Impact of RbF-PDT on Cu(In,Ga)Se2 solar cells with CdS and Zn(O,S) buffer layers

• Main Authors: Kanevce Ana, Paetel Stefan, Hariskos Dimitrios, Magorian Friedlmeier Theresa
• Format: Article
• Language: English
• Published: EDP Sciences 2020-01-01
• Series: EPJ Photovoltaics
• Subjects: cigs solar cells; rbf-pdt; zn(o,s); characterization
• Online Access: https://www.epj-pv.org/articles/epjpv/full_html/2020/01/pv200011/pv200011.html

Alkali-fluoride post-deposition treatments (PDTs) of Cu(In,Ga)Se2 (CIGS) absorbers have repeatedly resulted in device efficiency improvements, observed mainly due to an open-circuit voltage (Voc) enhancement. Replacement of the CdS buffer layer with a higher band gap alternative can increase the short-circuit current density (Jsc) and also eliminate the use of Cd. In many alternative-buffer attempts, however, the Jsc gain was accompanied by a Voc loss, resulting in some degree of performance loss. In order to better understand the impact of RbF-PDT, we analyze a combination of experimental devices produced in the same in-line CIGS run with and without RbF-PDT in combination with chemical-bath-deposited CdS and Zn(O,S) buffers. Low-temperature current–voltage curves indicate a difference in Rb impact on the CIGS/CdS and CIGS/Zn(O,S) p-n junctions. For example, the diode-current barrier which creates a rollover often observed in RbF-treated CIGS/CdS current–voltage curves is significantly reduced for the CIGS/Zn(O,S) junction. Although the RbF-PDT had a positive impact on both junction partner combinations, the CIGS/Zn(O,S) devices' Voc and fill factor (FF) benefited stronger from the RbF treatment. As a result, in our samples, the Jsc and FF gain balanced the Voc loss, thus reducing the efficiency difference between cells with CdS and Zn(O,S) buffers.