RU2462793C2 - Hybrid nanocomposite materials - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention is aimed at producing hybrid nanocomposite material which contains conducting inorganic elongated crystals with an electrically conducting organic compound of given formula grafted on at least part of its surface, said compound forming a self-organising layer. The invention also discloses thin films, solar batteries and switching devices containing said hybrid nanocomposite material.

EFFECT: production of original nanocomposite materials, especially for high-efficiency cheap solar batteries.

20 cl, 9 dwg

Description

FIELD OF THE INVENTION

The present invention relates to hybrid nanocomposite materials, their production process and their use, especially in components for solar cells and in switchable electrical devices.

BACKGROUND OF THE INVENTION

Solar energy is still a fairly uncompetitive alternative to other methods of energy production. The main reasons for this are the high production costs of existing silicon solar cells and the limited effectiveness of low-cost alternatives.

Research aimed at improving devices has led to numerous techniques, including, in particular, coaxial silicon nanowires (Lieber et al., Nature Lett., 449, (2007) 885). Nanowires consist of a silicon p-doped core coated with a sheath of pure and n-doped silicon. However, silicon-based devices are expensive due to material costs and manufacturing costs, which involve high temperature, high vacuum, and numerous lithography steps.

It has been proposed to replace silicon with organic or polymer semiconductors that can be processed from solution. However, photoexcitation in these materials does not directly lead to the appearance of free charge carriers, but creates pairs of electron-hole carriers, called excitons. In order to separate excitons into free charge carriers, the interface between the electron-donating (n-type) and electron-withdrawing (p-type) materials is required. Taking into account their short lifetime, only excitons generated near the interface are sources of charges. Thus, n- and p-type domains must have a large interface and at the same time form two continuous domains in order to ensure that the generated charges reach the electrodes.

Thus, nanocomposite materials are an interesting option for the manufacture of low-cost solar cells.

In the work of Yu, G .; Gao j; Hummelen, J.C .; Wudl, F .; Heeger, A.J .; Science 1995, 270, 1789; Shaheen, S.E .; Brabec, C.J .; Padinger, F .; Fromherz, T. solar cells based on a mixture of polymers containing electron-donor and electron-acceptor phases were proposed, from which fullerene-containing mixtures were most successful.

Hummelen, J.C .; Sariciftci, N.S. Appl. Phys. Lett. 2001, 78, 841; Wienk, M.N .; Kroon, J.M .; Verhees, W.J.H .; Knol, L .; Hummelen, J.C .; Van Hal, P.A .; Janssen, R.A.J. Angew. Chem., Int. Ed. 2003, 42, 3371, Shilinsky, P .; Waldauf, C .; Brabec, C.J. Appl. Phys. Lett. 2002, 81, 3885. Svensson, M .; Zhang, F .; Veenstra, S.C .; Verhees, W.J.H .; Hummelen, J.C .; Kroon, J.M .; Inganas, O .; Andersson, M.R. AdV. Mater. 2003, 15, 988. Two polymers form an interpenetrating lattice with phase separation on a nanometer scale, which leads to the formation of a highly efficient bulk heterojunction. Such organic solar cells can show up to 5% solar energy conversion efficiency. However, mixing two polymers often entails problems with controlling the morphology of the mixture and with stabilizing the phase separation between the two polymers. In addition, the electron transport and the stability of n-type organic semiconductors in the atmosphere are weak.

-диметилоктилокси)-1,4-фениленевинилена] (MDMO-PPV) в качестве донора электронов (Jenssen et al., J. Phys. Chem. B, 2005, 109, 9505). Солнечные батареи, изготовленные из ZnO наностержней вместо наносфер, не приводят к усовершенствованию работы солнечной батареи. Необходимость использования поверхностно-активного вещества для увеличения растворимости наностержней, в конечном счете, ведет к отсутствию усовершенствования работы солнечных батарей по сравнению с полимерными смесями.Recently, conjugated polymers have been mixed with n-type inorganic semiconductors, as in hybrid solar cells combining CdSe nanorods with poly-3 (hexylthiophene) (P3HT) (Alivisator et al., Science, 295 (2002) 2425) be made by processing the solution. The use of elongated nanoparticles instead of nanospheres can improve the operation of the device, because nanorods and P3HT have complementary absorption spectra, and the photocurrent spectrum of a device from the resulting nanorod-polymer mixture can be expanded to 720 nm. In another example of hybrid nanocomposite solar cells, ZnO nanoparticles as an electron acceptor are mixed with a matrix of conjugated polymers poly [2-labels-5 (

-dimethyloxythyloxy) -1,4-phenylene neovinylene] (MDMO-PPV) as an electron donor (Jenssen et al., J. Phys. Chem. B, 2005, 109, 9505). Solar panels made of ZnO nanorods instead of nanospheres do not lead to an improvement in the performance of the solar battery. The need to use a surfactant to increase the solubility of nanorods ultimately leads to a lack of improvement in the performance of solar cells compared to polymer mixtures.

Another limitation of hybrid or polymer nanocomposites is the fact that the original P3HT polymer absorbs mainly between 300 and 650 nm and thus cannot capture most of the solar spectrum. Modification of the polymer is difficult because any changes in its molecular structure affect other properties, such as morphology, carrier mobility between polymer chains, dispersion or purity.

SUMMARY OF THE INVENTION

The present invention is intended, therefore, to create original nanocomposite materials, especially for low-cost solar cells with high efficiency, which could overcome one or more of the previously existing disadvantages.

The result is achieved by providing a hybrid nanocomposite material, which includes elongated inorganic nanoparticles, especially nanorods, with grafted at least part of their surface electrically conductive organic compounds.

These materials demonstrate interesting properties, especially with respect to the transport of charge carriers, since they allow independent coaxial ambipolar transport of charge carriers to the inorganic and organic parts of the hybrid nanocomposite. Moreover, materials allow direct regulation of their absorption, organization and solubility.

