Argon vs. air atmosphere in close spaced vapor transport deposited tin sulfide thin films

The fundamental understanding and tailoring of material properties play a fundamental role on the performance of tin (II) sulfide (SnS)-based photovoltaic devices. In this regard, this work reports on the deposition of single-phase, p-type SnS thin films synthesized by close spaced vapor transport (CSVT) and the impact of employing argon (Ar) and bare vacuum (air) atmospheres on CSVT-SnS thin film properties is presented and compared for the first time. The analysis of film properties was performed by structural, directional, morphological, topographical, along with thermoelectric and optoelectronic characterizations of the samples. It is demonstrated that by changing the CSVT annealing atmosphere, the SnS grains change their orientation from perpendicular (respect to substrate) in Ar to parallel in a bare vacuumed (air) conditions. Furthermore, Hall measurements show that the hole concentration are mostly the same but that hole mobility depends, in turn, on the direction of preferred orientation of the SnS crystals. This translates into a twice higher lateral conductivity on the air- respect to the argon-SnS thin films. In this way, the different atmospheric exhibit a profound impact on the physical, morphological and structurally orientated properties of the SnS grains. These results demonstrate that photovoltaic grade p-type SnS films can be deposited in air without the need of an inert gas atmosphere which opens the way to a cost reduction in the fabrication of SnS-based photovoltaic devices.