LAYERED POLYCRYSTALLINE LEAD SELENIDE PHOTOELECTRIC FILM AND FABRICATION METHOD THEREOF

Abstract

The present invention relates to a photoelectric film and a fabrication method thereof, and in particular, to a layered polycrystalline lead selenide (PbSe) film and a fabrication method thereof. The fabrication method mainly includes: (1) fabricating a dense PbSe layer on a substrate through chemical bath deposition (CBD); (2) fabricating a loose plumbonacrite (Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6) layer on the dense PbSe layer through CBD; (3) placing a sample with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer in a selenium ion-containing solution to allow an ion exchange reaction to finally form the layered polycrystalline PbSe film. The fabrication method has the advantages of simple process, low cost, and high controllability. The PbSe film fabricated by the method is composed of a lower dense polycrystalline cubic PbSe layer and an upper loose polycrystalline cubic PbSe layer, which can be widely used in the fabrication of components in the field of photoelectric conversion or thermoelectric conversion, such as infrared (IR) sensors, solar cells, laser emitters, and thermoelectric converters.

Claims

1. A layered polycrystalline lead selenide film, comprising a substrate and a lead selenide film layer, characterized in that the lead selenide film layer is composed of a dense lead selenide layer on the substrate and a loose lead selenide layer on the dense lead selenide layer; the dense lead selenide layer is formed by close arrangement and stacking of cubic crystal grains with a grain size of 0.7 μm to 1.5 μm, and has a thickness of 1.5 μm to 5 μm; and the loose lead selenide layer is formed by random arrangement and stacking of cubic crystal grains with a grain size of 0.2 μm to 0.5 μm, and has a large number of micron-scale or submicron-scale voids among crystal grain stacks and among crystal grains, and the loose lead selenide layer has a thickness of 5 μm to 15 μm.

2. The layered polycrystalline lead selenide film according to claim 1, characterized in that the layered polycrystalline lead selenide film shows an average absorbance of 0.89 to 1.31, and an average optical reflectivity of 8.58% to 13.63% in a wavelength range of 450 nm to 5,000 nm.

3. The layered polycrystalline lead selenide film according to claim 1, characterized in that the layered polycrystalline lead selenide film has a band gap of 0.30 eV to 0.32 eV.

4. The layered polycrystalline lead selenide film according to claim 1, characterized in that the substrate is one selected from the group consisting of glass, silicon, silica, gallium nitride, and quartz.

5. A fabrication method of the layered polycrystalline lead selenide film according to claim 1, characterized by comprising the following steps: (1) substrate cleaning; (2) fabrication of the dense lead selenide layer through chemical bath deposition: adding a lead acetate solution with a concentration of 0.3 mol/L to 0.6 mol/L dropwise to a potassium hydroxide solution with a concentration of 0.45 mol/L to 1.1 mol/L to allow a complete reaction under stirring, adding a sodium selenosulfate solution with a concentration of 0.2 mol/L to 0.6 mol/L dropwise, and thoroughly stirring to obtain a yellow-brown suspension, wherein the potassium hydroxide solution, the lead acetate solution, and the sodium selenosulfate solution have a volume ratio of (2-4):1:1; placing the yellow-brown suspension in a 60° C. to 85° C. water bath, vertically inserting the substrate obtained in step (1) into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and conducting deposition for 3 h to 5 h to form the dense lead selenide layer on the substrate; (3) fabrication of a plumbonacrite layer through chemical bath deposition: pouring a sodium citrate solution with a concentration of 0.2 mol/L to 0.3 mol/L into a lead acetate solution with a concentration of 0.0164 mol/L to 0.0306 mol/L, stirring with a glass rod to obtain a milky white colloid, adding ammonia water, and stirring to obtain a clear solution, wherein the lead acetate solution, the sodium citrate solution, and the ammonia water have a volume ratio of (9.8-12.2):(2.8-3.2):(0.8-1.2); placing the clear solution in a 20° C. to 50° C. water bath, vertically inserting the substrate on which the dense lead selenide layer is deposited into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and conducting deposition for 8 h to 24 h to form the plumbonacrite layer on the dense lead selenide layer; and (4) fabrication of the loose lead selenide layer through ion exchange: placing the substrate with the dense lead selenide layer and the plumbonacrite layer obtained in step (3) in a selenium ion-containing solution to allow an ion exchange reaction at 20° C. to 40° C. for 0.5 h to 5 h, such that the plumbonacrite layer is transformed into the loose lead selenide layer.

