Halide perovskites are considered the champions of the next generation of solar cells. However, the instability of their power conversion efficiencies remains an issue. In this context, the EU-funded BOLLA project will couple perovskites with an electrochemical system to produce an inexpensive, solar-driven photo-oxidation water purification system. To that end, it will design a suitable solution-processed Sn–Pb hybrid perovskite material whose chemical composition will be improved to obtain narrow and wide band gap structures. BOLLA will advance the solid-state physics of halide perovskites, illuminating instability mechanisms driven by defects in Sn-containing materials. The project will also develop stable commercial tuneable solar cells and improve the process of removing pollutants from water.