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

Cu2ZnSn(S,Se)4 is a non-toxic, earth-abundant photovoltaic absorber. However, its efficiency is limited by a large open circuit voltage (VOC) 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 VOC 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 Ag2BaTiSe4, MoSe2, and interface defects maximum efficiency of > 28% is achieved with less VOC 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.