JP2010525566A - Manufacture of electroactive membranes based on multilayers - Google Patents

Abstract

  A continuous film with the desired electrical properties is obtained by successively printing and annealing two or three dispersions of pre-made nanoparticles.

Description

  The present invention relates to thin film materials, their manufacture and devices made therefrom, and more particularly to graded multijunction thin film semiconductor structures.

  Thin film technology is currently being developed for the purpose of reducing the cost of semiconductor devices, particularly photovoltaic cells (PV cells). Conventional solar cells are fabricated from multiple solid crystalline silicon wafers and typically have a thickness of a few hundred microns, whereas thin film materials are deposited directly on the substrate to form layers of 2 μm or less. Material costs and manufacturing costs will be reduced. Furthermore, thin film technology allows monolithic integration, i.e., in situ formation of electrical connections, which further reduces production costs.

  Thin film materials include cadmium telluride (CdTe), copper indium selenide (CIS) and its variants, amorphous silicon, and polycrystalline silicon (<50 μm). In recent years, technological advances have been made especially in the thin film technology of CdTe and CIS. Both materials have a high extinction coefficient, so most of the incident light will be absorbed within 1-2 μm of the film. When these materials are used as an absorption layer, for example, they are combined with a CdS layer to form a heterojunction, and are sandwiched between a front electrode and a back electrode to form a solar cell. In the absorption layer, incident photons generate electron-hole pairs.

  In order to gain broad support, thin film PV cells must exhibit high conversion efficiency of photon energy to current and operate reliably in outdoor environments for many years, ideally over 30 years. Techniques using CdTe and CIS have demonstrated long-term stability. However, performance degradation has also been observed. The efficiency of current thin film devices has reached 65% of the theoretical maximum (75% at the laboratory level) and still lags behind single crystal silicon and GaAs batteries demonstrating 90% of the ultimate achievable performance. Have taken. Improvements in the efficiency of thin film technology can be achieved through multi-junction and graded materials. For example, CIS studies have shown that adding gallium, forming a compound called CIGS, and showing a Ga and In concentration gradient lead to better efficiency.

  The complexity of thin film technology, which is essential for high efficiency, will adversely affect cost and manufacturability, necessitating the establishment of improved technology, especially low-cost technology that can be performed using off-the-shelf equipment. Become. Challenges to the development of low cost and reliable CIGS and CdTe devices include layer deposition, absorber layers with a thickness of 1 μm or less, and standardization of equipment for extensive film uniformity control.

  In various embodiments, the present invention provides a method of making a continuous film by sequentially printing and annealing two or three dispersions of pre-made nanoparticles. In particular, some embodiments of the present invention facilitate the fabrication of graded multijunction semiconductor films that can be used in PV cells and other semiconductor devices. The method does not require a vacuum and is therefore cheaper and easier to implement than a vacuum-based technique.

  The nanoparticles according to the present invention are particles having a specific elemental composition and have a diameter of 100 nm or less, preferably 20 nm or less. Exemplary nanoparticles include metal oxide particles that form a powder together. Some nanoparticle compositions suitable for semiconductor thin films include two or more of the chemical elements Cu, Ag, In, Ga, Al, Te, Se, S, Cd, and As. However, it should be emphasized that although the present invention is not limited to said elements, the method can generally be applied to any component of nanoparticles suitable for dispersions and series of printing. One of the advantages of the technology according to the present invention is the ability to optimize the composition of the thin film by providing composition control of the precursor nanoparticles. This facilitates the production of continuous films consisting of layers of specific chemical constituents, thereby enabling optimization of the composition of these layers and, as a result, the electrical properties of the films, in particular Improved control of changes in these properties across the thickness of the film is possible.

  Regardless of whether the dispersion according to the present invention is a solution, a colloid, or a suspension, any (homogeneous) mixture of nanoparticles and a carrier having an appropriate fluidity including a solvent or a dispersant is included. Contains. These dispersions of nanoparticles are referred to herein as “printing paints” or “inks based on nanoparticles”.