DEFINITIONS

In the next part of the document, the following terms are meant:

Elongated nanocrystals: crystalline, especially single-crystal nanostructures, including at least one elongated part, such as nanowires, nanorods, nanotubes, nanostructures with two branches, nanostructures with three branches, nanostructures with four branches and many nanostructures, such as nanostars. For nanowires, nanorods and nanotubes, the elongated part makes up the entire nanostructure. The aspect ratio of the elongated portion is usually greater than 2, preferably greater than 3, and most preferably from 5 to 200. Typical dimensions of the elongated portion are 3-100 nm in diameter and 10-2000 nm in length.

Nanocomposite material: a material comprising at least two finely dispersed immiscible components, the dimensions of the dispersed phase of a nanometer scale, usually in the range from 1 to 500 nm, preferably from 2 to 100 nm.

Hybrid material: includes inorganic components and organic components.

Organic Compounds: Compounds consisting predominantly of carbon and hydrogen and containing to a lesser extent oxygen, nitrogen, sulfur and phosphorus, other than elemental carbon, carbonates, carbon monoxide and carbon cyanide.

Vaccination: the process of combining molecules on a solid surface, including electrostatic interaction, adsorption and / or covalent binding.

Self-organizing monolayer: an ordered molecular ensemble formed by adsorption of a single layer of molecules on a solid surface.

Electrical conductor: material capable of transporting charge carriers, including metal conductors and semiconductors.

DETAILED DESCRIPTION

Nanocomposite material

In accordance with a first aspect, the invention relates to hybrid nanocomposite materials, including electrically conductive inorganic elongated nanocrystals grafted onto at least parts of its surface with electrically conductive organic compounds.

The hybrid nanocomposite material in accordance with the invention includes elongated nanocrystals as the main or sole inorganic component.

The anisotropic geometry of the elongated nanocrystals provides a simple, direct transport of charge carriers along their longitudinal axis, since they require much fewer hopping steps in order to reach an electrode of a device such as a solar battery compared to spherical nanocrystals.

Preferably, the nanocrystals have a preferred orientation in the nanocomposite. Such a preferred orientation can be obtained, in particular, by the intermolecular forces of surfactants (surface effects) or by applying an electric field. A well-ordered ensemble of elongated crystals improves the interaction between nanocrystals and allows the transport of charge carriers over long distances with high efficiency. The use of inorganic materials is more preferable, since these materials demonstrate high mobility of charge carriers, dimensional stability and resistance to external influences.

A hybrid nanocomposite material in accordance with the invention includes elongated electrically conductive inorganic nanocrystals. The elongated nanocrystals can be, in particular, semiconductor or metal. More often, nanocrystals will be n- or p-type semiconductors, depending on the concept of the device.

Such nanocrystals can be formed from a wide range of inorganic compounds, including, in particular: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, osmium, cobalt, nickel, copper, silver, gold, zinc, cadmium, scandium, yttrium, lanthanum, boron, gallium, indium, arsenic, thallium, silicon, germanium, tin, lead, magnesium, calcium, strontium, barium, aluminum and their simple and mixed chalcogenides, in particular their oxides and sulfides. The semiconductors may be elemental semiconductor materials, such as silicon and germanium, ultimately doped, or semiconductor compounds, such as gallium arsenide and indium phosphide, or alloys, such as a silicon and germanium alloy or a gallium aluminum-arsenide alloy.

Preferred metal conductors are materials with high mobility of charge carriers, such as gold, silver, copper and indium, doped with tin oxide (ITO).

Preferred semiconductors are semiconductors with a band gap of 0.4 eV to 4.1 eV, in particular with a band gap close to the solar spectrum. The band gap can be further adjusted by changing the diameter of the elongated nanocrystal or by additional doping. Particularly preferred semiconductors are zinc oxide, zinc sulfide and titanium dioxide.

A particularly preferred semiconductor is zinc oxide. This is an n-type semiconductor that combines a set of advantageous properties: it is cheap, has high carrier mobility, is transparent, non-toxic, and nanorods are readily available (Weller et al., Angew. Chem. Int. Ed., 41 (7), ( 2002) 1188).

Elongated nanocrystals are preferably single crystals. In fact, single crystals exhibit improved transport properties, and the absence of surface defects improves the ability of the grafted organic monolayer to form highly crystallized self-organizing ZAM monolayers.

The hybrid nanocomposite material in accordance with the invention also includes organic compounds grafted onto elongated nanocrystals as the main and only components.

According to the invention, the electrically conductive compounds are preferably n- or p-type semiconductors. They can also be metal-conductive organic compounds such as poly (3,4-ethylenedioxythiophene) (PEDOT), charge transfer complexes such as (BEDT-TTF) 2I3 or functionalized carbon nanotubes.

The surface of elongated nanocrystals contains a large cylindrical segment, which has a satisfactory curvature and, thus, enables the formation of an automatically organized monolayer (SAM) around the nanocrystal. For this reason, although this feature is not key to the invention, the organic compound forms SAM grafted onto the nanocrystals of the composite according to the invention. In some cases, ordered molecules in SAM can even be crystalline, as observed by x-ray diffractometry.

Although grafting due to pure electrostatic interaction is not excluded, it is believed that the presence of stronger bonds, such as covalent bonds, will improve the stability of the composites and, therefore, is preferred. Organic compounds thus preferably contain at least one fixed part suitable for forming a covalent bond with the surface of an inorganic nanocrystal. However, to facilitate the formation of crystalline SAM, it is preferable that the grafted bonds are moderately strong, which makes it possible to create two-way bonds and, thus, carry out position regulation. Moreover, while ensuring the effective adsorption of organic compounds on the nanocrystalline surface, the fixing part can also contribute to the efficient electronic bonding of the donor level of the organic compound and the acceptor level of the nanocrystal.

According to the invention, electrically conductive organic compounds of the formula (I) are used:

Where:

A is a fixed part, which may be, in particular, carboxylic acid, amine, phosphonic acid, phosphate, thiol or silane groups;

L is a non-conductive part, which may be, in particular, a saturated hydrocarbon, in particular a saturated, straight or branched alkyl group with 3-20 carbon atoms, or may be absent;

Y is the electrically conductive part containing a mating system allowing n- and p-type semiconductivity, such as pentacene, anthracene, phthalocyanines, porphyrins, fullerenes, oligothiophene, polypyrol, carotene, chlorophylls, bacteriochlorophylls and carotenoids or organic metals such as functionalized nanotubes, PEDOT, charge transfer complexes such as (BEDT-TTF) ₂ I ₃ .

