jp503699r_si_001.pdf (423.74 kB)
Precursor Stack Ordering Effects in Cu2ZnSnSe4 Thin Films Prepared by Rapid Thermal Processing
journal contribution
posted on 2014-08-07, 00:00 authored by Andrew Fairbrother, Lionel Fourdrinier, Xavier Fontané, Victor Izquierdo-Roca, Mirjana Dimitrievska, Alejandro Pérez-Rodríguez, Edgardo SaucedoSolar
cells based on Cu2ZnSnSe4 thin film absorber
layers have shown promise as an alternative to more mature thin film
technologies because they are composed of more earth abundant elements.
To increase device efficiencies there is still much to be investigated
about its properties, and film and device processing. Rapid thermal
processing is a more industrially viable method of forming thin film
absorber layers than time intensive conventional thermal processing.
However, optimized conditions for conventional processing are not
readily transferable to rapid thermal processing. Thermal processing
of this material is complicated through loss of volatile components
such as Zn and Sn–Se, in addition to decomposition at elevated
temperatures. In this study the effect of stack order has been investigated
for Cu–Zn(O)–Sn precursor stacks selenized by rapid
thermal processing to form Cu2ZnSnSe4 thin films.
Precursor stack ordering is shown to have significant effects on the
film properties, including precursor alloy formation, composition
and elemental loss, morphology, and secondary phase formation and
distribution. Optoelectronic properties of devices prepared from these
films also show a dependence on precursor stack order. Most notable
is the poor performance of devices with Zn as a bottom layer, due
to excessive ZnSe formation at the back contact region. The viability
of ZnO as a precursor layerin place of volatile Znis
also investigated, and shown to not completely react in the Se atmosphere,
leaving residual oxygen in the Cu2ZnSnSe4 films.
The best performing device has a conversion efficiency of 4.3%, and
uses a stack order of glass/Mo/Sn/Zn/Cu.