Photo de-mixing in mixed halide perovskites: the roles of ions and electrons

Mixed halide perovskites have attracted great interest for applications in solar cells, light emitting diodes and other optoelectronic devices due to their tunability of optical properties. However, these mixtures tend to undergo de-mixing into separate phases when exposed to light, which compromises their operational reliability in devices (photo de-mixing). Several models have been proposed to elucidate the origin of the photo de-mixing process, including the contribution of strain, electronic carrier stabilization due to composition dependent electronic energies, and light induced ionic defect formation. In this perspective we discuss these hypotheses and focus on the importance of investigating defect chemical and ion transport aspects in these systems. We discuss possible optoionic effects that can contribute to the driving force of de-mixing and should therefore be considered in the overall energy balance of the process. These effects include the selective self-trapping of photo-generated holes as well as scenarios involving multiple defects. This perspective provides new insights into the origin of photo de-mixing from a defect chemistry point of view, raising open questions and opportunities related to the phase behavior of mixed halide perovskites.

The effect of ionic defect interactions on the hydration of yttrium-doped barium zirconate

First principles calculations and Monte Carlo simulations reveal the impact of defect interactions on the hydration of barium-zirconate.

Probing the ionic defect landscape in halide perovskite solar cells

Point defects in metal halide perovskites play a critical role in determining their properties and optoelectronic performance; however, many open questions remain unanswered. In this work, we apply impedance spectroscopy and deep-level transient spectroscopy to characterize the ionic defect landscape in methylammonium lead triiodide (MAPbI3) perovskites in which defects were purposely introduced by fractionally changing the precursor stoichiometry. Our results highlight the profound influence of defects on the electronic landscape, exemplified by their impact on the device built-in potential, and consequently, the open-circuit voltage. Even low ion densities can have an impact on the electronic landscape when both cations and anions are considered as mobile. Moreover, we find that all measured ionic defects fulfil the Meyer–Neldel rule with a characteristic energy connected to the underlying ion hopping process. These findings support a general categorization of defects in halide perovskite compounds.

Highly stable inverted methylammonium lead tri-iodide perovskite solar cells achieved by surface re-crystallization

A long-term operational stability over 1000 hours in the inverted type perovskite solar cells based on the MAPbI3 layer is demonstrated under ionic defect-free conditions.

Influence of Ge and Si Doping on the Microstructure and Dielectric Properties of Barium Titanate Ceramics

GeO2 has been doped solely and together with SiO2 into barium titanate ceramics by mixing and calcination. The microstructure and dielectric properties of doped BaTiO3 have been characterized. When doped in BaTiO3, Ge4+ ion could incorporated into the crystal lattice of BaTiO3 to occupied Ti4+ sites. For relative smaller Ge4+ ion, the tetragonal phase could be enhanced. As dielectric properties have strong relation to tetragonal phase. The relative permittivity could be increased in this mechanism. However, the high leakage current which induced by more ionic defect was also lead to high dielectric loss. Besides, the assemble in grain boundary by Ge4+ ion may also have effect. Results on the GeO2-SiO2 co-doped sample showed that the mechanisms of Ge doping and Si doing could happen at one time.