Highly efficient emerging Ag ₂BaTiSe ₄ solar cells using a new class of alkaline earth metal-based chalcogenide buffers alternative to CdS

Abstract

Cu ₂ZnSn(S,Se) ₄ is a non-toxic, earth-abundant photovoltaic absorber. However, its efficiency is limited by a large open circuit voltage (V _OC) deficit occurring due to its antisite defects and improper band alignment with toxic CdS buffer. Therefore, finding an absorber and non-toxic buffers that reduce V _OC deficit is crucial. Herein, for the first time, Ag ₂BaTiSe ₄ is proposed as an alternative absorber using SCAPS-1D wherein a new class of alkaline earth metal chalcogenide such as MgS, CaS, SrS, and BaS is applied as buffers, and their characteristics are compared with CdS to identify their potential and suitability. The buffer and absorber properties are elucidated by tuning their thickness, carrier concentration, and defect density. Interestingly, optimization of the buffer’s carrier concentration suppressed the barrier height and accumulation of charge carriers at the absorber/buffer interface, leading to efficiencies of 18.81%, 17.17%, 20.6%, 20.85%, 20.08% in MgS, CaS, SrS, BaS, and CdS-based solar cells respectively. Upon optimizing Ag ₂BaTiSe _4, MoSe ₂, and interface defects maximum efficiency of > 28% is achieved with less V _OC loss (~ 0.3 V) in all solar cells at absorber’s thickness, carrier concentration, and defect density of 1 µm, 10 ¹⁸ cm ⁻³, 10 ¹⁵ cm ⁻³ respectively, underscoring the promising nature of Ag ₂BaTiSe ₄ absorber and new alkaline earth metal chalcogenide buffers in photovoltaics.