Polymer additive engineering of K2CuBr3 nanocrystalline films to achieve efficient and stable deep-blue emission

Recently, non-toxic alternatives to lead-halide perovskites have been greatly sought after in optoelectronics applications. Deep-blue luminescent material is mainly required for fabricating white light source and expanding the color gamut of full-color displays. However, the synthesis of high-performance lead-free perovskite films with efficient blue emission is still a critical challenge currently, limiting their further practical applications. Here, a novel strategy is reported to prepare non-toxic and deep-blue-emitting K2CuBr3 nanocrystalline films by introducing polymer poly(methyl methacrylate) (PMMA) additives into the anti-solvent. It is found that the PMMA additives could effectively reduce the grain size and improve the crystallinity of K2CuBr3 films, resulting in an enhanced radiative recombination by defect passivation and confinement of excitons in the nanograins. As a result, the PMMA-treated K2CuBr3 films achieve a bright deep-blue light with color coordinates at (0.155, 0.042), and the photoluminescence quantum yield obtained is about 3.3 times that of the pristine sample. Moreover, the treated K2CuBr3 films exhibit a substantially enhanced stability under harsh environmental conditions, maintaining >70% of their initial performances in high humidity environment (50‒70% humidity, 190 h) or under uninterrupted ultraviolet light radiation (254 nm, 3.4 mW/cm2, 150 h). These findings pave a promising strategy for achieving efficient and stable deep-blue metal halide films, showing their potential applications in optoelectronic devices.

Preparation and Study of the Effect of Annealing Temperature on the Structural, Optical, and Morphological Properties of Nanocrystalline SnO2 Doped with Cu

In this study, pure SnO2 nanocrystalline films were doped with copper using the spray pyrolysis technique. SnCl2.2H2O, CuCl2.2H2O were used as precursors. The preparation was done in the form of nanoparticles by chemical precipitation method. The prepared materials were annealed at 300°C and 500°C for 1 h to improve crystallization. XRD results of the samples prepared by spray pyrolysis of a solution containing nanoparticles showed that the samples were crystallized in the rutile tetragonal phase. The average crystal size of SnO2 annealed at 300°C is 3.36 and 3.37 nm for pure and doped samples, respectively, and it is 4.1 nm and 9.75 nm for pure and doped annealed at 500°C, respectively. It is noticed that the crystal structure of SnO2 does not change with the addition of copper, and the studies of Field Emission Scanning Electron Microscopy confirmed the results where the grain size was within the range (20-50) nm, and the thickness of the films obtained from this assay was in the range (0.9-1.15) µm, with the thickness of doped films at 500°C are higher than those at 300°C. The Atomic Force Microscopy results showed that the roughness rate of the pure films annealed at 300°C and 500°C is 7.99 and 17.4 nm, respectively, while roughness for doped annealed samples were 9.09 and 7.12 nm, respectively. The optical results obtained from UV-Vis analysis showed that the optical bandgap at 300°C for pure and doped samples was (3.40 and 2.8) eV, respectively, while it was (3.75 and 2.59) eV at 500°C for pure and doped samples, respectively. The transmittance decreases with increasing annealing temperature, because the absorbance increases. The extinction coefficient increases, while refractive index decreases with increasing annealing temperature. The absorbance was 0.94 and 1.17 for pure and doped samples at 300°C, and was 1.16 and 1.46 at 500°C.