Our school has a long, rich history in developing characterisation techniques for solar cells. One technology developed at our school has made a particularly big impact: photoluminescence (PL) imaging. In PL imaging, you look at the light emitted from the solar cell under illumination. A PL image is best compared to an X-ray image: it gives you spatially-resolved information on the solar cell's electronic quality, typically in a fraction of a second. By combining various PL images, one can get a spatially resolved image of almost all relevant solar cell parameters, which significantly expedites solar cell development.