Abstract
The application of polymers to replace oleylamine (OLA) and oleic acid (OA) as ligands for perovskite nanocrystals is an effective strategy to improve their stability and durability especially for the solution-based processing. Herein, we report a mechanosynthesis of lead bromide perovskite nanoparticles (NPs) stabilized by partially hydrolyzed poly(methyl methacrylate) (h-PMMA) and high-molecular-weight highly-branched poly(ethylenimine) (PEI-25K). The as-synthesized NP solutions exhibited green emission centered at 516 nm, possessing a narrow full-width at half-maximum of 17 nm and as high photoluminescence quantum yield (PL QY) as 85%, while showing excellent durability and resistance to polar solvents, e.g., methanol. The colloids of polymer-stabilized NPs were directly processable to form stable and strongly-emitting thin films and solids, making them attractive as gain media. Furthermore, the roles of h-PMMA and PEI-25K in the grinding process were studied in depth. The h-PMMA can form micelles in the grinding solvent of dichloromethane to act as size-regulating templates for the growth of NPs. The PEI-25K with large amounts of amino groups induced significant enrichment of PbBr2 in the reaction mixture, which in turn caused the formation of CsPb2Br5-mPbBr2 and CsPbBr3-Cs4PbBr6-nCsBr NPs. The presence of CsPbBr3-Cs4PbBr6-nCsBr NPs was responsible for the high PL QY, as the Cs4PbBr6 phase with a wide energy bandgap can passivate the surface defects of the CsPbBr3 phase. This work describes a direct and facile mechanosynthesis of polymer-coordinated perovskite NPs and promotes in-depth understanding of the formation and phase conversion for perovskite NPs in the grinding process.
Highlights
Owing to their broadly tunable photoluminescence (PL) across 400–700 nm, narrow PL full-width at half-maxima (FWHM) of 12–40 nm for a blue-to-red spectral region, and high PL quantum yields (QYs) of 50%–90%, all-inorganic CsPbX3 (X = Cl, Br, or I) perovskite nanoparticles (NPs) have attracted tremendous interest especially in photonic applications [1, 2], including electrically-driven light-emitting diodes (LEDs) [3, 4], color-conversion white LEDs (WLEDs) [5, 6], lasers [7, 8], and X-ray scintillators [9, 10]
The roles of hydrolyzed poly(methyl methacrylate) (h-poly(methyl methacrylate) (PMMA)) and PEI-25K in the grinding process were studied in depth
Perovskite NPs stabilized by h-PMMA/b-PEI were prepared based on our previous work with some modifications [36]
Summary
We reported that the CsPbBr3-CsPb2Br5 NPs coordinated by partially hydrolyzed PMMA (h-PMMA) and low-molecular-weight (800 g/mol) poly(ethylenimine) (PEI-0.8K) exhibited impressive water and UV resistance as well as thermal stability while maintaining high PL QY [36] We attributed this attractive improvement to the synergetic influence of the surface modification with strong binding ligands, polymer-encapsulation, and proper heterostructuring of the emitting and non-emitting perovskite-phases. The as-prepared NP solutions emit green light peaked at 516 nm; the PL is narrow (FWHM of 17 nm) and strong (PL QY of 85%) They exhibit excellent durability and resistance to methanol— the solvent typically used for processing colloidal NPs. Based on the results of the comprehensive characterization techniques, we clarified the roles of the h-PMMA and PEI-25K during the synthesis and confirmed the chemical composition and the structure of both the intermediate and final reaction products obtained under influence of the PEI. The resultant NPs were successfully utilized as a gain medium for amplified spontaneous emission (ASE), which is an example application in solution-processable optoelectronics
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