 The study reports a model for molecular orientation disorder in CH3NH3PBI3, which uses electronic structure calculations and a binitio-molecular dynamics to investigate temperature and electric field dependence of the equilibrium ferroelectric domain structure and resulting polarisability. A rich domain structure of twinned molecular dipoles is observed, and it is proposed that internal electrical fields associated with microscopic polarization domains contribute to hysteretic anomalies in the current voltage response of hybrid organic and organic parafskite solar cells due to variations in electron hole recombination in the bulk. This article was authored by Jarvis M. Frost, Keith T. Butler and Aaron Walsh.