In situ siloxane passivation of colloidal lead halide perovskite via hot injection for light-emitting diodes

Abstract

All-inorganic cesium lead halide perovskite (CsPbX3; X = Cl, Br) nanocrystals (NCs) are synthesized via a modified hot injection method using 3-mercaptopropyltrimethoxysilane (MPTMS), together with oleic acid and oleylamine, for in situ passivation of the surface defects. The surface chemistry, revealed by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) techniques, shows an absence of Si-O-Si network and C-O groups on these in situ passivated CsPbX3 NCs, denoted as InMP-CsPbX3, which is in strong contrast to the counterpart NCs obtained via a postsynthesis exchange strategy. The x-ray diffraction (XRD) pattern indicates a lattice structure significantly strained from the cubic structure. The synthesis of these InMP-CsPbX3 NCs is highly reproducible, and the colloids are stable in nonpolar solvents. The emission wavelength of CsPb(Cl/Br)3 mixed halide perovskite NCs is tuned from 405 nm to 508 nm by reducing the nominal Cl/Br ratio, while the photoluminescence quantum yield (PLQY) is greatly enhanced over the whole spectral range. More importantly, the InMP-treatment is among the few strategies that are promising for electroluminescence in light-emitting diodes.

Hybrid Ligand Polymerization for Weakly Confined Lead Halide Perovskite Quantum Dots

“…It is interesting to find that the charge transport capability is mostly determined by ligand bonding chemistry instead of the siloxane groups. Moreover, the current densities of the ExMP-CsPbBr 3 QD film in the <5 V bias range are superior to all other QD films, including the recently reported InMP-CsPbBr 3 QD films that were in situ passivated by MPTMS . Therefore, exploring hybrid ligand polymerization on the surface of lead halide PQDs is promising for electroluminescence applications.…”

“…In the case of in situ MPTMS passivation, by which the silyl ligand is introduced prior to hot injection, twin vibrations at 1641 and 908 cm –1 are more pronounced . The higher reaction temperature inhibits the formation of Si–O–Si, but accelerates the formation of silanol and strained edge-shared tetrahedra on the surface, ,,, which is conducive to achieving a higher electrical conductivity as it leads to lamellar polymerization with reduced thickness of the monolayer shell.…”

“…With the knowledge on surface chemistry and strain engineering, a diverse synthesis route can be designed for these perovskite QDs, and by further engineering the strain field within QD solid films, a higher-performance light-emitting layer can be developed for varied applications. For example, ExAP-CsPbBr 3 are found to be suitable for color conversion, while MPTMS treatment is conducive to achieve a higher performance in electroluminescence . Surprisingly, HLP with characteristic FTIR vibrations at 908 and 1641 cm –1 is the strongest feature for in situ APTMS-passivated CsPbBr 3 QDs, which are denoted by BrInAP-CsPbBr 3 , wherein ZnBr 2 was employed as the additive (Figure S9).…”

“…For example, ExAP-CsPbBr 3 are found to be suitable for color conversion, 42 while MPTMS treatment is conducive to achieve a higher performance in electroluminescence. 40 Surprisingly, HLP with characteristic FTIR vibrations at 908 and 1641 cm −1 is the strongest feature for in situ APTMS-passivated CsPbBr 3 QDs, which are denoted by BrInAP-CsPbBr 3 , wherein ZnBr 2 was employed as the additive (Figure S9). Therefore, the HLP process is solely ascribed to the methoxy silyl moiety of the ligands, independent of the bonding chemistry, but can be controlled by the stoichiometry of the precursor.…”

“…In the case of in situ MPTMS passivation, by which the silyl ligand is introduced prior to hot injection, twin vibrations at 1641 and 908 cm −1 are more pronounced. 40 The higher reaction temperature inhibits the formation of Si−O−Si, but accelerates the formation of silanol and strained edge-shared tetrahedra on the surface, 31,34,35,39 which is conducive to achieving a higher electrical conductivity 40 as it leads to lamellar polymerization with reduced thickness of the monolayer shell. This desirable surface structure is thereof easily identified by the diagnostic 1641 and 908 cm Desorption of OA upon introduction of the alkanethiol ligand has been confirmed by a transient dip in PL intensity, and the surface of perovskite QDs can be the catalytic site for thiol-ene reactions.…”