The method according to the present invention includes various printing techniques including, but not limited to, inkjet printing, pneumatic spraying, screen printing, pad printing, laser printing, dot matrix printing, thermal printing, lithography, or 3D printing. And a printing apparatus corresponding to the above. This versatility contributes to feasibility and cost effectiveness. In addition, the composition of the nanoparticles can vary through various deposition and annealing processes. For example, in one embodiment of the present invention, different printable components comprise different percentages of nanoparticles of the same element, for example, the nanoparticles have the chemical formula CuIn _1-X Ga _X Se _2. Here, x varies between 0 and 1 (ie 0 ≦ x ≦ 1), resulting in a concentration gradient of at least one element (In and Ga in this example) through the film.

  Accordingly, in a first aspect, the present invention provides a method for producing a film, the method providing a substrate and a printed paint having fluidity comprising different dispersions of pre-made nanoparticles. And subsequently printing these layers of printing paint and annealing to one continuous film. In some embodiments, two or more layers are printed sequentially before they are annealed. Further, in some embodiments, the etching process precedes annealing. Some individual printed layers may have a thickness of less than 1 μm.

  In certain embodiments, the printing paint comprises different proportions of the same type of nanoparticles or different proportions of nanoparticles of the same element, and the annealed layer has a concentration of at least one element A film having a gradient is formed. In another embodiment, each printed paint contains a different type of nanoparticles. In preferred embodiments, the nanoparticles have a size of 20 nm or less and a low size dispersion.

  In some embodiments, the film includes a semiconductor material and is electrically interacting with the substrate. Furthermore, this structure can be complemented by a conductive superstrate to form a semiconductor device. In a specific embodiment, the device is a solar cell.

  In a second aspect, the present invention provides a fluid printing paint having a flow rate substantially independent of viscosity. These printing paints comprise a carrier and a dispersion of nanoparticles, the nanoparticles comprising Cu and / or Ag as a first component and Se, Te and / or S as a second component. It is out. In addition, the printing paint may contain In, Ga, and / or Al as the third component.

  It should be emphasized that the method embodiments according to the invention are not limited to the printing paints described above.

  The foregoing discussion will be more readily understood from the following detailed description of the invention, taken together with the accompanying drawings.

FIG. 1 is a flowchart detailing the steps of a method for producing a film by a series of printing and annealing. FIG. 2 schematically illustrates a system and method for manufacturing a membrane in an embodiment of the present invention. FIG. 3A is a schematic elevation view of a representative solar cell manufactured in the present invention. FIG. 3B is a schematic elevational view of a tilted CIGS film and a solar cell fabricated therefrom, where the tilted CIGS film first deposits all the constituent layers and then anneals once to create a continuous film. Manufactured by.

1. Manufacturing Method Reference is first made to FIGS. Here, FIG. 1 and FIG. 2 respectively illustrate a representative series of processes 100 and an operating device that implements an embodiment of the present invention. The series of steps includes the steps detailed in the flowchart shown in FIG. 1, and the apparatus is used to obtain the intermediate and final structures shown in FIG. In the first step 110, a substrate 200 and a plurality of preprinted fluid paints containing different dispersions of nanoparticles are prepared as will be further described below. A print paint 202a is selected for the first layer at step 112 and the paint is printed onto the substrate 200 using the printer 204 at step 114. As described below, the etching step 116 may be performed after printing. In optional step 118, the deposited layer is dried and annealed using heat source 206 to form continuous film 208. “Annealing” means heating the deposited layer at a sufficient temperature and for a sufficient amount of time for the nanoparticles to dissolve into a continuous layer of uniform composition. Whether the annealing is performed after the deposition of a particular layer depends on the specifications of the printing paint, the layer thickness, and the desired film properties. In general, however, the paint is allowed to dry before depositing the next paint on the paint. The annealing source 206 may be a suitable heat source such as an oven, a vacuum oven, a heating furnace, an IR lamp, a laser, or a hot plate, and a suitable annealing time and temperature can be determined without undue experimentation in the printing device. And may be obtained by the calibration described below. The annealing temperature and time depend on the size and composition of the nanoparticles as in the ink paint. The annealing temperature is usually higher than 200 ° C.

