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Deep surface Cu depletion induced by K in high‐efficiency Cu(In,Ga)Se 2 solar cell absorbers
Author(s) -
DonzelGargand Olivier,
Thersleff Thomas,
Keller Jan,
Törndahl Tobias,
Larsson Fredrik,
Wallin Erik,
Stolt Lars,
Edoff Marika
Publication year - 2018
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.3010
Subject(s) - copper indium gallium selenide solar cells , layer (electronics) , materials science , diffusion , analytical chemistry (journal) , transmission electron microscopy , solar cell , copper , scanning electron microscope , potassium , chemistry , optoelectronics , nanotechnology , metallurgy , composite material , chromatography , physics , thermodynamics
Abstract In this work, we used K‐rich glass substrates to provide potassium during the coevaporation of Cu(In,Ga)Se 2 (CIGS) absorber layers. Subsequently, we applied a postdeposition treatment (PDT) using KF or RbF to some of the grown absorbers. It was found that the presence of K during the growth of the CIGS layer led to cell efficiencies beyond 17%, and the addition of a PDT pushed it beyond 18%. The major finding of this work is the observation of discontinuous 100‐ to 200‐nm‐deep Cu‐depleted patches in the vicinity of the CdS buffer layer, correlated with the presence of K during the growth of the absorber layer. The PDT had no influence on the formation of these patches. A second finding concerns the composition of the Cu‐depleted areas, where an anticorrelation between Cu and both In and K was measured using scanning transmission electron microscopy. Furthermore, a steeper Ga/(In+Ga) ratio gradient was measured for the absorbers grown with the presence of K, suggesting that K hinders the group III element interdiffusion. Finally, no Cd in‐diffusion to the CIGS layer could be detected. This indicates that if Cd Cu substitution occurs, either their concentration is below our instrumental detection limit or its presence is contained within the first 6 nm from the CdS/CIGS interface.