Synthesis and conductivity mapping of SnS quantum dots for photovoltaic applications

Quantum dots (QDs) are considered a possible solution to overcome the Shockley–Queisser efficiency limit of 31% for single junction solar cells by efficiently absorbing above band gap energy photons through Multiple Exciton Generation (MEG) or sub band gap energy photons using an Intermediate Band Solar Cell structure (IBSC). For the latter absorption process, we consider tin sulphide (SnS) as a promising candidate, having several advantages compared to the other nanoparticles studied extensively so far, such as CdS, CdSe, PbS, and PbSe; namely it is non-toxic and environmentally benign and thus will be most suitable in consumer products such as solar panels. In this work we propose a new colloidal synthesis method for SnS QDs. We have obtained mono-dispersive SnS and SnS/In2S3 core–shell nanoparticles with a size of ~4 nm. Energy dispersive X-ray spectroscopy (EDX) elemental analysis revealed that the particles are indeed SnS and not SnS2. Furthermore, the conductive nature of the nanoparticles has been inferred by conductivity mapping using a relatively new contactless technique, Torsional Resonance Tunneling AFM (TR-TUNA). These results confirm that the SnS QDs possess all the requirements to be applied as photoactive layers in photovoltaic devices.