  Steps 112 and 114 and optionally steps 116 and 118 are repeated to print the second printed paint 202b. As a result, a film 208 including two layers is obtained at this point. The second printing paint 202b is usually different from the paint 202a. The same printing and annealing devices 204, 206 may be used for this repetition, in which case the printer 204 will be replaced with new printing paint (eg, in the form of a cartridge). Alternatively, the series of processes 100 may be performed in the form of an assembly line with separate printing and annealing equipment dedicated to the deposition and annealing processes, respectively. A line configuration may be preferred when processing individual substrates 200 continuously, but using the same equipment in multiple processes produces multiple films in parallel (eg, multiple films It may be more useful if the same process is performed on the substrate simultaneously).

  Steps 110 to 118 may be repeated a plurality of times (although not necessarily repeated) to form a film having three or more layers 202a, 202b, 202c. Again, a particular printing paint can be used more than once, and in the case of a graded film, the paint will gradually change with each deposition step. After the last layer is printed, the etch step 120 is still optional, but the last anneal is performed to form a continuous final film 210 from multiple deposited layers, whether or not the previous anneal 116 has been performed. Step 122 must be performed. The number of layers deposited and annealed in this manner is at least two and is limited only by the desired thickness and composition of the final film 210. Thus, FIG. 2 illustrates the fabrication of a membrane having three layers, but this is for illustration only.

Each layer may contain a single type of nanoparticles, in which case different layers will usually contain nanoparticles having different chemical compositions. Alternatively (or in addition) each layer may contain multiple types of nanoparticles, in which case the same combination of nanoparticles may be used in different proportions in different layers. In some embodiments of the present invention, the method 100 is used to produce highly efficient graded films using a variety of printing paints that include nanoparticles having different proportions of the same component. For example, CIGS film may be produced by varying the chemical composition _{CuIn 1-X Ga X Se 2} . Here, x varies gradually between successively deposited layers (ie, continuous printing paint). For example, x is the distance from the film interface (eg, the top surface of the structure or the interface in contact with the substrate) to a predetermined position in the film divided by the film thickness. May be. Such films are created by chemical vapor deposition (CVD) and are used as absorbing layers in PV cells, with the gallium concentration increasing towards the back contacting molybdenum, resulting in concentration and corresponding As a result of the reduced backside recombination due to the pseudo-electric field defined by the slope of the band gap, the efficiency is significantly higher, 19.5%. The method 100 provides an alternative to the CVD process. That is, using a suitable substrate such as glass covered with Mo, CuInSe ₂ is deposited as a first layer, and then the Ga content gradually increases (linearly or non-linearly) in each layer. the printing compositions, the composition of the nanoparticles may be deposited to mainly a CuGaSe _2. Once the layers are printed in the preferred order, they are annealed to form a high performance graded CIGS film. Other nanoparticle-based inks may be introduced as an intermediate layer to further adjust the band structure of the material to optimize battery performance. The technique according to the present invention has the additional advantage that no vacuum device is required compared to CVD.

  In other embodiments of the invention, the printing paint comprises different types of nanoparticles. The method 100 can be used, for example, to make a CdS / CdTe thin film. In general, the method of the present invention can be applied to several materials for which a suitable nanoparticle source can be used.

2. Printing device 204
Well characterized, including but not limited to inkjet printing, pneumatic spraying, screen printing, pad printing, laser printing, dot matrix printing, thermal printing, lithography, and 3D printing for the execution of the printing process 114 The various printing methods provided can be advantageously used. Computer controlled ink jet printers are readily available and are particularly attractive for the practice of the invention due to the level of control they provide. Commercially available inkjet printers can be used with little or no modification to print ink based on nanoparticles (printing paint) as described herein. To avoid problems such as clogging of the printer head and other incompatibilities, the viscosity of the ink based on nanoparticles is manufactured by the printer manufacturer, as described in more detail below on the contents of the printing paint. The ink viscosity can be adjusted. One of the advantages is the ease of applying the method 100 to a readily available and low cost device such as an ink jet printer.

  The printer can be adjusted as follows to facilitate control of the individual layer and overall film thickness. A series of printing operations are executed for each printing paint, and each printing operation includes a different number of printing passes. Drying and annealing are performed after each printing pass or at the end of the run. The film thickness obtained from each run is different and is determined by scanning electron microscope (SEM), transmission electron microscope (TEM), or other suitable technique. As a result, a layer having a desired thickness may be produced with reference to the number of printing passes corresponding to that thickness. Similar adjustment techniques may be used to determine the optimum annealing temperature and time to obtain the desired film properties.

