Xinyu Shen

Abstract:

All-inorganic halide perovskite materials have attracted significant interest for display applications because of their narrow bandwidths and high photoluminescence quantum yields. However, the development of blue-light-emitting perovskite materials has been slower than that of green- and red-light-emitting perovskites. In this study, we successfully produced single-halide CsPbBr3 nanoplatelets with a quantum confinement effect using ligand-assisted reprecipitation techniques. NaBr, an inorganic ligand with strong binding affinity (adsorption energy, -2.13 eV) and low steric hindrance, was used to prevent the continued growth of nanoplatelets. A series of experimental results demonstrate that CsPbBr3 nanoplatelets with a dense Na+ shell on the surface exhibit stable deep blue emission. UV chip-based light-emitting devices activated by these nanoplatelets demonstrated remarkable spectral stability as the current injection increased. Moreover, the synthesis process is conducted under simple conditions at room temperature, demonstrating potential for batch production.

Abstract:

The use of a small organic molecular passivator is proven to be a successful strategy for producing higher-performing quasi-2D perovskite light-emitting diodes (PeLEDs). The small organic molecule can passivate defects on the grain surround and surface of perovskite crystal structures, preventing nonradiative recombination and charge trapping. In this study, a new small organic additive called 2, 8-dibromodibenzofuran (diBDF) is reported and examines its effectiveness as a passivating agent in high-performance green quasi-2D PeLEDs. The oxygen atom in diBDF, acting as a Lewis base, forms coordination bonds with uncoordinated Pb²⁺, so enhancing the performance of the device. In addition, the inclusion of diBDF in the quasi-2D perovskite results in a decrease in the abundance of low-n phases, hence facilitating efficient carrier mobility. Consequently, PeLED devices with high efficiency are successfully produced, exhibiting an external quantum efficiency of 19.9% at the emission wavelength of 517 nm and a peak current efficiency of 65.0 cd A-¹.

Abstract:

Surface defects of metal halide perovskite nanocrystals (PNCs) substantially compromise the optoelectronic performances of the materials and devices via undesired charge recombination. However, those defects, mainly the vacancies, are structurally entangled with each other in the PNC lattice, necessitating a delicately designed strategy for effective passivation. Here, a synergistic metal ion doping and surface ligand exchange strategy is proposed to passivate the surface defects of CsPbBr₃ PNCs with various divalent metal (e.g., Cd²⁺, Zn^2+, and Hg²⁺) acetate salts and didodecyldimethylammonium (DDA⁺) via one-step post-treatment. The addition of metal acetate salts to PNCs is demonstrated to suppress the defect formation energy effectively via the ab initio calculations. The developed PNCs not only have near-unity photoluminescence quantum yield and excellent stability but also show luminance of 1175 cd m⁻², current efficiency of 65.48 cd A⁻¹, external quantum efficiency of 20.79%, wavelength of 514 nm in optimized PNC light-emitting diodes with Cd²⁺ passivator and DDA ligand. The “organic–inorganic” hybrid engineering approach is completely general and can be straightforwardly applied to any combination of quaternary ammonium ligands and source of metal, which will be useful in PNC-based optoelectronic devices such as solar cells, photodetectors, and transistors.