Insights into kesterite's back contact interface: A status review

Recently, kesterite-based thin film solar cells (TFSCs) gained significant attention in the photovoltaic (PV) sector for their elemental earth abundancy and low toxicity. The emerging kesterite-based Cu2ZnSn(S,Se)4 (CZTSSe) TFSCs have gained a steady rise to the record power conversion efficiency (PCE) of 12.6%, which is still significantly lower than its predecessor chalcopyrite Cu(In, Ga)Se2 (CIGS) TFSCs. Relatively the low device efficiency in kesterite-based TFSCs is mainly observed due to the instability of back interface during the high temperature thermal annealing (HTTA) process. During the HTTA process the detrimental reactions at Mo/absorber create unsolicited defects like MoS(e)2 layer, secondary phases and voids which consequently reduce the device efficiency. The present review offers some deep insights of the back-contact interface and interface related defects, besides different solutions to overcome these defects in detail. The interfacial-defects like the formation of MoS(e)2 layer, secondary phases and voids at Mo/absorber interface are conversed broadly with their respective reaction mechanism. Moreover, the plausible band theory of back contact interface in the presence of interfacial MoS(e)2 layer and the criteria for ideal back contact are also addressed. In conclusion, this review envisions the contests and perception for achieving high efficiency in kesterite based TFSCs by signifying an improvement in back interface related defects.