Interaction between Ionic Defects and Grain Boundaries in Metal Halide Perovskites
Simone Meloni a, Nga Phung b, Amran Al-Ashouri b, Alessandro Mattoni c, Steve Albrecht b, Eva L. Unger b, Aboma Merdasa b, Antonio Abate b
a University of Ferrara, Italy, Via Fossato di Mortara, 17, Ferrara, Italy
b Helmholtz Zentrum - Berlin
c CNR -National Research Council
Proceedings of Atomic-level characterization of hybrid perovskites (HPATOM)
Online, Spain, 2021 January 26th - 28th
Organizers: Dominik Kubicki and Amita Ummadisingu
Oral, Simone Meloni, presentation 019
Publication date: 14th January 2021

Halide perovskites are emerging as revolutionary materials for optoelectronics. Their ionic nature and the presence of mobile ionic defects within
the crystal structure have a dramatic influence on the operation of thin-film devices such as solar cells, light-emitting diodes, and transistors. Thin films are often polycrystalline and it is still under debate how grain boundaries affect the migration of ions and corresponding ionic defects. PL dynamics resolved in time and space of single crystals and thin films with different grain sizes put in evidence the empirical correlation between the dynamics of charged defects and the structure of samples, namely the presence and density of grain boundaries. Atomistic simulations show that the interaction between selected grain boundaries and charged defects is due to electrostatic long-range interaction originating from charge polarization at specific grain terminations. This might induce the accumulation of point defects present in crystallites or formed under operation conditions at grain boundaries. Moreover, the selective attraction of specific defects by a grain boundary may help splitting Frenkel pairs formed in solar cells under illumination, thus preventing the quick annihilation of defects and enhancing the effect of light in inducing degradation processes.

With this study [1,2], a comprehensive picture highlighting a fundamental property of the material is provided while also setting a theoretical framework in which the interaction between grain boundaries and ionic defect migration can be understood.

S. M. acknowledges PRACE for awarding him access to Marconi KNL and Marconi 100 at CINECA, Italy, through projects PROVING-IL (2019204911) and University of Ferrara for financial support with the programme FIR

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