Annealing treatment of Cu(In, Ga)Se2 absorbers prepared by sputtering a quaternary target for 13.5% conversion efficiency device. (August 2015)

• Record Type: Journal Article
• Authors: Ouyang, Liangqi; Zhao, Ming; Zhuang, Daming; Han, Junfeng; Gao, Zedong; Guo, Li; Li, Xiaolong; Sun, Rujun; Cao, Mingjie
• Is Part Of: Solar energy. Volume 118(2015)
• Page Start: 375
• Page End: 383
• Publication Date: 2015-08
• Subjects: CIGS -- Solar cell -- Thin film -- Sputtering; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2015.05.019
• Languages: English
• ISSNs: 0038-092X

Abstract

Graphical abstract: Raman spectra of the as-deposited film and films annealed at various temperatures from 210 to 550 °C: (a) particle regions as indicated in SEM images; (b) absorber matrix regions as indicated in SEM images. Highlights: The CIGS absorbers were prepared by sputtering from a quaternary target. CIGS near the surface splitted into Cu–Se and Cu-poor phases at 210–380 °C. Recrystallization of sputtered CIGS film at high annealing temperature. A close relationship between CIGS electronic property and its microstructure. 13.5% conversion efficiency achieved by sputtering quaternary target technology. Abstract: Copper indium gallium selenide (Cu(In, Ga)Se2, CIGS) absorbers have been prepared by sputtering a CIGS quaternary target and imposing a subsequent annealing process. The influences of annealing temperatures on the morphology, chemical composition, microstructure and electronic properties as well as phase transformations have been investigated. Scanning Electron Microscope (SEM), X-Ray Fluorescence (XRF), Energy-dispersive X-Ray spectroscopy (EDX), X-Ray Diffraction (XRD), Raman spectroscopy and Hall analysis have been employed to analyze the morphology, chemical composition, microstructure and electronic properties, respectively. The results show that a phase separation process occurs in the CIGS absorbers when the as-deposited CIGS samples are annealed at the temperatures between 210 and 380 °C. The surfaces are partly covered by regular shaped grains and platelets, which are corresponding to Cu–Se phases. When the absorbers are annealed at the temperature higher than 410 °C, the CIGS absorbers recrystallize. This process improves the grains size and makes the absorbers become homogeneous and compact. Hall analysis shows the variation of electronic properties with the increase of annealing temperatures. The relationships between the electronic properties and the microstructure have been discussed in the paper as well. The solar cells have been fabricated with an optimized annealing temperature of 550 °C. The highest efficiency of the CIGS solar cell devices reaches 13.5%.