Evolution of Cu 2 ZnSnS 4 during Non-Equilibrium Annealing with Quasi-in Situ Monitoring of Sulfur Partial Pressure

• Published in: Chemistry of materials 2017-04, Vol.29 (8), p.3713-3722
• Main Authors: Ren, Yi, Ross, Nils, Larsen, Jes K., Rudisch, Katharina, Scragg, Jonathan J. S., Platzer-Björkman, Charlotte
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002; 1520-5002
• DOI: 10.1021/acs.chemmater.7b00671

Chalcogen-based materials like Cu 2 ZnSnS 4 (CZTS) have attracted extensive attention for applications such as photovoltaics and water splitting. However, an inability to monitor the sulfur partial pressure ( P S2 ) during the non-equilibrium annealing process at high temperatures complicates the synthesis of CZTS with controlled optoelectronic properties. Here we demonstrate that P S2 can be monitored by investigating the Sn–S phase transformation. We showed that P S2 drops considerably over the annealing time, causing gradual alterations in CZTS: (i) a change in defect type and (ii) evolution of ZnS and Sn x S y phases. With additional ordering treatment, we observed that the low room-temperature photoluminescence energy usually seen in CZTS can result from insufficient P S2 during annealing. It is proven that remarkable V oc beyond 700 mV for solar cells with nonoptimal CdS buffer can be repeatedly achieved when CZTS is prepared under a sufficiently high P S2 . An ordering treatment before CdS deposition can further improve V oc to 783 mV.