Laser heat treatment method of czts thin film and solar thin film cell

Abstract

The application provides a laser heat treatment method of a CZTS thin film and a solar thin film battery. The method comprises the following steps: obtaining a CZTS precursor thin film; introducing a laser beam from a tube furnace laser window; and controlling the laser beam to scan the surface of the CZTS precursor thin film to perform sulfuration and laser heat annealing of the CZTS precursor thin film, wherein the temperature in the tube furnace is 200-250 DEG C, the pressure is 0.01-0.05 MPa, and the tube furnace is in a sulfur atmosphere. Through the scanning of the laser beam under specific parameters, the defect density in the sulfuration and recrystallization process of the CZTS precursor thin film can be adjusted, so that the sulfuration and crystallization quality of the CZTS light absorption layer thin film is improved, and the photoelectric conversion efficiency of the CZTS solar thin film battery is improved.

Description

Technical Field

[0001] This invention relates to a laser heat treatment method for CZTS thin films and a solar thin film battery, belonging to the field of solar photovoltaic cell preparation technology. Background Technology

[0002] CZTS (Cu2ZnSnS4) has a stable zinc stansite structure. CZTS thin-film solar cells have a theoretical photoelectric conversion efficiency of up to 32.2%, making it a promising new type of thin-film solar cell. Currently, the photoelectric conversion efficiency of solar cells obtained through heterojunction thermal processing has exceeded 11%.

[0003] The quality of CZTS thin film fabrication is crucial for improving the photoelectric conversion efficiency of solar cells. Existing annealing heat treatment methods for CZTS thin films employ slow heat treatment in tube furnaces, typically lasting more than an hour. Excessive annealing time leads to an excessive number of defects in the CZTS light-absorbing layer film. Furthermore, prolonged annealing can cause changes in the substrate, such as softening or decomposition of organic materials like glass and flexible plastics like polyimide, and precipitation of film components or dopants. Longer annealing times also increase the formation of MoS2 at the back interface. Therefore, excessively long annealing times are detrimental to the overall device performance. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention aims to provide a laser thermal treatment method for CZTS thin films. The solar thin-film battery prepared by the laser thermal treatment method for CZTS thin films can significantly improve the quality of the CZTS light absorption layer film, thereby improving the photoelectric conversion efficiency of the solar thin-film battery.

[0005] According to an embodiment of the present invention, a first embodiment is provided: a laser heat treatment method for CZTS thin films, comprising the following steps:

[0006] Obtain CZTS precursor thin films;

[0007] A laser beam is introduced from the laser window of a tube furnace and controlled to scan the surface of the CZTS precursor film to perform vulcanization and laser thermal annealing of the CZTS precursor film. The temperature inside the tube furnace is 200℃-250℃, the pressure is 0.01MPa-0.05MPa, and the atmosphere inside the tube furnace is sulfur.

[0008] Furthermore, the CZTS precursor film is prepared by pulsed laser deposition.

[0009] Furthermore, a CdS buffer layer was deposited in a chemical bath on the CZTS precursor film after sulfurization and laser thermal annealing, and a Glass / Mo / CZTS / CdS structure sample was obtained.

[0010] Secondary heat annealing is carried out in a tube furnace at a temperature of 230℃-280℃ for 5-20 minutes.

[0011] Magnetron sputtering deposition of ITO window layer;

[0012] A thin-film solar cell with a Glass / Mo / CZTS / CdS / ITO / Ag / MgF2 structure was obtained by thermal evaporation of Ag electrode and antireflection layer MgF2.

[0013] Furthermore, the method of scanning the surface of the CZTS precursor thin film with the laser beam includes:

[0014] A laser beam, controlled by a robotic arm control system, scans the surface of the CZTS precursor thin film, with an energy density of 0.05 J / cm². 2 -5J / cm 2 The wavelength of the laser beam is 940nm.

