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Abstract:

For data security applications, the use of fluorescent inks has become the most promising approach because of their convenience and low cost. However, traditional fluorescent inks are usually visible either under ambient light or UV light, whereas the improved stimuli-responsive inks are restricted to a single color. For the first time, full-color stimuli-responsive inks for information coding, encryption, and decryption are reported, which rely on the facile preparation and conversion of perovskite quantum dots. The information printed by the halide salt solution is invisible under ambient and UV light but becomes readable under UV light after spraying a unique developer. Besides, the primitive information can be stored for many years, even decades. Even after the decryption process, it still can be stored for at least several weeks. Most importantly, using butyl amine and acetic acid as encryption and decryption reagents, respectively, can switch off/on the luminescence. In this way, the printed information can be encrypted and decrypted, which shows great potential for information security applications.

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.

Abstract:

A method is proposed to improve the photo/electroluminescence efficiency and stability of CsPbI₃ perovskite nanocrystals (NCs) by using SrCl₂ as a co-precursor. The SrCl₂ is chosen as the dopant to synthesize the CsPbI₃ NCs. Because the ion radius of Sr²⁺ (1.18 Ã…) is slightly smaller than that of Pb²⁺ (1.19 Ã…) ions, divalent Sr²⁺ cations can partly replace the Pb²⁺ ions in the lattice structure of perovskite NCs and cause a slight lattice contraction. At the same time, Cl^- anions from SrCl₂ are able to efficiently passivate surface defect states of CsPbI₃ nanocrystals, thus converting nonradiative trap states to radiative states. The simultaneous Sr²⁺ ion doping and surface Cl^- ion passivation result in the enhanced photoluminescence quantum yield (up to 84%), elongated emission lifetime, and improved stability. Sr²⁺ -doped CsPbI₃ NCs are employed to produce light-emitting devices with a high external quantum yield of 13.5%.

Abstract:

Cesium lead halide perovskite nanocrystals (NCs) have unique optical properties such as high color purity and high photoluminescence (PL) efficiency. However, the external quantum efficiency (EQE) of the corresponding light-emitting diodes (LEDs) is low, primarily as a result of the NC surface defects. Here, we report a method to reduce the surface defects by capping CsPbI₃ NCs with PbS. This passivation significantly enhanced the PL efficiency, reduced the Stokes shift, narrowed the PL bandwidth, and increased the stability of CsPbI₃ NCs. At the same time, CsPbI₃ NC films switched from n-type behavior to nearly ambipolar by PbS capping, which allowed us to fabricate electroluminescence LEDs using p-i-n structures. The thus-fabricated LEDs exhibited dramatically improved storage and operation stability, and an EQE of 11.8%. These results suggest that, with a suitable surface passivation strategy, the perovskite NCs are promising for next-generation LED and display applications.

Abstract:

Lead halide perovskite nanocrystals are currently under intense investigation as components of solution-processed light-emitting devices (LEDs). We demonstrate LEDs based on Ag doped-passivated CsPbI₃ perovskite nanocrystals with external quantum efficiency of 11.2% and an improved stability. Ag and trilayer MoO₃/Au/MoO₃ structure were used as cathode and anode, respectively, which reduce the electron injection barrier and ensure the high transparency and low resistance of the anode. Silver ions diffuse into perovskite film from the Ag electrode, as confirmed by the elemental mapping, the presence of Ag 3d peaks in the X-ray photoelectron spectrum, and the peak shift in the X-ray diffraction patterns of CsPbI₃. In addition to doping, silver ions play the beneficial role of passivating surface defect states of CsPbI₃ nanocrystals, which results in increased photoluminescence quantum yield, elongated emission lifetime, and improved stability of perovskite films.