Solar cells based on the wide band-gap Cu 2 BaSnS 4 (CBTS) photoabsorber have achieved open circuit voltages up to 1.1 V over a short development period, making CBTS an attractive material for tandem photovoltaic and photoelectrochemical cells. In this work, we explore an alternative CBTS growth route based on oxide precursors, and we propose TaS 2 as an alternative back contact material to the commonly used Mo/MoS 2 . The oxide precursor route does not require higher sulfurization temperatures than other more common fabrication routes, and it yields CBTS lms with negligible Stokes shift between photoluminescence maximum and band gap energy, while at the same time avoiding sulfur contamination of vacuum systems. The high work-function metallic TaS 2 compound is selected as a prospective hole-selective contact, which could also prevent the losses associated with carrier transport across the semiconducting MoS 2 layer. By comparing CBTS solar cells with Mo and TaS 2 back contacts, the latter shows 1 Page 1 of 29 ACS Paragon Plus Environment ACS Applied Energy Materials a signicantly lower series resistance, resulting in a 10% relative eciency improvement.Finally, we fabricate a proof-of-concept monolithic CBTS/Si tandem cell using a thin Ti(O,N) interlayer intended both as a diusion barrier and as a recombination layer between the two subcells.