The Role of Grain Boundaries in Charge Carrier Dynamics in Polycrystalline Metal Halide Perovskites

Boundaries of perovskite grains forming polycrystalline films are the most sensitive place for the formation of the defect states and accumulation of impurities. The intra-bandgap states located at the boundaries forming traps for charge carriers are commonly discussed as causing nonradiative carrier recombination and reducing carrier mobility. Grain boundaries (GB) may also disturb carrier motion by creating scattering centres and barriers, however, their role was less frequently considered. On the other hand, grain boundaries may also facilitate the splitting of exciton states and the generation of free charge carriers. Consequently, the grain boundaries are responsible or affect a wide range of perovskite properties and processes strongly influencing the performance of perovskite-based optoelectronic devices. Nevertheless, abundant literature data related to the properties of grain boundaries and their influence are highly controversial. In this minireview, we discuss the most importnat literature data related to the structure and properties of grain boundaries and their role in device performance.