DOI: https://doi.org/10.29363/nanoge.almips.2021.010
Publication date: 23rd September 2021
Among several intriguing properties of soft lead halide perovskite crystals, viscoelasticity describes well the mechanical response of the material. In this work we show a close connection between viscoelasticity and trap dynamics in lead halide perovskites. We studied PL fluctuation kinetics of MAPbI3 sub-micrometer crystals employing statistically correct power spectral density (PSD) estimation method which reveals 0.5-10 s as the working timescale of the intrinsic PL quenchers. This is also the maximal timescale of the reversible trap activation and deactivation in these crystals. Among many popular semiconductor materials (e.g., conjugated polymers, traditional quantum dots) only halide perovskites are found to possess such characteristic timescale which matches very well with its viscoelastic response time. Super-resolution Localization analysis demonstrates that this timescale is intrinsic to the material and polycrystalline nature of the microcrystals has negligible effect on it. Moreover, we reveal presence of photoinduced nonradiative recombination channels which work in faster timescale (>0.3 s).
In a film, grains and crystallites are spatially close or interconnected through grain boundaries. Consequently, carrier recombination and trap dynamics are found to be even more complex than that of an isolated crystal. We developed an advanced mapping method based on correlation of the PL signal to identify different regions in a film having variation in recombination behavior. Direct comparison of the PL fluctuation of each cluster in the map with electron microscopy image provides important insight about microscopic domains of the nonradiative traps. PSD of the PL fluctuation reveals that a large fraction of spatially isolated clusters has common timescale of fluctuation (0.3 s) which is again closely matching with the viscoelastic response time of the material.
This work was supported by the Swedish Research Council (2020-03530), Knut and Alice Wallenberg foundation (2016.0059) and postdoctoral scholarship from Wenner-Gren foundation (UPD2019-0230).
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