The optoelectronic properties of hybrid perovskites can be easily tailored by varying their components. Specifically, mixing the common short organic cation (methylammonium (MA)) with a larger one (e.g., butyl ammonium (BA)) results in 2-dimensional perovskites with varying thicknesses of inorganic layers separated by the large organic cation. In both of these applications, a detailed understan...

A Ruddlesden-Popper (RP) type structure is well-known in oxide perovskites and is related to many interesting properties such as superconductivity and ferroelectricity. However, the RP phase has not yet been discovered in inorganic halide perovskites. Here, we report the direct observation of unusual structure in two-dimensional CsPbBr3 nanosheets which could be interpreted as the RP phase base...

Long carrier lifetime is what makes hybrid organic-inorganic perovskites high-performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation ...

Here, we report the presence of defect-related states with magnetic degrees of freedom in crystals of LaAlO3 and several other rare-earth based perovskite oxides using inelastic light scattering (Raman spectroscopy) at low temperatures in applied magnetic fields of up to 9 T. Some of these states are at about 140 meV above the valence band maximum while others are mid-gap states at about 2.3 eV...

The pressure to move towards renewable energy has inspired researchers to look for ideas in photovoltaics that may lead to a major breakthrough. Recently the use of perovskites as a light harvester has lead to stunning progress. The power conversion efficiency of perovskite solar cells is now approaching parity (>22 %) with that of the established technology which took decades to reach this lev...

Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials. The key to the functional electronic properties exhibited by perovskites is often the so-called Jahn-Teller distortion. For applications, an electrical control of the Jahn-Teller distortions, which is so far out of reach,...

The performance of solar cells based on hybrid halide perovskites has seen an unparalleled rate of progress, while our understanding of the underlying physical chemistry of these materials trails behind. Superficially, CH3NH3PbI3 is similar to other thin-film photovoltaic materials: a semiconductor with an optical band gap in the optimal region of the electromagnetic spectrum. Microscopically, ...

Using density functional theory calculations, we investigate the feasibility of using silver on the perovskite A-site in high-performance lead-free piezoelectrics. The calculations show that silver atoms are ferroelectrically active and can off-center by 0.5 Å. To induce Ag ferroelctric behavior absent in pure AgNbO3 we explore solid solutions of AgNbO3 with well-known simple perovskites PbTiO3...

We developed lead halide perovskite quantum dot (QD) films with tuned surface chemistry based on A-site cation halide salt (AX) treatments. QD perovskites offer colloidal synthesis and processing using industrially friendly solvents, which decouples grain growth from film deposition, and at present produce larger open-circuit voltages (VOC's) than thin-film perovskites. CsPbI3 QDs, with a tunab...

Applications of computer-based group-theoretical methods to perovskite crystallography are reviewed. Such methods furnish a systematic account of the effects on the high-symmetry parent structure of diverse distortions. New results are presented for elpasolites (ordered double perovskites) when both ferroelectric cation displacement and simple octahedral tilting are allowed. Group-theoretical r...