Surface modification method of cadmium telluride nanocrystalline film

Abstract

The invention discloses a surface modification method of a cadmium telluride nanocrystalline thin film, which comprises the following steps: coating the surface of the cadmium telluride nanocrystalline thin film with a short-chain insulation ligand solution, standing for ligand exchange, cleaning, coating with a cadmium salt solution, and carrying out heat treatment. The CdTe nanocrystalline thin film is processed by using a surface ligand exchange method, so that the inherent defects of CdTe nanocrystalline are greatly reduced, the recombination problem of carriers in the transmission process is reduced, and the performance of the CdTe nanocrystalline solar cell is improved.

Description

Technical Field

[0001] The invention relates to the technical field of nanocrystalline solar cells, and in particular to a surface modification method of a cadmium telluride nanocrystalline film. Background Art

[0002] Nanocrystalline solar cells are solar cells that use nanocrystals (for example, nano-titanium dioxide) as photoelectric conversion materials. They have the advantages of low cost (the production cost is only 1 / 5 to 1 / 10 of that of silicon solar cells), simple process (can be processed and manufactured by solution method, with low consumption of raw materials, and can be quickly prepared on a large scale), stable performance (lifespan can reach more than 20 years), and stable conversion efficiency (stable at more than 10%), and have very broad application prospects.

[0003] Cadmium telluride (CdTe) is a direct bandgap semiconductor material with a bandgap width of 1.45 eV and an average light absorption coefficient within the bandgap range of nearly 1×10 5 / cm. Although the conversion efficiency of CdTe nanocrystal solar cells is lower than that of organic solar cells and perovskite solar cells, their stability is much better. At present, the conversion efficiency of CdTe nanocrystal solar cells processed by solution method can reach up to 12.3%, which is still far from its theoretical limit efficiency (29%), and there is still a lot of room for improvement. Studies have shown that the quality of CdTe nanocrystal film is a key factor affecting the performance (e.g. conversion efficiency) of CdTe nanocrystal solar cells. In the current mature CdTe nanocrystal synthesis technology, long-chain organic ligands such as tri-n-octylphosphine oxide (TOPO) are usually used as surfactants to increase particle stability, adjust optical properties and improve the physical properties of colloidal particles. However, in the further preparation of CdTe nanocrystal films and solar cells, due to the incomplete elimination of long-chain alkyl acid insulating ligands, surface defects in CdTe nanocrystal films will occur, which will affect the transmission of carriers and ultimately cause poor performance of solar cells.

[0004] Therefore, it is of great significance to develop a surface modification method for CdTe nanocrystalline films to improve the quality of CdTe nanocrystalline films and enhance the performance of CdTe nanocrystalline solar cells. Summary of the invention

[0005] The purpose of the present invention is to provide a surface modification method of a cadmium telluride nanocrystalline film.

[0006] The technical solution adopted by the present invention is:

[0007] A surface modification method for a cadmium telluride nanocrystalline film comprises the following steps: coating a short-chain insulating ligand solution on the surface of the cadmium telluride nanocrystalline film, standing the film for ligand exchange, washing the film, coating the film with a cadmium salt solution, and then performing heat treatment.

[0008] Preferably, the short-chain insulating ligand in the short-chain insulating ligand solution is at least one of 3-mercapto-1-propanol (MTP), 2-mercaptonicotinic acid (MTA), 3-mercaptopropionic acid (MPA), 1,2-ethanedithiol (EDT), tetrabutylammonium chloride (TBAC), hexadecyltrimethylammonium bromide (CTAB), tetrabutylammonium iodide (TBAI), and methylammonium iodide (MAI).

[0009] Further preferably, the short-chain insulating ligand in the short-chain insulating ligand solution is at least one of 3-mercapto-1-propanol, 2-mercaptonicotinic acid, and 3-mercaptopropionic acid.

[0010] Preferably, the solvent in the short-chain insulating ligand solution is at least one of water, methanol and ethanol.

[0011] Preferably, the concentration of the short-chain insulating ligand solution is 0.1 mg / mL to 10 mg / mL.

[0012] Preferably, the coating method is one of spin coating, brush coating, spray coating, printing and inkjet printing.

