Development of SnS/In2S3 Core-shell Nanoparticles for Solar Cell Application

Among the thin film semiconductor materials, chalcogenides based compound semiconductors namely CuInGaSe2 material, have shown the highest efficiency among thin film solar cells, whereas using a simpler compound CuInS2 (CIS) an efficiency over 11% can be achieved. The advantage of the latter type is the possibility to use a low temperature, chemical route and non vacuum deposition process that will decrease the capital expenditure of the solar cell production. The aim of this paper is to further improve the CIS type of solar cells by additional absorption by SnS quantum dots embedded in the n-type In2S3 matrix of a CIS/In2S3 solar cell. SnS nanoparticles (NPs) were synthesized by colloidal route at low temperatures and analyzed by several characterization techniques. Whereas transmission electron microscopy and atomic force microscopy (AFM) imaging conclusively proved quantum dot sized particles (~4 nm) with a narrow size distribution, Torsional Resonance-Tunneling AFM and Peak Force AFM proved the conductive nature of the particles. The chemical composition, studied by energy dispersive X-ray spectroscopy (EDX) showed the ratio S:Sn of 1:1, confirming that the semiconductor is SnS and not any other compound. To passivate the QD surface and protect it from reaction to ambient, core shell structures were made. The SnS nanoparticles (NPs) were immersed in a CBD bath for deposition of In2S3 layers. The formed core/shell SnS/In2S3 nanoparticles were separated by centrifugation and washed with ethanol. The structure of the core-shell SnS/In2S3 NPs has been studied by High Resolution TEM which showed the lattice fringes of the SnS core surrounded by amorphous matrix, tentatively attributed to In2S3. The EDX confirms the presence of the elements expected. The absorption spectra of SnS/In2S3 nanoparticles with increasing time of CBD In2S3 clearly showed increasing band gap, attributed to thicker In2S3 shell. Research on SnS QDs embedded in CIS solar cells is in progress.