In this talk, I will discuss the employment of state-of-the-art electronic structure theory for the modelling of novel perovskite-like materials within the Ag/Bi double salt and the vacancy ordered double perovskite (VODP) lattices. I will first discuss the case of halide double perovskites, and explore the link between the type and position of the atomic orbitals in the crystal and their electronic structure, and connect this established structure with the so-called rudorffites or Ag/Bi double salts. I will demonstrate the necessity of proper modelling of these, and present a symmetry-based method we developed [1], which correctly describes the exhibited electronic and optical properties of AgBiI₄, a prototypical material. I will employ this to probe other materials within the same family of double-salts, and further use the model to investigate the ideal (i.e., maximum limits) photovoltaic properties that these materials could achieve. In the second part, I will thoroughly analyze the properties of the VODP family of materials by employing state-of-art ab initio calculations and unveil key details of the electronic structure and the effects of electron-hole coupling on the optical properties [2]. I will discuss prototypical VODP structures by selecting members based on the electronic configuration of the tetravalent metal at the B-site (e.g. Sn, Te, Zr). I will go through their structural properties, and show that the size of the vacant site, can be tuned solely by the halogens. The electronic structures are investigated within the GW many-body green’s function method, and we obtain band-gaps spanning a range of 1.5-5.0 eV at G₀W₀. More importantly, the optical and excitonic properties of these compounds are probed within the independent particle approach, and by solving the Bethe-Salpeter equation (BSE). The exciton binding energies and dark-bright exciton exchange splitting are calculated for each type of VODP. Finally, the excitonic fine structure is unveiled by performing a complete symmetry analysis of the compound’s band structure and excitonic wavefunctions, on which a direct link between these and the metal site species is established. Overall, here I comment on the suitability and the prospect of the application in opto-electronics of Ag/Bi double salts, like AgBiI₄, and VODP, like Cs₂TeBr₆, might exhibit. I will identify the most and least promising materials that could act as photo-active materials or for selective charge transport layers, for light-emitting and solar-cell applications.