[0013] Preferably, the cadmium telluride nanocrystal film is made by a preparation method comprising the following steps: preparing cadmium telluride nanocrystals by a solvothermal method (refer to S. Sun, HM Liu, YP Gao, DH Qin, J. Materials. Chemistry., 2012, 517, 6853-6856), dispersing the cadmium telluride nanocrystals in a solvent to prepare a cadmium telluride nanocrystal dispersion, and then coating the cadmium telluride nanocrystal dispersion on a substrate surface to form a film; preferably, the solvent is at least one of water, methanol, ethanol, n-propanol, and pyridine; preferably, the coating method is one of spin coating, brush coating, spray coating, printing, and inkjet printing.

[0014] Preferably, the standing is performed at room temperature (25°C±5°C) for a standing time of 20s to 180s.

[0015] Preferably, the cleaning agent is at least one of water, methanol, ethanol, n-propanol and pyridine. The cleaning function is to remove the excess short-chain insulating ligands.

[0016] Preferably, the cadmium salt in the cadmium salt solution is at least one of cadmium chloride, cadmium nitrate, cadmium phosphate, cadmium sulfate and cadmium thiocyanate.

[0017] Preferably, the heat treatment is carried out at a temperature of 250° C. to 400° C., and the treatment time is 20 min to 50 min.

[0018] A cadmium telluride nanocrystalline film is surface-modified by using the surface modification method of the cadmium telluride nanocrystalline film.

[0019] A cadmium telluride nanocrystal solar cell comprises the cadmium telluride nanocrystal film.

[0020] Preferably, the cadmium telluride nanocrystal solar cell comprises a substrate, a zinc oxide layer, a cadmium selenide layer, a cadmium telluride nanocrystal film and a metal electrode which are stacked in sequence.

[0021] Preferably, the substrate is an ITO glass substrate.

[0022] Preferably, the zinc oxide layer has a thickness of 30 nm to 50 nm.

[0023] Preferably, the cadmium selenide layer has a thickness of 50 nm to 70 nm.

[0024] Preferably, the cadmium telluride nanocrystalline thin film has a thickness of 200 nm to 700 nm.

[0025] Preferably, the metal electrode is composed of at least one of Au, Ag, and Al.

[0026] Preferably, the thickness of the metal electrode is 60 nm to 90 nm.

[0027] A method for preparing a cadmium telluride nanocrystal solar cell comprises the surface modification method of the cadmium telluride nanocrystal film.

[0028] Preferably, the method for preparing the cadmium telluride nanocrystal solar cell comprises the following steps:

[0029] 1) depositing zinc oxide on a single side of a substrate to form a zinc oxide layer;

[0030] 2) depositing cadmium selenide on the surface of the cadmium selenide layer to form a cadmium selenide layer;

[0031] 3) depositing cadmium telluride nanocrystals on the surface of the cadmium selenide layer and performing surface modification treatment to form a cadmium telluride nanocrystal film;

[0032] 4) Depositing electrode metal on the surface of the cadmium telluride nanocrystal film to form a metal electrode, thereby obtaining a cadmium telluride nanocrystal solar cell.

[0033] Principle of the present invention: The present invention utilizes short-chain organic ligands to perform ligand exchange during the preparation process of CdTe nanocrystal film, replacing long-chain ligands (mainly L-type ligands, RNH2 and PR3 types with two lone pairs of electrons) on the surface of CdTe nanocrystals, which can passivate defects in CdTe nanocrystals and greatly reduce the distance between CdTe nanocrystals, thereby improving the quality of CdTe nanocrystal film, thereby reducing the probability of carrier recombination, improving carrier mobility, and ultimately comprehensively improving the performance of CdTe nanocrystal solar cells.

[0034] The beneficial effects of the present invention are as follows: the present invention utilizes the surface ligand exchange method to process the CdTe nanocrystal film, which greatly reduces the intrinsic defects of the CdTe nanocrystal and reduces the recombination problem of carriers during transmission, thereby improving the performance of the CdTe nanocrystal solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a flow chart of the preparation of the cadmium telluride nanocrystal solar cell.

[0036] Figure 2 Schematic diagram of ligand exchange between short-chain insulating ligands and cadmium telluride nanocrystal films.