3. Printing paint 202
The printing paint here is a dispersion of nanoparticles having fluidity. The particulate precursor material simplifies composition control for multi-component materials such as CIGS, for example, since the main components (eg, Cu, In, Ga) can be accurately mixed into the precursor powder. One method of making these powders is to mix the components in the required proportions, dissolve them in acid to form an aqueous mixture, and use the hydroxide precipitate to hydroxylate the components. Forming a gel-like mixture of the product, and drying the mixture to obtain a mixed oxide fines. Nanoparticle synthesis can also be performed, for example, using techniques described in US Pat. No. 6,379,635 and co-pending US patent applications 11/579050 and 11/588880.

  Methods for producing CdSe, InS, GaS, ZnS, CdS, ZnAs, CdAs, and more related nanocrystalline materials are described in Experimental Sections 1-10 of US Pat. No. 6,379,635. Yes. This describes how the nanocrystal precursor is provided in a single precursor complex (eg, but not limited to an alkyl carbonate complex of the required metal ion). The nanocrystal precursor is then thermally decomposed under appropriate conditions (for example, a temperature of about 200 to 300 ° C.) to finally produce a desired nanocrystal substance.

As an example, nanocrystalline CdSe can be formed as follows. That is, 1.2 MeCddsc (0.5 mmol) was placed in 10 ml of TOP (98%, Aldrich), the formed mixture was filtered and then poured into 30 g of TOPO at 200 ° C. Thereafter, the temperature of the solution was raised to 250 ° C. and heated for half an hour. After the deep red solution formed thereby was cooled to 75 ° C., excess dry CH ₃ OH (BDH) was added. The aggregated precipitate formed was separated by centrifugation and redispersed in toluene, after which all insoluble material was discarded. Toluene was evacuated under vacuum (10 ⁻² Torr) to produce a deep red material that was washed with CH ₃ OH. The solid was redispersed in toluene to produce a solution with a port wine red color that remained optically clear for several weeks. This procedure was subsequently applied until no light absorption was detected in the supernatant obtained during the fractionation step.

Using similar methods, producing III-VI nanocrystalline materials (eg, InS, GaS) by replacing MeCddsc with complexes of the general chemical formula (AlK1) ₂ M ^III E ₂ CN (AlK2) ₂ I can do it. Here, AlK1 and AlK2 are individually alkyl groups such as Me, Et, and Np, and each AlK1 and AlK2 are the same or different. M ^III is a group III metal ion such as In or Ga. E is a group VI ion such as S or Se. Also, using a similar method, by replacing MeCddsc with a complex of the general chemical formula [M ^II [E ₂ CN (AlK3) ₂ ] ₂ ], II-VI or II-V nanocrystalline materials (eg, ZnS , CdS, ZnAs, and CdAs). Here, each AlK3 is an alkyl group such as Me, Et, and Pr, and each AlK3 is the same or different. M ^II is a group II metal ion such as Zn or Cd. E is As or a V or VI group ion such as S or Se.

  Methods for producing large quantities of nanocrystalline material are described in US patent application Ser. Nos. 11 / 579,050 and 11 / 588,880. These applications describe for the first time how to use molecular clusters to control the growth of any preferred nanocrystalline material, thereby allowing the molecular clusters to be on the molecular cluster species. One or more outer shells of a material different from the material forming the nanocrystalline core grown in step 1 can be provided.

