- 學位論文
以四元靶濺鍍銅銦鎵硒薄膜之硒化研究
Selenization on the Polycrystalline CuIn1-xGaxSe2 Thin Films Sputtered from a Quaternary Target
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摘要
雖然目前仍以共蒸鍍製程製備的CIGS光電轉換效率較佳，但因侷限在小面積和均勻度等問題，其發展有限。然而二階段製程雖為目前量產的技術，但為求成分均勻，需搭配多層膜結構，硒化時，使用的H2Se為有毒氣體，又有組成成分不均勻等問題，製程較為煩瑣，因此，發展一套製程穩定及簡化的CIGS製程有其必要性。 CIGS薄膜的導電性是仰賴本質缺陷，以多晶結構為主的CIGS薄膜光電轉換效率最高，相關研究皆顯示多晶結構的CIGS缺陷，主導效能表現上的差異。而我們以四元靶材濺鍍之薄膜晶粒較小(Cu-poor)，根據Jesse A. Frantz等人研究顯示[1]，晶界會影響載子擴散行為，造成長波長的吸收變差，導致整體光電流較小。而我們的薄膜未經任何熱處理的元件表現有電流阻礙現象，如此大幅降低開路電壓(VOC)和填充因子(FF)，嚴重影響光電轉換效率，故本研究以四元靶材直接濺鍍均勻性高的CIGS薄膜，再經硒化處理，研究薄膜特性的影響，進而改善元件效率。 本實驗分兩部分，第一部分為以低溫鍍製的薄膜再經高溫硒化，研究升溫速率、壓力和溫度對晶粒成長的影響。但高溫下的硒化處理，不僅形成極厚的MoSe2，強烈的體積膨脹使CIGS和Mo的界面附著性變差，且薄膜內部發生嚴重的成分偏離，最終導致效率不佳。為了解決高溫下成分偏差及MoSe2大量生成的問題，4.2節以高溫鍍膜和低溫硒化方式將硒補足。第二部分為高溫鍍膜搭配低溫硒化，藉由更改石墨盒的機構以增加硒的活性，如此高活性之氣體可有效地和薄膜反應，將薄膜中之硒補足至計量比。最後搭配低溫電性量測進行分析，發現低溫硒化消除了N2缺陷，並改善開路電壓和填充因子，使效率大幅提升至8.6%。
並列摘要
Polycrystalline CuIn1-xGaxSe2 (CIGS) solar cell with the highest efficiency was reported using three-stage co-evaporation, which suffers from large-scaled mass manufacture. The alternative approach is to use two-step process. However, the annealing process is usually under H2Se which is toxic to get the high efficiency. Therefore, simplifying the process for fabricating CIGS thin films is very essential. Polycrystalline CuIn1-xGaxSe2 thin films sputtered from a quaternary target is a promising method. However, the small grain sizes are got by using Cu-poor target. According to Jesse A. Frantz’s research[1], the presence of grain boundaries would affect the diffusion length and transport of carriers through this layer reducing the short circuit current. Moreover, as-deposited films are with current-blocking effect which is very harmful to the fill factor and open circuit voltage. Therefore, we study selenization on the polycrystalline CuIn1-xGaxSe2 thin films sputtered from a quaternary target and try to improve the efficiency. There are two parts in the study. First, we deposited films under low temperatures and selenization under high temperatures. At high temperatures, MoSe2 is thick and the composition deviation of films was serious. The efficiency is not so good finally. In order to solve these problems, we deposited films under high temperatures and selenization under low temperatures to inhibit current-blocking effect. We increase the activity of selenium vapor by changing the graphite box design and improve the fill factor and open circuit voltage successfully. Finally, the device yielded the efficiency of 8.6%.
參考文獻
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