[0015] Furthermore, the step of controlling the laser beam to scan the surface of the CZTS precursor film via the robotic arm control system includes:

[0016] The laser beam is controlled by a robotic arm control system to scan the surface of the CZTS precursor film at a uniform speed of 0.5 cm / s to 2 cm / s.

[0017] Furthermore, the CZTS precursor film is square, and the scanning surface of the laser beam is circular. The effective radius of the laser beam is obtained, and the scanning trajectory of the laser beam is planned according to the effective radius. The robotic arm control system controls the laser beam to scan the surface of the CZTS precursor film at a uniform speed according to the scanning trajectory.

[0018] Furthermore, the steps for obtaining the effective radius of the laser beam include:

[0019] Obtain the energy density curve of the laser beam along the radial direction, and obtain the radius value at which the energy is reduced by half based on the energy density curve. Use the radius value as the effective radius.

[0020] Furthermore, the step of planning the scanning trajectory of the laser beam based on the effective radius includes:

[0021] The laser beam is controlled to scan the CZTS precursor film sequentially along a straight line. The overlap width of the scan cover formed on the CZTS precursor film by two adjacent scans is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam and the CZTS precursor film in the first scan is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam in the last scan and the optical center of the previous scan is twice the effective radius.

[0022] Furthermore, the step of planning the scanning trajectory of the laser beam based on the effective radius includes:

[0023] The laser beam is controlled to scan the CZTS precursor film sequentially along a straight line. The overlap width of the scan cover formed on the CZTS precursor film by two adjacent scans is 0. The distance between the optical center of the laser beam and the CZTS precursor film in the first scan is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam in the last scan and the optical center of the previous scan is twice the effective radius.

[0024] A second scan was performed along the midline of the scanning cover formed on the CZTS precursor film between two adjacent first scans. The laser beam parameters for the second scan were: a laser beam scanning speed of 0.5 cm / s–2 cm / s and a laser beam energy density of 0.05 J / cm². 2 -5J / cm 2 The wavelength of the laser beam is 940nm, and the energy density of the laser beam in the second scan is 40%-60% of the energy density of the laser beam in the first scan.

[0025] According to an embodiment of the present invention, utilizing the laser heat treatment method for CZTS thin films in the first embodiment of the present invention, a second embodiment is provided as follows:

[0026] A solar thin-film battery, the method for preparing the solar thin-film battery comprising:

[0027] Obtain CZTS precursor thin films;

[0028] A laser beam is introduced from the laser window of a tube furnace and controlled to scan the surface of the CZTS precursor film to perform vulcanization and laser thermal annealing of the CZTS precursor film. The temperature inside the tube furnace is 200℃-250℃, the pressure is 0.01MPa-0.05MPa, and the atmosphere inside the tube furnace is sulfur.

[0029] Compared with the prior art, the unique advantages of the technical solution provided in this application are as follows: This solution completes the heat treatment and recrystallization of the CZTS precursor film by scanning and irradiating the CZTS precursor film with a laser beam under a sulfur atmosphere. By scanning the laser beam with specific parameters, the defect density in the sulfurization and recrystallization process of the CZTS precursor film can be adjusted, thereby improving the sulfurization and crystallization quality of the CZTS light absorption layer film and thus improving the photoelectric conversion efficiency of the CZTS solar thin film cell. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] in:

[0032] Figure 1 This is a schematic diagram of the operation of a tube furnace in a laser heat treatment method for CZTS thin films in one embodiment;

[0033] Figure 2 This is a schematic flowchart of a laser heat treatment method for CZTS thin films in one embodiment;

[0034] Figure 3 This is an X-ray diffraction pattern of a CZTS light-absorbing layer film after laser thermal treatment of the CZTS film in one embodiment.

[0035] Figure 4 This is a SEM image of the surface morphology of the CZTS light-absorbing layer film before laser thermal treatment in one embodiment.

[0036] Figure 5 This is a SEM image of the surface morphology of a CZTS light-absorbing layer film after laser thermal treatment of the CZTS film in one embodiment.

