CN1300375C - Method of synthesizing ferrous disulfide film by electro deposition oxidation and hot sulfurization - Google Patents

Abstract

The invention discloses a method for synthesizing an iron disulfide thin film by electrodeposition oxidation and heat vulcanization. Conductive glass substrate is used to electrodeposit Fe-S compound film in FeSO ₄ and Na ₂ S ₂ O ₃ aqueous solution with a pH value of 5.0, and the Fe ₃ O ₄ prefabricated film is obtained by oxidation treatment at 180-220°C, and the prefabricated film is prepared at 20 ~40kPa nominal sulfur pressure and isothermal treatment at 350~450°C vulcanization temperature for 5~20h, transform into a cubic iron disulfide film. The present invention avoids the transition phase structure in the iron disulfide thin film, the prepared thin film substrate is transparent and there is no diffusion of metal or metalloid element atoms into the film body, the combination of the film layer and the substrate is reliable, the process and equipment are simple, and the efficiency is high. higher.

Description

Electrodeposition Oxidation and Thermal Vulcanization Method for Synthesizing Iron Disulfide Thin Film

technical field

The invention relates to a preparation technology of a functional thin film.

Background technique

With the advancement of science and technology and the development of human civilization, the primary energy such as coal, oil and natural gas can no longer meet the needs, and its reserves are also rapidly decreasing. Moreover, during the use of these disposable energy sources, a large amount of gases harmful to humans will be released, destroying the environment on which humans depend. Therefore, the utilization of renewable resources has become the primary content of current scientific research. Among various renewable resources, inexhaustible solar energy has become the focus of new energy utilization and development. One of the main forms of development is to effectively convert sunlight energy into electrical energy for the benefit of mankind.

A solar cell is a device that directly converts light energy into electrical energy. The photoelectrode material is the core of the solar cell. In addition to the commonly used silicon material, some new solar cell materials are being continuously developed. Among these materials, iron disulfide (FeS ₂ ) in the cubic crystal system has a suitable band gap (about 0.95eV), high photoelectric absorption coefficient (when λ≤700nm, d≥5×10 ⁵ cm ^-1 ), stable properties under natural conditions, good environmental compatibility, non-toxic, rich reserves of constituent elements and less material consumption, etc., have been highly valued by the scientific and technological circles.

As a solar cell material, _FeS2 should be used in the form of thin films, and there are many preparation techniques to artificially synthesize _FeS2 thin films. Patent US6635942 proposes a semiconductor device containing FeS ₂ film for solar cells. The single crystal or polycrystalline FeS ₂ can be obtained from natural minerals, but it must be treated with multi-zone cleaning technology to have a suitable carrier concentration. In addition, the above-mentioned patents propose that FeS ₂ can be prepared by gas-phase transport, sol-gel reaction deposition, FeS ₂ target sputtering, metal-organic chemical vapor deposition, spray pyrolysis, and molecular beam epitaxy. Similarly, the patent US6630257 proposes a preparation technology for thin film electrodes containing _FeS2 , in which _FeS2 is considered to be able to use chemical vapor transport, chemical vapor deposition, thermal spray deposition, iron oxide sulfidation, reactive sputtering, iron film Preparation by electrodeposition and screen printing.

Patent US4649227 discloses two kinds of photosensitive FeS ₂ film preparation processes with various doping elements. The first process is to obtain the desired crystal type, purity and metered composition of FeS ₂ through thermochemical treatment of natural materials, and to form thin films by chemical vapor transport. The second process is to prepare FeS ₂ through the synthesis reaction between iron or iron-containing compounds and sulfur or sulfur-containing compounds. The crystal growth can be realized by direct contact of reactants, temperature gradient conversion and gas phase transport, or by carbonyl iron or Iron halides are thermally decomposed with sulfur or hydrogen sulfide and then react to form _FeS2 films. Patent ZL02111221.5 discloses a preparation method of _FeS2 synthesized by magnetron sputtering iron film on a single crystal silicon wafer substrate, magnetron sputtering pure iron film on a single crystal silicon wafer, and then thermally vulcanizing the pure iron film The reaction forms a _FeS2 film with standard stoichiometric composition and no transition phase, and has high adhesion between the film and the substrate, which can be used as an experimental sample for _FeS2 film growth research.

