以電鍍法製備太陽能電池吸收層銅鋅錫硫與其性質之研究

Abstract

薄膜光伏元件為當前世界各國太陽能電池研究主流，相較於高成本的高效率 電池，使用薄膜光伏元件的太陽能電池，能夠達到輕量化與低成本的效果。目前 太陽能薄膜市場幾乎被碲化鎘（CdTe）型與銅銦鎵硒（CuInGaSe2）型所占有。然而近年來環保意識抬頭，此兩種太陽能薄膜電池因為含有污染性物質鎘、硒而開 使受到關注。從原物料稀缺性的角度觀看，碲、銦和鎵的天然蘊藏量有限，將會 限制薄膜太陽能電池的長期發展，而使用銅鋅錫硫（Cu2ZnSnS4）太陽能電池更俱 有著無毒及材料充足的優勢。本論文將以電化學沈積法製備 CuZnSn 金屬合金並以 硫化處理製備完整的 Cu2ZnSnS4 吸收層。 實驗分為三個部分，第一部分是利用電化學循環伏安法分析銅、鋅、錫金屬 離子與檸檬酸之間的錯合效果，以掌握此三元元素溶液中的電化學沈積適當操作 電位範圍。 第二部分是電化學沈積的探討，將利用在電鍍電位Ｅ＝−1.25 V/SCE 的條件下， 嘗試沈積出性質良好的鍍層，並用掃描式電子顯微鏡觀察鍍層的表面形貌、橫截 面，用 X 光繞射分析儀進行分析相鑑定。沈積結果為形貌緻密且均勻的鍍層，但 是其厚度和成分在一特定方向有變化的趨勢，原因將於內文探討。 第三部分是探討初鍍 CuZnSn 金屬合金的硫化熱處理製程，並探討硫化溫度、 升溫速率以及氰化鉀酸洗對 Cu2ZnSnS4 吸收層的影響。在此部分將用掃描式電子 顯微鏡、X 光繞射分析儀、拉曼光譜作分析。結果顯示在本實驗的系統中，Cu2ZnSnS4 於 500 °C 以上才有機會形成，而在緩慢升溫速率之下，其晶粒成長大，但表面批批覆性差，此現象在快速升溫有部明顯改善。最後，再以最佳條件之 Cu2ZnSnS4 浸泡在氰酸鉀去除表面二次相，得到成分相對均勻的 Cu2ZnSnS4 吸收層。

Thin-film photovoltaic is currently the mainstream of the photovoltaic technology.In contrast to high efficiencies solar cells that are usually expensive, thin-film photovoltaic are appealing for its low cost and facile approach. Among them, CdTe and CIGS technologies dominate the thin-film market share nowadays. But due to toxicity of Cd and Se and availability issues of Te, In and Ga, the production of photovoltaic based on these absorber layer could be limited. Indeed, other absorber layers must be developed and Cu2ZnSnS4 has emerged as an advantageous choice for its toxic-free and material abundant property. Hence, this study focuses on the preparation of Cu2ZnSnS4 by electrochemical deposition of CuZnSn alloy and completed the formation reaction by sulfurization process. The experiment is divided into three parts. Initially, cyclic voltammetry of electrolytic bath containing copper, zinc, tin metal ions and sodium citrate is analyzed, with the purpose of obtaining good deposition potential range. The second part aims on the analysis of CuZnSn films eletrodeposited at −1.25V/SCE. Surface and cross-section morphology was analyzed by SEM, and phase identification analyzed by XRD and Raman spectra. The results suggested a dense and compact film was electrodeposited, but thickness and composition variation was observed in a determined direction of the film; details are discussed in this work. In the last part, sulfurization process of as-deposited CuZnSn alloy is investigated. Effects of annealing temperature, temperature ramping rate, and KCN treatment on sulfurization process are subsequently studied. The measurements used are SEM, XRD and Raman spectra. The results indicated that the formation of Cu2ZnSnS4 was evidenced at temperature above 500 °C. The films sulfurized under slow heating rate consisted of larger grains but presented poor adhesion. This could be partially improved by raising the ramping rate of sulfurization. And finally, the films with best conditions were treated with KCN treatment in order to remove copper sulfides from the surface, and Cu2ZnSnS4 thin films with relative homogeneous composition were achieved.