6. The fabrication method of the layered polycrystalline lead selenide film according to claim 5, characterized in that in step (1), the substrate cleaning is conducted by washing the substrate successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min, respectively, taking the substrate out, blow-drying the substrate with a nitrogen gun, and then storing the substrate.

7. The fabrication method of the layered polycrystalline lead selenide film according to claim 5, characterized in that in step (2), the stirring is conducted at a rotational speed of 600 rpm.

8. The fabrication method of the layered polycrystalline lead selenide film according to claim 5, characterized in that in step (3), the ammonia water has a concentration of 28 wt %.

9. The fabrication method of the layered polycrystalline lead selenide film according to claim 5, characterized in that in step (4), the selenium ion-containing solution comprises one or a combination of two selected from the group consisting of sodium selenosulfate and selenourea at 0.01 mol/L to 0.1 mol/L.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings constituting a part of the present invention provide further understanding of the present invention. Schematic embodiments of the present invention and description thereof are intended to illustrate the present invention and do not constitute an undue limitation on the present invention.

[0025] FIG. 1 is a schematic diagram of a CBD device for fabricating the layered polycrystalline PbSe photoelectric film according to the present invention,

[0026] where 1 represents a mold; 2 represents a substrate; 3 represents a magnetic stirring bar; 4 represents a reaction solution; 5 represents silicone oil; 6 represents temperature adjustment and display; and 7 represents speed adjustment.

[0027] FIG. 2 is a flow chart of the fabrication method of the layered polycrystalline PbSe photoelectric film according to the present invention, where FIG. 2d is a schematic structural diagram of the layered polycrystalline PbSe photoelectric film.

[0028] FIG. 3 shows scanning electron microscopy (SEM) images of a typical sample of the layered polycrystalline PbSe film fabricated in the present invention, where (a) shows a surface of the dense PbSe layer, (b) shows a surface of the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer, (c) shows a surface of the loose PbSe layer, and (d) shows a cross section of the layered polycrystalline PbSe film.

[0029] FIG. 4 shows reflection and absorption spectra of typical samples of the layered polycrystalline PbSe film fabricated in the present invention, where (a) shows reflection spectra in a wavelength range of 450 nm to 2,500 nm; (b) shows reflection spectra in a wavelength range of 2,500 nm to 5,000 nm; (c) shows absorption spectra in a wavelength range of 450 nm to 2,500 nm; (d) shows absorption spectra in a wavelength range of 2,500 nm to 5,000 nm; and the layered polycrystalline PbSe film has an average absorbance of 0.89 to 1.31 and an average optical reflectivity of 8.58% to 13.63% in the wavelength range of 450 nm to 5,000 nm.

[0030] FIG. 5 shows optical band gaps of typical samples of the layered polycrystalline PbSe film fabricated in the present invention, where (a) is for a dense PbSe layer, (b) is for sample 1, (c) is for sample 2, and (d) is for sample 3; and the layered polycrystalline PbSe film has a band gap of 0.30 eV to 0.32 eV.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to further illustrate the technical solutions of the present invention and characteristics thereof, the layered polycrystalline PbSe photoelectric film and the fabrication method thereof proposed according to the present invention are further described below in conjunction with FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, and typical implementation examples, and fabrication steps include: (1) substrate cleaning; (2) fabrication of a dense PbSe layer through CBD; (3) fabrication of a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer through CBD; and (4) fabrication of a loose PbSe layer through ion exchange. It should be noted that the described specific examples are merely used to explain the present invention and are not intended to limit the present invention.

