Structure-property relations in organic/inorganic perovskite hybrids

The organic/inorganic perovskite hybrid CH₃NH₃PbI₃ belongs to the group of organic/inorganic hybrid materials that consist of organic cations and metal halides that have attracted much attention as efficient absorber materials in planar heterojunction solar cell devices. Very high power-conversion efficiencies of up to 20.1% have been reported for lead iodide-based materials. In addition to solar light conversion, other optoelectronic applications of this class of materials have recently been reported owing to their outstanding optical properties. Light emitting diodes, lasers and photodetectors have extended not only the scope of these materials but also the spectrum of interesting band gaps. We synthesize high-quality single crystals of organic/inorganic perovskite hybrids and tune the chemical composition by substitutions of the organic and inorganic part. Using X-ray diffraction techniques, we study the crystal structure in great detail and investigate structure-property relations in these materials. The objective of our research is to provide insight into how chemical substitutions allow for direct tuning of the physical properties that are of interest for optoelectronic applications.

In recent work, we show how bismuth-based organic/inorganic perovskite hybrids are non-toxic, air-stable and high dielectric constant alternatives for lead-based organic/inorganic hybrid photovoltaic devices. We investigate the polar nature of methylammonium bismuth iodide and show how dipolar ordering of the methylammonium cation at lower temperature gradually converts the hexagonal structure into a monoclinic phase, while the phase transition at 143K is governed by in-plane ordering of the bismuth lone pair. The decoupled ordering of the bismuth lone pair and of the methylammonium dipole gives access to different functionalities associated with both polar and non-polar states.

In our recent work on low-dimensional phenylalkylammonium lead iodide perovskite hybrids, we show how confinement effects are responsible for peak shifts in photoluminescence for the different phenylalkylammonium lead iodide hybrids. Our results show how the connectivity of the octahedra leads to confinement effects that directly tune the optical band gap.