[0037] Figure 3 1 is the JV curve of the cadmium telluride nanocrystal solar cell in Examples 1 to 3 and the comparative example. DETAILED DESCRIPTION

[0038] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0039] Embodiment 1:

[0040] A cadmium telluride nanocrystal solar cell, the preparation method thereof is as follows (the preparation flow chart is as follows Figure 1 shown):

[0041] 1) preparing a substrate composed of an ITO glass substrate (150 nm thick), a zinc oxide layer (40 nm thick) and a cadmium selenide layer (60 nm thick) stacked in sequence from bottom to top;

[0042] 2) Cdtelluride nanocrystals were prepared by a solvothermal method (see S. Sun, HM Liu, YP Gao, DH Qin, J. Materials. Chemistry, 2012, 517, 6853-6856). The Cdtelluride nanocrystals were then dispersed in a pyridine-n-propanol mixed solvent (the volume ratio of pyridine to n-propanol was 1:1) to prepare a Cdtelluride nanocrystal dispersion (black). The Cdtelluride nanocrystal dispersion was then spin-coated on the surface of the CdSe layer in the substrate to form a Cdtelluride nanocrystal film. 0.1 mL of a 0.1 mg / mL methanol solution of 3-mercapto-1-propanol was then spin-coated on the surface of the Cdtelluride nanocrystal film. The spin coater had a rotation speed of 1100 rpm and a spin coating time of 20 s. The film was allowed to stand at room temperature for 30 s for ligand exchange (a schematic diagram of ligand exchange between short-chain insulating ligands and Cdtelluride nanocrystal film is shown in FIG. Figure 2 As shown), then spin-coat 0.1 mL of anhydrous methanol twice, the speed of the spin coater is 1100 rpm, the spin coating time is 10 s, repeat the above operation until the thickness of the cadmium telluride nanocrystalline film reaches 400 nm, then spin-coat 0.1 mL of saturated CdCl2 methanol solution, the speed of the spin coater is 1100 rpm, the spin coating time is 20 s, and then heat-treat at 350 ° C for 30 min to form a cadmium telluride nanocrystalline film (surface modified);

[0043] 3) A gold layer with a thickness of 80 nm is evaporated on the surface of the cadmium telluride nanocrystal film and patterned to form a metal electrode, thereby obtaining a cadmium telluride nanocrystal solar cell (with a structure of ITO / ZnO / CdSe / CdTe / Au).

[0044] Embodiment 2:

[0045] A cadmium telluride nanocrystal solar cell is prepared in the same manner as in Example 1 except that "3-mercapto-1-propanol" in step 2) is replaced with "2-mercaptonicotinic acid".

[0046] Embodiment 3:

[0047] A cadmium telluride nanocrystal solar cell is prepared in the same manner as in Example 1 except that "3-mercapto-1-propanol" in step 2) is replaced with "3-mercaptopropionic acid".

[0048] Comparative Example:

[0049] A cadmium telluride nanocrystal solar cell, the preparation method of which is as follows:

[0050] 1) Spin coating a cadmium telluride nanocrystal dispersion (same as in Example 1) on the surface of the cadmium selenide layer in the substrate (same as in Example 1) to form a film, then spin coating 0.1 mL of a saturated CdCl2 methanol solution, the spin coater speed is 1100 rpm, the spin coating time is 20 s, and then heat treatment is performed at 350° C. for 30 min to form a cadmium telluride nanocrystal film with a thickness of 400 nm (without surface modification treatment);

[0051] 2) A gold layer with a thickness of 80 nm is evaporated on the surface of the cadmium telluride nanocrystal film and patterned to form a metal electrode, thereby obtaining a cadmium telluride nanocrystal solar cell (with a structure of ITO / ZnO / CdSe / CdTe / Au).

[0052] Performance Testing:

[0053] The cadmium telluride nanocrystalline solar cells in Examples 1 to 3 and the comparative example were placed under a Keithley SourceMeter 2420 solar simulation lamp (Beijing Saifan Optoelectronics Instrument Co., Ltd., model 7-IV50S) and the light intensity was controlled to be 1000 W / m 2 The JV curve of the cadmium telluride nanocrystal solar cell tested at room temperature is as follows: Figure 3 The corresponding parameters of the JV curve are shown in the following table:

[0054] Table 1 Corresponding parameters of J-V curve

[0055]

[0056]

[0057] Note: V oc is the open circuit voltage, J sc is the short-circuit current density, FF is the fill factor, PCE is the energy conversion efficiency, R s is the series resistance, R sh is a parallel resistor.

