Crown Ethers Enable Room-Temperature Synthesis of CsPbBr₃ Quantum Dots for Light-Emitting Diodes

Abstract

The synthesis of all-inorganic cesium lead halide perovskite quantum dots (QDs) typically requires high temperatures, stringent conditions, large quantities of surface ligands, and judicious purification steps to overcome ligand-induced charge injection barriers in optoelectronic devices. Low-temperature syntheses generally require lower ligand concentrations, but are severely limited by the low solubility of the Cs precursor. We describe an innovative and general approach under ambient conditions to overcome these solubility limitations, by employing crown ethers. The crown ethers facilitate complete dissolution of the CsBr precursor, rendering CsPbBr3 QD inks practical for device fabrication. The resultant LEDs displayed bright green emission, with a current efficiency, and external quantum efficiency of 9.22 cd A -1 and 2.64%, respectively. This represents the first LED based on CsPbBr3 QDs prepared at room temperature. Lastly, the crown ethers form core-shell structures, opening new avenues to exploit their strong coordination strength.

High-Efficiency Light-Emitting Diodes Based on Formamidinium Lead Bromide Nanocrystals and Solution Processed Transport Layers

“…A post-synthesis treatment with PbBr2 (185 mg/ml) dissolved in 1:1:1 Propionic Acid:Butylamine:Hexane in volume was carried out to enhance the PLQY (see ref. 25,12 l for a typical synthesis). After the treatment, oleic acid (35 l for a typical synthesis) was added to the solution to dissolve the NC aggregates observed under TEM.…”

All‐Inorganic Perovskite Nanocrystals‐Based Light Emitting Diodes and Solar Cells

“…In addition, it was shown by Fang et al that polar solvent controlled ionization method was used to obtain CsPbX 3 NCs with high PLQYs, narrow FWHM, large Stokes shifts, and particular morphology. [36]…”

“…Besides, they also found the CsPbBr 3 NCs have better stability (Figure d). Veldhuis et al . used crown ethers to increase solubility of Cs precursors in polar media where they obtained bright green emission LEDs (Figure e).…”

Ligand‐Exchange of Low‐Temperature Synthesized CsPbBr3 Perovskite toward High‐Efficiency Light‐Emitting Diodes

“…These ligands can saturate the dangling bonds on the NC surface, increase solubility, and control the nucleation and growth kinetics of NCs, as well as screen the NCs to avoid sedimentation. For example, Veldhuis et al found that crown ethers can increase the solubility of the Cs 2 CO 3 precursor, which allowed for low‐temperature synthesis …”