"Tuning Optical and Electronic Properties in Low-Toxicity Organic–Inorganic Hybrid (CH3NH3)3Bi2I9 under High Pressure"

Long Zhang: Chunming Liu, Yu Lin, Kai Wang, Feng Ke, Cailong Liu, Wendy L. Mao and Bo Zou; The Journal of Physical Chemistry Letters, 03/25/19.

Additional Authors: Chunming Liu, Yu Lin, Kai Wang, Feng Ke, Cailong Liu, Wendy L. Mao and Bo Zou

Abstract:

Low-toxicity, air-stable methylammonium bismuth iodide (CH3NH3)3Bi2I9 has been proposed as a candidate to replace lead-based perovskites as highly efficient light absorbers for photovoltaic devices. Here, we investigated the effect of pressure on the optoelectronic properties and crystal structure of (CH3NH3)3Bi2I9 up to 65 GPa at room temperature. We achieved impressive photoluminescence enhancement and band gap narrowing over a moderate pressure range. Dramatic piezochromism from transparent red to opaque black was observed in a single crystal sample. A structural phase transition from hexagonal P63/mmc to monoclinic P21 at 5.0 GPa and completely reversible amorphization at 29.1 GPa were determined by in situ synchrotron X-ray diffraction. Moreover, the dynamically disordered MA+ organic cations in the hexagonal phase became orientationally ordered upon entering into the monoclinic phase, followed by static disorder upon amorphization. The striking enhancement of conductivity and metallization under high pressure indicate wholly new electronic properties.