Z is a solvent part, which may, in particular, be a non-conjugated hydrocarbon group, such as a straight or branched, saturated or unsaturated alkyl group with 1-20 carbon atoms, in particular n-butyl, n-pentyl, n-hexyl, n -heptyl and n-octyl, or may be absent; and

X is a stabilizing part, capable of forming intermolecular bonds, which may, in particular, be absent, forming a hydrogen bond, such as hydroxy, amino, amido or carboxylic acid.

In order to be grafted onto nanocrystals, the organic compound of formula (I) has one or more fixed parts A capable of forming bonds with the surface.

Preferably, the bonds formed by the fastening part allow for a displacement (or desorption-re-adsorption cycle) on the surface, which is an advantage for the crystallization process.

Organic compounds of formula (I) also contain an electrically conductive part Y, which enables the transport of charge carriers, absorption of light, and generation of excitons. The portion may be monomeric, oligomeric or polymeric. Preferably, the compound includes a pi-conjugated system, in particular obtained from compounds such as pentacene, anthracene, oligothiophenes, polythiophenes such as poly-3 (hexylthiophene) (P3HT), poly- (3,4-ethylenedioxythiophene) (PEDOT) and polypyrol, or non-pi non-conjugated systems, such as fullerenes, phthalocyanines, porphyrins. Other preferred portions are derived from naturally conjugated compounds with photosensitive, conductive properties resulting from biomass that can be obtained by extraction from natural systems such as trees, algae, photosynthetic bacteria such as chlorophylls, bacteriochlorophylls and carotenoids.

Preferably in organic compounds there are LUMO (Lowest Unoccupied Molecular Orbit) and HOMO (Higher occupied molecular orbital) levels compared to the valence and conduction bands of an inorganic nanocrystal, so as to enable efficient exciton dissociation at the interface of the hybrid material by a significant shift in the energy zone. This energy zone shift can be improved by adapting the Fermi level of an inorganic nanocrystal using targeted doping.

Particularly preferred conjugated systems that absorb in the solar spectrum. Aromatic constituents are also preferred in which pi-orbitals overlap to stabilize the organic shell.

The organic compound of formula (I) may also further comprise non-conductive parts L between the fixing part A and the conductive part Y. Such a non-conductive part may be a saturated hydrocarbon group, in particular a saturated straight or branched acrylic group with 3 to 20 carbon atoms.

According to a preferred embodiment, the organic compound of formula (I) may also contain a solvent part Z capable of improving the solubility of the grafted nanocomposite with the graft solution. This fact indicates a further exchange of molecules in solution and, thus, is favorable for the formation of a crystalline monolayer.

The organic compound of formula (I) may also optionally contain a stabilizing part X capable of stabilizing the aggregate of molecules on the surface of the nanocrystals through intermolecular interaction. This part allows for intensive grafting and, thus, promotes a crystalline monolayer. Such parts may be, in particular, groups such as hydroxy acid, amino acid, amide or carboxylic acid. Amide groups and moieties derived from alpha amino acids, oligopeptides, urea, nucleosides, cholesterol and triple alkyl benzene are particularly preferred.

The formation of gels may be of interest for the production of fiber optic networks, which enable the structuring and orientation of nanocrystals and conjugated organic compounds, which lead to anisotropic changes in transport. The formation of the gel also makes it possible to control the viscosity of solutions, which is an important parameter for precipitation from solution.

Organic compounds of formula (I) associated with inorganic nanocrystals can impart self-organization properties to the nanostructure.

Therefore, the organic compound can be chosen so that the formation or ordering of a monolayer on the surface of elongated nanocrystals can be advanced or, conversely, suppressed.

In particular, the presence of a destabilizing terminal group, in particular spatially blocked groups, is a convenient means to avoid ordering of the grafted molecules on the surface of the nanocrystal and to obtain amorphous SAM.

Organic compounds are preferably asymmetrically substituted molecules with three different functional parts, namely a binding part, a conductive part and a self-organizing part.

In a simple implementation, the organic compounds may be a carboxylic acid having 3-10 carbon atoms linked to a pi-conjugated system substituted with one or more groups formed by hydrogen bonds, such as amide groups. A carboxylic acid group will connect the surface of the nanocrystal, while terminal amide groups will form intermolecular hydrogen bonds.

An example of such organic compounds are compounds of formula (II) obtained from oligothiophene:

Where:

R is a fixed part, in particular a carboxylic acid containing from 3 to 6 carbon atoms, in addition to the carboxyl group;

R 'is a straight, branched or cyclic hydrocarbon group, in particular an alkyl or aromatic group containing 1-20 carbon atoms.

A self-organizing effect can also be obtained by grafting two or more different compounds on the surface of a nanocrystal. For such a mixed monolayer, one organic compound has electrical conductivity and, optionally, self-organizing properties, while the second or other compounds can have only self-organizing properties without any conductive properties.

The orientation order of the nanocrystals inside the nanocomposite can be increased by using organic compounds with a fixing component with the characteristics of a liquid crystal.

Particularly preferred organic compounds are the following:

The characteristics of a liquid crystal can also be obtained by multiple grafting of two or more different organic compounds onto the surface of nanocrystals. For such a mixed monolayer, one compound has electrical conductive properties and optionally LC properties, while the second or other compounds may also carry one or more LC groups.

Nanocrystals with organic compounds grafted, as described, form a hybrid nanocomposite material containing parallel channels for ambipolar coaxial transport of charge carriers.

Particularly preferred materials with adjustable absorbing and transport properties, which makes it possible to manufacture solar cells that absorb in a certain range of wavelengths.

In order to produce efficient solar cells, the absorption spectrum of the organic compound should preferably be close to or lying in the region of the solar spectrum. Usually this is not achieved for individual species. However, grafting of many species with complementary absorption spectra can lead to a black nanocomposite capable of absorbing a radiation range that exceeds the entire solar spectrum. Especially preferred is the combined grafting of pentocene or oligothiophenes with phthalocyanines, which leads to the absorption of the wavelength spectrum from 300 nm to 900 nm.