[0037] Figure 6 This is an IV characteristic curve of a CZTS solar thin-film cell after laser thermal treatment of the CZTS thin film in one embodiment.

[0038] Figure 7 The external quantum efficiency curve of a CZTS solar thin-film cell after laser thermal treatment of the CZTS thin film in one embodiment is shown.

[0039] Figure 8The image shows the CV characteristic curve and DLCP curve of a CZTS solar thin-film cell after laser thermal treatment of the CZTS thin film in one embodiment. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Example 1

[0042] The technical problem addressed in this embodiment is that, during the fabrication of CZTS solar thin-film batteries, the high defect density of the CZTS light-absorbing layer film is a key factor restricting the improvement of the overall device efficiency. Therefore, how to fabricate a high-quality CZTS light-absorbing layer film is a research hotspot in the field of CZTS solar thin-film battery device fabrication.

[0043] The conventional preparation process for CZTS light-absorbing layer films involves: first preparing an amorphous CZTS precursor film, then performing sulfurization and thermal annealing in a sufficient sulfur atmosphere to transform the amorphous CZTS precursor film into a crystalline CZTS light-absorbing layer film. The thermal annealing process typically involves slow thermal annealing in a high-temperature furnace. While this can yield a crystalline CZTS light-absorbing layer film to some extent, the process usually exceeds one hour. Excessive annealing time leads to an excessive number of defects in the CZTS light-absorbing layer film. Furthermore, prolonged annealing can cause changes in the substrate, such as softening or decomposition of organic materials like glass and flexible polyimide, precipitation of film components or dopants, and increased formation of MoS2 at the back interface. Therefore, excessively long annealing times are detrimental to the overall device performance.

[0044] Secondly, the cooling process of slow hot annealing in high-temperature furnaces is usually cooled by means of room temperature dissipation, or by adding a fan to speed up the cooling process. Existing cooling methods prioritize shortening the cooling process, which limits the improvement of film crystallization quality by the cooling process of hot annealing.

[0045] To address the shortcomings of traditional slow thermal annealing in high-temperature furnaces, this embodiment provides a laser heat treatment method for CZTS thin films, such as... Figure 1As shown, this method combines pulsed laser deposition and laser thermal annealing to prepare CZTS light-absorbing layer films, namely CZTSSe films.

[0046] A laser heat treatment method for CZTS thin films, such as Figure 2 As shown, it includes the following steps:

[0047] S20: Obtain CZTS precursor thin film;

[0048] S30: The laser beam is introduced from the laser window of the tube furnace and controlled to scan the surface of the CZTS precursor film to perform vulcanization and laser thermal annealing of the CZTS precursor film. The temperature inside the tube furnace is 200℃-250℃, the pressure is 0.01MPa-0.05MPa, and the atmosphere inside the tube furnace is sulfur.

[0049] The laser thermal annealing process selected in this scheme has advantages such as high crystal quality, short annealing time, fast cooling rate, ability to maintain a low base temperature, and no limitation by the solid solubility of dopant ions. However, due to its high energy density, the laser beam can easily damage the film surface when irradiating and scanning it. Furthermore, the CZTS precursor film has a certain thickness, which places high demands on the penetration ability of the laser beam. Through laboratory experiments, this scheme has selected suitable laser beam parameters, which can greatly improve the quality of the CZTS light absorption layer film and further improve the photoelectric conversion efficiency of CZTS solar thin film cells.

[0050] Example 2

[0051] This embodiment provides a process for preparing a thin-film solar cell, including the following steps:

[0052] S10: CZTS precursor films were prepared by pulsed laser deposition.

