Highly efficient emerging Ag₂BaTiSe₄ solar cells using a new class of alkaline earth metal-based chalcogenide buffers...

Cu₂ZnSn(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, Ag₂BaTiSe₄ 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 Ag₂BaTiSe_4, MoSe₂, 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, 10¹⁸ cm^-3, 10¹⁵ cm^-3 respectively, underscoring the promising nature of Ag₂BaTiSe₄ absorber and new alkaline earth metal chalcogenide buffers in photovoltaics.