Organo-halide lead perovskites are revolutionizing the photovoltaic scenario, with efficiencies exceeding 15%. The orientational dynamics disorder of the methylammonium cations (MA) is one of the most peculiar features of these materials. Here, we perform ab initio molecular dynamics simulations and IR spectroscopic measurements on lead halide hybrid perovskites to elucidate the rotational motion of the MA cations in these systems and its effects on the structural and electronic properties of hybrid perovskites. In the investigated time frame, the MA cations are found to rotate within the inorganic framework on a timescale of a few ps. A variation of ±0.1 to 0.2 eV of the electronic properties with the ion dynamics is found, which increases upon increasing the temperature.

Real-time stimulation and recording of neural cell bioelectrical activity could provide an unprecedented insight in understanding the functions of the nervous system, and it is crucial for developing advanced in vitro drug screening approaches. Among organic materials, suitable candidates for cell interfacing can be found that combine long-term biocompatibility and mechanical flexibility. Here, we report on transparent organic cell stimulating and sensing transistors (O-CSTs), which provide bidirectional stimulation and recording of primary neurons. We demonstrate that the device enables depolarization and hyperpolarization of the primary neuron membrane potential. The transparency of the device also allows the optical imaging of the modulation of the neuron bioelectrical activity. The maximal amplitude-to-noise ratio of the extracellular recording achieved by the O-CST device exceeds that of a microelectrode array system on the same neuronal preparation by a factor of 16. Our organic cell stimulating and sensing device paves the way to a new generation of devices for stimulation, manipulation and recording of cell bioelectrical activity in vitro and in vivo.

The dynamic evolution of the vibrational interactions in the prototypical CH NH PbI was studied through a comprehensive experimental and theoretical investigation with a focus on the interactions between the organic cations and the inorganic cage. To date, no clear picture has emerged on the critical and fundamental interactions between the two perovskite components, despite the relevance of phonons to the electronic properties of several classes of perovskites. For the first time, we have monitored the IR and nonresonant Raman response in the broad frequency range 30-3400 cm and in the temperature interval 80-360 K. Strong changes in the energies of different vibrational modes with temperature are observed and examined in the framework of phonon-phonon interactions considering a significant anharmonic contribution to the phonon relaxation process. The vibrational relaxation of the bending modes and their reorientation activation energies identify that such mechanisms are governed by medium-to-strong hydrogen bonds in the orthorhombic phase; however, any ferroelectric ordering in the orthorhombic phase is governed mostly by dipole interactions. These changes imply that charge localization mechanisms play a primary role, and our study enriches the fundamental knowledge of phonon interactions and charge transport in CH NH PbI for the further development of optoelectronic applications.