[0032] Detailed description is as follows.

Example 1

[0033] (1) A two-inch glass wafer substrate was washed successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min respectively, blow-dried with nitrogen, and stored.

[0034] (2) A Pb(AC).sub.2 solution with a concentration of 0.45 mol/L was added dropwise to a KOH solution with a concentration of 0.667 mol/L to allow a complete reaction under stirring at 600 rpm, then a Na.sub.2SeSO.sub.3 solution with a concentration of 0.56 mol/L was added dropwise, and a resulting mixture was thoroughly stirred to obtain a yellow-brown suspension, where the KOH solution, the Pb(AC).sub.2 solution, and the Na.sub.2SeSO.sub.3 solution had a volume ratio of 3:1:1.

[0035] The 4.62 g of a selenium powder (Se) and 14.749 g of anhydrous sodium sulfite (Na.sub.2SO.sub.3) (a molar ratio of the Se to the Na.sub.2SO.sub.3 was 1:2) were weighed and added to 105 ml of deionized water, a resulting mixture was subjected to reflux at 85° C. for 3 h, and insoluble impurities were filtered out to obtain a clear and transparent Na.sub.2SeSO.sub.3 solution with a concentration of 0.56 mol/L.

[0036] The yellow-brown suspension was placed in a 75° C. water bath, the substrate obtained in step (1) was vertically inserted into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 4 h to form a dense PbSe layer on the substrate.

[0037] The dense PbSe layer fabricated by this process had a crystal grain size of 0.98 μm and a thickness of 2.4 μm. In the present invention, the sample was named a dense PbSe layer, its surface morphology was shown in FIG. 3a, and the optical reflection, optical absorption, and band gap of the dense PbSe layer were shown in FIG. 4 and FIG. 5. The dense PbSe layer had an optical reflectivity of about 24.37% in a range of 450 nm to 2,500 nm and about 28.26% in a range of 2,500 nm to 5,000 nm, an optical absorbance of about 0.61 in a range of 450 nm to 2,500 nm and about 0.55 in a range of 2,500 nm to 5,000 nm, and a band gap of about 0.5 eV.

[0038] (3) A C.sub.6H.sub.5Na.sub.3O.sub.7 solution with a concentration of 0.2 mol/L was poured into a Pb(AC).sub.2 solution with a concentration of 0.1812 mol/L, a resulting mixture was stirred with a glass rod to obtain a milky white colloid, 28 wt % NH.sub.4OH was added, and a resulting mixture was stirred to obtain a clear solution, where the Pb(AC).sub.2 solution, the C.sub.6H.sub.5Na.sub.3O.sub.7 solution, and the 28 wt % NH.sub.4OH had a volume ratio of 11:3:1.

[0039] The clear solution was placed in a 25° C. water bath, the substrate on which the dense PbSe layer was deposited was vertically inserted into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 9 h to form a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer on the dense PbSe layer.

[0040] The surface morphology of the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer fabricated on the dense PbSe layer was shown in FIG. 3b.

[0041] (4) The substrate with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer obtained in step (3) was placed in a Na.sub.2SeSO.sub.3 solution with a concentration of 0.026 mol/L to allow an ion exchange reaction at 25° C. for 2 h, such that the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer was transformed into the loose PbSe layer.

[0042] The layered polycrystalline PbSe film with high light absorption and low band gap fabricated by this process was named “Sample 1” in the present invention, where a loose PbSe layer had a crystal grain size of about 0.42 μm and a thickness of about 5.2 μm, and a surface morphology thereof was shown in FIG. 3c. The optical reflection, optical absorption, and band gap of Sample 1 were shown in FIG. 4 and FIG. 5, and the results showed that, compared with the dense PbSe layer, Sample 1 had an optical reflectivity reduced by 59.62% in a range of 450 nm to 2,500 nm and reduced by 55.01% in a range of 2,500 nm to 5,000 nm, and an optical absorbance increased by 65.34% in a range of 450 nm to 2,500 nm and increased by 63.24% in a range of 2,500 nm to 5,000 nm. Sample 1 had an average absorbance of 0.95 and an average optical reflectivity of about 11.41% in a wavelength range of 450 nm to 5,000 nm, and a band gap reduced from about 0.5 eV to 0.307 eV.