By way of example, US patent application Ser. No. 11 / 579,050 describes Examples 1-9 in conjunction with appropriately controlling the temperature increase of the reaction mixture over a suitable period of time (eg, TOPSe and Cd (CH ₃ CO ₂ ) in order to produce a CdSe nanocrystal by controlling the addition of) Cd ions and Se ions from _2, clusters can be used _{[HNEt 3] 2 [Cd 4} (SPh) 10] and [HNEt _{3] 4} The generation of [Cd ₁₀ Se ₄ (SPh) ₁₆ ] is described. For example, Example 1 describes the production of CdSe nanoparticles from [Et ₃ HN] ₄ [Cd ₁₀ Se ₄ (SPh) ₁₆ ] / TOPSe / Cd (CH ₃ CO ₂ ) ₂ in HDA. HDA (300 g) was placed in a 3-neck flask and dried / degassed by heating to 120 ° C. for 1 hour under dynamic vacuum. The solution was then cooled to 70 ° C. To this, 1.0 g of [Et ₃ HN] ₄ [Cd ₁₀ Se ₄ (SPh) ₁₆ ] (0.311 mmol), TOPSe (20 ml, 40.00 mmol) [generated from pre-dissolving selenium powder in TOP And Cd (CH ₃ CO ₂ ) ₂ (10.66 g, 40.00 ml) were added and the temperature of the reaction mixture was gradually increased from 70 ° C. to 180 ° C. over 8 hours. Progressive nanoparticle formation / growth was observed by their emission wavelength by taking fractions from the reaction mixture and measuring their UV-visible and PL spectra. When the emission spectrum reached 572 nm, the reaction was stopped by cooling to 60 ° C., followed by the addition of 200 ml of dry “warm” ethanol, resulting in a nanoparticle precipitate. The resulting CdSe was dried, then redissolved in toluene and filtered through celite, followed by reprecipitation from warm ethanol to remove excess HDA and Cd (CH ₃ CO ₂ ) ₂ . This produced 9.26 g of CdSe nanoparticles capped by HDA.

As a further example, U.S. Patent Application No. _11/588880, by dropwise addition of Me 2 CdTOP, in _{HDA [HNEt 3] 4 [Cd} 10 Se 4 (SPh) 16] / TOPSe / Me 2 CdSe nano from CdTOP Describes the generation of particles and the formation of ZnS nanoparticles from [Et ₃ HN] ₄ [Zn ₁₀ S ₄ (SPh) ₁₆ ] species in HDA by dropwise addition of Et ₂ Zn and S-octylamine. . The nanoparticles formed by this method can then be provided with one or more shell layers to provide nanoparticles capped with CdSe / ZnS-HDA and ZnSe / ZnS nanoparticles. For example, ZnS nanoparticles can be formed by dropping Et ₂ Zn and S-octylamine from [Et ₃ HN] ₄ [Zn ₁₀ S ₄ (SPh) ₁₆ ] species in HDA as follows. A 200 g quantity of hexadecylamine (HDA) was placed in a three neck round bottom flask and dried and degassed by heating to 120 ° C. for> 1 hour under dynamic vacuum. The solution is cooled to 60 ° C., the reaction flask is filled with nitrogen, and the following reagents are used: 0.6 g [HNEt ₃ ] ₄ [Zn ₁₀ S ₄ (SPh) ₁₆ ] (0.2 mmol), trioctylphosphine ( 4 mL of 0.5 M solution containing Et ₂ Zn in 2 mmol) and 4 mL 0.5 M solution containing elemental sulfur in octylamine (2 mmol) are placed in the flask using standard airless techniques. It was. The temperature was raised to 120 ° C. and stirred for 2 hours. At this time, a programmed temperature gradient from 120 ° C to 210 ° C was activated at a rate of ~ 0.2 ° C / min. At the same time, 8 mL of 0.5 M Et ₂ Zn and 8 mL of 0.5 M S-octylamine were added dropwise at a rate of ˜0.05 mL / min. When the PL emission maximum required emission (λ _max = 391 nm, FWHM = 95 nm) is reached, the reaction is stopped by cooling to 60 ° C., followed by the addition of 300 ml of dry ethanol or acetone. Particles were allowed to settle. This precipitate was separated by filtration. The resulting ZnS particles were further purified (to remove excess HDA, sulfur, and zinc) by redissolving in toluene, filtering the solution through celite, and reprecipitating from warm ethanol. (Production amount 0.9 g). The CdSe nanoparticle capping or shelling is then dried and degassed by placing HDA (800 g) in a 3-neck round bottom flask, for example as follows, and heating to 120 ° C. for> 1 hour under dynamic vacuum. Executed by letting. The solution was then cooled to 60 ° C. and to this was added 9.23 g of CdSe nanoparticles having a PL maximum emission of 585 nm. The HDA was then heated to 220 ° C. To this, a total amount of 20 ml of 0.5M Me ₂ Zn · TOP dissolved in octylamine and 0.5M, 20 ml of sulfur were alternately added dropwise. Three additions of 3.5, 5.5, and 11.0 ml respectively were made, whereby 3.5 ml of sulfur was first added dropwise until the PL maximum strength was near zero. Thereafter, 3.5 ml of Me ₂ Zn · TOP was dropped until the intensity of the PL maximum reached the maximum value. This cycle was repeated and the PL maximum reached a higher strength in each cycle. In the last cycle, when the PL maximum strength was reached, additional precursor was added until the maximum strength was between 5-10% and the reaction was annealed at 150 ° C. for 1 hour. The reaction mixture was then cooled to 60 ° C. and immediately 300 ml of dry “warm” ethanol was added, causing precipitation of the particles. The resulting CdSe-ZnS particles were dried, then redissolved in toluene and filtered through celite, followed by reprecipitation from warm ethanol to remove excess HDA. This resulted in 12.08 g of CdSe—ZnA core-shell nanoparticles capped by HDA. According to elemental analysis, C = 20.27, H = 3.37, N = 1.25, Cd = 40.11, Zn = 4.43%, maximum PL 590 nm, and FWHM 36 nm.