Multiple grafting nanocomposite materials can be obtained by grafting various materials simultaneously or sequentially onto a group of nanoparticles or by mixing groups of nanoparticles with one type of grafted organic semiconductor.

After grafting, organic compounds form around the nanocrystal a clearly defined and stable domain with adjustable absorbing and conductive properties. A nanocomposite material containing n- or p-type inorganic semiconductor nanocrystals grafted with n- or p-type organic semiconductor compounds, respectively, makes coaxial ambipolar conductivity possible, electrons mainly transfer to the nanocrystal, while holes mainly go into the organic shell.

Organic compounds are grafted onto at least a portion of the surface of the elongated nanocrystal. In most cases, grafting of the entire monolayer is preferred to support the formation of a well-ordered or crystalline SAM.

However, in some cases, an incomplete SAM hybrid nanocomposite material may be preferred.

In fact, a hybrid nanocomposite material with incomplete or mixed SAM can promote conductivity between hybrid nanocrystals. This is because carrier transport between two adjacent hybrid nanocrystals involves the intersection of two SAMs, which for the n-p configuration is equivalent to the n-p-p-n junction. The probability that an electron is effective, i.e. without loss of resistance, crosses such a transition, can be increased if a certain amount of organic compound with a different type of conductivity is grafted onto the nanocrystal, as described above, or if direct mechanical contact with the surface of the nanocrystal is possible.

The result is the creation of "transport channels" for electrons, which simplify the transport of charge carriers in nanocrystals.

The grafting of electrically conductive organic compounds onto the surface of electrically conductive inorganic elongated nanocrystals allows the production of hybrid nanocomposite materials that can form the following transitions between nanoparticles:

- hybrid nanocomposites containing metal nanocrystals grafted with organic compounds with the transport properties of n- or p-type charge carriers, respectively, make it possible to produce m-p or m-n Schottky diodes;

- hybrid nanocomposites containing metal and semiconductor nanocrystals, grafted with organic compounds with the transport properties of n-type, p-type or metal charge carriers, make it possible to form pn, p-p, nn, m-m, m-p, m-n inter-particle transitions, respectively; and

- hybrid nanocomposites in which the organic compound contains an insulating part can, taking into account the clearly ordered SAMs that can be obtained, form p-i-n, p-i-p, n-i-n, m-i-m, m-i-p, m-i-n junctions.

Production process

The second object of the invention is a method for the production of nanocomposite materials according to the invention.

The nanocomposite material according to the invention is easily obtained by performing conventional operations from reagents, nanocrystals and an organic compound, without the need for specific equipment. The technology does not require the use of high temperatures, high vacuum or various lithographic operations. The nanocomposite material according to the invention can thus be produced at low cost.

The manufacturing process of a hybrid nanocomposite material in accordance with the invention comprises steps including:

(i) providing electrically conductive inorganic elongated nanocrystals;

(ii) contacting the nanocrystals with electrically conductive organic compounds, optionally in an appropriate solvent, under conditions suitable for grafting the organic compound onto the nanocrystals;

(iii) isolation of the obtained grafted nanocrystals from a mixture of reagents; and

(iv) cleaning the composite, if applicable.

Preferably, the nanocrystals are provided in step (i) in the form of a suspension in an appropriate solvent. Preferably, the nanocrystals are used as such, without any further processing, and, in particular, without any surfactant. In fact, the presence of any foreign compound can impede the process of grafting and the formation of a crystalline self-organizing layer and, thus, reduce the achieved efficiency of the device.

The solvent, if used, is selected according to the nature of the nanocrystal, however, in general, it is a non-polar solvent such as a chlorine-containing aromatic series or an aliphatic hydrocarbon, ether or the like. Particularly preferred are chlorobenzene, dichlorobenzene, chloroform, dichloromethylene, dimethylformamide, tetrahydrofuran. But depending on the nature of the nanoparticles and the grafting molecule, polar solvents such as methanol, ethanol, propanol and acetone may also be suitable.

Step (ii) of the method is preferably performed with agitation. The reaction time significantly depends on the reactivity of the attached fusing group and on the material of the nanocrystal. The reaction, however, most often ends within 1-48 hours, and the morphological evolution of the grafted monolayer in the direction of crystalline organization can take several days.

In accordance with a specific embodiment of the invention, the nanocrystal is grafted with organic compounds having different absorption spectra.

In accordance with another embodiment of the invention, the nanocrystal is grafted with two organic compounds characterized by preferential transport of charge carriers.

According to another embodiment of the invention, the nanocrystal is grafted with two organic compounds characterized by conductive and self-organizing properties.

According to another embodiment of the invention, the nanocrystal is grafted with two organic compounds characterized by conductive properties and liquid crystal properties.

In all cases, specific grafting of various compounds is preferred.

However, grafting organic compounds at specific positions on the surface of nanocrystals is difficult, because in most cases, the surface lacks selectivity for the compound. In such cases, the surface of the nanocrystal must first be prepared to become selective. The following two performances enable selective grafting of nanocrystals. They are explained for n- and p-type organic compounds grafted together on the surface of an n-type inorganic semiconductor, but can also be applied to other types of compounds.

According to a first embodiment of the invention, grafting of the p-type organic compound onto the surface of the nanocrystal was not completed, leaving the nanocrystal with a surface coverage of less than 100%. If there is enough coverage, a stable SAM can be formed. Incomplete SAM can then function in the second step as a template for sequentially grafting an n-type organic compound selectively to the surface of the nanocrystal.

According to a second embodiment of the invention, a p-type organic compound is first grafted onto the nanocrystals to obtain complete SAM on the surface (the surface of the nanocrystal is 100% coated). At the second stage, the obtained hybrid nanocomposite is subjected to treatment with a solution containing an n-type semiconductor, while p-type organic compounds will be partially replaced by p-type compounds, especially in those positions where SAM is less stable, such as, for example, the edges of an elongated nanocrystal.

In a third step (iii), the hybrid nanocomposite material is isolated by conventional methods. When using a solvent, the separation can be conveniently performed by filtration and / or centrifugation and / or evaporation.

In addition to washing with a solution, separate cleaning is usually not required.

