利用熱濺鍍法成長ITO透明電極於偏壓式MOS結構矽太陽能電池之研究

Silicon MOS-structure Solar Cell Based on a Biasing ITO Transparent Electrode Deposited by Thermally Sputtering Method

賴冠儒(Kuan-Ju Lai)

指導教授 ： 何文章

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00473

摘要

本論文是利用金屬/二氧化矽/半導體(MOS)結構的概念導入到單晶矽太陽能電池製作，以提升光電流及轉換效率之研究。利用熱濺鍍的方式將氧化銦錫(ITO)濺鍍在介電層二氧化矽(SiO2)上作為透明金屬電極，本研究之SiO2/ITO結構除具有抗反射效果外，當ITO透明電極加偏壓後會使底層pn半導體之空乏區增大，如此可增加其有效光吸收體積；由於入射光在半導體內吸收增加，太陽能電池的
短路電流及轉換效率隨之提高。
本論文首先利用旋轉塗佈(Spin-on film, SOF)方法，將磷擴散源與硼擴散源分別塗佈在p--Si正面與背面，在高溫爐進行擴散製程後，製作出正面n+-Si Emitter與背面p+/p-Si BSF層。其次，利用電子槍將Al與Ti/Al蒸鍍於p+-Si與n+-Si表面形成電極，再經由熱退火處理形成良好歐姆接觸，完成單晶矽太陽能裸電池結構製作。最後，利用電子槍蒸鍍二氧化矽(SiO2)與濺鍍機以250℃濺鍍氧化銦錫(ITO)製作透明閘電極於裸電池表面。本文所獲得之ITO透明電極平均穿透率約80%以上(350~1100 nm)及片電阻約為453.2Ω/□。
在AM1.5G、25℃條件下，量測所完成之單晶矽太陽電池於不同製程階段之特性參數如下：(1)裸電池(電池遮蔽率最佳化設計為10.14%)：開路電壓(Open circuit voltage, Voc)為0.55V，短路電流密度(Short circuit current density, Jsc)為27.05 mA/cm2，填充因子(Fill factor, FF)為76.1%，轉換效率(Conversion efficiency, η)為11.52%；(2)經蒸鍍完SiO2與熱濺鍍ITO透明電極(MOS結構)後：開路電壓(Voc)為0.56V，短路電流密度(Jsc)為33.86mA/cm2，填充因子(FF)為76.1%，轉換效率(η)為13.93%；(3)ITO閘電極加順向偏壓 +2.5V時，太陽能電池的開路電壓(Voc)提升至0.56V，短路電流密度(Jsc)提升至44.81 mA/cm2，轉換效率(η)提升至16.73%。

關鍵字

單晶矽太陽能電池 ； ITO抗反射層 ； 背面電場 ； 金屬/二氧化矽/半導體

並列摘要

This study demonstrated the concept of a Metal / Silica / Semiconductor (MOS-device) to fabricated a MOS-structure single crystal silicon solar cell which can be increased the photocurrent and conversion efficiency. The transparent indium tin oxide (ITO) electrode upon the SiO2 layer was deposited by a thermally sputtering. The depletion width of p-n junction under the region of the biased ITO transparent electrode would be extended more deeply and obtained more large volume of absorption when the biasing voltage was increased. Beside the SiO2/ITO layer also presented a good anti-reflection (AR) properties. Increasing in absorption of incident light in the solar cell, thus the solar cell short-circuit current and conversion efficiency are enhanced.

Firstly, the liquid type phosphorus (P) source and Boron (B) source were spin upon the front-side and the back-side of p--Si wafer, respectively, and then annealed treatment by RTA at 900°C.Therefore the n+-Si Emitter on the front side and p+/p-Si BSF on the back side were formed. Secondly, Al electrode on p+/p-Si and Ti/Al electrode on n+-Si were evaporated by electron beam and annealed in the RTA chamber to obtain a good ohmic-contact. After annealing, the bare-type single-crystal silicon solar cells was obtained. Finally, the SiO2 layer upon the surface of bare cell was firstly evaporated by electron beam and an indium tin oxide (ITO) upon SiO2 layer was then deposited by a thermally sputtering at temperature above 250°C.Transmittance of 80% measured (wavelength range 350~1100 nm) and sheet
resistance of 453.2Ω/□ were obtained from the obtained ITO film in this study.

Under AM1.5G illumination and at temperatures of 25°C, the characteristics of the fabricated cell are characterized in different stages. (1) Bare solar cell (without any surface coating and the shadowing of 10.14%) : The open-circuit voltage (Voc) of 0.55V, short-circuit current density (Jsc) of 27.05 mA/cm2, fill factor (FF) of 76.1%, and conversion efficiency (η) of 11.52% are presented. (2) Solar cell with SiO2 and ITO layer：Voc of 0.56V, Jsc of 33.86 mA/cm2, FF of 76.1%, and η of 13.93% are obtained. (3) Solar cell with SiO2 / ITO layers and ITO electrode biased + 2.5V：Voc is increased from 0.55V to 0.56V, Jsc is increased to 44.81mA/cm2, and η is increased to16.73%

並列關鍵字

Single crystal silicon solar cells ； ITO anti-reflection ； Back surface field ； Metal / Silica / Semiconductor

參考文獻

[1] K. N. Amulya and J. Goldemberg, “Energy for the developing world,” Sci. Amer, vol. 263, 1990, pp. 63-71.

[3] D. M. Chapin and C. S. Fueller, “A new silicon p-n junction photocell for converting solar radiation into electrical power, ” Journal of Applied Physics, vol. 25, 1954, pp. 676-677.

[6] G. Hass and J. B. Ramsey, “Vacuum deposition of dielectric and semiconductor films by a CO2 laser,” Applied Optics, 8, pp. 1115-1118, 1969.

[7] A. P. Bradford, G. Hass, M. McFarland, and E. Ritter, “Effect of Ultraviolet Irradiation on the OpticalProperties of Silicon Oxide Films,” Applied Optics, 8, pp. 971-976, 1965.

[8] E. Klemberg-Sapieha, "Mechanical characteristics of optical coatings prepared by various techniques : a comparative study," Appl. Opt., Vol. 43, no. 13, 2004, pp. 2670-2679.