Example 2

[0043] (1) A two-inch glass wafer substrate was washed successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min respectively, blow-dried with nitrogen, and stored. [0044] (2) A Pb(AC).sub.2 solution with a concentration of 0.45 mol/L was added dropwise to a KOH solution with a concentration of 0.667 mol/L to allow a complete reaction under stirring at 600 rpm, then a Na.sub.2SeSO.sub.3 solution with a concentration of 0.56 mol/L was added dropwise, and a resulting mixture was thoroughly stirred to obtain a yellow-brown suspension, where the KOH solution, the Pb(AC).sub.2 solution, and the Na.sub.2SeSO.sub.3 solution had a volume ratio of 3:1:1.

[0045] The yellow-brown suspension was placed in a 75° C. water bath, the substrate obtained in step (1) was vertically inserted into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 4 h to form a dense PbSe layer on the substrate.

[0046] (3) A C.sub.6H.sub.5Na.sub.3O.sub.7 solution with a concentration of 0.2 mol/L was poured into a Pb(AC).sub.2 solution with a concentration of 0.1812 mol/L, a resulting mixture was stirred with a glass rod to obtain a milky white colloid, 28 wt % NH.sub.4OH was added, and a resulting mixture was stirred to obtain a clear solution, where the Pb(AC).sub.2 solution, the C.sub.6H.sub.5Na.sub.3O.sub.7 solution, and the 28 wt % NH.sub.4OH had a volume ratio of 11:3:1.

[0047] The clear solution was placed in a 25° C. water bath, the substrate on which the dense PbSe layer was deposited was vertically inserted into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 8 h to form a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer on the dense PbSe layer.

[0048] (4) The substrate with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer obtained in step (3) was placed in a Na.sub.2SeSO.sub.3 solution with a concentration of 0.026 mol/L to allow an ion exchange reaction at 25° C. for 1 h, such that the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer was transformed into the loose PbSe layer.

[0049] The layered polycrystalline PbSe film with high light absorption and low band gap fabricated by this process was named “Sample 2” in the present invention, where a loose PbSe layer had a crystal grain size of about 0.2 m and a thickness of about 6.1 μm. The optical reflection, optical absorption, and band gap of Sample 2 were shown in FIG. 4 and FIG. 5, and the results showed that, compared with the dense PbSe layer, Sample 2 had an optical reflectivity reduced by 54.74% in a range of 450 nm to 2,500 nm and reduced by 44.09% in a range of 2,500 nm to 5,000 nm, and an optical absorbance increased by 57.07% in a range of 450 nm to 2,500 nm and increased by 46.2% in a range of 2,500 nm to 5,000 nm. Sample 2 had an average absorbance of 0.89 and an average optical reflectivity of about 13.63% in a wavelength range of 450 nm to 5,000 nm, and a band gap reduced from about 0.5 eV to 0.309 eV.

Example 3

[0050] (1) A two-inch glass wafer substrate was washed successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min respectively, blow-dried with nitrogen, and stored.

[0051] (2) A Pb(AC).sub.2 solution with a concentration of 0.45 mol/L was added dropwise to a KOH solution with a concentration of 0.667 mol/L to allow a complete reaction under stirring at 600 rpm, then a Na.sub.2SeSO.sub.3 solution with a concentration of 0.56 mol/L was added dropwise, and a resulting mixture was thoroughly stirred to obtain a yellow-brown suspension, where the KOH solution, the Pb(AC).sub.2 solution, and the Na.sub.2SeSO.sub.3 solution had a volume ratio of 3:1:1.

