Bidentate oxalate ion enhancing water-resistant stability and exciton recombination behavior of blue CsPb(Br/Cl)3 quantum dots

Mixed halide CsPb(Br/Cl)3 quantum dots (QDs) exhibit fine tunable blue light and narrow photoluminescence (PL) full-width at half-maximum (FWHM), which has attracted significant attention as a promising candidate to realize a new generation of blue light technology. However, the introduction of Cl- makes it very easy to be eroded by water in the environment, which will lead to deep-level defects and degrade the luminescence and stability of QDs. Here, we propose to introduce tetra-n-octylammonium oxalate (TOAOxa) to improve the water-resistance stability and exciton recombination of CsPb(Br/Cl)3 QDs and QD-based light-emitting diodes (QLEDs). The oxalate ion (Oxa2-) of TOAOxa could form strong interaction with undercoordinated Pb2+ on CsPb(Br/Cl)3 QD surface, which was confirmed by FTIR and XPS analysis. Oxa2-passivated QDs (Oxa-QDs) exhibited improved photoluminescence quantum yield (PLQY) and enhanced water-resistance stability compared to pristine QDs. For example, after soaking in water-acetone co-solvent for 1 h, Oxa-QDs can maintain the initial cubic morphology and 43.9% of initial PL intensity, while the morphology and luminescence of pristine QDs are almost damaged. Based on the above concept, the Oxa-QD-based QLED presented a maximum external quantum efficiency (EQE) of 4.0%, and operational lifetime (T50) of 84 s, which was a 5-fold enhancement in EQE, and 7 -fold enhancement in stability compared to pristine QLED, respectively. Besides, the Oxa-QD-based QLED exhibits better stability in high-humidity air. To sum up, the Oxa2-passivation strategy has significantly improved the efficiency and water-resistant stability of QDs and devices and would rapidly promote the development of blue-emitting QDs.