Deep Defects in Cu2ZnSn(S,Se)4 Solar Cells with Varying Se Content

Electronic defects in Cu2ZnSn(SexS1-x)(4) (x = 0, 0.4, 0.6, and 1) kesterite solar cells are studied by temperature-dependent admittance spectroscopy and photoluminescence studies. Using admittance spectroscopy, we find that the substitution of sulfur by selenium decreases the depth of a dominant acceptor level from 0.29 to 0.12 eV. In addition, a deep-acceptor defect at about 0.5 eV above the valence band is found for the x = 0.4-1 devices. A shallow transition level with an energy of 0.14-0.09 eV is deduced from the thermal quenching of the photoluminescence yield, which we attribute to a donor level.