There is a great demand for novel opto-electronic materials for use in solar cells and light-emitting diodes (LEDs), as well as applications in medical and technical sensors. Researchers at the Nano-Institute Munich (Chair of Photonics and Optoelectronics, LMU led by Prof. Dr. Jochen Feldmann) are currently investigating the potential of synthetic nanocrystalline semiconductors based on the so-called perovskite lattice, which have already shown great potential as photovoltaic devices. LMU physicist Tushar Debnath is studying how the atoms in perovskite nanocrystals respond to electromagnetic excitation with laser light, using a method that makes it possible to determine how much energy is absorbed or emitted under these circumstances. Both parameters are important for the function of these structures in solar cells and LEDs, respectively.
The perovskite structure was first described for the natural mineral calcium titanate. The atoms in its crystal lattice are organized into octahedral unit cells, and this basic form can be chemically manipulated to create the materials that are currently of great interest for opto-electronic and photovoltaic applications. “These perovskites are synthetic structures, and they differ in fundamental ways from those that occur naturally in minerals,” says Debnath, who works with organometallic halide perovskites. As their name suggests, these are hybrid structures that contain both inorganic and organic constituents. Perovskites in general conform to the chemical formula ABX3. In the present context, A is a positively charged ion (in this case, formamidinium), B is a divalent metal (here, lead) and X is a negatively charged halide anion (either iodide or bromide). In a new paper, Debnath and colleagues demonstrate how these organic and inorganic constituents interact in atomic scale that determines their stability as a function of halide-ion in the perovskite crystal lattice.