[0053] S20: Obtain CZTS precursor thin film;

[0054] S30: A laser beam is introduced through the laser window of a tube furnace and controlled to scan the surface of the CZTS precursor film for vulcanization and laser thermal annealing. The temperature inside the tube furnace is 200℃-250℃, the pressure is 0.01MPa-0.05MPa, and the atmosphere inside the tube furnace is sulfur. The laser beam is controlled by a robotic arm control system to scan the surface of the CZTS precursor film at a uniform speed of 0.5cm / s-2cm / s, and the energy density of the laser beam is 0.05J / cm². 2 -5J / cm 2 The wavelength of the laser beam is 940 nm;

[0055] S40: A CdS buffer layer was deposited in a chemical bath on the CZTS precursor film after sulfurization and laser thermal annealing, and a Glass / Mo / CZTS / CdS structure sample was obtained.

[0056] S50: Secondary heat annealing is carried out in a tube furnace at a temperature of 230℃-280℃ for 5-20 minutes.

[0057] S60: Magnetron sputtering deposited ITO window layer;

[0058] S70: Thermally evaporate Ag electrode and antireflection layer MgF2 to obtain Glass / Mo / CZTS / CdS / ITO / Ag / MgF2 structured thin-film solar cell.

[0059] The photoelectric conversion efficiency of the solar thin-film battery prepared by the above method can be significantly improved.

[0060] Example 3

[0061] This embodiment provides an optimized fabrication process for thin-film solar cells, including the following steps:

[0062] S10: CZTS precursor films were prepared by pulsed laser deposition.

[0063] S20: Obtain CZTS precursor thin film;

[0064] S30: A laser beam is introduced through the laser window of a tube furnace and controlled to scan the surface of the CZTS precursor film for vulcanization and laser thermal annealing. The temperature inside the tube furnace is 220℃, the pressure is 0.03MPa, and the atmosphere inside the furnace is sulfur. The laser beam is controlled by a robotic arm control system to scan the surface of the CZTS precursor film at a uniform speed of 1cm / s, and the energy density of the laser beam is 0.1J / cm². 2 The wavelength of the laser beam is 940 nm;

[0065] S40: A CdS buffer layer was deposited in a chemical bath on the CZTS precursor film after sulfurization and laser thermal annealing, and a Glass / Mo / CZTS / CdS structure sample was obtained.

[0066] S50: Secondary heat annealing is performed in a tube furnace at a temperature of 250°C for 10 minutes.

[0067] S60: Magnetron sputtering deposited ITO window layer;

[0068] S70: Thermally evaporate Ag electrode and antireflection layer MgF2 to obtain Glass / Mo / CZTS / CdS / ITO / Ag / MgF2 structured thin-film solar cell.

[0069] pass Figure 3 The X-ray diffraction pattern of the CZTS light absorption layer film shows that the CZTS light absorption layer film obtained by laser beam thermal treatment of the CZTS precursor film with the above parameters has strong

[112] orientation and the composition has stoichiometry.

[0070] pass Figures 4-5 The SEM surface morphology image of the CZTS light absorption layer film shows that the CZTS light absorption layer film obtained by laser beam thermal treatment of the CZTS precursor film with the above parameters has a surface morphology of micron-sized grains that are tightly packed.

[0071] The solar thin-film cells prepared by laser thermal annealing were tested, such as... Figures 6-7 As shown, both the photocurrent density and the fill factor were optimized. Specifically, the current density increased from 17.2 mA / cm2 to 22.79 mA / cm2, and the fill factor increased from 49.25% to 62.49%.

[0072] Through further testing, such as Figure 8 As shown, the interfacial state density of the solar thin-film battery prepared by this method is reduced from 1.25×10¹⁶ cm⁻³ to 6.7×10¹⁵ cm⁻³, which reduces recombination losses caused by defects and enhances the separation and transport of charge carriers in the CZTS absorber layer.

[0073] Based on the above optimizations, the CZTS thin-film solar cell obtained by this method has a high photoelectric conversion efficiency of 8.26%.

