Proceedings of nanoGe Spring Meeting 2022 (NSM22)
DOI: https://doi.org/10.29363/nanoge.nsm.2022.092
Publication date: 7th February 2022
Colloidal semiconductor nanocrystals (NCs) are a class of nanomaterials that exhibit intriguing physical properties for application in optoelectronic devices such as solar cells, photodetectors, lasers, and light-emitting diodes (LEDs). Colloidal NCs are typically synthesized with wet-chemistry approaches that require further post-synthesis treatments to tune the properties of the obtained nanomaterial for the desired application. For example, the organic ligands that passivate the NC surface can be replaced by careful surface-engineering via ligands exchange reactions, and ad-hoc purification procedures must be employed to remove impurities in the NC solution which can tamper with the material in solid-state. Post-synthesis treatments are particularly relevant in the case of perovskite NCs CsPbBr3 [1] to improve the photoluminescence quantum yield [2] and device performance [3]. Nevertheless, other types of colloidal NCs benefit from post-synthesis treatments leading to tailored device performance and increased stability [4].
Here, I will show how post-synthesis treatments can be employed to improve the performance of LEDs based on colloidal semiconductor NCs. In the case of perovskite NCs, I will discuss a novel purification process based on fractional freezing of solutions. In fact, we exploited the solubility differences between ligands and NC at low temperatures by precipitating the excess of organics freezing the NC dispersion at -20°C. The obtained LEDs demonstrated a noticeable improvement in performance upon fractional freezing of impurities, achieving an external quantum efficiency up to 8.9%, which is 3 times the maximum EQE obtained with the classical antisolvent approach (EQEmax = 2.4%).
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