Development of the IBC or interdigitated back contact solar cell began in 1976 and it has only recently entered commercial production. With 4 technical papers published in 2012, 1400 in 2015 and over 2000 published in 2016 on the use of perovskite materials for photovoltaic applications, there is hope that 40 years will not elapse before the technology is commercialised. However, many fundamental questions remain as to the detailed understanding of the operation of these perovskite-based PV devices. A complete understanding is not necessary in order to introduce a product into the market and indeed, many years elapsed between the first silicon solar cell from AT&T Bell Labs in 1954 until an electrical model of the junction was available. Oxford PV (OxPV), a University of Oxford spin-out company is endeavouring to commercialise one form of this technology in less than 40 years – perovskite on silicon tandem solar cells which have the potential to exceed the conversion efficiency of the highest performing single junction silicon cells (IBC or HJT).Any new PV technology must meet or exceed key market drivers. These are related to the economics of the manufacturing process at or above 100MW/annum, absolute performance across a range of conditions and of course reliability. Ideally, a complete understanding starting with the fundamental atomic arrangement of the atoms in the material, details of the composition and homogeneity of the deposited thin films is desirable. In order to accelerate the development, the use of appropriate optical and structural models and theoretical calculations that can predict or support the understanding of the various changes in the intrinsic material and its interactions with the surrounding layers is valuable. OxPV collaborates with many research and industrial groups and works with supplier partners to broaden its understanding of these parameters.We will report on some of our findings on non-uniformity at the nano-scale with high spatial resolution, through the use of characterisation techniques such as RBS, neutron diffraction, nano-scale FTIR, electron microscopy and optical modelling. These techniques, along with computational screening, have allowed us to create a reliable and stable device. Long term test data based upon the IEC61646 suite of tests will be presented along with the scaling challenges of 157 mm x 157 mm substrates. Optical models will be used to highlight the annualised energy yield of tandem modules. We will also report on cost of ownership (CoO) models that validate the commercial business case for these silicon perovskite tandem solar cells.