Entropic Stabilization of Hybrid Perovskites

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Hybrid perovskites have revolutionized solar research in the past decade. Materials such as MAPI (CH3NH3PbI3) can act as absorber and is also able to separate charge over large distances, and power conversion efficiencies have risen beyond 20% as a result of this. One of the concerns that has troubled researchers is the degradation of the materials in the presence of water via transfer of the methylammonium proton. Approaches that currently exist to depress these effects include the engineering of PKa of the proton at the A site, as well as the replacement of the organic ion with an inorganic ion e.g. Cs+. However, the materials still show varying amounts of instability. However, recently a new paradigm has emerged that has defied the traditional picture of crystalline solids, which is the notion of high entropy materials.These are very different to traditional materials because they utilise increased disorder to minimise their free energy. In simple terms, this is achieved by adding various elements in equivalent amounts to either the cationic or anionic sublattices in the crystalline state to maximise the entropic mixing term, which in turn minimises the free energy of the solid. There are now a number of materials stabilised in this way including metals, metal oxides and metal sulfides and oxysulfides. In this PhD programme we will test the hypothesis that stabilization can be conferred on hybrid perovskites using this approach. We will make thin films of these new materials by both spin coating and CVD, and test their stability vs water using the latest operando XPS techniques. It is envisaged that a new paradigm for stabilization of hybrid perovskite materials will be established.