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Influence of iron on defect concentrations and device performance for Cu(In,Ga)Se 2 solar cells on stainless steel substrates
Author(s) -
Eisenbarth Tobias,
Caballero Raquel,
Kaufmann Christian A.,
Eicke Axel,
Unold Thomas
Publication year - 2012
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/pip.2260
Subject(s) - materials science , acceptor , analytical chemistry (journal) , solar cell , doping , diffusion , cadmium telluride photovoltaics , foil method , substrate (aquarium) , optoelectronics , chemistry , composite material , physics , oceanography , chromatography , geology , thermodynamics , condensed matter physics
Thin film Cu(In , Ga)Se 2 (CIGSe) solar cells deposited on flexible steel foil substrates by coevaporation are investigated. Iron diffusion from the steel foil substrate material into the CIGSe absorber layers is studied by secondary ion mass spectroscopy (SIMS) for different maximum absorber growth temperatures and solar cell back‐contact configurations. The optimization of the absorber growth temperature, the introduction of a diffusion barrier layer at the back contact, and the adjustment of the sodium doping lead to device efficiencies above 14%. Defect spectroscopy by means of admittance measurements shows a clear correlation of the deep defect concentration with the Fe content in the CIGSe absorber layer and a correlation between the sodium incorporation and the net carrier concentration. It is found that too much Na supports the diffusion of Fe, inducing an increased deep defect concentration. The Fe‐induced deep defects, which form a broad acceptor‐type defect band at 0.44 eV above the valence band maximum, are identified as the cause of bulk recombination, limiting the device performance in these solar cells. Copyright © 2012 John Wiley & Sons, Ltd.