51ÁÔÆæÈë¿Ú

Abstract:

Metal halide perovskites are promising candidates for use in light emitting diodes (LEDs), due to their potential for colour tuneable and high luminescence efficiency. While recent advances in perovskite-based light emitting diodes have resulted in external quantum efficiencies exceeding 12.4 % for the green emitters, and infrared emitters based on 3D/2D mixed dimensional perovskites have exceeded 20%, the external quantum efficiencies of the red and blue emitters still lag behind. A critical issue to date is creating highly emissive and stable perovskite emitters with the desirable emission band gap to achieve full-colour displays and white LEDs. Herein, we report the preparation and characterization of a highly luminescent and stable suspension of cubic-shaped methylammonium lead triiodide CH3NH3PbI3 perovskite nanocrystals, where we synthesise the nanocrystals via a ligand-assisted re-precipitation technique, using an acetonitrile/methylamine compound solvent system to solvate the ions, and toluene as the anti-solvent to induce crystallisation. Through tuning the ratio of the ligands, the ligand to toluene ratio, and the temperature of the toluene, we obtain a solution of CH3NH3PbI3 nanocrystals with a photoluminescence quantum yield exceeding 93%, and tuneable emission between 660 nm and 705 nm. We also achieved red emission at 635 nm by blending the nanocrystals with bromide salt and obtained perovskite-based light emitting diodes with maximum electroluminescent external quantum efficiency of 2.75%.

Abstract:

Cesium lead halide perovskites emitting blue light in the 460-470 nm range of wavelengths have so far been plagued with rather poor luminescent performance, placing inevitable limitations on the development of perovskite nanocrystal-based blue light-emitting devices. Herein, a selective surface defect elimination process with the help of hydrated nitrates was introduced into the perovskite/toluene solution to strip the undesired surface defects and vacancies and to boost the photoluminescence quantum yield of true-blue-light-emitting (at 466 nm) CsPb(Cl/Br)₃ perovskite nanocrystals to the impressive value of 85%. Unlike the conventional passivation strategy, the anionic nitrate ions are able to desorb the undesired surface metallic lead and combine with excess surface metal ions, leaving perovskite quantum dots with better crystallinity and fewer surface defects.