Abstract
AbstractHalide 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. Laser excitation during photoluminescence (PL) microscopy experiments leads to formation and subsequent migration of ionic defects, which affects the dynamics of charge carrier recombination. From the microscopic observation of lateral PL distribution, the change in the distribution of ionic defects over time can be inferred. Resolving the PL dynamics in time and space of single crystals and thin films with different grain sizes thus, provides crucial information about the influence of grain boundaries on the ionic defect movement. In conjunction with experimental observations, atomistic simulations show that defects are trapped at the grain boundaries, thus inhibiting their diffusion. Hence, with this study, 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.
Highlights
Halide perovskites have rapidly become an attractive class of materials for optoelectronic applications, including photovoltaics,[1] light-emitting diodes (LEDs),[2] light detection,[3] and energy storage.[4]
With the support of atomistic simulations, we conclude that the grain boundaries (GBs) inhibit the lateral movement of defects in the material, i.e., their spreading across the sample, which we demonstrate with devices comprised of perovskite absorbers of different grain sizes
By analyzing the lateral evolution of PL intensity in thin films and single crystals induced by a focused excitation beam, we conclude that grain boundaries inhibit ion movement
Summary
Halide perovskites have rapidly become an attractive class of materials for optoelectronic applications, including photovoltaics,[1] light-emitting diodes (LEDs),[2] light detection,[3] and energy storage.[4]. Others and some of us have observed a reduction in hysteresis for devices containing an absorber layer with larger grain size.[19,20] It was concluded from intensity-modulated photocurrent spectroscopy that ionic defect movement is faster when the number of GBs is reduced,[19] which points to GBs inhibiting their migration. Another recent report has shown that even though mobile ions is a prerequisite for hysteresis, the trapping and detrapping of ionic defects plays an important role for slow transients seen in devices.[21]. Our study gives a broader understanding of how ionic defect migration in halide perovskite relates to the microstructure of the material
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