Dynamic emission Stokes shift and liquid-like dielectric solvation of band edge carriers in lead-halide perovskites.

Lead-halide perovskites have emerged as promising materials for photovoltaic and optoelectronic applications. Their significantly anharmonic lattice motion, in contrast to conventional harmonic semiconductors, presents a conceptual challenge in understanding the genesis of their exceptional optoelectronic properties. Here we report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals.

Unbalanced Hole and Electron Diffusion in Lead Bromide Perovskites.

We use scanning photocurrent microscopy and time-resolved microwave conductivity to measure the diffusion of holes and electrons in a series of lead bromide perovskite single crystals, APbBr, with A = methylammonium (MA), formamidinium (FA), and Cs. We find that the diffusion length of holes (L ∼ 10-50 μm) is on average an order of magnitude longer than that of electrons (L ∼ 1-5 μm), regardless of the A-type cation or applied bias. Furthermore, we observe a weak dependence of L across the A-cation series MA > FA > Cs.

Infrared Spectroscopic Study of Vibrational Modes in Methylammonium Lead Halide Perovskites.

The organic cation and its interplay with the inorganic lattice underlie the exceptional optoelectronic properties of organo-metallic halide perovskites. Herein we report high-quality infrared spectroscopic measurements of methylammonium lead halide perovskite (CH3NH3Pb(I/Br/Cl)3) films and single crystals at room temperature, from which the dielectric function in the investigated spectral range is derived. Comparison with electronic structure calculations in vacuum of the free methylammonium cation allows for a detailed peak assignment.