  A method for making any preferred stoichiometric CIGS nanoparticles using a selenol compound is disclosed in US Provisional Application No. 60/991510. Embodiments of the method include at least a first of the nanoparticle precursor compositions (comprising at least one of Al, Ga, and / or In and at least one source of Cu, Ag, Zn, and / or Cd). Dispersing one part in a solvent (eg, a long chain hydrocarbon solvent), heating the solvent to a first temperature for an appropriate length of time, adding a selenol compound to the solvent to heat the solvent, Adding a second portion of the particle precursor composition to the reaction mixture, heating the mixture to a second temperature above the first temperature for a suitable length of time, and maintaining the temperature for up to 10 hours. including. When the particles are formed, the surface atoms of the particles are usually coordinated to a capping agent, which can include the selenol compound used in the method. When volatile selenol compounds are used, this capping agent can be removed by heating to produce “naked” nanoparticles that are susceptible to capping ligand coordinating effects and further processing. Examples 1 and 2 provide further details regarding the performance of this method.

  Example 1: Cu (I) acetate (1 mmol) and In (III) acetate (1 mmol) are added to a clean and dry RB-flask. Octadecene ODE (5 mL) is added to the reaction mixture heated under vacuum at 100 ° C. for 30 minutes. The flask is backfilled with nitrogen and the temperature is increased to 140 ° C. Add 1-octane selenol and lower the temperature to 120 ° C. The resulting orange suspension is heated with stirring and a clear orange / red solution is obtained when the temperature reaches 140 ° C. This temperature is maintained for 30 minutes, after which 1 M tri-octyl-phosphine selenide TOPSe (2 mL, 2 mmol) is added dropwise and the solution is heated at 160 ° C. PL is observed until it reaches the desired wavelength, then cooled and the resulting oil is washed 4-5 times with methanol / acetone (2: 1) and finally acetone is To separate by precipitation.

Example 2 (mass production): A stock solution of TOPSe was produced by dissolving Se powder (10.9, 138 mmol) in TOP (60 mL) under nitrogen. To dry, degassed ODE was added to Cu (I) acetate (7.89 g, 64.4 mmol) and In (III) acetate (20.0 g, 68.5 mmol). The reaction vessel was evacuated and heated at 140 ° C. for 10 minutes, backfilled with N ₂ and cooled to room temperature. 1-Octane selenol (200 mL) was added to make a bright orange suspension. The temperature of the flask was increased to 140 ° C and acetic acid was distilled from the reaction at 120 ° C. When the temperature reached 140 ° C., the TOPSe solution was added dropwise over the course of 1 hour. After 3 hours, the temperature was increased to 160 ° C. The progress of the reaction was monitored by periodically obtaining resolution from the reactants and measuring UV / visible light and emission spectra. After 7 hours, the reaction was cooled to room temperature and the resulting black oil was washed with methanol. Methanol washing was continued until it was possible to precipitate pure black material from the oil by addition of acetone. The black precipitate was separated by centrifugation, washed with acetone and dried under vacuum. The amount produced was 31.97 g.