[0074] Example 4

[0075] In further optimizing the laser thermal annealing process of CZTS precursor films, to further improve the sulfurization and laser thermal annealing processes of CZTS precursor films and obtain high-quality CZTS light-absorbing layer films with more complete sulfurization and better crystallization, this embodiment further optimizes the scanning trajectory of the laser beam. Since the scanning surface of the laser beam is circular and the energy distribution of the laser beam conforms to a Gaussian distribution with high energy at the center and low energy at the edges, when the laser beam scans the surface of the CZTS precursor film along a straight line, the laser irradiation energy density is high at the center position and low at the edge position. Therefore, the crystallization effect at the edge position is worse than at the center position. To further improve the quality of the CZTS precursor film, this embodiment provides a laser heat treatment method for CZTS films, which further includes the following steps:

[0076] S30: A laser beam is introduced through the laser window of a tube furnace and controlled to scan the surface of the CZTS precursor film for vulcanization and laser thermal annealing. The temperature inside the tube furnace is 220℃, the pressure is 0.03MPa, and the atmosphere inside the furnace is sulfur. The laser beam is controlled by a robotic arm control system to scan the surface of the CZTS precursor film at a uniform speed of 1cm / s, and the energy density of the laser beam is 0.1J / cm². 2 The wavelength of the laser beam is 940 nm;

[0077] The CZTS precursor film is square, and the scanning surface of the laser beam is circular to obtain the effective radius of the laser beam;

[0078] The steps for obtaining the effective radius of a laser beam include: obtaining the energy density curve of the laser beam along the radial direction, obtaining the radius value at which the energy is attenuated by half based on the energy density curve, and taking the radius value as the effective radius.

[0079] The scanning trajectory of the laser beam is planned according to the effective radius, and the robotic arm control system controls the laser beam to scan the surface of the CZTS precursor film at a uniform speed according to the scanning trajectory.

[0080] Scheme 1 for planning the scanning trajectory of the laser beam based on the effective radius:

[0081] This scheme uses a single laser beam scan. To improve the heat treatment effect after the laser beam edge scan, i.e., the sulfidation and crystallization effect of the CZTS precursor film, in subsequent laser scans, the laser beam is controlled to partially overlap with the edge of the previous laser scan to improve the film quality at the laser beam edge. Specifically, the step of planning the laser beam scanning trajectory according to the effective radius includes:

[0082] The laser beam is controlled to scan the CZTS precursor film sequentially along a straight line. The overlap width of the scan cover formed on the CZTS precursor film by two adjacent scans is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam and the CZTS precursor film in the first scan is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam in the last scan and the optical center of the previous scan is twice the effective radius.

[0083] The above scheme can further optimize the sulfidation and crystallization effect at the edge of the CZTS precursor film, thereby improving the film quality of the CZTS light absorption layer.

[0084] Scheme 2: Planning the scanning trajectory of the laser beam based on the effective radius:

[0085] This scheme uses a laser beam to perform a secondary scan. After receiving the conventional first-stage non-overlapping edge scan, a secondary scan is performed at the mid-slit position of the two scans, and the laser beam of the secondary scan is controlled to be weaker than that of the first scan.

[0086] The laser beam is controlled to scan the CZTS precursor film sequentially along a straight line. The overlap width of the scan cover formed on the CZTS precursor film by two adjacent scans is 0. The distance between the optical center of the laser beam and the CZTS precursor film in the first scan is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam in the last scan and the optical center of the previous scan is twice the effective radius.

[0087] A second scan was performed along the midline of the scanning cover formed on the CZTS precursor film between two adjacent first scans. The laser beam parameters for the second scan were: a laser beam scanning speed of 0.5 cm / s–2 cm / s and a laser beam energy density of 0.05 J / cm². 2 -5J / cm 2 The wavelength of the laser beam is 940nm, and the energy density of the laser beam in the second scan is 40%-60% of the energy density of the laser beam in the first scan.

[0088] The above scheme can further optimize the sulfidation and crystallization effect at the edge of the CZTS precursor film, thereby improving the film quality of the CZTS light absorption layer.