Hybrid nanocomposites obtained in this way are stable over time and can be stored until use in solution. In fact, electrostatic or covalent bonds that bind organic and inorganic materials interfere with the separation of the phases of the nanocomposite in solution. The formation of a self-organizing monolayer (SAM) can also contribute to the stabilization of the hybrid nanocomposite.

Because elongated nanocrystals are dimensionally stable; nanocomposites are also stable in the manufacture of thin films. The hybrid nanocomposites of this invention thus provide access to a variety of time-stable electro-optical and electronic switching devices.

Thin film

Thin films with coaxial ambipolar conductive properties can be obtained both by deposition of the hybrid nanocomposite according to the invention, and from a solution also containing auxiliary substances, such as polymers.

A thin film can be made from the hybrid nanocomposite according to the invention by standard methods using solutions, such as a coating obtained by centrifugation, immersion or printing, which, in general, is followed by a drying step.

The organization and orientation of hybrid nanocrystals inside a thin film can be controlled using various technologies, in particular using an electric field, i.e. a constant or alternating electric field, forming a thin film by Langmuir Blodgett methods, the technology of slow drying of the film using solvents with a high boiling point.

The organization and orientation of nanocrystals within the nanocomposite can also be controlled by selectively grafting various organic compounds at specific positions of the nanocrystals, such as terminal endings or side walls.

In addition, grafting of various organic compounds can be used to ensure the amphiphilic properties of nanocrystals. In addition, a change in the number of molecules grafted onto the surface makes it possible to regulate the interaction with a hybrid nanocomposite and, thus, the organization of grafted compounds with self-organizing and LC properties on the surface.

For some applications, it may be interesting to obtain thin films of a nanocomposite with partial or complete separation or separation of organic and inorganic components. This can be obtained through the use of grafted compounds, which form only weak bonds with the surface of the elongated nanocrystal or, ultimately, through additional annealing operations.

Solar panels

A third aspect of the invention relates to solar cells containing composite materials in accordance with the invention.

Advantageously, the hybrid nanocomposite according to the invention can be made from a solution and can even be printed.

A solar battery may, in particular, be manufactured using the following steps, including:

(a) coating a structured conductive transparent substrate, such as an ITO substrate with a conductive film, such as a PEDOT film; a conductive film provides efficient hole extraction and injection into the organic part of the hybrid composite;

(b) coating a hybrid nanocomposite layer with a surface of a conductive layer;

(c) attaching electrical contacts, typically aluminum, to the surface of the hybrid nanocomposite layer for efficient electron extraction and injection into the organic part of the hybrid composite.

Preferred solar cells are formed in the form of a thin film on a hybrid nanocomposite deposited on the surface of a conductive substrate in the form of a photovoltaic active layer. In addition, through the use of a hybrid nanocomposite with an internal n-p junction, light absorption and dissociation of excitons at the interface of the hybrid can occur, followed by ambipolar transport to external electrodes. In all cases, the organic compound plays an active photovoltaic role and / or leads to improved solubility, carrier injection and self-organization properties of an inorganic elongated nanocrystal.

In general, a hybrid nanocomposite is based on a combination of metal and semiconductor nanocrystals, with grafted organic compounds with metallic, p- or n-type transport properties of charge carriers assembled in ensembles, with the following internal transitions of nanoparticles in accordance with the invention: pn, pp, nn , mm, mp, mn, where m, n and p are organic or inorganic metallic, n- and p-type semiconductor properties, respectively, also have charge separation properties and, therefore, are znymi as active photovoltaic materials for solar cells.

In addition, the insulating component introduced into the organic compound can, taking into account the clearly ordered SAMs that can be obtained, play the role of an insulating layer in traditional devices. Therefore, the use of nanocomposites with p-i-p, p-i-n, n-p-i-n, m-i-m, m-i-p, m-i-n transitions, which make it possible to better separate the electronic properties of each part of the hybrid nanocomposite, can lead to an improvement in the performance of solar cells compared to the hybrid nanocrystals mentioned above.

Hybrid composites forming p-i-p, p-i-n, n-i-n junctions can be useful as an active layer for field effect transistors (FETs).

Switchable devices

A fourth aspect of the invention relates to switchable devices that comprise a composite material in accordance with the invention.

Switchable devices can be, in particular, in the simplest case, field effect transistors (FETs) using a thin film of a nanocomposite as an electrically active layer, i.e. layer for transport of charge carriers. Furthermore, by using a hybrid nanocomposite material with internal n-p junctions, ambipolar transistors can be formed. In all cases, the organic compound has active electrical transport properties and / or leads to improved solubility, carrier injection and self-organization properties of an inorganic elongated crystal.

Materials with other modes of transport of charge carriers can be obtained by changing the electronic characteristics of organic and inorganic materials. For example, hybrid nanocomposites with internal (interparticle) p-n, p-p, n-n junctions can be used as the active layer for FET field effect transistors.

In addition, an insulating part is represented between the fixing and conductive fractions, and taking into account the clearly ordered SAM that can be obtained, such a part can play the role of an insulating layer in conventional devices. Therefore, the use of nanocomposites with p-i-n, p-i-p, n-i-n junctions, which make it possible to better separate the electronic properties of each part of the hybrid nanocomposite, can lead to improved carrier transport in hybrid field effect transistors using hybrid nanocomposite materials.

Switchable devices can be made of hybrid nanocomposite materials according to the invention by traditional methods in which the hybrid nanocomposite is coated by centrifugation or other solution processing technologies on a treated or untreated SiO ₂ substrate.

It is also contemplated to use the hybrid nanocomposite according to the invention as LEDs (LED light emitting diode) and as nanoscale power supplies.

The invention will now be described using examples with reference to the following figures:

Figure 1: schematic representation of an ensemble of n-p junctions in a hybrid nanocomposite in accordance with a preferred embodiment of the invention;

Figure 2: (a) Electronic absorption spectrum (i) of ZnO nanorods; (ii) an organic compound of AO; (iii) a hybrid nanocomposite according to Example 1, all in a THF solution;

(b) Electronic absorption spectrum (i) of ZnO nanorods; (ii) an organic compound of ADO; (iii) a hybrid nanocomposite according to Example 2, all in a THF solution;

Figure 3: Electronic absorption spectrum (A): (i) a Ds2T solution (THF, concentration of 8 · 10 ^-8 molecular weight), (ii) a thin Ds2T film on a polarized quartz substrate H obtained by evaporation in high vacuum, 50 nm thick . (B) The electronic absorption spectrum of (i) an AO solution, grafted nanorods (TFH, concentration), and (ii) a solution of the corresponding AO grafted spherical nanocrystals.

