Perovskite solar cells (PSCs) show unprecedented levels of efficiency for such easy to process solar cells, and are higher than those of most common, but more expensive, silicon cells. They have an excellent potential to provide low-cost solar electricity. Spectacular impact is expected but is hindered by poor stability of the perovskite phase and concerns about the use of lead and especially its potential release into the environment. Lead is also a relatively highly regulated element. In this proposal, our team of leading chemists, materials scientists, device physicists and theorists, will address these issues through an integrated collaborative study. Building on our previous work we will improve the understanding of the key mechanisms responsible for PSC degradation, by exploring new perovskites, morphologies and stabilisation by the use of additives. The link between defects (structural imperfections) and PSC performance/stability will be investigated experimentally and using state-of-the-art modelling techniques. The approach will provide a sound basis for predictive guidelines for perovskite formulation to enable stable environmentally benign, inexpensive PV units for mass use. Among the most intriguing aspects of perovskite materials are the high efficiency of charge pair photo-generation and the long lifetime of these charges. We will use new ultrafast timescale spectroscopic techniques to obtain new insights concerning the dynamics of the perovskite photo-excited states. We will address issues of potential heavy metal contamination, in the event of PSC failure (and water ingress) by studying new lead-free perovskites as well as by developing new heavy metal self-scrubbing scaffolds within lead- and tin-containing PSCs. A new aerosol-assisted film deposition approach for fabrication of large area, high performance, stable and environmental safe PSCs will result. Our ambition is to provide prototype environmentally safe, demonstration, large area PSCs with enhanced operational stability that could be mass produced and have power conversion efficiencies exceeding 20%. A successful outcome to this project would provide improved fundamental understanding of the interplay between perovskite composition and device performance and new PSCs that would bring about the large-scale deployment of perovskite photovoltaics for CO2-free electricity generation closer.