[0052] The yellow-brown suspension was placed in a 75° C. water bath, the substrate obtained in step (1) was vertically inserted into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 4 h to form a dense PbSe layer on the substrate.

[0053] (3) A C.sub.6H.sub.5Na.sub.3O.sub.7 solution with a concentration of 0.2 mol/L was poured into a Pb(AC).sub.2 solution with a concentration of 0.1812 mol/L, a resulting mixture was stirred with a glass rod to obtain a milky white colloid, 28 wt % NH.sub.4OH was added, and a resulting mixture was stirred to obtain a clear solution, where the Pb(AC).sub.2 solution, the C.sub.6H.sub.5Na.sub.3O.sub.7 solution, and the 28 wt % NH.sub.4OH had a volume ratio of 11:3:1.

[0054] The clear solution was placed in a 25° C. water bath, the substrate on which the dense PbSe layer was deposited was vertically inserted into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 8 h to form a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer on the dense PbSe layer.

[0055] (4) The substrate with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer obtained in step (3) was placed in a Na.sub.2SeSO.sub.3 solution with a concentration of 0.026 mol/L to allow an ion exchange reaction at 25° C. for 2 h, such that the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer was transformed into the loose PbSe layer.

[0056] The layered polycrystalline PbSe film with high light absorption and low band gap fabricated by this process was named “Sample 3” in the present invention, where a loose PbSe layer had a crystal grain size of about 0.38 μm and a thickness of about 6.4 μm. The optical reflection, optical absorption, and band gap of Sample 3 were shown in FIG. 4 and FIG. 5, and the results showed that, compared with the dense PbSe layer, Sample 3 had an optical reflectivity reduced by about 63.3% in a range of 450 nm to 2,500 nm and reduced by 55.64% in a range of 2,500 nm to 5,000 nm, and an optical absorbance increased by 72.46% in a range of 450 nm to 2,500 nm and increased by 64.42% in a range of 2,500 nm to 5,000 nm. Sample 3 had an average absorbance of 0.97 and an average optical reflectivity of about 10.91% in a wavelength range of 450 nm to 5,000 nm, and a band gap reduced from about 0.5 eV to 0.313 eV.

Example 4

[0057] (1) A two-inch polycrystalline silicon substrate was washed successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min respectively, blow-dried with nitrogen, and stored.

[0058] (2) A Pb(AC).sub.2 solution with a concentration of 0.3 mol/L was added dropwise to a KOH solution with a concentration of 0.45 mol/L to allow a complete reaction under stirring at 600 rpm, then a Na.sub.2SeSO.sub.3 solution with a concentration of 0.2 mol/L was added dropwise, and a resulting mixture was thoroughly stirred to obtain a yellow-brown suspension, where the deionized water, the KOH solution, the Pb(AC).sub.2 solution, and the Na.sub.2SeSO.sub.3 solution had a volume ratio of 4:1:1.

[0059] The yellow-brown suspension was placed in a 60° C. water bath, the substrate obtained in step (1) was vertically inserted into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 3 h to form a dense PbSe layer on the substrate.

[0060] The dense PbSe layer had a crystal grain size of about 0.7 μm and a thickness of about 1.5 μm.

[0061] (3) A C.sub.6H.sub.5Na.sub.3O.sub.7 solution with a concentration of 0.2 mol/L was poured into a Pb(AC).sub.2 solution with a concentration of 0.0164 mol/L, a resulting mixture was stirred with a glass rod to obtain a milky white colloid, 28 wt % NH.sub.4OH was added, and a resulting mixture was stirred to obtain a clear solution, where the Pb(AC).sub.2 solution, the C.sub.6H.sub.5Na.sub.3O.sub.7 solution, and the 28 wt % NH.sub.4OH had a volume ratio of 12.2:2.8:0.8.

[0062] The clear solution was placed in a 20° C. water bath, the substrate on which the dense PbSe layer was deposited was vertically inserted into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 10 h to form a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer on the dense PbSe layer.