Among the above-mentioned technologies for preparing _FeS2 film, in comparison, the electrodeposition prefabricated film reheat vulcanization technology has the advantages of easy control of process parameters, uniform film formation, low cost, and easy practical application. Thermal vulcanization process parameters improve film quality and performance. Yamamoto et al. (SolarEnergy Materials and Solar Cells, 2003, vol.75, pp.451-456) reported a FeS ₂ thin film preparation technology with similar electrochemical deposition effects, mainly FeSO ₄ and (NH ₄ ) ₂ S _x The aqueous solution is sprayed on glass and Si sheets, and heated at 120°C to form a prefabricated film, and then sulfurized and annealed in H ₂ S to form a p-type conductive FeS ₂ film. Regarding the preparation of FeS ₂ thin films by electrodeposition and thermal sulfidation, Nakamura et al. (Solar Energy Materials and Solar Cells, 2001, vol.65, pp.79-85) proposed to electrolyze FeSO ₄ and Na ₂ S ₂ O ₃ aqueous solutions on Ti substrates. The _FeS2 film was synthesized by depositing FeS prefabricated film and then sulfurized, and the sulfur vapor was transported with _N2 . Gomes et al. (Materials Research Bulletin, 2003, vol.38, pp.1123-1133; Electrochimica Acta, 2004, vol.49, pp.2155-2165) used 1:3 (NH ₄ ) ₂ Fe(SO ₄ ) ₂ Aqueous solution and Na ₂ S ₂ O ₃ electrodeposit Fe-S transition compound film, add H ₂ SO ₄ to the electroplating solution to adjust to pH = 3, the substrate is Ti sheet, the molar ratio of S ₂ O ₃ ²⁺ /Fe ²⁺ in the solution It cannot be equal to 1, and then annealing the Fe-S film in a sulfur atmosphere at 250-500 °C can be converted into an n-type conductive FeS ₂ film. Li Enling et al. (Journal of Xi'an University of Technology, 2002, vol.18, pp.48-50) used FeSO ₄ 7H ₂ O+Na ₂ S ₂ O ₃ 5H ₂ O aqueous solution to electrodeposit FeS on Si(111) substrates. _2. A thin film with a mixed structure of FeS and Fe ₇ S ₈ is then dried at 400-500°C under N ₂ or vacuum conditions, and the thin film is not vulcanized and annealed.

However, the FeS ₂ film prepared by electrodeposition and reheat sulfidation is often a transitional Fe-S compound phase, and the sulfidation process is difficult to completely transform the transition phase into FeS ₂ , or make the S vacancies in FeS ₂ unavoidable. Lattice defects are formed. In addition, in order to achieve electrodeposition, the substrate is made of elemental metal or single crystal Si. During the vulcanization process, the diffusion of substrate atoms into the film cannot be controlled, resulting in abnormal doping of the film and unstable conductivity. At the same time, these substrates are opaque. will block incoming light.

If the prefabricated film is iron oxide, the iron oxide directly reacts with active S atoms to form _FeS2 film during the vulcanization process, which can avoid the occurrence of S-depleted transition phase. Smestad et al. (Solar Energy Materials, 1990, vol.20, pp.149-165) prepared a Fe ₃ O ₄ or Fe ₂ O ₃ prefabricated film on a glass substrate by pyrolyzing FeCl ₂ or FeCl ₃ , and then placed the prefabricated film in Sulfurization treatment at 350°C forms _FeS2 film. In addition, the prefabricated film can also be obtained by evaporating pure Fe film and then oxidation treatment. Raturi et al. (Renewable Energy, 2000, vol.20, pp.37-43) sprayed FeCl ₃ solution on flat glass at 370°C to oxidize to form Fe ₂ O ₃ , and then annealed in a sulfide atmosphere to transform the prefabricated film into a FeS ₂ film .