Figure 4: (A) Schemes of extraplanar x-ray diffraction of thin films and AO powder of example 1; (B) Schemes of in-plane X-ray diffraction of thin films of the hybrid nanocomposite of Example 1 and Ds2T deposited on a SiO ₂ substrate at different temperatures;

5: Schematic representation of a solar cell fabricated using a hybrid nanocomposite according to the invention;

6: Current-voltage characteristics of solar cells containing a hybrid nanocomposite with 80-100% coating (black and red) or with 50-70% coating (green and blue) of the ZnO surface of the nanorods of Example 1 (AO-ZnO (A) and Example 2 ADO-ZnO (B) when illuminated with AMO 1.5 spectrum.

7: (a) External quantum efficiency as a function of wavelength for solar cells containing the hybrid nanocomposite of Example 1; a monolayer of an organic compound almost completely (80-100% of the surface coating, black and green) or only partially (50-70% of the surface coating, red) covers the surface of ZnO nanorods. (b) External quantum efficiency as a function of wavelength for solar cells containing the hybrid nanocomposite of Example 2; a monolayer of an organic compound almost completely (80-100% of the surface coating, black and red) or only partially (50-70% of the surface coating, green) covers the surface of ZnO nanorods;

Fig: HFET scheme made using thin films of a hybrid nanocomposite material; and

Fig. 9: (a) Hybrid field effect transistor: graph of IDs from VDs for various gate voltages in devices based on thin films of a hybrid nanocomposite material, according to examples made by coating using centrifugation (A), hole transport mode, electronic mode transport.

EXAMPLES

Example 1: Preparation of a hybrid nanocomposite material with ZnO nanorods

A. Fabrication of ZnO Nanorods

In a suitable flask, sodium hydroxide (288.8 mg, 7.22 mmol) and methanol (23 ml) are dispersed by ultrasound to obtain a high degree of dispersion. In a separate flask, zinc acetate (818.2 mg, 4.46 mmol), methanol (42 ml) and water (318 ml) are dispersed by ultrasound until completely dissolved and heated by centrifugation to 60 ° C. In an argon atmosphere, a solution of sodium hydroxide is added dropwise to a solution of zinc acetate. After 2 hours and 15 minutes at 60 ° C, the solution for growing the epitaxial layer condenses in 10 ml under reduced pressure at 55 ° C (the solution becomes colorless) and is heated for 48 hours at 60 ° C. The decanted dispersion is transferred to a distillation flask, then 50 ml of methanol is added, the solution is centrifuged for 5 minutes, and then the supernatant is decanted and removed. This washing process is repeated 3 times.

ZnO nanorods with an average diameter of 10-12 nm and an average length of 60 nm were obtained according to the results of transmission electron microscopy (TEM - transmission electron microscopy). High resolution TEM images (HRTEM) reveal that pure ZnO rods are single crystal nanocrystals with exceptionally flat surfaces at atomic resolution.

Following a similar chemical procedure, but without the last stage of condensation and subsequent growth, spherical ZnO nanoparticles with a diameter of 4 nm were obtained, which were used as comparative ones.

B. Production of a hybrid nanocomposite

Semiconductor oligothiophene (AO) having the following formula is grafted onto nanorods obtained in accordance with the previous section:

This asymmetrically substituted derivative of distyryl biophene, in the para position of which is an n-octyl oxygen chain and a carboxylic acid that functions as terminal groups, was synthesized in accordance with the protocol presented below:

A semiconductor oligothiophene compound AO was grafted onto nanorods in accordance with the following protocol. A highly concentrated solution of ZnO nanorods in methanol (50-70 mg / ml) was mixed with a solution of AO in tetrahydrofuran (THF - tetrahydrofuran) (the usual ratio of 10-7 mol per mg of ZnO nanorods used) was shaken, and the mixture was left for 3 days at room temperature temperature.

The functionalized nanorods were collected by centrifugation and washed several times with THF until the absorption spectrum of UV-VIS of the surface fluid showed any absorption in the transition zones of the AO chromophore. The results showed complete grafting to a concentration of 10 ^-6 mol per mg of ZnO nanorods. This leads to packing densities corresponding to the literature values for Ds2T polycrystalline films (see C. Videlot-Ackermann, J. Ackermann, H. Brisset, K. Kawamura, N. Yoshimoto, P. Raynal, A. El Kassmi, F. Fages, J. Am. Chem. Soc. 127, 16346-16347 (2005)). TEM did not show any modification to the shape and size of the inorganic rods after functionalization.

Example 2: Production of a hybrid nanocomposite with ZnO nanorods

Semiconductor oligothiophene (ADO) with the following formula is grafted onto nanorods prepared in accordance with Example 1 A:

This compound differs from the AO compound in that distyryl biothiophene has linear n-octyloxy chains in the twp meta-position. The compound was synthesized according to the synthesis protocol of ADO and ATO, we used a process similar to that described for AO, starting with 3,5-dihydroxybenzyl alcohol and 3,4,5-trihydroxybenzyl alcohol, respectively.

The nanorods were grafted with the ADO oligothiophene semiconductor compound according to the following protocol. A highly concentrated solution of ZnO nanorods in methanol (50-70 mg / ml) was mixed with a solution of ADO in tetrahydrofuran (THF) (the usual ratio of 10 ^-7 mol per mg ZnO nanorods used) with agitation, then the mixture was left for 3 days at room temperature.

Characterization of hybrid nanocomposite materials

FT-IR spectroscopy provided experimental evidence for AO adsorption on nanorods using carboxylate species. The spectrum of a solid sample of nanorods grafted in AO showed two groups of zones at 1580-1510 cm ^-1 and 1380-1450 cm ^-1 for asymmetrically and symmetrically stressed characters of carboxylate groups, respectively, as well as a complete loss of a sharp peak at 1686 cm ^-1 , corresponding to free acid in KBr (T. Antoun, R. Brayner, S. Al Terary, F. Fievet, M Chehimi, A. Yassar, Eur. J. Inorg. Chem. 1275-1284 (2007)). This heterogeneity of the spectrum reflects the mixing of various types of bonds of carboxylate groups with ZnO (KD Dobson, AJ McQuillan, Spectrochimia Acta Part A 55, 1395-1405 (1999)).

