溶液製程製備銅銦鎵硒太陽電池之吸收層與緩衝層薄膜材料與其光電特性分析

Solution Synthesis and Photovoltaic Properties of the Absorber Layers and Buffer Layers in Cu(In,Ga)Se2 Solar Cells

馬正鑫(Jeng-Shin Ma)

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(2014年)

https://doi.org/10.6342/NTU.2014.11186

摘要

本論文針對CIGS太陽電池之緩衝層材料與吸收層材料進行製備與元件光電特性之探討。為了簡化製備CIGS太陽電池之製程複雜度，本論文提出針對CdS緩衝層及黃銅礦相光吸收層開發新式溶液法製程。為了探討CdS緩衝層之材料特性對於CIGS太陽電池之光電特性之影響，論文中使用化學浴沉積法及微波輔助化學浴沉積法進行CdS薄膜之製備，並藉由元件之組成進行光電特性之分析。為取代傳統高溫硒化法，本研究使用水熱輔助硒化製程及直接加熱法進行CIGS光吸收層薄膜材料之製備，並針對反應條件對於CIGS薄膜之結晶結構、顯微結構、光電特性等之影響進行探討。
論文中首先選擇對於CdS緩衝層薄膜厚度對於CIGS太陽電池光電特性之影響進行研究。在化學浴沉積法中，當薄膜沉積時間達到14分鐘時，連續且緻密之CdS薄膜成功被製備在CIGS光吸收層上。CIGS太陽電池的I-V特性分析顯示元件光電轉換效率隨著CdS緩衝層薄膜厚度而提升至11.9%。二極體參數亦隨著CdS薄膜厚度的提升而改進，並在薄膜較厚時劣化。UV-vis光譜及EQE指出短波長之光吸收耗損隨著CdS緩衝層之厚度增加而增加。
為縮短CdS薄膜之製程時間，本論文提出以微波輔助化學浴沉積法進行CdS緩衝層之製備。透過此製程之使用，製備CdS薄膜之反應溫度可以降低至55oC。反應時間大幅縮短至4分鐘。隨著反應溫度增加，CdS薄膜厚度降低。當沉積溫度為55oC時，所製備元件之光電轉換效率達到10.2%。透過二極體分析得知，分流電導、理想因子、及飽和電流皆隨著反應溫度提升而大幅劣化。此微波輔助化學浴沉積法具有潛力用以短時間內製備應用於高效率CIGS太陽電池之CdS緩衝層薄膜。
另針對有別於傳統高溫硒化製程之新式黃銅礦相薄膜製備製程進行探討。本論文提出以水熱輔助硒化法於銅箔上進行CuInSe2薄膜之製備。透過在此合成方法並添加三乙醇基胺進行反應可以大幅降低製備單相薄膜之硒化溫度至220oC。當水熱反應及水熱時間增加時，可以生成單相且具有緻密結構之CuInSe2薄膜。GIXD與SIMS分析指出銦離子的擴散促進了CuInSe2薄膜之生成。本製程之反應機制被提出。硒離子在低溫時與銅箔反應形成Cu2-xSe相，接著銦離子與硒離子於Cu2-xSe相表面形成In2Se3相，之後Cu2-xSe相與In2Se3相交互反應形成CuInSe2相。
此外本論文提出以不使用含氣氛之直接加熱製程進行CIGS薄膜之製備。透過於還原氣氛中直接加熱含有硒離子之前驅薄膜，可以於較低溫之350oC下成功合成得到CIGS單相薄膜。更進一步提升加熱溫度導致薄膜之結晶性增加以及薄膜中多面體狀晶粒之生成。當加熱溫度為550oC時，所製備元件光電轉換效率為8.3%。對含有硒離子之前驅薄膜進行直接加熱方法為一具有潛力之製備高效率CIGS太陽電池之製程。
本研究提出應用於CIGS太陽電池之CdS緩衝層材料的厚度與顯微結構對於電池元件之光電效率有重大之影響。此外本研究成功開發微波輔助化學浴沉積法製備高品質CdS緩衝層薄膜與高效率CIGS太陽電池元件。而在開發CIGS吸收層之無後硒化製程方面，藉由水熱輔助硒化法成功於低溫環境製備黃銅礦相薄膜，並藉由直接加熱法以硒離子添加之前驅膜成功快速製備具高品質與高光電轉換效率之CIGS太陽電池。

關鍵字

銅銦鎵硒 ； 硫化鎘 ； 溶液製程 ； 薄膜

並列摘要

The photovoltaic properties of buffer layers and absorber layers of Cu(In,Ga)Se2 solar cells were investigated in this thesis. For decreasing the processing complexity, solution processes were applied to prepare CdS buffer layers and the chalcopyrite absorber layers in Cu(In,Ga)Se2 solar cells. The chemical bath deposition process and the microwave-assisted chemical bath deposition process were studied for preparing CdS layers. On the other hand, the hydrothermal-assisted selenization and the direct heating process with selenium-ions containing precursors were applied to prepared the chalcopyrite-phased absorber layers instead of the employment of the conventional high-temperature selenization process.

The effects of the thickness of CdS buffer layers on the photovoltaic properties of Cu(In,Ga)Se2 solar cells were investigated. The continuous and dense films were obtained with the deposition time for 14 min. The I-V characteristics of the cells showed that the efficiency of Cu(In,Ga)Se2 solar cells increased and then decreased with further increasing CdS film thickness. A conversion efficiency of 11.9% was obtained with the dense CdS films without cracking.

For shortening the reaction duration during the conventional chemical bath deposition process, CdS buffer layers were successfully prepared on Cu(In,Ga)Se2 absorber layers via the microwave-assisted chemical bath deposition process at a temperature as low as 55oC. The reaction duration for obtaining the dense CdS films was shortened for 4 min. A conversion efficiency of 10.24% was achieved.

The investigation related to the preparation of Cu(In,Ga)Se2 without the conventional selenization process was also presented. CuInSe2 films were successfully prepared on copper foils via the hydrothermally-assisted selenization process. The selenization temperature was decreased significantly to as low as 220oC. Se2- ions first react with copper foils to form Cu2-xSe at low temperatures, then In3+ ions and Se2- ions react to form In2Se3 on the Cu2-xSe surface, finally Cu2-xSe and In2Se3 react with each other to yield CuInSe2.

Cu(In,Ga)Se2 absorber layers were successfully prepared via heating the selenium-ions containing precursor films in a reducing atmosphere instead of selenium-containing vapor in this study. Cu(In,Ga)Se2 films were obtained with selenium-ions containing precursors at the heating temperature as low as 350oC. Further elevating the heating temperature to 550oC resulted in the enhancement of crystallinity and the formation of the densified films. A conversion efficiency of 8.27% was achieved.

The film thickness and microstructures of CdS buffer layers applied to Cu(In,Ga)Se2 solar cells significantly affect the photovoltaic properties of the prepared solar cells. In addition, the microwave-assisted process was successfully employed to prepare CdS films for high-efficiency Cu(In,Ga)Se2 solar cells for a shortened duration. The hydrothermal-assisted selenization process was developed for preparing the chalcopyrite materials at low temperature. Moreover, the direct heating process with selenium-ion containing precursors was successfully applied to prepare Cu(In,Ga)Se2 for obtaining high conversion efficiency.

並列關鍵字

CIGS ； CdS ； Solution process ； Thin films

參考文獻

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