Hybrid lead halide DMAPbX3 hexagonal perovskites

Article: Hybrid lead halide [(CH3)2NH2]PbX3 (X = Cl- and Br-) hexagonal perovskites with multiple functional properties

Hybrid lead halide DMAPbX3hexagonal perovskites with multiple functional properties

We have been able to prepare two new lead halides with the formula DMAPbX3 (where DMA is dimethylammonium and X is Cl- and Br-), which display a 4H-hexagonal perovskite polytype, an unusual crystal structure in hybrid organic–inorganic perovskites. Both compounds experience a first-order phase transition, the chloride at ∼320 K and the bromide at ∼250 K, which involves two cooperative processes: an off-center shift of the lead cations and an order-disorder process of the DMA cations. Additionally, a sharp dielectric transition is associated with this structural transition in both hybrids. Both compounds are semiconductors with band gap values of 3.5 eV (X: Cl- ) and 3.0 eV (X: Br-). Also, the LT-phase of the Br- compound displays a broad red light photoluminescence (PL) emission (620 nm) and PLE excitation with the maximum at a soft UV wavelength (360 nm). This broadband emission and large Stokes-shifted PL seem to be related to a self-trapped exciton mechanism. Therefore, the uncommon 4H-hexagonal perovskite is a promising crystal structure for understanding and designing new hybrid materials with broad photoluminescent emission and dielectric properties.

The pseudopotentials used with the Siesta program can be downloaded here.