The absorber fabrication by sputtering and selenization processes in Cu(In,Ga)Se2 thin film solar cells
Han-Ping D. Shieh
|Abstract:||銅銦鎵硒是一種具有潛力的薄漠太陽能電池材料。在此論文中針對硒化製程中的附著度，均勻的鎵分佈和緻密的表面做研究。首先論文中提出了一種適合硒化法的成長路徑，經由二元相的討論，提出了三種不同的成長路徑，分別由 Cu2-xSe、 β-In2Se3和 Cu2-xSe及β-In2Se3。經由此研究結果發現由Cu2-xSe及β-In2Se3，所生成的銅銦硒具有附著性佳和緻密的表面，更進一步的提出了三階段的製程。在鎵分佈方面，提出了四階段退火，來解決鎵在銅銦鎵硒中分佈不均的問題。在此研究結果中，先以125OC 預熱，再以350OC、450OC和550OC的退火，具有最佳化的結果，所生成的銅銦鎵硒具有附著性佳、緻密的表面、高強度比值的(220/204)/(112)和較均勻的鎵分佈。|
Thin film solar cells with Copper Indium Gallium Diselenide ( CIGS ) absorber layers are one of the most promising candidates to emerge as an efficient solar cell technology in the near future. The aim of this thesis is to develop a fabrication method for the CIGS absorber with densely-packed, well adhered, and uniform Ga depth-profiled properties by sputtering and selenization processes. Firstly, the growing mechanism of CuInSe2 (CIS) films by using sputtered precursor films and selenization process was presented. Three dominant growing paths of selenized CIS films, including Cu2-xSe, β-In2Se3, and Cu2-xSe/β-In2Se3 binary compounds paths, were determined by analyzing Cu-Se and In-Se binaries. The CIS films with the Cu2-xSe/β-In2Se3 growing path exhibited relatively uniform and larger grain size in surface morphology. As a result, an well-defined formation path for CIS-based chalcopyrite films with three-step annealing process was achieved. Moreover, a four-step annealing process consisting of pre-heating treatment and followed annealing at elevated temperatures was studied to improve the depth-profiled Ga distribution of CIGS films. The pre-heating of the sputtered Cu-Ga-In and evaporated Se film was utilized to mitigate the adhesion and Ga accumulation issues in the formation of CIGS films. The optimized annealing temperatures were 125oC in preheating procedure, 350oC, 450oC, and 550oC in the followed annealing processes, respectively. In this study, resulting films with four-step annealing exhibited large-grained, and 112/220/204-orientation chalcopyrite CIGS phase, as well as smooth depth-profiled distribution in the Ga concentration.
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