Photoinstable hybrid all-inorganic halide perovskite quantum dots as single downconverters for white light emitting devices

All-inorganic CsPbX3 (X = I, Br, Cl) perovskite quantum dots (QDs) are emerging as potential candidates for photoelectric devices such as light-emitting diodes (LEDs), solar cells etc. due to their outstanding optical properties including tunable bandgap, narrow size distribution and high photoluminescence (PL) quantum yield (QY). However, instability originated from the strong anion-exchange effect and the lower melting temperature hinders their further practical application. Here, blue emission CsPbBr1.5Cl1.5 QDs with peak wavelength similar to 450 nm are prepared by means of hot injection method, and mesoporous silica particles are introduced to wrap them. On one hand, the silica coat, protecting the core QDs from oxygen and humidity somewhat, the stability of the PL QYs and the luminescence of the CsPbBr1.5Cl1.5 QDs, as well as the emission and vision properties of the devices based on these QDs are improved evidently. On the other hand, by integrating the prepared blue emission CsPbBr1.5Cl1.5 QDs or the silica-coated CsPbBr1.5Cl1.5 QDs as single downconverters on violet chips with emission wavelength 365 nm, surprisingly, we observe a new peak similar to 550 nm in the PL spectrum of the resultant devices, except for the originate blue emission. We speculate that the new emission peak, which is helpful for the construction of white LEDs (WLEDs), is originated from the bromide-enriched majority domains resulted from the photo-induced segregation of CsPbBr1.5Cl1.5 QDs. The fabricated WLEDs based on CsPbBr1.5Cl1.5@SiO2 QDs, in comparison with that based on CsPbBr1.5Cl1.5 QDs, exhibits stable color rendering index (CRI) with the least variation of 1.4, and stable color correlated temperature (CCT) with the least variation of 325 K. These results suggest that the large full width of half maximum of the new emission benefits for the construction of WLEDs, and mesoporous silica particles serving as coat layer hold great promise for the improvement of performance stability for the devices based on CsPbBr1.5Cl1.5@SiO2 QDs.