METHOD FOR SYNTHESIZING TUNGSTEN OXIDE NANOPARTICLES

Abstract

The present invention relates to a method for synthesizing tungsten oxide nanoparticles and to the tungsten oxide nanoparticles obtainable on the basis of the claimed synthesis method.

Claims

1. A method for synthesizing tungsten oxide nanoparticles, comprising the following consecutive steps: a) dissolving a halogenated tungsten compound in an alcohol having a standard boiling point of greater than or equal to 120° C., b) controlling the temperature to a value of between 60° C. and the standard boiling point of the alcohol less 5° C., c) adding oxalic acid, d) controlling the temperature to a value of between 80° C. and the standard boiling point of the alcohol less 5° C., at least greater than the temperatures of step b), and e) obtaining tungsten oxide nanoparticles comprising oxalic acid ligands.

2. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the halogenated tungsten compound is tungsten hexachloride.

3. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the alcohol is a polyol and/or a polyol derivative.

4. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the alcohol is a glycol, a glycol ether, a glycol ether acetate, and/or a mixture of these aforesaid alcohols.

5. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the alcohol is ethylene glycol and/or diethylene glycol.

6. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the solution obtained at the outcome of steps a) and b) is characterized by a molar ratio of the halogenated tungsten compound to the alcohol of between 0.005 and 0.1.

7. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the oxalic acid, before being used in step c), is dissolved in water, with a molar ratio of the oxalic acid to the water of between 0.001 and 0.1.

8. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the tungsten oxide nanoparticles are spheroidal.

9. The method for synthesizing tungsten oxide nanoparticles according to claim 8, wherein the average area of the nanoparticles, by measurement of an image obtained by transmission electron microscopy, is between 1 and 20 nm2, and and/or the average perimeter of the nanoparticles is between 3 and 20 nm, and/or the average diameter of the nanoparticles is between 0.5 and 7 nm.

10. The method for synthesizing tungsten oxide nanoparticles according to claim 8, wherein the nanoparticles have D50 values of less than 10 nm.

11. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the tungsten oxide nanoparticles obtained in step e) are subjected to washing which allows removal of everything not chemically or physically bonded to the nanoparticles, said washing taking place using ethanol, and said tungsten oxide nanoparticles being subsequently kept in ethanol, with a concentration of tungsten oxide nanoparticles in ethanol of greater than 25 mg/g.

12. The method for synthesizing tungsten oxide nanoparticles according to claim 1 wherein the tungsten oxide nanoparticles comprise oxalic acid ligands, and the amount of oxalic acid ligand is controlled via the temperature and/or the concentration of oxalic acid during steps c) and d) of the synthesis method.

13. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the tungsten oxide nanoparticles comprise oxalic acid ligands.

14. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the tungsten oxide nanoparticles comprise oxalic acid ligands in an ink formulation, wherein a liquid phase is always present during the steps of synthesizing the tungsten oxide nanoparticles, and during all of the steps before the formulation of ink.

15. The method for synthesizing tungsten oxide nanoparticles according to claim 1, wherein the alcohol of step a) has a standard boiling point of greater than or equal to 150° C., wherein the temperature of step b) is controlled between 70° C. and 100° C., and wherein the temperature of step d) is at least greater than the temperature of step b).

16. The method for synthesizing tungsten oxide nanoparticles according to claim 6 wherein the molar ratio is between 0.010 and 0.025.

17. The method for synthesizing tungsten oxide nanoparticles according to claim 7 wherein the molar ratio is between 0.005 and 0.020.

18. The method for synthesizing tungsten oxide nanoparticles according to claim 8, wherein the average area of the nanoparticles, by measurement of an image obtained by transmission electron microscopy, is between 5 and 15 nm2, the average perimeter of the nanoparticles is between 5 and 15 nm, and the average diameter of the nanoparticles is between 1 and 5 nm.

Description

[0044] Examples—the WO3 nanoparticles were obtained in accordance with the particular synthesis example described in the text above. They were kept in ethanol in accordance with the indication in the description above.

[0045] Measurement of the % of Organic Phase (Water Trapped in the Crystal Lattice+Oxalic Acid) by Thermogravimetric Analysis

[0046] These measurements were made using a Thermogravimetric Analyzer (TGA) instrument from TA Instruments, according to the following characteristics: [0047] a) Measurement method: TGA [0048] b) Temperature rise: 20° C./min [0049] c) Temperature range: Ambient.fwdarw.600° C.

[0050] The % of organic phase is between 10 and 15%.