The technology of using iron oxide prefabricated film to vulcanize to form _FeS2 film can effectively prevent the appearance of S-poor transition phase, and generally use glass substrate, which avoids the barrier of the substrate to the incident light and the uncontrollable abnormal doping caused by the diffusion of substrate atoms into the film body. However, the prefabricated film must be prepared by evaporation or chemical vapor deposition. Compared with the electrodeposition technology, the equipment is more complicated, the film and the substrate are not firmly bonded, and the efficiency is not high.

Contents of the invention

The purpose of the present invention is to provide a method for synthesizing iron disulfide film by electrodeposition oxidation and thermal vulcanization, the process parameters are easy to control, there is no transition phase and abnormal doping atoms in the film, the film body is reliable in adhesion and the substrate is transparent.

In order to achieve the above object, the technical scheme adopted in the present invention is:

1) The substrate of the carrier film is conductive glass, which is ultrasonically cleaned in acetone and ethanol solutions for 15 minutes, and then rinsed with deionized water;

2) The electrodeposition solution is an aqueous solution of FeSO ₄ and Na ₂ S ₂ O ₃ with a molar concentration ratio of 1:5 and a pH value of 5.0;

3) Use a Pt sheet as a counter electrode, and deposit at a current of 0.75mA for 20min to obtain a deposited film;

4) Oxidizing the electrodeposited film to obtain a prefabricated film with a Fe ₃ O ₄ structure;

5) Encapsulate the prefabricated membrane and the sublimed sulfur powder with a purity of 99.5% in a quartz tube, vacuumize to less than 1×10 ^-2 Pa before encapsulation, and repeat the substitution with argon for 3 to 8 times;

6) Sulfurize the encapsulated sample in an isothermal furnace to obtain a _FeS2 film.

The carrier film substrate is ITO conductive glass whose conductive film composition is In ₂ O ₃ :SnO ₂ =9:1.

The oxidation treatment process of the electrodeposited film is to keep warm in dry air at 180-220° C. for 2 hours.

In the vulcanization treatment, the sulfur vapor pressure is 20-40kPa, the vulcanization temperature is 350-450°C, and the vulcanization time is 5-20h.

The beneficial effects that the present invention has are:

1) An oxidation link is introduced after electrodeposition to pre-convert the Fe-S compound formed by electrodeposition into Fe ₃ O ₄ , avoiding the residual harmful transition phase structure in the FeS ₂ film after thermal sulfidation;

2) The ITO conductive glass substrate is used, which avoids the blocking effect of the substrate material on the incident light, and provides convenient conditions for the practical application in solar cells and the test of the photoelectric properties of _FeS2 thin films;

3) There is no diffusion of metal or metalloid elemental atoms into the film body in the substrate, causing abnormal doping and affecting the electrical properties of the film;

4) Compared with evaporation and chemical vapor deposition, due to the strong bond between the _FeS film prepared by electrodeposition and the substrate, the film has higher adhesion;

5) The preparation process and equipment are simple and the efficiency is high.

Description of drawings

Fig. 1 is the X-ray diffraction spectrum of the prefabricated film crystal structure in the embodiment of the present invention 1;

Fig. 2 is FeS in the embodiment of the present invention ₁ Film crystal structure X-ray diffraction spectrum;

Fig. 3 is the X-ray diffraction spectrum of the prefabricated film crystal structure in the embodiment 2 of the present invention;

Fig. 4 is the X-ray diffraction spectrum of the FeS ₂ film crystal structure in Example 2 of the present invention.

Detailed ways

Example 1:

Use ITO conductive glass with a size of 20×15mm2 as the substrate of the carrier film, and the composition of the conductive film is In ₂ O ₃ : SnO ₂ =9:1. First, ultrasonically clean it in acetone solution for 15 minutes, and then ultrasonically clean it in ethanol solution for 15 minutes. After ultrasonic cleaning, thoroughly rinse with ionized water to remove residual organic solution.

