Improved performance of Ge-alloyed CZTGeSSe thin-film solar cells through control of elemental losses

• Published in: Progress in photovoltaics 2015-03, Vol.23 (3), p.376-384
• Main Authors: Hages, Charles J., Levcenco, Sergej, Miskin, Caleb K., Alsmeier, Jan H., Abou-Ras, Daniel, Wilks, Regan G., Bär, Marcus, Unold, Thomas, Agrawal, Rakesh
• Format: Article
• Language: English
• Subjects: Alloying elements; Charge carriers; Collection; CZTGeSSe; CZTSSe; Ge alloying; Germanium; Nanocrystals; Performance enhancement; Photovoltaic cells; selenization; Solar cells; solution processing; Thin films
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2442

Nanocrystal‐based Cu2Zn(SnyGe1‐y)(SxSe4‐x) (CZTGeSSe) thin‐film solar cell absorbers with tunable band gap have been prepared. Maximum solar‐conversion total area efficiencies of up to 9.4% are achieved with a Ge content of 30 at.%. Improved performance compared with similarly processed films of Cu2ZnSn(SxSe4‐x) (CZTSSe, 8.4% efficiency) is achieved through controlling Ge loss from the bulk of the absorber film during the high‐temperature selenization treatment, although some Ge loss from the absorber surface is still observed following this step. Despite limitations imposed by elemental losses present at the absorber surface, we find that Ge alloying leads to enhanced performance due to increased minority charge carrier lifetimes as well as reduced voltage‐dependent charge carrier collection. Copyright © 2013 John Wiley & Sons, Ltd. Improved performance of nanocrystal ink‐based CZTGeSSe solar cells has been achieved through minimization of bulk Ge loss from the absorber film during selenization. Here, total area power conversion efficiencies of 9.4% are reported for CZTGeSSe with 30 at.% Ge incorporation compared with 8.4% for CZTSSe. Despite elemental losses measured at the absorber film surface, improved performance of CZTGeSSe over CZTSSe is chiefly attributed to increased charge carrier lifetimes as well as reduced voltage‐dependent charge carrier collection upon Ge alloying.