4.8 Article

Elucidating the Role of Antisolvents on the Surface Chemistry and Optoelectronic Properties of CsPbBrxI3-x Perovskite Nanocrystals

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AMER CHEMICAL SOC
DOI: 10.1021/jacs.2c02631

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Colloidal lead-halide perovskite nanocrystals (LHP NCs) have shown promising properties for efficient optoelectronic devices, but their purification is crucial for achieving high performance. In this study, the authors investigated the surface chemistry of purified CsPbBrxI3-x NCs and found that the polarity of the antisolvent used for purification affects the photoluminescence properties of the NCs. Increasing the polarity of the antisolvent led to a blueshift in the photoluminescence peak and a decrease in the photoluminescence quantum yield. The authors proposed that these changes were due to the removal of iodide anions from the NC surface caused by the detachement of oleic acid and oleylamine ligands. This work highlights the importance of carefully selecting low-polarity antisolvents for synthesizing NCs with high photoluminescence quantum yields and minimal phase segregation.
Colloidal lead-halide perovskite nanocrystals (LHP NCs) have emerged over the past decade as leading candidates for efficient next-generation optoelectronic devices, but their properties and performance critically depend on how they are purified. While antisolvents are widely used for purification, a detailed understanding of how the polarity of the antisolvent influences the surface chemistry and composition of the NCs is missing in the field. Here, we fill this knowledge gap by studying the surface chemistry of purified CsPbBrxI3-x NCs as the model system, which in itself is considered a promising candidate for pure-red light-emitting diodes and top-cells for tandem photovoltaics. Interestingly, we find that as the polarity of the antisolvent increases (from methyl acetate to acetone to butanol), there is a blueshift in the photoluminescence (PL) peak of the NCs along with a decrease in PL quantum yield (PLQY). Through transmission electron microscopy and X-ray photoemission spectroscopy measurements, we find that these changes in PL properties arise from antisolvent-induced iodide removal, which leads to a change in halide composition and, thus, the bandgap. Using detailed nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) measurements along with density functional theory calculations, we propose that more polar antisolvents favor the detachment of the oleic acid and oleylamine ligands, which undergo amide condensation reactions, leading to the removal of iodide anions from the NC surface bound to these ligands. This work shows that careful selection of low-polarity antisolvents is a critical part of designing the synthesis of NCs to achieve high PLQYs with minimal defect-mediated phase segregation.

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