[0089] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A laser heat treatment method for CZTS thin films, characterized in that, Includes the following steps: Obtain CZTS precursor thin films; A laser beam is introduced from the laser window of a tube furnace and controlled to scan the surface of the CZTS precursor film to perform vulcanization and laser thermal annealing of the CZTS precursor film. The temperature inside the tube furnace is 200℃-250℃, the pressure is 0.01MPa-0.05MPa, and the atmosphere inside the tube furnace is sulfur.

2. The laser heat treatment method for CZTS thin films according to claim 1, characterized in that: The CZTS precursor film was prepared by pulsed laser deposition.

3. The laser heat treatment method for CZTS thin films according to claim 1, characterized in that: CZTS precursor films that have undergone sulfurization and laser thermal annealing are subjected to chemical bath deposition of CdS buffer layers, and Glass / Mo / CZTS / CdS structure samples are obtained. Secondary heat annealing is carried out in a tube furnace at a temperature of 230℃-280℃ for 5-20 minutes. Magnetron sputtering deposition of ITO window layer; A thin-film solar cell with a Glass / Mo / CZTS / CdS / ITO / Ag / MgF2 structure was obtained by thermal evaporation of Ag electrode and antireflection layer MgF2.

4. The laser heat treatment method for CZTS thin films according to claim 1, characterized in that, The method for scanning the surface of the CZTS precursor thin film with a laser beam includes: A laser beam, controlled by a robotic arm control system, scans the surface of the CZTS precursor thin film, with an energy density of 0.05 J / cm². 2 -5J / cm 2 The wavelength of the laser beam is 940nm.

5. The laser heat treatment method for CZTS thin films according to claim 4, characterized in that, The step of controlling the laser beam to scan the surface of the CZTS precursor film using a robotic arm control system includes: The laser beam is controlled by a robotic arm control system to scan the surface of the CZTS precursor film at a uniform speed of 0.5 cm / s to 2 cm / s.

6. The laser heat treatment method for CZTS thin films according to claim 5, characterized in that, The CZTS precursor film is square, and the scanning surface of the laser beam is circular. The effective radius of the laser beam is obtained, and the scanning trajectory of the laser beam is planned according to the effective radius. The robotic arm control system controls the laser beam to scan the surface of the CZTS precursor film at a uniform speed according to the scanning trajectory.

7. The laser heat treatment method for CZTS thin films according to claim 6, characterized in that, The steps to obtain the effective radius of the laser beam include: Obtain the energy density curve of the laser beam along the radial direction, and obtain the radius value at which the energy is reduced by half based on the energy density curve. Use the radius value as the effective radius.

8. The laser heat treatment method for CZTS thin films according to claim 6, characterized in that, The step of planning the scanning trajectory of the laser beam based on the effective radius includes: The laser beam is controlled to scan the CZTS precursor film sequentially along a straight line. The overlap width of the scan cover formed on the CZTS precursor film by two adjacent scans is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam and the CZTS precursor film in the first scan is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam in the last scan and the optical center of the previous scan is twice the effective radius.

9. The laser heat treatment method for CZTS thin films according to claim 6, characterized in that, The step of planning the scanning trajectory of the laser beam based on the effective radius includes: The laser beam is controlled to scan the CZTS precursor film sequentially along a straight line. The overlap width of the scan cover formed on the CZTS precursor film by two adjacent scans is 0. The distance between the optical center of the laser beam and the CZTS precursor film in the first scan is the difference between the laser beam radius and the effective radius. The distance between the optical center of the laser beam in the last scan and the optical center of the previous scan is twice the effective radius. A second scan was performed along the midline of the scanning cover formed on the CZTS precursor film between two adjacent first scans. The laser beam parameters for the second scan were: a laser beam scanning speed of 0.5 cm / s–2 cm / s and a laser beam energy density of 0.05 J / cm². 2 -5J / cm 2 The wavelength of the laser beam is 940nm, and the energy density of the laser beam in the second scan is 40%-60% of the energy density of the laser beam in the first scan.

10. A solar thin-film battery, characterized in that, The solar thin-film battery is prepared by laser thermal treatment of the CZTS thin film as described in any one of claims 1-9.

Images