Innovative structural engineering of sustainable and environment-friendly Cu2ZnSnS4 solar cell for over 20% conversion efficiency

Abstract

Kesterite Cu<inf>2</inf>ZnSnS<inf>4</inf>(CZTS) thin-film technology has been comprehensively investigated over the last decade as a promising candidate in the field of photovoltaic technologies. However, despite numerous strategies to improve the performance, the efficiencies remain stagnant at around 11%. Poorly optimized absorber/buffer interface, non-absorption of higher wavelength photons, and non-ohmic back contact are the primary reasons for the poor performance of the CZTS solar cell. The authors of this paper propose a cadmium-free buffer layer, multiple quantum wells (MQWs) structure, and a back surface field (BSF) layer to overcome these issues, respectively. In this study, the buffer layer, zinc oxysulfide (Zn[O<inf>1−x</inf>S<inf>x</inf>]) is considered as an alternative to toxic Cadmium Sulfide (CdS) for better band alignment with the CZTS absorber layer. Cu<inf>2</inf>ZnSn(S<inf>x</inf>Se<inf>1−x</inf>)<inf>4</inf> (CZTSSe) is used as a quantum well material in MQWs to increase photon absorption in CZTS solar cells. Tin selenide (SnSe) is used as the BSF layer to reduce the effect of non-ohmic back contact and to improve the open-circuit voltage (V<inf>oc</inf>) of MQW incorporated CZTS solar cells. Detailed analysis and optimization of the modified structure with higher performance are presented. The simulation results obtained provide imperative guidelines for the fabrication of high-efficiency CZTS solar cells using non-toxic and earth-abundant materials. © 2022 John Wiley & Sons Ltd.