矽奈米線的製備與在太陽能電池的應用

Fabrication of Silicon Nanowires and Applications to Solar Cells

林信伯(Shin-Bo Lin)

指導教授 ： 林清富

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.02033

摘要

近幾年來，由於化石燃料所帶來的嚴重的環境問題，因此乾淨可再生的替代能源受到公眾關注，太陽能電池成為當前重要課題。而由於便宜的成本，使第二代的薄膜太陽能電池受到注目，甚至是到第三代結合奈米結構材料的高效率低成本太陽能電池，更成為炙手可熱的話題。由於矽奈米線獨特物性，具有低反射率與強的寬頻光吸收，所以矽奈米線結構在新世代太陽能電池的應用上引起相當大的關注。
在本篇論文中主要是為了實現低成本與高效率的新世代太陽能電池，藉由單晶矽奈米線與有機導電高分子作結合之混成異質接面太陽能電池。論文的第一部分將先介紹以金屬輔助化學蝕刻法來製備矽奈米線，此方法具製作過程簡單且快速，低成本且適合用於大面積製作，相較於一些需要在複雜環境下的製程便宜且容易許多，有效降低生產成本。然而，由於金屬輔助蝕刻法當中帶水溶液的製程，矽奈米線會因此聚集而改變形貌，將會造成許多製程應用上的不便，例如欲在矽奈米線上要塗布量子點等結構，然而由於奈米線聚集，可能使量子點無法塗布在每一根奈米線上，使量子點的附著面積大大地降低。因此我們發展了簡單而低成本的方法來改善團簇現象，不需任何昂貴的設備，符合目前太陽能電池製程的需求，其中藉由低表面張力的溶液與提升乾燥溫度處理，成功了改善奈米線團簇的現象，其中長度約為3.5μm的矽奈米線束狀結構的密度從4.06*105 mm-2提昇至10.31*105 mm-2。
接著論文的第二部分，我們首先利用第二章所介紹的矽奈米線與PEDOT:PSS做結合，成功製作出混成異質接面太陽能電池元件。我們發現，具有矽奈米線結構的太陽能電池元件較單純拋光無結構矽晶片的元件效率高出甚多，從原本沒奈米線的0.083%，到有矽奈米線結構元件的3.54%，光電轉換效率明顯提高，幅度將近有3.5%，而這效率的提升顯示來自於矽奈米線的貢獻，提供了低的反射率與大的接觸表面積與，使光的吸收增加以及大的載子分離面積。其後將第三章所探討的解決團簇方法應用於太陽能電池上，發現經過改善的矽奈米線做成的太陽能電池元件，其光電轉換效率從未經過改善的3.81%提升至4.58 %。經過處理矽奈米線，其反射率有下降的現象，波長在400-1000 nm範圍間，平均反射率可以下降至1.5%，而原先沒有經過處理而有團簇情形的矽奈米線反射率高於3%。而改善後的矽奈線由於增加光的吸收以及與PEDOT:PSS接觸介面，使太陽能電池元件的光電轉換效率有效提升。
本論文所使用的製程方法兼具簡單而低成本，不需昂貴的儀器及複雜嚴苛的工作環境，將有助於實現低成本高效率的新一代太陽能電池。

關鍵字

矽奈米線 ； 混成太陽能電池 ； 表面張力 ； 聚集 ； 金屬輔助化學蝕刻法

並列摘要

In recent years, the disastrous environmental pollution problem arising from fossil fuels has heightened public concern, and thus the increasing reliance on renewable clean energy alternative. There is an enormously growing interest in the development of thin film (2nd generation) solar cells on cheap, for example, glass substrates or even third generation (nanostructured materials with high efficiency and low cost) solar cell materials systems. Feasible silicon based third generation solar cell approaches can base on silicon nanostructures such as silicon nanowires (SiNWs) which have gained much attention due to their unique physical properties and possible applications.
In the study, we focus on fabrications of single-crystallinie silicon nanowires (SiNWs)/organic conductive polymer hybrid solar cells. In the first part of work, SiNWs were fabricated by using a metal-assisted chemical etching method for the requirements of simple and low-cost fabrication processes in silicon photovoltaic applications. Then we studied the relationship between etching time and SiNWs. Bulk silicon were first etched by assisted with silver ions and became SiNWs with diameter about 100 nm. High flexibility of the long SiNWs causes its morphology to be varied by weak force. Water solution induces the series aggregation of the SiNWs. This effect significantly influences the coating of materials on these SiNWs. Here, we use solution with small surface tension and rise drying temperature to prevent the aggregation of the SiNWs. Thus, bundle density of 3.5 μm SiNW increased from 4.06*105 mm-2 to 10.31*105 mm-2.
In the second part of the work, we combined SiNWs with PEDOT:PSS to fabricate conjugated polymer-based organic solar cells. We found that solar cells with SiNWs have enhanced efficiency about 3.54% compared with no-structure solar cells with 0.083% efficiency. Enhanced interface raise the change of carriers’ separation and low reflectance makes light absorption increase. In addition, the aggregation of the SiNWs greatly influences the reflection spectrum. The reflectance of SiNWs with modified aggregation is only 1.5% or less from 400 nm to 1000 nm. However, the reflectance of the SiNWs with large bundles is higher than 3%. It is over 4% in the IR region. The SiNWs improved were used to solar cells, and the power conversion efficiency of the cell was improved from 3.81% to 4.58% due to enhanced contact interface and light absorption of SiNWs.
The devices in this study are fabricated by simple and low-cost process without expensive equipments and complex environment. These are helpful for commercial realization of low-cost and large-area new generation solar cells.

並列關鍵字

silicon nanowires ； hybrid solar cells ； surface tension ； aggregation ； metal-assisted chemical etching method

參考文獻

[4] 蕭傑予，”無機奈米線與有機材料混成太陽能電池之研究”，國立台灣大學光電工程研究所碩士班論文(2008)

[2] S.O. Kasap, Optoelectronics and Photonics: Principles and Practices, Prentice Hall, Upper Saddle River, NJ (2001)

[7] Cheng-Lun Hsin, Wenjie Mai, Yudong Gu, Yifan Gao, Chi-Te Huang, Yuzi Liu, Lih-Juann Chen, and Zhong-Lin Wang, Adv. Mater. 2008, 20, 3919–3923

[9] S. Hoffmann, I. Utke, B. Moser, J. Michler, S. H. Christiansen, V. Schmidt, S. Senz, P. Werner, U. Gosele, and C. Ballif. Nano Lett. Vol. 6, No. 4, 2006

[13] B. Z. Tian, X. L. Zheng, T. J. Kempa, Y. Fang, N. F. Yu, G. H. Yu, J. L. Huang, and C. M. Lieber, Nature London 449, 885 (2007).