Homogeneous mono-layer mixed-halide perovskite quantum dots towards blue light-emitting diodes with stable spectra under continuous driving

Mixed-halide perovskite quantum dots (QDs) light-emitting diodes (QLEDs) with blue emission still suffer from low efficiency due to surface defects and halide migration. The issue of halide migration in the mixed-halide perovskite QLEDs under increasing biases have been basically solved. However, under continuous driving, the QLEDs still face the problem of halide migration or electroluminescence (EL) peak shift. In this work, we found that when ligand passivation effects on mixed-halide perovskite QDs are similar, the homogeneity of a mono-layer QDs film plays a decisive role in suppressing halide migration and improving the EL spectral stability of the QLEDs under continuous driving. Moreover, 4 and 64 mm2 QLEDs with emission peaks from pure-blue to deep-blue and low efficiency roll-off were fabricated and the analysis results show that factors, such as chlorine content or defects in the QDs, driving bias, operation time at the driving bias and current density, also matter in the EL spectral stability of the QLEDs. In addition, we found that the devices exhibit similar performance after being stored for a year, demonstrating high stability of the devices with homogeneous mono-layer QDs structure. Our work provides a timely and systematic guide on achieving spectrally stable and efficient blue QLEDs with high color purity based on mixed-halide perovskite QDs.