X-ray diffraction (XRD), UV / visible / near-infrared spectroscopy, scanning or transmission electron microscope (SEM / TEM), energy dispersive X-ray to optimize particle properties or selection of appropriate dispersant Nanoparticles can be characterized in terms of their composition, size, and charge by conventional techniques including microanalysis (EDAX), emission spectroscopy, and / or elemental analysis. A representative Cu / In / Se core particle produced in a 1-octane selenol capping agent that is later removed is the result of inductively coupled plasma atomic emission spectrometry (ICPAES) analysis and the following suitable nanoparticles: Cu 16.6%, In 36, 6%, Se 48.3% corresponding to Cu / In ratio of Cu _1.00 , In _1.22 , Se _2.34 and 0.82 in composition. .

  In a preferred embodiment of this invention, the nanoparticles have an average size of 20 nm or less and a low size dispersion of ± about 2 nm or less. By conforming to these restrictions, it becomes easy to print a thin film while controlling the band structure through the film, and as a result, high conversion efficiency is obtained. Furthermore, the low size dispersion allows for excellent packing of nanoparticles and uniform melting temperature of the nanoparticle film, which contributes to proper film formation.

The nanoparticles are dispersed in a carrier containing a solvent such as toluene and a dispersant to form a printing paint. The dispersion may be in the form of a solution, colloid, or suspension, generally depending on the particle size, as long as it has fluidity, and the concentration of the liquid, paste, or other viscoelastic material. You may have. The viscosity should be in the range of ^{0.158 × 10 11 cP~2.3 × 10 11} cP.

  In embodiments in which aqueous inks are formed using insoluble nanoparticles, the surface area and charge of the particles determine the choice of suitable dispersant for ink formation. For example, in pigment ink jet printing, the overall charge (ie, zeta potential) obtained by particles dispersed in the medium must be high enough to ensure dispersion stability. However, excessive dispersion stability can result in agglomeration and printer head clogging. The average agglomerate size should be minimized to ensure ink ejection potential through the nozzles. In the printing industry, it is generally recognized that particle sizes greater than 500 nm can block inkjet nozzles and reduce print quality.

  To reduce the risk of printhead blocking, the nanoparticles can be covered with a water-soluble capping agent such as mercaptocarboxylic acid (eg, mercaptoacetic acid). For example, US Pat. No. 6,140,038 describes a method for exchanging a coating group of water-insoluble, pyridine-capped nanocrystals with a large excess of pure mercaptocarboxylic acid to obtain water-soluble capped nanocrystals. Teaching. That is, pyridine capped nanocrystals are precipitated with hexane and centrifuged. The residue is dissolved in pure mercaptoacetic acid and incubated at room temperature for at least 6 hours. Chloroform is added to precipitate the nanocrystals, and excess thiol is washed away. The nanocrystals are then centrifuged again, washed with chloroform and hexane, and dried with argon. The viscosity of the printing paint (ink based on nanoparticles) is preferably adjusted to achieve plastic fluidity. That is, here, the viscosity is basically independent of the fluidity. This facilitates control of the coating properties. The capping agent required for solubilization or suspension can be removed to stop the formation of carbon deposits in the film. In some cases, this removal occurs naturally as a result of annealing at an elevated temperature, while if not, it can be assisted by previous etching steps 116, 120.

