Methylammonium lead halide


Methylammonium lead halides are solid compounds with perovskite structure and a chemical formula of, where X = Cl, Br or I. They have potential applications in solar cells, lasers, light-emitting diodes, photodetectors, radiation detectors, scintillator, magneto-optical data storage and hydrogen production.

Properties and synthesis

The first MALHs to be synthesized were the methylammonium derivatives and. Their potential in the area of energy conversion wasn't realized until decades later.
In the cubic crystal structure the methylammonium cation is surrounded by octahedra. The X ions are not fixed and can migrate through the crystal with an activation energy of 0.6 eV; the migration is vacancy assisted. The methylammonium cations can rotate within their cages. At room temperature the ions have the CN axis aligned towards the face directions of the unit cells and the molecules randomly change to another of the six face directions on a 3 ps time scale.
The solubility of MALHs strongly decreases with increased temperature: from 0.8 g/mL at 20 °C to 0.3 g/mL at 80 °C for in dimethylformamide. This property is used in the growth of MALH single crystals and films from solution, using a mixture of [Methylammonium halide|] and powders as the precursor. The growth rates are 3–20 mm3/hour for and reach 38 mm3/hour for crystals.
The resulting crystals are metastable and dissolve in the growth solution when cooled to room temperature. They have bandgaps of 2.18 eV for and 1.51 eV for, while their respective carrier mobilities are 24 and 67 cm2/. Their thermal conductivity is exceptionally low, ~0.5 W/ at room temperature for.
Thermal decomposition of gives methyl iodide and ammonia.

Applications

MALHs have potential applications in solar cells, lasers, light-emitting diodes, photodetectors, radiation detectors, scintillator and hydrogen production. The power conversion efficiency of MALH solar cells exceeds 19%.

Historic references

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