An aqueous solution of FeSO ₄ and Na ₂ S ₂ O ₃ with a molar concentration ratio of 1:5 was prepared, and the pH value of the solution was adjusted to 5.0 with diluted H ₂ SO ₄ . A Pt sheet was used as a counter electrode to deposit a Fe-S compound film on the substrate, maintaining a constant current of 0.75mA, and the deposition time was 20min. The deposited sample was rinsed with deionized water, soaked in absolute ethanol for 1 h, and then placed in a dry air oven at 180 °C for 2 h for oxidation treatment to obtain a Fe ₃ O ₄ prefabricated film with the crystal structure shown in Figure 1.

Calculate the mass required to produce 20kPa nominal sulfur pressure sublimation sulfur powder (purity: 99.5%) at 350°C, package the prefabricated membrane and the required mass of sulfur powder in a quartz tube, vacuumize and replace with argon for 3 times before packaging , when packaging, vacuumize until the residual gas pressure is lower than 1×10 ^-2 Pa. The encapsulated samples were vulcanized in an isothermal oven at 350°C for 20h. In order to prevent cracks and peeling of the film, the heating rate was controlled not to be higher than 4°C/min before isothermal, and the cooling rate was not to be higher than 2°C/min after isothermal. The obtained _FeS2 film structure after sulfidation is shown in Fig. 2.

Example 2:

The Fe-S compound film was prepared according to the method of Example 1, and the electrodeposited film was kept in an oven with dry air at 220°C for 2 hours for oxidation treatment to obtain a Fe ₃ O ₄ prefabricated film, whose crystal structure is shown in Figure 3 .

Can produce the required mass of 40kPa nominal sulfur pressure sublimation sulfur powder (purity is 99.5%) under the condition of calculating 450 ℃, then according to the method in the embodiment 1, the prefabricated film is converted into FeS at 450 ℃ under vulcanization treatment _5h Thin film (quartz tube Vacuuming and argon replacement were repeated 8 times before packaging), and the crystal structure is shown in Figure 4.

Claims (4)

1. The method for the synthesis of iron disulfide film by electrodeposition oxidation and heat vulcanization, is characterized in that: 1) The substrate of the carrier film is conductive glass, which is ultrasonically cleaned in acetone and ethanol solutions for 15 minutes, and then rinsed with deionized water; 2) The electrodeposition solution is an aqueous solution of FeSO ₄ and Na ₂ S ₂ O ₃ with a molar concentration ratio of 1:5 and a pH value of 5.0; 3) Use a Pt sheet as a counter electrode, and deposit at a current of 0.75mA for 20min to obtain a deposited film; 4) Oxidizing the electrodeposited film to obtain a prefabricated film with a Fe ₃ O ₄ structure; 5) Encapsulate the prefabricated membrane and the sublimed sulfur powder with a purity of 99.5% in a quartz tube, vacuumize to less than 1×10 ^-2 Pa before encapsulation, and repeat the substitution with argon for 3 to 8 times; 6) Sulfurize the encapsulated sample in an isothermal furnace to obtain a _FeS2 film. 2. The method for synthesizing iron disulfide thin films by electrodeposition oxidation and thermal vulcanization according to claim 1, characterized in that: the base of the carrier film is a conductive film whose composition is In ₂ O ₃ : SnO ₂ =9:1 ITO conductive glass. 3. The method for synthesizing iron disulfide thin film by electrodeposition oxidation and thermal vulcanization according to claim 1, characterized in that: the electrodeposition film oxidation treatment process is to keep warm in dry air at 180-220°C for 2 hours. 4. The method for synthesizing iron disulfide films by electrodeposition oxidation and thermal vulcanization according to claim 1, characterized in that: in the vulcanization treatment, the sulfur vapor pressure is 20-40kPa, the vulcanization temperature is 350-450°C, and the vulcanization The time is 5-20 hours.

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