Micellar-Encapsulated Nanocrystals

Halide perovskite nanocrystal can be synthesized through many different approaches. Many of which stop crystal growth by adding ligands at a precise temperature and/or specific timing.

These ligands coordinate themselves towards the surface atoms and therefor stop the ongoing reaction. Controlling critical parameters like the temperature of solvents is mandatory during these methods. Slight deviations can lead to unusable products.

We developed a facile synthesis technique that yields to polymer-encapsulated perovskite nanocrystals, without the need of ligands limiting the crystal size. First, micelles are formed by adding polymers to the solvent. This happens, when the polymer concentration is higher than the critical micelle concentration. Secondly, precursor salts are added separately. Ions from these salts diffuse into the micelles where the crystal is formed.

Crystal size is determined by the size of the polymer micelle. Thirdly, the solution is purified. This is needed because crystals grow not only inside micelles but also in all different sizes and shapes outside of micelles. All steps lead to a chemical equilibrium. That is why parameters like timing or temperature are not so crucial anymore and a high reproducibility can be ensured.

With this technique, we were able to cover the whole visible range with narrow emission spectra. Furthermore, micelle encapsulated nanocrystals are protected from environmentally induced degradation, such that even after 75 days of complete submersion in water photoluminescence can be measured. Additionally, halide ion migration is suppressed and nanocrystal layers of MAPI and MAPBr show Förster resonance energy transfer (FRET). All of these characteristics are very promising for integration into optoelectronic devices.

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Polymer Nanoreactors Shield Perovskite Nanocrystals from Degradation, V. A. Hintermayr, C. Lampe, M. Löw, J. Roemer, W. Vanderlinden, M. Gramlich, A. X. Böhm, C. Sattler, B. Nickel, T. Lohmueller, and A. S. Urban, Nano Lett., 2019, 19, 4928-4933

Doubly Stabilized Perovskite Nanocrystal Luminescence Downconverters, Q. Xue, C. Lampe, T. Naujoks, K. Frank, M. Gramlich, M. Schoger, W. Vanderlinden, P. Reisbeck, B. Nickel, W. Brütting, A. S. Urban, Adv. Optical Mater., 2022, 10, 2102791