Invited Speech:

Above 10% Efficiency Cu₂ZnSn(S,Se)₄ Thin Film Solar Cell
Fabricated by Magnetron Sputtering

Prof. Yi Zhang Professor, College of Electronic Information and Optical Engineering, NanKai University, Tianjin 300071, China

Date: 12 Dec 2016 (Mon)
Time: 4:30 - 5:00pm
Venue: TY Wong Hall, 5/F, Ho Sin Hang Engineering Building, CUHK

Abstract:

Thin film solar cells based on Cu₂ZnSn(S,Se)₄ (CZTSSe) light absorbing materials continue to attract attention from both scientific and industrial community owing to their advantage of using earth abundant and low cost source elements. The remarkable performance enhancement of CZTSSe solar cells to over 12% has indicated the huge potential of this type of new PV technology to deliver cost-effective solar electricity to meet the demand of rapidly increasing electricity usage in today’s world. To date, most of the reported high performance CZTSSe solar cells with efficiency above 10% were fabricated by hydrazine-based process, including the 12.7% champion device. However, the extremely toxic and explosive hydrazine may cause practical issues that can restrict the large scale production of CZTS solar cells by this method in the future.  Thus development of safe method for fabrication of high performance CZTS solar cells is of highly importance for this new PV technology to fulfill its mission in the future.

Herein, we present the study of fabrication of high performance CZTSSe thin film solar cells with efficiency above 10% using magnetron sputtering deposition. First, CZTSSe film with different stacking sequence are investigated systematically to uncover the growth mechanism of CZTSSe layer and the effect of stacking order in precursor films on the performance of solar cells. It is disclosed that Cu layer should be prepared as the top layer and S will be substituted mostly because of its high saturation vapor pressure. Because Mo/CZTSSe interface is unstable and the interfacial MoSe2/MoS2 will be formed during high temperature annealing process, which increases the series resistance and deteriorate the performance of CZTSSe solar cells dramatically. For this problem, a simple, feasible and effective way to control the formation of interfacial MoSe2 in fabricating Cu₂ZnSnSe₄ (CZTSe) solar cells without any additional barrier layer is studied. On this basis, the growth of CZTSSe film under controllable Se vapour composition and impact of low Cu content on solar cell efficiency are studied and a 10.4% efficiency CZTSe solar cell is fabricated. We also study the effect of depletion region width of CZTSSe on the performance of solar cell.

About speaker:

Prof. Yi Zhang received his Ph.D degree in Condensed Matter Physics from Institute of Physics, Chinese Academy of Sciences in 2006. Before working in the College of Electronic Information and Optical Engineering, Nankai University as an associate Professor in 2008, he worked in Max-Planck Institute for Metals Research as a Postdoc. He is currently the professor and the vice director of the Institute of Photoelectronic Thin Film Devices and Technology in College of Electronic Information and Optical Engineering, Nankai University, China. His research interests include compounds thin film solar cells and light converting materials for LED lighting.