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Similarities and Critical Differences in Heavy Alkali-Metal Rubidium and Cesium Effects on Chalcopyrite Cu(In,Ga)Se2 Thin-Film Solar Cells
journal contribution
posted on 2019-07-02, 00:00 authored by Shogo Ishizuka, Noboru Taguchi, Paul J. FonsBoth
elemental Rb and Cs are known as effective dopants in enhancing
Cu(In,Ga)Se2 (CIGS) thin-film photovoltaic device performance.
It is, however, found that there are critical differences in the effects
of these two alkali metals on CIGS thin-film properties. Namely, CIGS
film surfaces show RbInSe2 compound formation after RbF
postdeposition treatment (PDT), whereas no such segregated compound
formation is observed with CsF-PDT. On the other hand, both Rb and
Cs have the effect of increasing effective hole carrier density, photoluminescence
intensity, and carrier lifetime in CIGS similar to the effects of
the lighter alkali-metals Na and K. The fundamental mechanism behind
metastable acceptor formation, which is known as the light-soaking
or bias-soaking effect leading to CIGS photovoltaic performance enhancement,
is experimentally revealed to be independent of the presence of alkali
metals in CIGS, and alkali-metals still have an effect of facilitating
metastable acceptor formation.