Synthesis And Properties Of Highly Stable CsPbBr₃ Perovskite Nanocrystal Composites For White Light-Emitting Diodes

Recently,all-inorganic lead-halide perovskite nanocrystals（PNCs）have become one of the most popular materials for optoelectronic devices.However,PNCs will decompose under the conditions of moisture,oxygen,light and heat,as well as polar solvents,which will result in the sharp decrease of luminescent properties and greatly hinders their practical applications.In this paper,8-hydroxyquinoline（HQ）,alginic acid（AA）and porous silica KIT-6（KIT-6）were used as the encapsulation substrates to composite with PNCs,respectively,and then the highly stable CsPbBr₃nanocrystal composites were prepared.Not only the effects of different matrices on the luminescent properties and stability of CsPbBr₃ nanocrystals were systematically studied,but the mechanism of the stability improvement was analyzed.Finally,the white LEDs with ultra-wide color gamut were successfully fabricated by using green perovskite nanocrystal composites combining with blue LED chips and red K₂Si F₆:Mn⁴⁺phosphors.The main findings are as follows:1.The brightly green-emitting CsPbBr₃@HQ composites were prepared by using HQ containing with hydrophobic quinoline ring,carbon nitrogen pyridine bonds,and hydroxyl as the encapsulation matrices.The emission peak of the green perovskite nanocrystal composites locates at 520 nm,the full width at half maximum（FWHM）is 20nm,the photoluminescent quantum yield（PLQY）achieves 88.23%,and the average particle size is 9.98 nm.The environmental stability of composites has been significantly improved besides the excellent luminescent properties.The PL intensity of green perovskite nanocrystal composites can still maintain more than 75%of the initial value after being stored for 10 days at 60°C and a humidity of 60%.Finally,a white LED was successfully fabricated by using as-prepared composites as the green phosphor combined with red commercial K₂Si F₆:Mn⁴⁺phosphor and blue LED chip.Its luminous efficiency reaches 34.1 lm/W,the CIE coordinates locate at（0.3226,0.3381）,and 125%of the National Television Standards Committee（NTSC）standard is achieved.2.The brightly green-emitting CsPbBr₃@AA composites without luminescent quenching in solid state were prepared by using long-chain AA containing with the rich hydroxyl and carboxy functional groups as the encapsulation framework.After optimizing the content of AA,the highest PLQY of CsPbBr₃@AA reaches 86.43%,the emission peak is located at 521 nm,the FWHM is 23 nm,the average particle size is 9.57nm,and the thermal stability is significantly improved.When the ambient temperature is heated to 60°C,the PL intensity CsPbBr₃@AA composites still retains 90%of the initial value.Finally,a white LED device with 124%of the NTSC standard was prepared by combining the green perovskite nanocrystal composites with the red commercial K₂Si F₆:Mn⁴⁺phosphors and blue LED chip,the luminous efficiency reaches 36.4 lm/W,and the CIE coordinates locate at（0.3351,0.3438）.3.The brightly green-emitting CsPbBr₃@KIT-6 composites without luminescent quenching in solid state were prepared by using porous silica molecular sieve KIT-6 with better hydrophobicity as the encapsulation framework.By optimizing the content of KIT-6,the highest PLQY of the resultant composites reaches 89.14%,the emission peak is located at 519 nm,the FWHM is 19 nm,and the average particle size is 9.21 nm.At the same time,the environmental stability especially water stability is significantly enhanced.The PL intensity of green perovskite nanocrystal composites can still maintain more than77%of the initial value after being stored for 10 days at 60°C and 60%RH.Finally,a white LED was successfully fabricated by using as-prepared composites as the green phosphor combined with red commercial K₂Si F₆:Mn⁴⁺phosphor and blue LED chip.Its luminous efficiency is improved to 43.5 lm/W in further,the CIE coordinates locate at（0.3271,0.3369）,and 125%of the NTSC standard is achieved,which shows the potential applications in the future wide color gamut displays and lightings.