Ionic liquid assisted pure blue emission CsPbBr3 quantum dots with improved optical properties and alkyl chain regulated stability

Abstract Stability issue of blue emitting CsPbX3 quantum dots (QDs) remains a great challenge for their application in optoelectronic devices. In this work, hydrophobic ionic liquids (ILs) 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (NTf2) were used to obtain blue emission CsPbBr3 QDs with high color purity featured with a 16 nm full width at half-maximum (FWHM). Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results elucidated ILs formed effective passivation on QDs through stronger interaction with surface Pb2+ compared to OA/OAm. This passivation effect led to the enhancement of photoluminescence quantum yields (PLQYs) from 33% for the pristine sample to 51% for QDs modified by ILs. And the stability of the modified QDs was enhanced by keeping the blue emitting even after 32 h UV irradiation. More interestingly, there is an alkyl chain effect existed that QDs with longer alkyl chain ILs exhibit better stability than the ones with shorter alkyl chains. It may relate to the higher hydrophobicity originated from long alkyl chain. Resultantly, warm white light emitting diode (WLED) based on the IL-contained QDs was fabricated which qualified with a Commission Internationale de L'Eclairage (CIE) color coordinates of (0.33,0.35), correlated color temperature (CCT) of 5416 K and maximum luminance of 9062.9 cd/m2. The demonstrated ILs passivation strategy might be an effective method for preparing blue emitting perovskite QDs with high PLQYs and stability.