Abstract
Despite the swift surge of lead halide perovskites, research in dye-sensitized solar cells (DSCs) has continued over the last few years, with a steady increase in record device efficiencies. A major requisite of an efficient solar cell sensitizer is that of showing an extended UV/Vis absorption spectrum closely matching that of solar radiation. This has given rise to what we call here the hunt for red photons, and ab initio computational modeling plays a major role in designing and screening new dyes with tailored characteristics. In this microreview, we highlight recent developments in modeling transition metal polypyridyl dyes by means of advanced ab initio simulations, including solvation and relativistic effects. We illustrate the molecular design rules that have led to the best performing ruthenium and osmium dyes to date, showing the information which can be extracted from ab initio simulations and how to exploit such information for engineering novel dye candidates.