Impacts of surface and thermal treatments on the performance of Cu2ZnSnS4 (CZTS) thin films photovoltaic device

As for the absorber layer preparation, the kesterite structure of the CZTS has been successfully obtained, but
a secondary phase was formed as well, which was detectable via both scanning electron microscopy and X-ray
diffraction. The X-Ray diffraction analysis suggests the presence of Cu2S secondary phase.
The secondary phase was successfully removed with both etching solutions under the following conditions:
10% w/v KCN has been sufficient in removing the Cu2S at room temperature if the etching time has been 60
minutes. From Fig.10 it can be deduced that 45 minutes of etching is not sufficient enough to remove the secondary
phase which is still detectable via XRD. Etching with 10% v/v HCl has been successful as well, but the etching
solution needs to be heated to at least 75◦C to remove all the secondary phase after 10 minutes: it is shown in
Fig.14 that the same amount of time but a small temperature difference of 3◦C does not remove all of the secondary
phase.
The surface analysis via scanning electrode microscopy revealed an effect of etching time on the complete removal
of secondary phase. It is worth to note that not all samples contain the exact same amount of secondary phase.
It is yet to be decided whether the etching will further proceed with either 10% w/v KCN or 10% v/v HCl since
both etchants have been equally successful in removing the secondary phase: The removal with 10% w/v KCN is
convenient in a way that the solution does not need to be heated but KCN is considered as toxic. The method of
using 10% v/v HCl is very time efficient since the secondary phase can be removed after 10 minutes but the solution
needs to be heated up to at least 75◦C.