溶液製程塗佈銅銦鎵硒薄膜太陽電池之製備與光電特性分析

Preparation and Photovoltaic Characterization of Solution-coated Cu(In,Ga)Se2 Thin-Film Solar Cells

宋仁正(Jen-Cheng Sung)

指導教授 ： 呂宗昕

國立臺灣大學/工學院/化學工程學研究所/博士(2016年)

https://doi.org/10.6342/NTU201603612

摘要

本論文針對Cu(In,Ga)Se2太陽電池之光吸收層材料及透明導電層材料進行製備與特性分析。利用溶液塗佈法結合無毒硒化製程合成具黃銅礦結構之Cu(In,Ga)Se2薄膜，並作為光吸收層材料應用於Cu(In,Ga)Se2太陽電池。將溶液塗佈法製備之Cu(In,Ga)Se2薄膜進行鉀離子摻雜，有效減少薄膜中二次相的生成並改善其光電特性。為提升Cu(In,Ga)Se2薄膜之表面能隙及減少硒空缺之缺陷，藉由硫離子導入Cu(In,Ga)Se2薄膜之表面以提升薄膜之光電特性。並製備氧離子摻雜氧化鋁鋅(Al:ZnO, AZO)薄膜作為透明導電層材料以增加電池元件在近紅外光波長區段之光穿透率，可進一步提升所製備Cu(In,Ga)Se2太陽電池之電性表現。本研究針對所製備Cu(In,Ga)Se2太陽電池元件之光電特性與理想因子分析進行深入探討。

本論文第一部分採用溶液塗佈法結合無毒硒化製程製備Cu(In,Ga)Se2薄膜，以簡化製程並降低製程危險性。隨著硒蒸氣流量增加，可促進硒化反應之進行與Cu(In,Ga)Se2薄膜之晶粒成長。增加硒蒸氣的量可提高鎵梯度分布，並增強鎵梯度所造成之背電場效應。所製備之Cu(In,Ga)Se2太陽電池光電轉換效率為10.21%。本研究展示利用溶液塗佈法製備之Cu(In,Ga)Se2薄膜於合適的硒蒸氣流量下進行硒化反應，可作為一有效的製程用以製備Cu(In,Ga)Se2相關的薄膜材料。

本論文的第二部分中，為減少二次相化合物之生成並改善光吸收層材料之光電特性，開發利用鉀離子添加入溶液塗佈法製備之Cu(In,Ga)Se2薄膜中。當鉀離子加入溶液塗佈之前驅薄膜中，經硒化反應後可形成單相的Cu(In,Ga)Se2薄膜。鉀離子摻雜Cu(In,Ga)Se2薄膜具有平整之表面形貌，可有效改善CdS緩衝層的均勻覆蓋並減少載子分流路徑。所製備之鉀離子摻雜Cu(In,Ga)Se2太陽電池不需額外KCN處理，其光電轉換效率可提升至10.90%。

於論文第三部分中，探討硒化製程後進行表面硫化處理所製備之Cu(In,Ga)(Se,S)2薄膜特性變化。經表面硫化處理後，因硫離子進入Cu(In,Ga)Se2薄膜表面而形成反向能隙梯度分布，可製得具有雙能隙梯度分布之Cu(In,Ga)(Se,S)2薄膜。透過良好控制硫化反應過程中之硫化氫氣體濃度，可有效減少Cu(In,Ga)(Se,S)2薄膜中硒空位缺陷之生成。表面硫化反應處理可有效增加Cu(In,Ga)(Se,S)2太陽電池之開路電壓，因此光電轉換效率可提高至12.40%。

