White-emitting film of diblock copolymer micelles with perovskite nanocrystals

Abstract

Perovskite nanocrystals are synthesized in diblock copolymer micelles to improve their processability and stability. The copolymer micelle approach allows fluorescence from a stretchable or flexible substrate by coating processes, and stable emission in water by protecting the nanocrystals in the micelles. Fluorescent films in three primary colors of blue, green, and red are also produced with the assistance of anion exchange reactions for perovskite nanocrystals in the micelles. Then, by stacking films in three primary colors, we are able to produce a white-emitting film of copolymer micelles containing only perovskite nanocrystals without the support of other kinds of emissive materials.

Fig. 1. Schematic illustration of the preparation procedure of the PS-b-P2VP micelles with CsPbBr₃ nanocrystals in the P2VP core.

Fig. 2. PS-b-P2VP micelles having CsPbBr₃ nanocrystals: (a) UV-Vis (dashed line) and fluorescence (solid line) spectra in a toluene solution with an excitation wavelength of 365 nm; (b) TEM image with a scale bar of 25 nm. The insets in (a) and (b) are a photograph of a green-emitting solution under UV illumination and a high-resolution TEM image of a single nanocrystal with dimensions of 15 nm × 15 nm, respectively.

Fig. 3. Spin-coated monolayer of PS-b-P2VP micelles having CsPbBr₃ nanocrystals: (a) SEM image with the scale bar representing 200 nm; (b) fluorescence spectrum with an excitation wavelength of 365 nm. The inset in (b) shows a green-emitting film under UV illumination.

Fig. 4. (a) Photographs of the stretchable PDMS elastomer coated with a monolayer of PS-b-P2VP micelles having CsPbBr₃ nanocrystals under UV illumination before, during, and after extension; (b) fluorescence spectrum with an excitation wavelength of 365 nm.

Fig. 5. Solutions of PS-b-P2VP micelles having CsPbBr₃ nanocrystals after treatment with ZnCl₂ or ZnI₂: (a) photographs under UV illumination; (b) fluorescence spectra with an excitation wavelength of 365 nm. PL intensities in (b) are not normalized. For a PL spectrum of the green emission, a 1/3 diluted solution was used.

Fig. 6. SEM image of a spin-coated film of PS-b-P2VP micelles having CsPbBr₃ nanocrystals. The scale bar is 200 nm. The inset (400 nm × 300 nm) is a side view image of the film with the arrow indicating the thickness of ∼129 nm.

Fig. 7. Photographs of flexible PET films coated with films of micelles having blue-, green-, and red-emitting perovskite nanocrystals. Fluorescence spectra are displayed together without intensity normalization. The excitation wavelength was 365 nm.

Fig. 8. Fluorescence spectrum of a white-emitting film fabricated by sequential coating of micelles having red-, green-, and blue-emitting perovskite nanocrystals. The inset is a CIE chromaticity diagram with marks of blue (0.26, 0.15), green (0.11, 0.68), red (0.58, 0.30), and white (0.29, 0.31) colors from the film. The excitation wavelength was 400 nm.

Fig. 9. Photographs of the freestanding films of the PS-b-P2VP micelles having blue-, green-, and red-emitting perovskite nanocrystals under UV illumination. The inset shows a green-emitting film just after delamination from the substrate. A fluorescence spectrum of the green-emitting film with an excitation wavelength of 365 nm is displayed together in the photograph.

Fig. 10. A freestanding film of the PS-b-P2VP micelles having green-emitting perovskite nanocrystals immersed in water under UV illumination. The right image shows a green-emitting film after 30 min in water.