4). Applications Semiconductor thin film structures made according to the method shown in FIG. 1 can be used in photovoltaic cells, LEDs, transistors, and other semiconductor devices. FIG. 3A shows a typical structure of a solar cell having a CIGS absorber film. Substrate 305 has molybdenum on glass and a submicron Mo layer provides the back contact for battery 300. The absorber film 307 has a series of CIGS annealed layers and shows an increase in Ga concentration and a decrease in In concentration towards the Mo contact 300. This film can be produced by successively printing and annealing each layer. Alternatively, as shown in FIG. 3B, it may be made by first depositing all the layers and then combining these layers into one continuous film in a single annealing step. FIG. 3B illustrates the contents of In and Ga in each layer. The buffer layer 312 forms a junction with the CIGS film. Conventionally, this junction has CdS. However, due to environmental and health concerns associated with Cd, the preferred PV cell is cadmium free using ZnS, ZnO (O, OH), or In ₂ S ₃ instead. Therefore, the ZnO layer 314 on the glass cover 316 forms a superstrate of the battery 300. The performance of the ZnO / ZnO (O, OH) / CIGS / Mo battery can be improved or optimized by introducing layers of other semiconductor materials in the absorber layer 307. CIGS variants in which, for example, Se is replaced by S or Te, Cu is replaced by Ag, or In or Ga is replaced by Al (for example, as shown in Table 1 below) It can be used to manipulate the band energy to assist electron-hole capture. Embodiments of the present invention provide a convenient means for combining these additional layers. In addition, if a nanoparticle source is available for the bonding layer and / or the substrate or superstrate, these layers will likewise be used unless the required annealing temperature is detrimental to other layers in the device. Can be bonded into the device by printing or annealing.

  Although the invention has been described with reference to specific details, such details are not intended to limit the scope of the invention unless they are included in the appended claims.

Claims (21)

A method of manufacturing a membrane comprising:
(A) a step of providing a substrate and a plurality of printed paints having fluidity, each of the plurality of paints including different dispersions of nanoparticles prepared in advance from a specific elemental composition and having a thickness of 100 nm A process having the following average size:
(B) printing one layer of printing paint on the substrate;
(C) annealing the printed layer to form a continuous film;
(D) A step of forming the film by repeating steps (b) and (c) using another or the same printing paint.   The method of claim 1, wherein at least some of the printed layers have a thickness of less than 1 μm.   The method according to claim 1 or 2, further comprising repeating step (b) at least once before step (c).   The method according to claim 1, 2, or 3, further comprising performing etching after printing and before annealing.   The method according to claim 1, wherein the printing paint is a suspension.   The method according to claim 1, wherein the printing paint is a solution.   The printing process is any of the above performed by a printing technique selected from the group consisting of inkjet printing, pneumatic spraying, screen printing, pad printing, laser printing, dot matrix printing, thermal printing, lithography, or 3D printing. The method of claim.   A method according to any preceding claim, wherein each printing paint comprises a different type of nanoparticles.   8. At least some of the printing paints contain different proportions of the same type of nanoparticles, and applying the layer creates a concentration gradient of at least one material through the membrane. The method according to one.   A method according to any preceding claim, wherein the nanoparticles of each paint comprise the same element in different proportions, and the application of the layer creates a concentration gradient of at least one material through the membrane. The first set of _{nanoparticles} includes a _{CuIn 1-X Ga X Se 2} , or essentially consists of _{CuIn 1-X Ga X Se 2} , where a 0 ≦ x ≦ 1 x change through printing composition The method according to claim 10.   The method according to any one of the preceding claims, wherein the nanoparticles have a size of 20 nm or less and a low size dispersion.   A method according to any preceding claim, wherein the thin film comprises a semiconductor and electrically interacts with the substrate.   14. The method of claim 13, further comprising making a semiconductor device by adding a conductive superstrate and external contacts.   The method of claim 14, wherein the semiconductor device is a solar cell.   A fluidized printing paint comprising a carrier and a dispersion containing nanoparticles therein, the nanoparticles comprising first and second components, wherein the first component is at least one of Cu or Ag. While the second component contains at least one of Se, Te, or S, and has a fluidity that is substantially independent of viscosity.   The printing paint according to claim 16, wherein the first component contains Cu or Ag but not both.   18. A printing paint according to claim 16 or 17, wherein the second component contains exactly one of the elements Se, Te or S.   A fluidized printing paint containing a carrier and a dispersion containing nanoparticles therein, the nanoparticles each including a first, second, and third component, wherein the first component is Cu or Ag Wherein the second component includes at least one of Se, Te, or S, and the third component includes at least one of In, Ga, or Al, Above, a printing paint having a fluidity independent of viscosity.   The printing paint according to claim 19, wherein the first component contains Cu or Ag but not both.   21. A printing paint according to claim 19 or 20, wherein the second component contains exactly one of the elements Se, Te or S.

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