Successes and Challenges Associated with Solution Processing of Kesterite Cu2ZnSnS4 Solar Cells on Titanium Substrates

Zhengfei Wei*, Thomas Dunlop, Peter J Heard, Cecile Charbonneau, David Worsley, Trystan Watson*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

Roll-to-roll (R2R) processing of solution-based Cu2ZnSn(S,Se)4
CZT(S,Se)) solar cells on flexible metal foil is an attractive way to achieve cost-effective manufacturing of photovoltaics. In this work we report the first successful fabrication of solution-processed CZTS devices on a variety of titanium substrates with up to 2.88% power conversion efficiency (PCE) collected on flexible 75 μm Ti foil. A comparative study of device performance and properties is presented aiming to address key processing challenges. First, we show that a rapid transfer of heat through the titanium substrates is responsible for the accelerated crystallisation of kesterite films characterised with small grain size, a high density of grain boundaries and numerous pore sites near the Mo/CZTS interface which affect charge transport and enhance recombination in devices. Following this, we
demonstrate the occurrence of metal ion diffusion induced by the
high temperature treatment required for the sulfurization of the
CZTS stack: Ti4+ ions are observed to migrate upwards to the Mo/CZTS interface whilst Cu1+ and Zn2+ ions diffuse through the Mo layer into the Ti substrate. Finally, residual stress data confirm the good adhesion of stacked materials throughout the sequential solution process. These findings are evidenced by combining electron imaging observations, elemental depth profiles generated by secondary ion mass spectrometry, and x-ray residual stress analysis of the Ti substrate.
Original languageEnglish
Number of pages8
JournalACS Applied Energy Materials
Early online date24 Mar 2020
DOIs
Publication statusE-pub ahead of print - 24 Mar 2020

Keywords

  • CZTS
  • titanium
  • solar cell
  • stress
  • SIMS

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