Multifunctional Materials by Self-Assembly of Perovskite Nanocrystals

Metal halide perovskite nanocrystals (NCs) have gained much attention in the last years due to their unique optical properties. In particular, cesium lead halide NCs (CsPbX₃, X = Br, Cl and I) present excellent photoluminescence quantum yields and narrow emission line widths. However, CsPbX₃ tend to be unstable under environmental conditions (humidity, UV radiation, water, oxygen, heat, polar solvents...), which limits their viability in long-term applications on an industrial scale. Embedding the CsPbX₃ NCs in a polymer matrix improves their stability while maintaining their optoelectronic properties. In addition, the possibility of creating a micropattern with the polymer matrix allows the development of multifunctional materials, expanding the number of potential applications.^1,2<br/>In this context, breath figures (BF) is a bioinspired, bottom-up approach that allows the creation of honeycomb-patterned porous surfaces with controlled topography and composition in one single step by solvent casting. The surfaces are formed by condensation of micron-sized water droplets and self-assembly of amphiphilic compounds (e.g. block copolymers or surfactants), which migrate towards the interface between the water droplets and the organic polymeric solution. When the experimental conditions are optimized, the surface porosity after the BF approach also provides self-cleaning properties to the material, in agreement with the Cassie-Baxter model.^3,4<br/>We report on the development of a method to prepare nanocomposites by embedding CsPbBr₃ NCs in a polystyrene matrix by BF. As a result, a hierarchically structured, hybrid film with double functionality is obtained in one single step within few seconds: the formation of a well-arranged, honeycomb-patterned porous structure confers the hybrid film with self-cleaning properties while the CsPbBr₃ NCs keep their luminescent behavior within the polymer. This allows to have a film with controlled composition and topography, being an interesting alternative to top-down techniques as lithography, which are more time consuming and require expensive equipment.<br/>This approach has also been applied onto LED lenses demonstrating its applicability in real-life applications. The strategy herein proposed can potentially be extended to other perovskite NCs and other nanomaterials in order to obtain new hybrid coatings with different functionalities, paving the way to multifunctional materials with self-cleaning properties with potential applications in optoelectronics or photovoltaics.<br/><br/>¹Brittman, S. <i>et al.</i> <i>Nano Letters.</i> <b>2018</b>, <i>18</i>, 2747–2750.<br/>² Huang, H. <i>et al.</i> <i>ACS Energy Letters.</i> <b>2017</b>, <i>2</i>, 2071–2083.<br/>³ A. S. de León <i>et al</i>. <i>Journal of Colloid and Interface Science.</i> <b>2015</b>, <i>440</i>, 263–271.<br/>⁴ A. S. de León <i>et al</i>. <i>ACS Applied Materials & Interfaces.</i> <b>2022</b>, <i>14</i>, 20023–20031.