Strong interest exists in the development of organic-inorganic lead halide perovskite photovoltaics and of photoelectrochemical (PEC) tandem absorber systems for solar fuel production. However, their scalability and durability have long been limiting factors. In this work, we reveal how both fields can be seamlessly merged together, to obtain scalable, bias-free solar water splitting tandem devices. For this purpose, state-of-the-art cesium formamidinium methylammonium (CsFAMA) triple cation mixed halide perovskite photovoltaic cells with a nickel oxide (NiOx) hole transport layer are employed to produce Field’s metal-epoxy encapsulated photocathodes. Their stability (up to 7h), photocurrent density (–12.1 0.3mAcm 2 at 0V vs.RHE) and reproducibility enables a matching combination with robust BiVO4 photoanodes, resulting in 0.25cm2 PEC tandems with an excellent stability of up to 20h and a bias-free solar-to-hydrogen efficiency of 0.35 0.14%. The high reliability of the fabrication procedures allows scaling of the devices up to 10cm2, with a slight decrease in bias-free photocurrent density from 0.39 0.15mAcm 2 to 0.23 0.10mAcm 2 due to an increasing series resistance. To characterise these devices, a versatile 3D-printed PEC cell was also developed. The modular PEC cell represents an affordable alternative to existing designs and can be easily adjusted for a broad range of samples. Overall, these findings shed further light on the factors required to bring both perovskite photovoltaics and photoelectrocatalysis into large-scale applications, revealing some key aspects for device fabrication, operation and implementation.