In this fun and fast paced course we describe the fundamental structure of solar cells at the atomic level. We explain about p-type and n-type doping and how photons of light create hole-electron pairs. We describe the energy band theory of silicon and give you a detailed explanation of what’s going on inside a cell at Voc and Isc, and how we end up with the familiar I-V curve shape that we all take for granted but don’t really understand. You finally get the real story of why cells lose voltage when they get hot! We finish with a discussion of how local shading results in cells 'dragging down' the curves of unshaded cells, and how the operation of bypass diodes reduces this effect.