Different distances between adjacent surface zinc atoms, depending on the faces of the nanocrystals, can make both types of coordination of carboxylation possible: the formation of chelate compounds and the formation of cross-links. In addition, the presence of surface defects in the form of oxygen vacancies was observed using fluorescence emission spectroscopy. Such nodes favor a single-tooth type of coordination (K.D. Dobson, A.J. McQuillan, Spectrochimia Acta Part A 55, 1395-1405 (1999)). The elongated peak position of methylene and methyl CH turned out to be in good agreement with the positions of the free acid peaks in KBr and the thin film of methyl ester deposited in vacuum from AO, AOMe, which is indicative of the crystalline organization of n-octyl chains when the oligomers are bound to the surface metal oxide (DL Allara, RG Nuzzo, Langmuir 1, 52-66 (1985)).

Electron absorption spectroscopy provided an understanding of the organization of ligand chromophores on the surface of a nanorod. The spectrum of the AO solution with grafted nanorods in THA showed a large shift to the blue region of the spectrum and a noticeable exacerbation of the transition zone with minimum energy for oligothiophene (max = 368 nm) compared to the transition zone in the AO in THF (max = 465 nm) (see Fig. . 2A). In fact, the spectrum of nanorods grafted into AO resembles in many respects the spectrum of a thin continuous Ds2T film (max = 342 nm) (see Fig. 3A) by evaporation in high vacuum at a substrate temperature of 80 ° C, which corresponds to the conditions under which highly crystalline thin films are produced . The corresponding electronic absorption spectra of the solution grafted in ADO nanorods in THF showed completely different behavior. Figure 2B shows that in the case of nanorods grafted with ADO, even after several days of grafting, only a weak blue shift and a very large absorption zone were obtained.

When the AO compound was grafted onto spherical zinc oxide nanoparticles, instead of nanorods, a less shifted and broadened spectrum was obtained (Fig. 3B). The center of the absorption zone lies in the region of 400 nm, which indicates a weaker exciton bond for surface chromophores attached to spherical crystals relative to rod-like particles. Due to their characteristic geometric features, zinc oxide nanorods accelerate the self-organization of AO in a monolayer with a crystalline organization similar to that prevailing in relatively thin films of relatively rigid conjugated systems.

The adsorption of molecules from a solution on the surface of nanoparticles is a very fast process. In fact, the characteristic hypo DS2T chromic shift of the H-aggregated signature is usually obtained within 1 hour after inoculation. This step is followed by the ordering of the grafted molecules on the surface, similar to the crystallization process, leading to a final spectrum (see Fig. 2A). This is consistent with the well-known property of carboxylic acids to form surface organic dynamic phases. It is noteworthy that this effect was also observed under conditions of partial grafting, namely, for a surface functionalization density of 50%. This means that, with incomplete AO coverage, molecules are still able to assemble and self-organize into small crystalline domains on the surface of the nanorod.

The X-ray diffraction data of thin films of a hybrid nanocomposite deposited from a solution confirm the crystalline organization of oligothiophene molecules on the ZnO surface. The traditional Θ / 2Θ off-plane scanning schemes contain 2 broadened peaks at 2Θ = 32 ° and 2Θ = 36 °, corresponding to the reflection from the (100) and (101) faces of ZnO zincite (with the wurtzite crystal structure). Reflection from the (002) face was not observed during out-of-plane detection, since the nanorods are mainly oriented parallel to the surface of the substrate. At lower angular values, sets of sharp peaks not observed in the diffraction pattern of uncoated ZnO nanorods indicated a crystal lattice parameter of 6.75 nm, which is associated with the interparticle distance in the vertical packing of the hybrid nanocomposite in the film (see Fig. 4A). This periodic length is close to the value determined from the diffraction pattern of a thin film of pure AO (lattice parameter 6.44 nm). This corresponds to almost double the molecular length of AO. In the pattern of moving X-ray diffraction (GIXD) in a plane on a hybrid nanocomposite, 2 peaks are still observed at 2Θ = 32 ° and 2Θ = 36 °, but, as expected, they are not accompanied by a strong and sharp peak at 2Θ = 35 °, corresponding to reflection from the (002) ZnO face. It is noteworthy that at lower 2Θ values shown in FIG. 4B, the position of the peaks corresponds to that observed for thin films of distirilic analogues (C. Videlot-Ackermann, J. Ackermann, K. Kawamura, N. Yoshimoto, H. Brisset, P. Raynal, A. El Kassmi, F. Fages, Org. Electron . 7, 465-473 (2006)), which form a crystalline organization. They can be attributed to the lattice parameter inside the monolayer of AO molecules on the ZnO surface.

These results indicate that the organic component of the hybrid nanocomposite of Example 1 has crystalline ordering, while the absence of such peaks for the nanocomposite of Example 2 means that such ordering is absent.

Production of solar cells from a hybrid nanocomposite

Solar cells were made from a hybrid nanocomposite prepared in examples 1 and 2, as shown below.

The active layer of the hybrid nanocomposite obtained in examples 1 and 2 was deposited on an appropriate conductive substrate (ITO on glass), coated before this corresponding layer with hole conductivity PEDOT: PSS obtained by centrifugation [2000 rpm, drying at 120 ° C in the atmosphere of N2]. After drying and annealing the sample at 120 ° C for 15 minutes, the aluminum layer was evaporated from the surface of the active layer using masks to form a sputter contact.

The operation of the resulting solar battery, schematically represented in FIG. 5, was characterized by about 40 mW / cm ² under the influence of the simulated solar spectrum AM1.5.

