Journal
ACTA MATERIALIA
Volume 60, Issue 19, Pages 6732-6741Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2012.08.043
Keywords
CZTS; Phase stability; Decomposition; Thermal effects; Kinetic analysis
Funding
- Clean Energy Research Programme under Singapore EDB and DuPont Apollo [NRF2008EWT-CERP002-041, NUS R284-000-081-592]
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Thermal stability is essential for the potential solar cell material Cu2ZnSnS4 (CZTS) in achieving a satisfactory photovoltaic device performance. Although the loss of Sn from CZTS has been reported, the basic decomposition mechanism of a CZTS system has not been well established yet, especially with regard to the role of active Cu1+ ions. This paper not only provides a deeper understanding of the change of Sn species, which includes an equimolar isobaric vaporization mode transition and a solid vapor phase transition in a self-generated atmosphere, but also reveals the oxidation state alternation (Cu1+/Cu2+) and transfer mechanism of Cu species through carefully designed experiments and a reaction kinetic study. Cu ions are unexpectedly found to be active in affecting the degradation reaction by valance alternation and ion movement upon the application of a heat field to balance the derivation caused by a non-uniform temperature gradient. As a result, a Cu-Zn separation appears, with Cu accumulating near the hot area and Zn near the cold area. A decomposition reaction model of CZTS under a directional heat field is proposed to describe the elemental and electronic state change in atomic scale, and a perfect match is obtained between the model and the experimental results. This paper paves a way to solve the thermal stability issue of Cu2ZnSnS4. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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