Investigation of Cu(In,Ga)Se2 Solar Cell Performance Deviations in Nominally Equal Absorbers

Cu(In,Ga)Se 2 (CIGSe) solar cells were fabricated independently by industrial scale co-evaporation in two separate production lines with the same nominal composition and thickness of the absorber film. Although the device properties were believed to be the same we observed substantial deviations of...

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Bibliographic Details
Published inJpn J Appl Phys Vol. 51; no. 10; pp. 10NC07 - 10NC07-4
Main Authors Knecht, Robin, Parisi, Jürgen, Riedel, Ingo, Schäffler, Raymund, Dimmler, Bernhard
Format Journal Article
LanguageEnglish
Japanese
Published The Japan Society of Applied Physics 25.10.2012
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Summary:Cu(In,Ga)Se 2 (CIGSe) solar cells were fabricated independently by industrial scale co-evaporation in two separate production lines with the same nominal composition and thickness of the absorber film. Although the device properties were believed to be the same we observed substantial deviations of the respective values of the open circuit voltage ($\Delta V_{\text{OC}} = 40$ mV) and of the fill factor ($\Delta\mathrm{FF}= 4$%), whereas the short circuit current was essentially the same. We performed fundamental device analysis, space charge and defect spectroscopy, transient photoluminescence as well as in-depth profiling of the chemical gradients of the absorber films. Using the results from the experiments we set up a simulation baseline which allowed us to conclude that the apparent deviations can be related to the presence of deep recombination centers with different concentration within the CIGSe absorber as well as to variations of the band gap grading.
Bibliography:Experimental $I$--$V$ characteristics (standard test conditions) of two CIGSe samples nominally processed under the same conditions in two independent co-evaporation chambers. TRPL: The slope of the high sample (straight) shows a slower decay than the low sample (dotted) thus indicating reduced charge carrier recombination. Bandgap profile as determined from GDOES measurements. The slope of the bandgap grading in the high sample (straight) is weaker and the minimum bandgap higher than in the low sample (dashed). The heterojunction is situated at 1000 nm, the back contact at about 3750 nm. Simulated $I$--$V$ characteristics: low sample (dashed) and low model adjusted with high reflection and bandgap grading (dotted). The open circuit voltage increases but only about half as much as measured. The high sample simulation (straight) incorporates adjusted midgap defect concentrations. The symbols represent the measurement data ( : low, : high).
ISSN:0021-4922
1347-4065
DOI:10.1143/JJAP.51.10NC07