[0063] (4) The substrate with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer obtained in step (3) was placed in a Na.sub.2SeSO.sub.3 solution with a concentration of 0.01 mol/L to allow an ion exchange reaction at 20° C. for 5 h, such that the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer was transformed into the loose PbSe layer. The loose PbSe layer in the layered polycrystalline PbSe film had a crystal grain size of about 0.2 μm and a thickness of about 5 μm. The sample had an average absorbance of 0.87 and an average optical reflectivity of about 14.43% in a wavelength range of 450 nm to 5,000 nm, and a band gap of about 0.32 eV.

Example 5

[0064] (1) A two-inch silica substrate was washed successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min respectively, blow-dried with nitrogen, and stored.

[0065] (2) A Pb(AC).sub.2 solution with a concentration of 0.6 mol/L was added dropwise to a KOH solution with a concentration of 1.1 mol/L to allow a complete reaction under stirring at 600 rpm, then a Na.sub.2SeSO.sub.3 solution with a concentration of 0.6 mol/L was added dropwise, and a resulting mixture was thoroughly stirred to obtain a yellow-brown suspension, where the KOH solution, the Pb(AC).sub.2 solution, and the Na.sub.2SeSO.sub.3 solution had a volume ratio of 2:1:1.

[0066] The yellow-brown suspension was placed in an 85° C. water bath, the substrate obtained in step (1) was vertically inserted into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 5 h to form a dense PbSe layer on the substrate.

[0067] The dense PbSe layer had a crystal grain size of about 1.5 μm and a thickness of about 5 μm.

[0068] (3) A C.sub.6H.sub.5Na.sub.3O.sub.7 solution with a concentration of 0.3 mol/L was poured into a Pb(AC).sub.2 solution with a concentration of 0.0306 mol/L, a resulting mixture was stirred with a glass rod to obtain a milky white colloid, 28 wt % NH.sub.4OH was added, and a resulting mixture was stirred to obtain a clear solution, where the Pb(AC).sub.2 solution, the C.sub.6H.sub.5Na.sub.3O.sub.7 solution, and the 28 wt % NH.sub.4OH had a volume ratio of 9.8:3.2:1.2.

[0069] The clear solution was placed in a 50° C. water bath, the substrate on which the dense PbSe layer was deposited was vertically inserted into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 24 h to form a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer on the dense PbSe layer.

[0070] (4) The substrate with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer obtained in step (3) was placed in a mixed selenium ion-containing solution with 0.05 mol/L Na.sub.2SeSO.sub.3 and 0.05 mol/L NH.sub.2CSeNH.sub.2 to allow an ion exchange reaction at 40° C. for 0.5 h, such that the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer was transformed into the loose PbSe layer. The loose PbSe layer in the layered polycrystalline PbSe film had a crystal grain size of about 0.5 μm and a thickness of about 15 μm. The sample had an average absorbance of 1.31 and an average optical reflectivity of about 8.58% in a wavelength range of 450 nm to 5,000 nm, and a band gap of about 0.30 eV.

Example 6

[0071] (1) A gallium nitride substrate was washed successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min respectively, blow-dried with nitrogen, and stored.

[0072] (2) A Pb(AC).sub.2 solution with a concentration of 0.4 mol/L was slowly added dropwise to a KOH solution with a concentration of 1 mol/L to allow a complete reaction under stirring at 600 rpm, then a Na.sub.2SeSO.sub.3 solution with a concentration of 0.5 mol/L was added dropwise, and a resulting mixture was thoroughly stirred to obtain a yellow-brown suspension, where the KOH solution, the Pb(AC).sub.2 solution, and the Na.sub.2SeSO.sub.3 solution had a volume ratio of 2:1:1.

[0073] The yellow-brown suspension was placed in an 80° C. water bath, the substrate obtained in step (1) was vertically inserted into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 4 h to form a dense PbSe layer on the substrate.