於本論文之第四部份，利用反應濺鍍製程製備氧離子摻雜AZO薄膜材料作為透明導電層。當基板溫度增加，促進AZO薄膜之晶粒成長並減少晶界密度，可有效降低AZO薄膜之電阻率。隨著濺鍍氣氛中的氧氣濃度增加，所製備AZO薄膜於近紅外光波長區段之平均透光率可由86.2%提高至91.4%。AZO薄膜透光率的改善可增加Cu(In,Ga)Se2¬太陽電池之光電流及光電轉換效率。於論文之最後部分，將本研究所提出之鉀離子摻雜Cu(In,Ga)Se2薄膜結合表面硫化反應製程以及氧離子摻雜AZO薄膜，可進一步提升Cu(In,Ga)(Se,S)2太陽電池之光電特性。本論文成功開發製備高效率Cu(In,Ga)(Se,S)2太陽電池之相關製程技術，有效改善Cu(In,Ga)Se2太陽電池之光電特性，可應用於提昇Cu(In,Ga)Se2薄膜太陽電池之元件表現與發展應用。

關鍵字

溶液塗佈製程 ； 銅銦鎵硒 ； 薄膜太陽能電池

並列摘要

Chalcopyrite-based absorber layers and transparent conducting layers were prepared for the application of Cu(In,Ga)Se2 thin-film solar cells in this thesis. Cu(In,Ga)Se2 films were synthesized via a solution coating route with a non-toxic selenization process. Potassium ions were doped into the solution-coated Cu(In,Ga)Se2 films to reduce the formation of secondary phases and improve the photovoltaic properties of the obtained films. Additionally, sulfur ions were incorporated into Cu(In,Ga)Se2 films for increasing the band gaps and reducing the vacancy defects of selenium near the surface region of the obtained films. For further improving the photovoltaic performance of Cu(In,Ga)Se2 solar cells, Al-doped zinc oxide (AZO) films were prepared as the transparent conducting layers for increasing the optical transmittance in near infrared (NIR) region. The photovoltaic characteristics and diode analysis of the fabricated solar cells were investigated in detail.

For reducing the processing complexity and dangerously, a solution coating process combined with a non-toxic selenization treatment were applied to prepared Cu(In,Ga)Se2 films in the first section of thesis. The increase in Se-vapor flow-rate promoted selenization reaction and grain growth of Cu(In,Ga)Se2 films. Increasing the amount of selenium vapor also elevated the gallium grading profile and enhanced the effects of back surface field. The conversion efficiency of the solar cells achieved 10.21%. The solution-coated Cu(In,Ga)Se2 films selenized with appropriate selenium-vapor flow-rate were presented to be an effective approach for the preparation of Cu(In, Ga)Se2-based absorber layers.

In the second section, for reducing the secondary compounds and improving the photovoltaic properties of absorber layers, potassium ions were added into Cu(In,Ga)Se2 films. The monophasic Cu(In,Ga)Se2 films were obtained as potassium ions were incorporated into the precursor films. The potassium-ion doped Cu(In,Ga)Se2 films with smooth morphology improved the coverage of CdS buffer layer and suppressed the additional shunt paths. The conversion efficiency of the solar cells fabricated without KCN treatment was increased to 10.90 %.

In the third section, the preparation of Cu(In,Ga)(Se,S)2 films via a surface sulfurization treatment followed by selenization process was investigated. After sulfurization treatment, the Cu(In,Ga)(Se,S)2 films with a double-graded band gap profiles were obtained because the incorporation of sulfur-ion into Cu(In,Ga)Se2 films formed an inverse band gap grading near the surface region. The formation of selenium vacancies in the Cu(In,Ga)(Se,S)2 films were effectively reduced with the well-controlled H2S concentration during the sulfurization. The open-circuit voltage of the prepared solar cells was increased, thereby boosting the conversion efficiency to 12.40%.

In the fourth section, the oxygen-doped AZO films were deposited using a reactive sputter process. The increment in the substrate temperatures promoted the grain growth and reduced the grain boundaries of AZO films, thereby resulting in the reduction of resistivity. As oxygen concentration in the sputtering gas was raised, the average transmittance of AZO films in NIR region was increased from 86.2% to 91.4%. The improvement in the optical transmittance of AZO films led to increase the conversion efficiency of solar cells. Moreover, the photovoltaic performance of the potassium-ion doped Cu(In,Ga)(Se,S)2 films was further improved by combining with the modified AZO films. This thesis demonstrated that the new preparation processes for fabricating high-efficiency Cu(In,Ga)Se2-based solar cells were successfully developed.

並列關鍵字

solution coating process ； CIGS ； thin-film solar cells

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