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Lead halide perovskites and other metal halide complexes as inorganic capping ligands for colloidal nanocrystals.

Dirin DN, Dreyfuss S, Bodnarchuk MI, Nedelcu G, Papagiorgis P, Itskos G, Kovalenko MV - J. Am. Chem. Soc. (2014)

Bottom Line: We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals.In particular, we show that the Lewis acid-base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability.High luminescence quantum efficiencies of 20-30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50-65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface.

View Article: PubMed Central - PubMed

Affiliation: Institute of Inorganic Chemistry, Department of Chemistry and Applied Bioscience, ETH Zürich , CH-8093 Zürich, Switzerland.

ABSTRACT
Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MX(n), where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals. In particular, we show that the Lewis acid-base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20-30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50-65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface.

No MeSH data available.


(a, from left to right) Illustration of the phase-transferof PbSNCs from nonpolar solvent (hexane) to polar solvent (MFA) caused bythe exchange of oleate capping with MAPbI3; other examplesof halometallate-capped NCs (CdS-SbCl3, InP-InCl3, CdSe-FeCl2, Au-InCl3, Pd-InCl3 in PC as a solvent). (b) FTIR spectra before and after exchangeof oleate-capping on the surface of PbS NCs with KPbI3.(c) Electrophoretic mobility for oleate-capped PbS NCs in toluene(black) and MAPbI3-stabilized PbS NCs in PC. (d, e) TEMimages of PbS-MAPbI3 and PbS-PbI2 NCs.
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fig1: (a, from left to right) Illustration of the phase-transferof PbSNCs from nonpolar solvent (hexane) to polar solvent (MFA) caused bythe exchange of oleate capping with MAPbI3; other examplesof halometallate-capped NCs (CdS-SbCl3, InP-InCl3, CdSe-FeCl2, Au-InCl3, Pd-InCl3 in PC as a solvent). (b) FTIR spectra before and after exchangeof oleate-capping on the surface of PbS NCs with KPbI3.(c) Electrophoretic mobility for oleate-capped PbS NCs in toluene(black) and MAPbI3-stabilized PbS NCs in PC. (d, e) TEMimages of PbS-MAPbI3 and PbS-PbI2 NCs.

Mentions: In a typical ligand-exchange procedure [for details, see the Supporting Information(SI)], a 0.05 M solutionof a metal halide complex or neutral metal halide salt in N-methylformamide (MFA, 1 mL) was stirred with a hexanesolution of NCs (2–5 mg in 1 mL) for several hours until theNCs were completely transferred to the polar phase (Figure 1a). NCs were precipitated from MFA by adding a nonsolventsuch as acetone, centrifuged, and redissolved in propylene carbonate(PC) or MFA. No air- or moisture-free techniques were needed, exceptfor FeCl2, SnX2, and BiX3 (X = Br,I). Completeness of the exchange of the initial organic ligands withhalometallates was confirmed by Fourier-transform infrared (FTIR)spectroscopy (Figure 1b), as seen from thedisappearance of the characteristic C–H and O–H stretchingmodes (2800–3500 cm–1), C–H bendingvibrations, and carboxylic C–O and vinyl C=C stretchingmodes (600–1500 cm–1). Transmission electronmicroscopy (TEM) images for PbS NCs capped with MAPbI3 (Figure 1d) and PbI2 (Figure 1e), as well as for other NC-ligand combinations (Figures S1and S2 in SI), confirmed the integrityof the NCs and retention of their narrow size distribution. The truecolloidal nature of halometallate-capped NCs, apart from the photographs(Figure 1a), was also confirmed by single-particlepopulation in the measurements of dynamic light scattering (DLS, Figure S3). Colloidal solutions of PbS NCs stabilizedwith MAPbI3 were stable for months without noticeable aggregationor precipitation. Pb and Cd chalcogenide NCs showed high affinityto nearly all studied ligands, whereas much fewer ligands formed stablecolloidal solutions with metallic NCs (Table S1). Importantly, only in the case of CdSe NCs metal-free halide ionsI–, Br– (as salts with K+ and MA+ cations) can partially displace oleate ligands,yet without the formation of colloidally stable solutions. Elementalanalysis of purified halometallate-capped NCs confirmed the expectedoverall compositions (7–32 at% of ligand atoms for 3–5nm NCs, Table S2). Halometallate-cappedNCs are negatively charged, as seen from electrophoretic measurementsproviding ξ-potentials of at least −40 mV for MAPbI3-stabilized PbS NCs (Figures 1c and S4; see Table S3 forother NC-ligand combinations). Highly negative ξ-potentials,caused by the surface-bound anions such as [PbI3]− or [PbBr3]−, were measured for bothpreformed complexes (e.g., KPbI3) and for neutral halidesalts MXn (e.g., PbI2). Thelatter can be attributed to the well-known self-ionization in polarsolvents:141


Lead halide perovskites and other metal halide complexes as inorganic capping ligands for colloidal nanocrystals.

