This work deals with the soda-lime glass/Mo/Cu2ZnSnSe4/CdS/ZnS/i-ZnO/ITO solar cells. CdS/ZnS bilayers were synthesized by chemical bath deposition (CBD) method as buffer layers for Cu2ZnSnSe4 (CZTSe) solar cells. The depositions were carried out by varying the deposition time of the CdS film, while keeping the deposition time of the ZnS film constant. The devices went from 7.2% efficiency in a reference device using CdS to 10% in a device including a thin film of ZnS. All devices were processed without any additional annealing treatment on CdS/ZnS layers. J–V, EQE, SEM, Raman, and C–V characterizations were performed to investigate the properties of the solar cells as a function of the thickness of the CdS layer and to shed light on the origin of influence of the ZnS layer to the device performance. Moreover, the influence of physical properties of the buffer bilayers on the electrical parameters of the solar cells are discussed by means of numerical simulation.

Tin sulfide (SnS) semiconductor has recently attracted a great deal of attention from the scientific community regarding its application in solar cells. However, SnS solar cell efficiencies are still limited to less than 5%. The incorporation of nanostructures into solar cells has been demonstrated to be a potential route to improve device performance. So far, there have been no reports on the incorporation of nanostructures into SnS solar cells. In this work, a theoretical study on the incorporation of tin sulfide selenide (SnSSe) nanostructures in the form of quantum wells (QWs) into SnS solar cells under the radiative limit is presented, for the first time. In particular, the impact of well number, well thickness, and Se/(S + Se) compositional ratio at the wells, on solar cell characteristics, is evaluated. An efficiency enhancement of 11.1% is found for a SnS/SnSSe QW solar cell, compared to the optimized device without nanostructures, for 50 wells of 54 nm width with a Se/(S + Se) well composition of 0.4 and considering barrier thicknesses of 5 nm, which is a result of the increase in short-circuit current density of 14.5%. The influence of defects at wells and barriers, as well as defects at interfaces, on solar cell behavior is also presented, demonstrating that the introduction of QWs can result in higher efficiencies than that of the device without nanostructures. In this sense, the addition of SnSSe nanostructures to SnS solar cells is introduced as a potential route to promote the absorption of photons with energy lower than the SnS band-gap, while keeping open-circuit voltage values similar to those of a SnS solar cell without nanostructures, thereby increasing solar cell efficiency.

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This work presents current advances and perspectives on SnSe thin film solar cell technology. Nowadays, SnSe solar cells have not been able to achieve efficiency values higher than 7%. In this sense, it is necessary to study the potentiality of SnSe compound in solar cells that could help to understand further routes to promote this technology. It is demonstrated that efficiencies about 25% are expected under the ideal conditions of a low density of defects at SnSe bulk, the SnSe/buffer interface and the use of a buffer layer with a high band-gap, so that most photons get absorbed in the SnSe material with a good lattice matching to the SnSe and the negligible contribution of resistances. The comparison of our results with the one experimentally reported demonstrates that Jsc values constitute the first main issue to be solved in this technology.