[0058] Depend on Figure 3 From Table 1, we can see that:

[0059] a) Compared with the cadmium telluride nanocrystalline solar cells in Examples 1 to 3 (using MTP / MTA / MPA to modify the surface of the CdTe nanocrystalline film) and the cadmium telluride nanocrystalline solar cells in the comparative example (without modifying the surface of the CdTe nanocrystalline film), V oc , J sc , FF and PCE are significantly improved, indicating that the surface modification method of the cadmium telluride nanocrystalline film of the present invention can indeed effectively improve the performance of the cadmium telluride nanocrystalline solar cell;

[0060] b) Compared with the cadmium telluride nanocrystalline solar cell in Example 3 (using MPA to modify the surface of the CdTe nanocrystalline film) and the cadmium telluride nanocrystalline solar cell in the comparative example (without modifying the surface of the CdTe nanocrystalline film), V oc , J sc and PCE are increased by 0.02 V, 28.2% and 37.7% respectively, and the increase is higher than that of the cadmium telluride nanocrystal solar cell in Example 1 (the CdTe nanocrystal film is surface modified by MTP) and the cadmium telluride nanocrystal solar cell in Example 2 (the CdTe nanocrystal film is surface modified by MTA), indicating that the surface modification effect of MPA is the best and MPA plays a better organic passivation role (MPA has a short alkyl carbon chain, which can well replace the tetradecanoic acid insulating ligand on the CdTe nanocrystal film and fill more vacancies, making it easier to form bonds with the CdTe nanocrystal film).

[0061] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A surface modification method for cadmium telluride nanocrystalline thin film, characterized in that: The method comprises the following steps: coating a short-chain insulating ligand solution on the surface of a cadmium telluride nanocrystalline film, allowing the film to stand for ligand exchange, washing the film, coating the film with a cadmium salt solution, and then performing heat treatment.

2. The surface modification method of cadmium telluride nanocrystalline thin film according to claim 1, characterized in that: The short-chain insulating ligand in the short-chain insulating ligand solution is at least one of 3-mercapto-1-propanol, 2-mercaptonicotinic acid, 3-mercaptopropionic acid, 1,2-ethanedithiol, tetrabutylammonium chloride, hexadecyltrimethylammonium bromide, tetrabutylammonium iodide and methylammonium iodide.

3. The surface modification method of cadmium telluride nanocrystalline thin film according to claim 1 or 2, characterized in that: The concentration of the short-chain insulating ligand solution is 0.1 mg / mL to 10 mg / mL.

4. The surface modification method of cadmium telluride nanocrystalline thin film according to claim 1 or 2, characterized in that: The standing is performed at room temperature for a time of 20s to 180s.

5. The surface modification method of cadmium telluride nanocrystalline thin film according to claim 1 or 2, characterized in that: The cleaning reagent is at least one of water, methanol, ethanol, n-propanol and pyridine.

6. The surface modification method of cadmium telluride nanocrystalline thin film according to claim 1 or 2, characterized in that: The cadmium salt in the cadmium salt solution is at least one of cadmium chloride, cadmium nitrate, cadmium phosphate, cadmium sulfate and cadmium thiocyanate.

7. The surface modification method of cadmium telluride nanocrystalline thin film according to claim 1 or 2, characterized in that: The heat treatment is carried out at a temperature of 250° C. to 400° C., and the treatment time is 20 min to 50 min.

8. A cadmium telluride nanocrystalline film, characterized in that: The surface modification is carried out by using the surface modification method of the cadmium telluride nanocrystalline film described in any one of claims 1 to 7.

9. A cadmium telluride nanocrystal solar cell, characterized in that: Contains the cadmium telluride nanocrystalline film as described in claim 8.

10. A method for preparing a cadmium telluride nanocrystal solar cell, characterized in that: A surface modification method for a cadmium telluride nanocrystalline film as described in any one of claims 1 to 7.

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