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研究生:黃昱綸
研究生(外文):Yu-Lun Huang
論文名稱:以不同射頻頻率與氫流量製作非晶矽薄膜太陽能電池之研究
論文名稱(外文):Study on the Fabrication of a-Si:H Thin Film Solar Cell under Different Radio Frequency and Hydrogen Flow Rate
指導教授:劉漢文
學位類別:碩士
校院名稱:國立中興大學
系所名稱:光電工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
畢業學年度:97
語文別:英文
論文頁數:117
中文關鍵詞:射頻頻率氫流量非晶矽薄膜太陽能電池
外文關鍵詞:a-Si:HSolar CellRadio FrequencyHydrogen Flow Rate
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在本論文中,是以電漿輔助化學氣相沉積方式在製程溫度350℃、壓力設在1torr、射頻功率為20W的條件下製作氫化非晶矽薄膜,沉積設備的腔體長寬高分別為44cm、44cm與15.8cm,內部的上電極直徑為23.5cm,而上電極與基板之間的距離為5cm。接著以不同射頻頻率以及氫氣與四氫化矽的比值(R)分別為0、5、10、20、30、40、60、80、100來探討各種薄膜的特性,進而觀察氫化非晶矽薄膜太陽能電池元件效率變化。

從傅立葉轉換紅外線光譜儀量測結果顯示,氫含量隨著R值上升而有三個轉折點,而在RSi-H2的部分,隨著氫氣與四氫化矽的比值上升而有一個轉折點,主要由腔體內混合氣體的氫濃度所導致,造成Si-H鍵的形成、Si-H鍵的破壞、Si-H2鍵的形成之間互相消長,並且在較高射頻頻率下,氫含量轉折點出現位置會較晚發生以及有比較大的RSi-H2。

從拉曼量測結果顯示,隨著R值上升,結晶率也會逐漸上升,在較大的射頻頻率下,從非晶矽轉變為結晶矽的過度期相對的比較小的射頻頻率來的短暫,且在相同的R值下有較大的結晶率。

在能隙量測方面,隨著R值上升,線條分成兩段式的下降,前一段來自於氫含量的減少使得能隙下降,後一段由於結晶矽的形成,使得能隙回升到一個高點然而隨著結晶顆粒變大而再次下降。

在電性上的量測,短路電流在非晶矽薄膜的部分隨著RSi-H2上升而下降直到變成結晶矽之後才回升,而影響開路電壓的原因則來自於結晶率(主因)與氫含量(次因)的交互作用,大致上可以發現隨著R值上升,開路電壓會逐漸下降。而在轉換效率部分,由於控制變因繁雜,並無法完全的找出規律性,但可找出最佳值。

在本論文中,鍍率最高為9.09Å/s,發生在R=0,射頻頻率13.56MHz之下。氫含量大致上都是低於10%,RSi-H2的轉折點都發生在R=10的位置,在非晶矽轉變為結晶矽之後的能隙方面,在射頻頻率為13.56MHz之下能隙為1.710eV,而射頻頻率為40.68MHz之下能隙為1.727eV。轉換效率部分在射頻頻率為13.56MHz之下,最高為3.106%,發生在R=10,而在射頻頻率為40.68MHz之下,最高為3.057%,發生在R=10。
In this thesis, thin films are deposited by plasma enhanced chemical vapor deposition (PECVD) under pressure 1torr and at temperature 350℃ with RF power 20W. We investigate the characteristics of thin films with various H2 diluted ratio of silane from 0 to 100 under different radio frequency, and discuss the electrical characteristics of solar cells.

As results from Fourier transform infrared spectrum (FTIR), there are three turn-around points on hydrogen content (CH) curve and one turn around point on SiH2/(SiH+SiH2) (RSi-H2) curve with increase in H2 diluted ratio of silane. The main domination is increasing concentration of hydrogen in the chamber and leads to form Si-H bonds, break Si-H bonds, and form Si-H2 bonds. Under 40.68 MHz RF power, the turn-around point occurs on larger R than 13.56 MHz.

For Raman spectrum measurement, we observe that the Raman crystalline factor increases with H2 diluted ratio of silane increasing. The transformation from a-Si:H to c-Si under 40.68 MHz RF power is in shorter range H2 diluted ratio of silane than under 13.56 MHz RF power. With the same H2 diluted ratio of silane, each Raman crystalline factor in the c-Si thin film under 40.68 MHz RF power is larger than that of 13.56 MHz.