In both cases, the current-voltage characteristic in the absence of light was diode-like, while under the influence of light the response was photovoltaic with well-defined open-circuit voltages V _oc and short-circuit currents I _sc (see Figs. 6A and 6B). This shows that hybrid composites behave like a pn junction and are capable of dissociating excitons, followed by the collection of holes and electrons from the interface of the hybrid to external electrodes. It is noteworthy that the highest photocurrent for both types of batteries was obtained only with 70% coverage of the surface of a hybrid nanocomposite instead of using a nanocomposite completely coated with a monolayer. This was attributed to better mechanical contact with the nanorods transporting the electrons, as well as to a larger amount of the nanocomposite ordered inside the thin film, so that their longitudinal axes are perpendicular to the ITO substrate. This can be ascertained from the results of GIXD measurements using a hybrid nanocomposite with a variable surface coating.

External quantum efficiency (EQE - external quantum efficiency) at the maximum absorption of solar cells using the hybrid nanocomposite of example 2 is about 14%, which is a very interesting photovoltaic response of such a device (see Fig. 7A and 7B).

Fabrication of hybrid nanocomposite transistors

Hybrid field effect transistors (HFETs) were made from the hybrid nanocomposites of Examples 1 and 2 as follows.

By centrifugation deposition, a nanocomposite was deposited on a silicon substrate coated with SiO ₂ , and the gold contacts of the source and drain were successively deposited on the surface of the obtained layer. In FIG. 8 is a schematic representation of an HFET.

The HFETs thus obtained were electrically characterized at negative and positive gate voltages. At a negative voltage of the grid bias, the current increases along with the voltage (see Fig. 9A). This indicates that the active channel of the transistor has the ability to hole transport.

With a positive grid voltage, polarization reversal is observed, even with an increase in voltage (see Fig. 9B). This indicates that the active layer of the transistor exhibits a field effect for electron transport.

In conclusion, the active HFET layer, which is the hybrid nanocomposite according to the invention, has the ability to ambipolar transport of charge carriers.

Claims (20)

1. A hybrid nanocomposite material comprising electrically conductive inorganic elongated nanocrystals grafted onto at least parts of its surface by an electrically conductive organic compound, wherein the organic compound forms a self-organizing layer (SAM), and the organic compound is a compound of formula (I ):

where A is the fixed part, which is a carboxylic acid, amine, phosphonic acid, phosphate, thiol or silane group;
L is the non-conductive part, which is a saturated hydrocarbon group or is absent;
Y is the electrically conductive part containing a conjugated system such as pentacene, anthracene, phthalocyanines, porphyrins, fullerenes, oligothiophene, PEDOT, polypyrol, chlorophylls, bacteriochlorophylls and carotenoids ;.
Z is a solvent part, which is a non-conjugated hydrocarbon group, such as a straight or branched, saturated or unsaturated alkyl group with 1-20 carbon atoms, in particular n-butyl, n-pentyl, n-hexyl, n-heptyl and n-octyl, or absent; and
X is a stabilizing part capable of forming intermolecular bonds and may, in particular, be a group forming hydrogen bonds, such as hydroxy, amino, amido or carboxylic acid, or may be absent. 2. The hybrid nanocomposite material according to claim 1, wherein the elongated nanocrystals are nanowires, nanorods, nanotubes, nanostructures with two branches, nanostructures with three branches, nanostructures with four branches and nanostars. 3. The hybrid nanocomposite material according to claims 1 or 2, in which the elongated nanocrystals are metal conductors. 4. The hybrid nanocomposite material according to claim 1, in which the elongated nanocrystals are made of gold, silver, copper or tin oxide doped with indium. 5. The hybrid nanocomposite material according to claim 1, in which the elongated nanocrystals are semiconductors. 6. The hybrid nanocomposite material according to claim 1, in which the elongated nanocrystals are made of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, osmium, cobalt, nickel, copper, silver, gold, zinc, cadmium, scandium, yttrium, lanthanum, boron, gallium, indium, antimony, thallium, silicon, germanium, tin, lead, magnesium, calcium, strontium, barium and aluminum and simple or mixed chalcogenides, in particular oxides and sulfides. 7. The hybrid nanocomposite material according to claim 1, wherein the elongated nanocrystals are made of zinc oxide, zinc sulfide and titanium dioxide. 8. The hybrid nanocomposite material according to claim 1, comprising metal nanocrystals, grafted with an organic compound with the transport properties of p- or n-type charge carriers, respectively. 9. The hybrid nanocomposite material according to claim 1, comprising metal or semiconductor nanocrystals, grafted with an organic compound with the transport properties of metal, p- or n-type charge carriers, forming one or more of the following inter-particle transitions: pn, pp, nn, mm, mp, mn, where m, n and p are organic and inorganic metallic, n-type or p-type semiconductor properties. 10. The hybrid nanocomposite material according to claim 1, including metal or semiconductor nanocrystals, grafted with an organic compound with the transport properties of metal type, p- or n-type charge carriers, including an insulating component forming one or more of the following inter-particle transitions: pin, pip, nin, mim, mip, min. 11. The hybrid nanocomposite material according to claim 1, in which the self-organizing monolayer (SAM) is crystalline. 12. The hybrid nanocomposite material according to claim 1, in which the self-organizing monolayer (SAM) is amorphous. 13. The hybrid nanocomposite material according to claim 1, in which SAM includes two organic compounds with different absorption spectra. 14. The hybrid nanocomposite material according to claim 1, in which SAM includes two organic compounds with different preferred modes of transport of charge carriers. 15. A method of manufacturing a material according to any one of claims 1 to 14, containing stages including:
(i) providing electrically conductive inorganic elongated nanocrystals;
(ii) contacting the nanocrystals with an electrically conductive organic compound, optionally in an appropriate solvent, under conditions suitable for grafting the organic compound onto the nanocrystals;
(iii) isolation of grafted nanocrystals obtained from the reaction mixture; and
(iv) cleaning the composite, if applicable. 16. A thin film comprising a hybrid nanocomposite material according to any one of claims 1 to 14. 17. A solar battery comprising a hybrid nanocomposite material according to any one of claims 1 to 14. 18. An electronic switching device containing a semiconductor layer comprising a hybrid nanocomposite according to claims 1-14. 19. The electronic switching device according to claim 18, wherein the switching device is a pn junction or np junction. 20. The electronic switching device according to claim 18 or 19, wherein the switching device is a p-i-n junction.

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