23 October 2014
Venue: GO Jones Room 410
In recent years, some of the organic-inorganic "hybrid" perovskites (OIPs) have been discovered to be efficient photovoltaics. However, there is a wide variety of structural tunability and behaviour that could be of future interest in improving devices, which remains unexplored by device makers. OIPs combine the well-known perovskite and "perovskite-like" structure types with amine-based molecular cations. Their phase diagrams combine effects from the Rigid Unit Mode/tilt instabilities of the inorganic framework and layer structures with molecular order-disorder of the cations, and stereoactive s2 lone pairs on the metals; the two sublattices interact via hydrogen bonding in the ordered phases. OIPs show some extreme structural properties; e.g., (i) in their ordered phases, they have some of the most distorted octahedra reported in perovskites; (ii) they are also "the most compressible perovskites known.". The low energy penalty for re-orienting a cation may be of interest in reports of what appears to be ferroelectric effects in thin films.