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Metal halide perovskite light-emitting diodes (PeLEDs) have exceptional color purity but designs that emit deep-blue color with high efficiency have not been fully achieved and become more difficult in the thin film of confined perovskite colloidal quantum dots (PeQDs) due to particle interaction. Here it is demonstrated that electronic coupling and energy transfer in PeQDs induce redshift in the emission by PeQD film, and consequently hinder deep-blue emission. To achieve deep-blue emission by avoiding electronic coupling and energy transfer, a QD-in-organic solid solution is introduced to physically separate the QDs in the film. This physical separation of QDs reduces the interaction between them yielding a blueshift of ≈7 nm in the emission spectrum. Moreover, using a hole-transporting organic molecule with a deep-lying highest occupied molecular orbital (≈6.0 eV) as the organic matrix, the formation of exciplex emission is suppressed. As a result, an unprecedently high maximum external quantum efficiency of 6.2% at 462 nm from QD-in-organic solid solution film in PeLEDs is achieved, which satisfies the deep-blue color coordinates of CIEy < 0.06. This work suggests an important material strategy to deepen blue emission without reducing the particle size to <≈4 nm.
Jang et al. (Wed,) studied this question.