickness effects on efficiency 36
3.3.4 SiC emitter effects on output current 37
3.3.5 SiC emitter effects on output voltage 37
3.3.6 Efficiency of SiC emitter cells 37
3.4 Front contact effects 37
3.4.1 Front contact width effects on output current 37
3.4.2 Front contact width effects on output voltage 38
3.4.3 Front contact width effects on efficiency 38
3.5 Lateral tunneling structure 38
3.5.1 Lateral tunneling structure 38
3.5.2 I-V curve of tunneling structure 39
3.5.3 Efficiency of tunneling structure 39
3.5.4 Doping concentration effects in tunneling structure 39
3.5.5 Gate voltage effects on tunneling structure 40
3.5.6 Shallow junction tunneling structure 40
3.6 SiGe tunneling structure 40
3.6.1 I-V curve of SiGe tunneling structure 41
3.6.2 Mole fraction effects in SiGe tunneling cell 41
3.6.3 Gate voltage effects in SiGe tunneling cell 41
3.6.4 Doping concentration effects in SiGe tunneling cell 42
3.7 Lateral long channel structure 42
3.7.1 Thickness effects on long channel structure 42
3.7.2 Channel length effects on long channel structure 43
3.7.3 Shallow junction long channel structure 43
Chapter 4 94
References 96

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