Dirin DN, Dreyfuss S, Bodnarchuk MI, Nedelcu G, Papagiorgis P, Itskos G, Kovalenko MV - J. Am. Chem. Soc. (2014)

(a, from left to right) Illustration of the phase-transferof PbSNCs from nonpolar solvent (hexane) to polar solvent (MFA) caused bythe exchange of oleate capping with MAPbI3; other examplesof halometallate-capped NCs (CdS-SbCl3, InP-InCl3, CdSe-FeCl2, Au-InCl3, Pd-InCl3 in PC as a solvent). (b) FTIR spectra before and after exchangeof oleate-capping on the surface of PbS NCs with KPbI3.(c) Electrophoretic mobility for oleate-capped PbS NCs in toluene(black) and MAPbI3-stabilized PbS NCs in PC. (d, e) TEMimages of PbS-MAPbI3 and PbS-PbI2 NCs.
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fig1: (a, from left to right) Illustration of the phase-transferof PbSNCs from nonpolar solvent (hexane) to polar solvent (MFA) caused bythe exchange of oleate capping with MAPbI3; other examplesof halometallate-capped NCs (CdS-SbCl3, InP-InCl3, CdSe-FeCl2, Au-InCl3, Pd-InCl3 in PC as a solvent). (b) FTIR spectra before and after exchangeof oleate-capping on the surface of PbS NCs with KPbI3.(c) Electrophoretic mobility for oleate-capped PbS NCs in toluene(black) and MAPbI3-stabilized PbS NCs in PC. (d, e) TEMimages of PbS-MAPbI3 and PbS-PbI2 NCs.
Mentions: In a typical ligand-exchange procedure [for details, see the Supporting Information(SI)], a 0.05 M solutionof a metal halide complex or neutral metal halide salt in N-methylformamide (MFA, 1 mL) was stirred with a hexanesolution of NCs (2–5 mg in 1 mL) for several hours until theNCs were completely transferred to the polar phase (Figure 1a). NCs were precipitated from MFA by adding a nonsolventsuch as acetone, centrifuged, and redissolved in propylene carbonate(PC) or MFA. No air- or moisture-free techniques were needed, exceptfor FeCl2, SnX2, and BiX3 (X = Br,I). Completeness of the exchange of the initial organic ligands withhalometallates was confirmed by Fourier-transform infrared (FTIR)spectroscopy (Figure 1b), as seen from thedisappearance of the characteristic C–H and O–H stretchingmodes (2800–3500 cm–1), C–H bendingvibrations, and carboxylic C–O and vinyl C=C stretchingmodes (600–1500 cm–1). Transmission electronmicroscopy (TEM) images for PbS NCs capped with MAPbI3 (Figure 1d) and PbI2 (Figure 1e), as well as for other NC-ligand combinations (Figures S1and S2 in SI), confirmed the integrityof the NCs and retention of their narrow size distribution. The truecolloidal nature of halometallate-capped NCs, apart from the photographs(Figure 1a), was also confirmed by single-particlepopulation in the measurements of dynamic light scattering (DLS, Figure S3). Colloidal solutions of PbS NCs stabilizedwith MAPbI3 were stable for months without noticeable aggregationor precipitation. Pb and Cd chalcogenide NCs showed high affinityto nearly all studied ligands, whereas much fewer ligands formed stablecolloidal solutions with metallic NCs (Table S1). Importantly, only in the case of CdSe NCs metal-free halide ionsI–, Br– (as salts with K+ and MA+ cations) can partially displace oleate ligands,yet without the formation of colloidally stable solutions. Elementalanalysis of purified halometallate-capped NCs confirmed the expectedoverall compositions (7–32 at% of ligand atoms for 3–5nm NCs, Table S2). Halometallate-cappedNCs are negatively charged, as seen from electrophoretic measurementsproviding ξ-potentials of at least −40 mV for MAPbI3-stabilized PbS NCs (Figures 1c and S4; see Table S3 forother NC-ligand combinations). Highly negative ξ-potentials,caused by the surface-bound anions such as [PbI3]− or [PbBr3]−, were measured for bothpreformed complexes (e.g., KPbI3) and for neutral halidesalts MXn (e.g., PbI2). Thelatter can be attributed to the well-known self-ionization in polarsolvents:141

Bottom Line: We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals.In particular, we show that the Lewis acid-base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability.High luminescence quantum efficiencies of 20-30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50-65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface.

View Article: PubMed Central - PubMed

Affiliation: Institute of Inorganic Chemistry, Department of Chemistry and Applied Bioscience, ETH Zürich , CH-8093 Zürich, Switzerland.

ABSTRACT
Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MX(n), where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals. In particular, we show that the Lewis acid-base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20-30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50-65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface.

No MeSH data available.