Phases, morphology, and diffusion in CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2} thin films
- Institute of Energy Conversion, United States Department of Energy Center of Excellence for Photovoltaic Research and Education, University of Delaware, Newark, Delaware 19716 (United States)
- Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716 (United States)
- National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)
CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2} thin films, with various Ga/(Ga+In) ratios, suitable for solar cells were processed by selenizing stacked Cu, Ga, and In precursor layers in a H{sub 2}Se reactor in the temperature range of 400{endash}500{degree}C. Cu/Ga/In and Cu/In/Ga precursors were obtained by sequential sputtering of the elemental layers. The Cu/Ga/In and Cu/In/Ga precursors, and the selenized films were characterized by scanning electron microscopy, x-ray diffraction, energy dispersive spectroscopy, and Auger electron spectroscopy. The precursors contained only binary and elemental phases in the as-deposited condition and after annealing. The selenized films had a nonuniform distribution of Ga and In. The surface of the selenized films were In rich, while the Mo/film interface in these films was Ga rich. The selenized films with Ga/(Ga+In) ratios greater than 0.25 contain graded Ga and In compositions, and the selenized films with Ga/(Ga+In) ratios less than 0.6 contain a phase-separated mixture of CuInSe{sub 2} and CuGaSe{sub 2} with the CuInSe{sub 2} near the surface and the CuGaSe{sub 2} near the Mo/film interface. Single phase, homogeneous CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2} films were obtained by annealing the as-selenized films in argon in the temperature range of 500{endash}600{degree}C for 60 min. Interdiffusion of In and Ga between the CuGaSe{sub 2} and the CuInSe{sub 2} phases was found to be responsible for the homogenization process. This homogenization process does not occur in the presence of a selenium atmosphere. Diffusion measurements yielded similar interdiffusion coefficients for Ga and In. The annealing temperature and time to effect homogenization depends on the Ga/(Ga+In) ratio of the absorber films. Films with lower Ga/(Ga+In) ratios require a homogenization temperature of 600{degree}C or more and films with higher Ga/(Ga+In) ratios homogenize at a lower temperature of 400{endash}500{degree}C, for an annealing time of 60 min.
- OSTI ID:
- 542156
- Journal Information:
- Journal of Applied Physics, Vol. 82, Issue 6; Other Information: PBD: Sep 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
A crystallographic description of experimentally identified formation reactions of Cu(In,Ga)Se{sub 2}
Structure, chemistry, and growth mechanisms of photovoltaic quality thin-film Cu(In,Ga)Se[sub 2] grown from a mixed-phase precursor
Related Subjects
14 SOLAR ENERGY
COPPER SELENIDES
THIN FILMS
INDIUM SELENIDES
GALLIUM SELENIDES
SOLAR CELLS
MATERIALS
COPPER COMPOUNDS
INDIUM COMPOUNDS
GALLIUM COMPOUNDS
SCANNING ELECTRON MICROSCOPY
X-RAY DIFFRACTION
AUGER EFFECT
ANNEALING
PHASE STUDIES
SPUTTERING
MORPHOLOGY
MOLYBDENUM
INTERFACES
DIFFUSION