Event Details

The remarkable success of organic-inorganic Pb-halide perovskites as solar absorbers has drawn attention towards a broader family of ionic semiconductors having fascinating optoelectronic properties. Many of these compounds have favorable characteristics in terms of their band gap, carrier mobility, lifetime, and tolerance towards deleterious effect of deep defects. The crystals, loosely termed as perovskites, encompass a large group of structures built from metal-halogen octahedral framework, [MX6] (M = metal, X = halogen) that may lead to interesting properties and applications. Here, we will discuss the structure-property relation of CH3NH3PbI3 (MAPbI3) as representative of hybrid perovskites and Cs4PbBr6/CsPbBr3 as that of the all-inorganic variety. The hybrid halides feature organic cations whose molecular orientations clearly influence the fundamental electronic band gap and Rashba-type energy band splitting resulting in indirect gap behavior. Among the all-inorganics, highly luminescent CsPbBr3 nanocrystals and Cs4PbBr6/CsPbBr3 composite crystals have been reported as bright green emitters with fast radiative lifetime. CsPbBr3 (band gap ~2.3 eV) is built from corner sharing 3-dimensional (3D) network of [PbBr6], whose bulk crystals are not known as efficient light emitters. Cs4PbBr6 structure is comprised of almost disjointed [PbBr6] octahedra held together by Cs-Br bridges. Using density functional calculations, we will discuss the electronic consequences of the two different crystal structures. The emergence of strongly bound excitonic features in Cs4PbBr6 and Type-I band alignment with CsPbBr3 support the notion of carrier confinement causing fast, green luminescence in samples containing CsPbBr3 nano-islands embedded within Cs4PbBr6.