Investigation of SnS thin film as a BSF layer in Cu2ZnSnS4-based solar cells: a strategy to improve efficiency using SCAPS-1D

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Résumé

Photovoltaic devices based on the quaternary material Copper-Zinc-Tin-Sulfide (Cu2ZnSnS4) commonly called CZTS have shown promising conversion efficiency in the last decade. However, this conversion efficiency still remains below expectations due to several factors including the high recombination rate at the CZTS/Mo rear contact. Indeed, this high recombination process at the rear contact is due, on the one hand, to the appearance of a MoS2 layer caused by the reaction between sulfur (S) from the CZTS and Mo, and, on the other hand, to the presence of voids in the lower part of the CZTS absorber, caused by the volatilization of sulfur (S) from the CZTS absorber for high sulfurization temperatures. In this study, a numerical simulation of the architecture of Al:ZnO/i–ZnO/n–CdS/p-CZTS/SnS/Mo photovoltaic device was carried out to investigate the effect of the Tin Sulfide (SnS) as a Back Surface Field (BSF) layer on the overall performance of CZTS-based solar cells. Thus, using Solar Cell Capacitance Simulator in one dimension (SCAPS-1D), the thickness, bandgap energy and the Acceptor density (NA) of the p-SnS layer were varied to observe their effects on the performance of the CZTS solar cell. In addition, the band alignments at the Mo/SnS/CZTS interface were analyzed to elucidate the impact of this layer on the transport properties of photogenerated charges. The results show that the insertion of a 30 nm thin SnS BSF layer, with a band gap of 1.30 eV and doping greater than 1016 cm􀀀 3 is ideal for boosting the efficiency of the CZTS cell from 7.0% to 13.33%. This improvement in device performance shows that SnS BSF layer can reduce carrier recombination processes at the CZTS/Mo back contact. Incorporation of SnS BSF layer gives the best conversion efficiency (η) of 11.17% followed by fill factor (FF) of 74.2%, and open circuit voltage (VOC) of 0.97V, but a low short circuit current density (JSC) of 16.65 mA/cm2 with an ultrathin 600 nm CZTS layer thickness.
The novelty in this work is that for the first time with the SnS BSF layer, 11.17% conversion efficiency is reported at 600 nm CZTS layer thickness that’s avoid material waste, reduce manufacturing costs and consequently reduce the price of CZTS solar cells and make them more competitive in the photovoltaic market.

Mots-clés

Solar cells, Cu2ZnSnS4, Back surface field, SnS, SCAPS-1D