[0051] Determination of the Size and Morphology of Nanoparticles+Statistics

[0052] These measurements were made using a transmission electron microscope (TEM) instrument from ThermoFisher Scientific, according to the following characteristics: [0053] a) TEM-BF (Bright Field images) were made at 300 kV [0054] b) 50 μm objective lens diaphragm for low magnifications [0055] c) No objective lens diaphragm for high resolution [0056] d) The dimensional measurements were made on TEM images using the Digital Micrograph software.

[0057] The measurements are reported in the table below (average over 20 particles).

TABLE-US-00001 TABLE 1 Area Perimeter Major diameter Minor diameter (nm.sup.2) (nm) (nm) (nm) 7 ± 4 10 ± 3 3 ± 1 2 ± 1

[0058] The table below contains ink compositions (formulated from the same WO3 nanoparticles) which are particularly suited to the electronics sectors.

TABLE-US-00002 TABLE 2 Reference/ % by weight WO3 2-propanol Water Additive Total SW91011 2.5 97.5 0.0 0.0 100.0 SW91014 2.5 15 82.5 0.0 100.0 SW91018 2.5 14.875 82.375 0.25 100.0

[0059] The additive is a rheology modifier agent selected from cellulosic rheology modifier agents.

[0060] The constituents are indicated in the table along with their concentration by weight for each of the compositions.

[0061] The three formulas described above have the following physicochemical characteristics:

[0062] Viscosity measurements were carried out for these three ink compositions.

[0063] Measurement of Ink Viscosity

[0064] These measurements were made using an AR-G2 Rheometer instrument from TA

[0065] Instruments, according to the following characteristics: [0066] a) Temperature: 20° C. [0067] b) Shear: 10-40-1000 s-1 [0068] c) 1° conical spindle

[0069] The measurements are reported in the table below.

TABLE-US-00003 TABLE 3 SW91011 SW91014 SW91018 3 cP 3 cP 5.5 cP

[0070] Particle size distribution studies were also carried out for these three ink compositions.

[0071] These measurements were made using a Nanosizer S instrument from Malvern, according to the following characteristics: [0072] a) Measurement method: DLS [0073] b) Cell type: optical glass [0074] c) Material: WO3 [0075] d) Temperature: 20.0° C. [0076] e) Viscosity 3 cP for ink SW91011 and viscosity 3 cP for ink SW91014 and viscosity 5.5 cP for ink SW91018. [0077] f) Refractive index: 1.380 for ink SW91011 and 1.340 for inks SW91014 and SW91018.

[0078] The hydrodynamic diameter and D50 values are reported in the table below.

TABLE-US-00004 TABLE 4 SW91011 SW91014 SW91018 Hydrodynamic 10-30 nm 5-10 nm 5-10 nm diameter D50 10-30 nm 5-10 nm 5-10 nm

[0079] Surface tension measurements were also carried out for these three ink compositions.

[0080] These measurements were made using a tensiometer instrument from Apollo Instruments, according to the following characteristics: [0081] a) Pendant drop method [0082] b) Temperature: 20° C. [0083] c) Density of 0.803 for ink SW91011 and 0.981 for ink SW91014 and 0.985 for ink SW91018.

[0084] The surface tension values are reported in the table below.

TABLE-US-00005 TABLE 5 SW91011 SW91014 SW91018 Surface 21 mN/m 31 mN/m 32 mN/m tension

[0085] The three formulas described above were applied to rigid and flexible supports, and give promising results in terms of roughness and electrical properties.

[0086] Roughnesses <5 nm for the three inks were measured on an Alpha Step IQ mechanical profilometer from KLA Tencor.

[0087] The following electrical properties were measured by Hall effect on an AMP55T instrument from Microworld for SW91011:

TABLE-US-00006 TABLE 6 WF Conductivity Mobility [eV] [S .Math. cm] [cm2/V .Math. S] 5.2 eV 4−8E−02 21 for 300 nm

[0088] The three formulas were also integrated into multi-layer photovoltaic systems, and the electrical performances are promising.

[0089] We are therefore able to envisage their use in the printed electronics sector, more particularly for realizing OPV (organic photovoltaic) modules, as sources for the HTL (hole transport layer) layers.

[0090] The inks are particularly suited to the following printing method and following types of OPV structure:

TABLE-US-00007 TABLE 7 Ink Printing method OPV structure SW91011 Slot die Inverse structure SW91014 Slot die Normal structure SW91018 Ink jet Inverse and normal structure