Solar cell simulations have become an essential tool for the design of more efficient types of photovoltaic devices. However, it is not widely known that in principle, the simulation of a solar cell can be done entirely on a computer, starting from a fundamental atomistic level and ending up with an accurate prediction of the J-V characteristics of the final device. We will illustrate the use of ab initio methods to study fundamental light-matter interactions, and we will point out how to combine these methods with simple model approaches and state-of-the-art device simulations to obtain powerful numerical tools that may be used alongside experimental studies. Being work in progress, the suggested approaches are marked by a variety of open technical problems, but they also provide interesting new opportunities to develop more accurate types of solar cell device simulations.