Blue-Emitting Cs(Pb,Cd)Br₃ Nanocrystals Resistant to Electric Field-Induced Ion Segregation

High-performance solution-processed perovskite light-emitting diodes (PeLEDs) have emerged as a good alternative to the well-established technology of epitaxially grown A^IIIB^V semiconductor alloys. Colloidal cesium lead halide perovskite nanocrystals (CsPbX₃ NCs) exhibit room-temperature excitonic emission that can be spectrally tuned across the entire visible range by varying the content of different halogens at the X-site. Therefore, they present a promising platform for full color display manufacturing. Engineering of highly efficient PeLEDs based on bromide and iodide perovskite NCs emitting green and red light, respectively, does not face major challenges except low operational stability of the devices. Meanwhile, mixed-halide counterparts demonstrating blue luminescence suffer from the electric field-induced phase separation (ion segregation) phenomenon described by the rearrangement (demixing) of mobile halide ions in the crystal lattice. This phenomenon results in an undesirable temporal redshift of the electroluminescence spectrum. However, to realize spectral tuning and, at the same time, address the issue of ion segregation less mobile Cd²⁺ ion could be introduced in the lattice at Pb²⁺-site that leads to the band gap opening. Herein, we report an original synthesis of CsPb_0.88Cd_0.12Br₃ perovskite NCs and study their structural and optical properties, in particular electroluminescence. Multilayer PeLEDs based on the obtained NCs exhibit single-peak emission centered at 485 nm along with no noticeable change in the spectral line shape for 30 min which is a significant improvement of the device performance.