Successesand Challenges Associated with SolutionProcessing of Kesterite Cu2ZnSnS4 Solar Cellson Titanium Substrates
2020
Roll-to-roll
(R2R) processing of solution-based Cu2ZnSn(S,Se)4 (CZT(S,Se)) solar cells on the 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 the key processing challenges. First,
we show that a rapid transfer of heat through the titanium substrates
is responsible for the accelerated crystallization of kesterite films
characterized 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 upward to the Mo/CZTS interface
while 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.
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