The band gap of Si thin film decreases with decreasing in hydrogen content and increasing in crystalline size which is the main domination. With lower H2 diluted ratio of silane, thin films are belong to a-Si:H and band gap decreases with hydrogen content decreasing. When the H2 diluted ratio of silane is higher, band gap rises again like the first value, and decreases slowly with increasing in crystalline size and increasing in hydrogen content. Last, it decreases clearly with increasing in crystalline size and decreasing in hydrogen content.

In the measurement of the electrical characteristic of the solar cell, short-circuit current decreases with increasing in RSi-H2 until transformation from a-Si:H to c-Si in the thin films. The domination of open-circuit voltage interacts with hydrogen content and Raman crystalline factor which is the main domination. Thus, open-circuit voltage decreases with increasing in R.

In this study, the highest deposition rate is 9.09 Å/s with R=0 under 13.56 MHz RF power. hydrogen content in the a-Si:H and c-Si thin films is found less than 10%. The turn around point of RSi-H2 occurs with R=10. Band gap is equal to 1.710 eV under 13.56 MHz RF power and equal to 1.727 eV under 40.68 MHz RF power at the transformation from a-Si:H to c-Si. The best transformed efficiency is 3.106% under 13.56 MHz and 3.057% under 40.68 RF power with R=10.
Acknowledgment…………………………………………………………………i
Abstract (Chinese)……………………………………………...……………….ii
Abstract (English)………………………………………………………………iii
Contents……………………………………………………………………………..iv
Table List………………………………………………………………………...…vi
Figure Captions…………………………………………………………………vii
Chapter 1 Introduction 1
1.1 Background 1
1.2 Motivation 2
1.3 Thesis Organization 3
Chapter 2 Basic Concept of Solar Cells 4
2.1 Operating Principle of Solar Cell 4
2.2 Types of Solar Cell’s Structure 5
2.2.1 PN Solar Cell 5
2.2.2 PIN Solar Cell 5
2.2.3 Tandem Solar Cell 6
2.3 The Characteristics of Hydrogenated Amorphous Silicon Film 7
2.4 Extraction of Device Electrical Parameters 8
2.4.1 Determination of Short-Circuit Current (Isc) 8
2.4.2 Determination of the Open-Circuit Voltage (Voc) 8
2.4.3 Determination of the Maximum Output Power (Pm) 8
2.4.4 Determination of the Power Conversion Efficiency (η) and Fill Factor (FF) 9
2.5 Review of the Study on H2 Diluted Ratio of Silane 10
Chapter 3 Experiment Procedure and Measuring Equipment 12
3.1 Fabrication and Measuring Equipments 12
3.1.1 Steps of Cleaning Substrate by Wet Bench 12
3.1.2 Plasma Enhanced Chemical Vapor Deposition System 13
3.1.3 Thermal Evaporation Coater 15
3.1.4 Configuration of the Measuring Equipments 15
3.2 Devices Fabrication 18
3.2.1 Fabrication Procedures of a-Si:H Thin Films 18
3.2.2 Fabrication Procedures of a-Si:H Solar Cells 19
3.3 Measuring Methods and Sequences 20
3.3.1 Fourier transform Infrared Spectrum (FTIR) 20
3.3.2 Raman Scattering Spectrometer 23
3.3.3 Keithley I-V Measuring System 24
Chapter 4 Results and Discussion 25
4.1 The Deposition Rates of a-Si:H Thin Films with Various H2 Diluted Ratio of Silane under Different Radio Frequency 25
4.2 Hydrogen Content (CH) and SiH2/(SiH+SiH2) (RSi-H2) under Various H2 Diluted Ratio of Silane and Different Radio Frequency 27
4.2.1 Hydrogen Content (CH) with Various H2 Diluted Ratio of Silane under Different Radio Frequency 27
4.2.2 The Ratio of SiH2/(SiH+SiH2) (RSi-H2) with Various H2 Diluted Ratio of Silane under Different Radio Frequency 52
4.3 Crystalline Volume Fraction (Xc) and Band Gap (Eg) with Various H2 Diluted Ratio of Silane under Different Radio Frequency. 77
4.3.1 Crystalline Volume Fraction (Xc) with Various H2 Diluted Ratio of Silane under Different Radio Frequency. 77
4.3.2 Band Gap (Eg) with Various H2 Diluted Ratio of Silane under Different Radio Frequency. 101
Chapter 5 Conclusions 113
Reference 115
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