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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) Absorption and steady-statePL spectra of PbS NCs before andafter ligand exchange. (b) Time-resolved PL spectra of the ∼3.8nm PbS NC solutions capped with oleic acid (black), MAPbI3 (red), and K3AsS4 (blue) ligands.
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fig2: (a) Absorption and steady-statePL spectra of PbS NCs before andafter ligand exchange. (b) Time-resolved PL spectra of the ∼3.8nm PbS NC solutions capped with oleic acid (black), MAPbI3 (red), and K3AsS4 (blue) ligands.

Mentions: For PbS NCs, there is growing recognition that halide ions reducethe density of surface trapping states and therefore enhance the performanceof solar cells based on PbS NCs, reaching power conversion efficienciesof 6% and 7%.18 The authors of ref (18) used solid-state ligandexchange or partial halide passivation via solution-phase treatmentof oleate-capped PbS NCs, maintaining most of the oleate capping forefficient colloidal stabilization in nonpolar solvents. Our presentstudy shows the possibility of obtaining fully inorganic, halide-coveredPbS NCs in the form of stable colloidal solutions. The integrity ofPbS NC cores after the ligand exchange with MAPbI3 is evidencedby absorption spectra (Figure 2), which containsharp excitonic features, slightly red-shifted with respect to theoleate-capped NCs. The extent of electronic passivation was monitoredwith steady-state and time-resolved PL measurements. Colloidal solutionsof MAPbI3-PbS NCs exhibit PL quantum yields (QY) of 20–30%,comparable with the QYs of NCs capped with oleic acid before the ligandexchange and much higher than the QY of PbS NCs capped with [AsS4]3– (QY ≤ 1%). A similar perovskitecompound, MAPbBr3, also preserved the efficient and stablePL properties of PbS NCs. Enhanced surface passivation, suggestedby the high PL QY, is also evidenced by the retention of a long-livedcomponent in the corresponding PL decays of PbS NCs (Figure 2B). The long component, usually on the order ofsub-μs, is characteristic of the intrinsic recombination rateof the exciton, screened by the high dielectric constant of PbS. Time-resolvedPL traces for NCs capped with the three different ligand materialsare adequately fitted with double exponential fits (see Figure S5and Table S4 in SI for 3.8 and 4.5 nm PbSNCs). Oleate-capped NCs are characterized by two time constants inthe range of 300 ns and 80 ns. The faster component can be attributedto recombination on the surface states. MAPbI3-capped NCsshow average PL lifetimes of similar magnitude to the oleate-cappedones, in agreement with the comparable QY of the two NC materials.The decays consist of a fast component of 10–30 ns during which20–30% of the photogenerated carriers recombine, presumablyvia trapping, and a longer decay in the range 600–700 ns thatcan be attributed to excitonic recombination. Contrary to the abovetwo cases, the fast PL decays of K3AsS4-cappedNCs (two time constants in the range of 10 ns and 20–40 ns,respectively) strongly suggest fast carrier trapping as the dominantrecombination channel, consistent with the low QYs.


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) Absorption and steady-statePL spectra of PbS NCs before andafter ligand exchange. (b) Time-resolved PL spectra of the ∼3.8nm PbS NC solutions capped with oleic acid (black), MAPbI3 (red), and K3AsS4 (blue) ligands.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4524702&req=5

fig2: (a) Absorption and steady-statePL spectra of PbS NCs before andafter ligand exchange. (b) Time-resolved PL spectra of the ∼3.8nm PbS NC solutions capped with oleic acid (black), MAPbI3 (red), and K3AsS4 (blue) ligands.
Mentions: For PbS NCs, there is growing recognition that halide ions reducethe density of surface trapping states and therefore enhance the performanceof solar cells based on PbS NCs, reaching power conversion efficienciesof 6% and 7%.18 The authors of ref (18) used solid-state ligandexchange or partial halide passivation via solution-phase treatmentof oleate-capped PbS NCs, maintaining most of the oleate capping forefficient colloidal stabilization in nonpolar solvents. Our presentstudy shows the possibility of obtaining fully inorganic, halide-coveredPbS NCs in the form of stable colloidal solutions. The integrity ofPbS NC cores after the ligand exchange with MAPbI3 is evidencedby absorption spectra (Figure 2), which containsharp excitonic features, slightly red-shifted with respect to theoleate-capped NCs. The extent of electronic passivation was monitoredwith steady-state and time-resolved PL measurements. Colloidal solutionsof MAPbI3-PbS NCs exhibit PL quantum yields (QY) of 20–30%,comparable with the QYs of NCs capped with oleic acid before the ligandexchange and much higher than the QY of PbS NCs capped with [AsS4]3– (QY ≤ 1%). A similar perovskitecompound, MAPbBr3, also preserved the efficient and stablePL properties of PbS NCs. Enhanced surface passivation, suggestedby the high PL QY, is also evidenced by the retention of a long-livedcomponent in the corresponding PL decays of PbS NCs (Figure 2B). The long component, usually on the order ofsub-μs, is characteristic of the intrinsic recombination rateof the exciton, screened by the high dielectric constant of PbS. Time-resolvedPL traces for NCs capped with the three different ligand materialsare adequately fitted with double exponential fits (see Figure S5and Table S4 in SI for 3.8 and 4.5 nm PbSNCs). Oleate-capped NCs are characterized by two time constants inthe range of 300 ns and 80 ns. The faster component can be attributedto recombination on the surface states. MAPbI3-capped NCsshow average PL lifetimes of similar magnitude to the oleate-cappedones, in agreement with the comparable QY of the two NC materials.The decays consist of a fast component of 10–30 ns during which20–30% of the photogenerated carriers recombine, presumablyvia trapping, and a longer decay in the range 600–700 ns thatcan be attributed to excitonic recombination. Contrary to the abovetwo cases, the fast PL decays of K3AsS4-cappedNCs (two time constants in the range of 10 ns and 20–40 ns,respectively) strongly suggest fast carrier trapping as the dominantrecombination channel, consistent with the low QYs.

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.