四元靶材濺鍍方式製備銅銦鎵硒太陽能電池

One-step sputtering process for CIGS solar cells application from a single quaternary target

陳家庠(Chia-Hsiang Chen)

指導教授 ： 賴志煌

國立清華大學/工學院/材料科學工程學系/博士(2012年)

摘要

近年來再生能源的議題持續發酵，太陽能便是其中一種深具潛力的選擇，許多類型的太陽能電池，包括單多介面砷化鎵、單多晶矽太陽能電池以及其他正在興起的技術已經被廣泛的研究，以期能取帶現有的發電技術。本論文主要的研究為銅銦鎵硒薄膜技術的開發，我們成功開發出簡單的一段式濺鍍銅銦鎵硒薄膜之製備方法並研究以此方式製備的薄膜及元件特性。
在第四章的部分，我們的結果證明一段式濺鍍應用於製備銅銦鎵硒薄膜的可行性，藉由單一銅銦鎵硒四元靶材搭配脈衝直流濺鍍鍍方式在五百度的基版溫度下，即便沒有額外的硒供應，我們仍可製備出具有黃銅礦結構的銅銦鎵硒薄膜。而由此方式製備的銅銦鎵硒薄膜不同於傳統蒸鍍方式製備之特性，為具有（112）優選方向的柱狀晶結構，此外我們也針對此方式製備之薄膜及元件特性作進一步的探討與分析。在此章節，利用接近計量比的銅銦鎵硒靶材製備之元件，其最高效率可達到8.22 %。
在第五章的部分，我們探討靶材成分對於銅銦鎵硒薄膜及元件的影響。藉由控制靶材成分，我們可以調變薄膜的組成從富銅相變至缺銅相，而富銅相銅銦鎵硒薄膜常見的銅硒二次相也可經由此方式有效降低，因此即便沒有氫化鉀處理的薄膜仍可得到極佳的元件表現，使用稍微缺銅且富硒的銅銦鎵硒四元靶材，我們得到最高效率達10.14 %之元件。此外我們也在銅銦鎵硒薄膜上開發出非破壞性的成分分析技術，藉由歐傑電子顯微鏡及場發式電子微探針技術，可以分析表面及內部成分之分布，我們發現造成富銅的銅銦鎵硒元件在長波長範圍的光電流響應較低的原因，應該跟不均勻的硒分布有關。
在第六章的部分，我們探討如何藉由光學及電性的觀點改善元件之表現，包括鈉的摻雜以及奈米結構的導入。濺鍍氟化鈉製程目前的文獻中尚無報導，在本論文我們已成功將其與一段式濺鍍銅銦鎵硒薄膜製程整合，並觀察到明顯元件表現之提升，最高效率可達10.41 %。此外我們也開發出不需模版的方式製備銅銦鎵硒奈米針尖陣列，此奈米結構可以有效提升光捕獲效率並提升光電流之收集。

關鍵字

薄膜太陽能電池 ； 銅銦鎵硒 ； 四元靶 ； 一段式 ； 濺鍍

並列摘要

Recently, solar energy has drawn much attention due to the development of renewable energy. Various solar cells have been widely studied for the application of solar energy to replace the conventional power for terrestrial application, including single/multi junction GaAs, crystalline Si cells (single/ multi crystalline), thin film technologies (CIGS, CdTe, amorphous-Si), and other emerging technologies. In this dissertation, the main research focus is on CIGS thin film technology. We have developed a simplified fabrication process and investigated the characteristics of CIGS solar cells prepared by the one-step sputtering process.
In the first topic of this dissertation, we demonstrated the feasibility of one-step sputtering process for the fabrication of CIGS absorbers. By using pulse DC sputtering from a single quaternary CIGS target, the chalcopyrite structure is spontaneously developed on the substrate at 500 oC even without extra Se supply. The obtained CIGS absorber layer possesses unique columnar grains with (112) preferred orientation, which is quite different from those prepared by co-evaporation process. In addition, the characterization of one-step sputtered CIGS films and devices were also addressed. The best efficiency of 8.22 % was achieved at the area of 0.4 cm2 with open circuit voltage (Voc) of 505 mV, short circuit current density (Jsc) of 24.76 mA/cm2 and the fill factor (FF) of 0.66 by using a nearly stoichiometric CIGS target.
The second topic of this dissertation focuses on the target composition effect on the CIGS films and devices. By tuning the composition of CIGS targets, we modified the film composition from Cu-rich to slight Cu-poor. In addition, the Cu2-xSe second phase was suppressed by using a modified CIGS target. Even no KCN treatment is required to obtain device quality CIGS films. The best device efficiency of 10.14 % was achieved at the area of 0.4 cm2 with open circuit voltage (Voc) of 505 mV, short circuit current density (Jsc) of 32.3 mA/cm2 and the fill factor (FF) of 0.63 by using a modified CIGS target. Furthermore, a non-destructive compositional mapping is demonstrated for the investigation of compositional distribution on the top surface and at deep level of CIGS films by using surface sensitive Auger electron spectroscopy (AES) and bulk sensitive field emission micro-analyzer (FE-EPMA). We found the inhomogeneous distribution of Se in the Cu-rich CIGS films may be related to the low photocurrent response in the long wavelength region. .
The third topic in this dissertation focuses on the improvement of device performance. Na incorporation and nanostructure were introduced to modify the electrical and optical behaviors of CIGS solar cells. Sputtered NaF was first reported in this dissertation which could be integrated with our one-step sputtering process of CIGS absorbers. Better device efficiency of 10.41 % was observed while the NaF was added. Furthermore, we also developed a template-free technique to create nanotip arrays on the surface CIGS absorbers to enhance light harvesting, which could improve the collection of photocurrent.

並列關鍵字

thin film solar cells ； CIGS ； quaternary target ； one-step ； sputter

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