Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent.

Metal halide perovskite materials are an emerging class of solution-processable semiconductors with considerable potential for use in optoelectronic devices1-3. For example, light-emitting diodes (LEDs) based on these materials could see application in flat-panel displays and solid-state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4-8. However, the highest reported external quantum efficiencies of green- and red-light-emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively-still well behind the performance of organic LEDs10-12 and inorganic quantum dot LEDs13. Here we describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device-an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3), the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi-core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display.

Mechanisms of LiF Interlayer Enhancements of Perovskite Light-Emitting Diodes.

The use of LiF as a thin interlayer between the electron transport layer and cathode has played a pivotal role in remarkable advances in perovskite LEDs (PeLEDs); however, the mechanism behind the effect of LiF remains to be fully understood. Here, we report a combined experimental and computational study, from which we ascribe the benefits of a LiF interlayer to the migration of dissociated Li into the cathode and dissociated F into the anode. Electronic device simulations reveal that the former improves electron injection by lowering the Schottky barrier height, while the latter reduces the barrier width. These reduce turn-on voltage and improve current density and charge balance in LEDs. We fabricate PeLEDs with and without the LiF interlayer and link these materials and electronic phenomena to the device light-current-voltage characteristics. X-ray photoelectron spectroscopy obtained in sputter profiling of PeLEDs corroborates the dissociation of LiF.

In vitro detection of porphyrin-producing wound bacteria with real-time fluorescence imaging.

Aim: Fluorescence imaging can visualize polymicrobial populations in chronic and acute wounds based on porphyrin fluorescence. We investigated the fluorescent properties of specific wound pathogens and the fluorescence detected from bacteria in biofilm. Methods: Utilizing Remel Porphyrin Test Agar, 32 bacterial and four yeast species were examined for red fluorescence under 405 nm violet light illumination. Polymicrobial biofilms, supplemented with δ-aminolevulinic acid, were investigated similarly. Results: A total of 28/32 bacteria, 1/4 yeast species and polymicrobial biofilms produced red fluorescence, in agreement with their known porphyrin production abilities. Conclusion: These results identify common wound pathogens capable of producing porphyrin-specific fluorescence and support clinical observations using fluorescence imaging to detect pathogenic bacteria in chronic wounds.