Optimization of absorber layer for band gap energy moderation of nanostructured SnS thin films

In the present work, band gap energy moderated nanostructured Sn_1−xZn_xS thin film solar cell devices are investigated in details in order to optimize the number of their layers, which can enhance their efficiency. Sn_1−xZn_xS nanostructures were synthesized by simple and cost-effective co-precipitation method and were primarily characterized for the study of their structural and phase purification as well as morphological and optical properties. Structural results confirmed the formation of polycrystalline orthorhombic and hexagonal phase of SnS and ZnS nanostructures, respectively. Morphological studies showed that increasing the Zn concentrations changed the morphology of samples from the rod- to spherical- and hexagonal-like particles. Electrical characterization also presented the highest carrier concentration and conductivity conversion in the Sn_1/2Zn_1/2S sample. Photovoltaic devices were deposited using the ethyl cellulose as a green binder on the transparent substrates and TiO₂ buffer layers. Photovoltaic characterization showed that a sample moderated from low-to-high values of band gap energy and with four layers has better efficiency (3.17%) because of factors such as having a wide broadband range of band gap energy in absorber layer, increase in carrier lifetimes, presence of minor carriers in output current, and an increase in carrier concentration of the moderated layers. This paper also investigates and compares our results with the literature and gives some suggestions for coping with the problems involved in having a high number of layers in the fabricated devices.