 Paravskite solar cells have recently achieved 15% conversion efficiency for small area devices, but the fundamental properties of their active absorber layers are largely unknown, and they are semiconductors with direct band gaps at the first Brillouin zone boundary. Their calculated dielectric constants and band gaps show orientation dependence, and a photophoroic effect may be accessible due to the electric dipole of the methyl ammonium cation. This article was authored by Federico Brivio, Allison B Walker and Aaron Walsh.