Phases, morphology, and diffusion in CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2} thin films

Journal Article · Mon Sep 01 04:00:00 EDT 1997 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.366122· OSTI ID:542156

Marudachalam, M; Birkmire, R W; Hichri, H ^[1]; Schultz, J M ^[2]; Swartzlander, A; Al-Jassim, M M ^[3]

---

1. 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)
2. Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716 (United States)
3. 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, Journal Name: Journal of Applied Physics Journal Issue: 6 Vol. 82; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
ANNEALING
AUGER EFFECT
COPPER COMPOUNDS
COPPER SELENIDES
DIFFUSION
GALLIUM COMPOUNDS
GALLIUM SELENIDES
INDIUM COMPOUNDS
INDIUM SELENIDES
INTERFACES
MATERIALS
MOLYBDENUM
MORPHOLOGY
PHASE STUDIES
SCANNING ELECTRON MICROSCOPY
SOLAR CELLS
SPUTTERING
THIN FILMS
X-RAY DIFFRACTION