[0074] The dense PbSe layer had a crystal grain size of about 1 μm and a thickness of about 4.45 μm, as shown in FIG. 3d.

[0075] (3) A C.sub.6H.sub.5Na.sub.3O.sub.7 solution with a concentration of 0.25 mol/L was poured into a Pb(AC).sub.2 solution with a concentration of 0.0229 mol/L, a resulting mixture was stirred with a glass rod to obtain a milky white colloid, 28 wt % NH.sub.4OH was added, and a resulting mixture was stirred to obtain a clear solution, where the Pb(AC).sub.2 solution, the C.sub.6H.sub.5Na.sub.3O.sub.7 solution, and the 28 wt % NH.sub.4OH had a volume ratio of 10.9:3:1.

[0076] The clear solution was placed in a 40° C. water bath, the substrate on which the dense PbSe layer was deposited was vertically inserted into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 24 h to form a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer on the dense PbSe layer.

[0077] (4) The substrate with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer obtained in step (3) was placed in a solution with 0.05 mol/L Na.sub.2SeSO.sub.3 to allow an ion exchange reaction at 35° C. for 2.5 h, such that the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer was transformed into the loose PbSe layer. The loose PbSe layer in the layered polycrystalline PbSe film with high light absorption and low band gap had a crystal grain size of about 0.42 μm and a thickness of about 15 μm. The sample had an average absorbance of 0.95 and an average optical reflectivity of about 10.65% in a wavelength range of 450 nm to 5,000 nm, and a band gap of about 0.30 eV.

Example 7

[0078] (1) A quartz substrate was washed successively in deionized water, a sulfuric acid-hydrogen peroxide solution, deionized water, and absolute ethanol for 5 min, 10 min, 5 min, and 5 min respectively, blow-dried with nitrogen, and stored.

[0079] (2) A Pb(AC).sub.2 solution with a concentration of 0.6 mol/L was added dropwise to a KOH solution with a concentration of 0.76 mol/L to allow a complete reaction under stirring at 600 rpm, then a Na.sub.2SeSO.sub.3 solution with a concentration of 0.4 mol/L was added dropwise, and a resulting mixture was thoroughly stirred to obtain a yellow-brown suspension, where the KOH solution, the Pb(AC).sub.2 solution, and the Na.sub.2SeSO.sub.3 solution had a volume ratio of 2.5:1:1.

[0080] The yellow-brown suspension was placed in a 70° C. water bath, the substrate obtained in step (1) was vertically inserted into the yellow-brown suspension thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 3 h to form a dense PbSe layer on the substrate.

[0081] The dense PbSe layer had a crystal grain size of about 0.9 μm and a thickness of about 3.1 μm.

[0082] (3) A C.sub.6H.sub.5Na.sub.3O.sub.7 solution with a concentration of 0.25 mol/L was poured into a Pb(AC).sub.2 solution with a concentration of 0.0283 mol/L, a resulting mixture was stirred with a glass rod to obtain a milky white colloid, 28 wt % NH.sub.4OH was added, and a resulting mixture was stirred to obtain a clear solution, where the Pb(AC).sub.2 solution, the C.sub.6H.sub.5Na.sub.3O.sub.7 solution, and the 28 wt % NH.sub.4OH had a volume ratio of 9.9:3:0.9.

[0083] The clear solution was placed in a 45° C. water bath, the substrate on which the dense PbSe layer was deposited was vertically inserted into the clear solution thermally stabilized in the water bath, with one side of the substrate exposed through a mold, and deposition was conducted for 15 h to form a Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer on the dense PbSe layer.

[0084] (4) The substrate with the dense PbSe layer and the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer obtained in step (3) was placed in a solution with 0.05 mol/L NH.sub.2CSeNH.sub.2 to allow an ion exchange reaction at 40° C. for 2.5 h, such that the Pb.sub.10O(OH).sub.6(CO.sub.3).sub.6 layer was transformed into the loose PbSe layer. The loose PbSe layer in the layered polycrystalline PbSe film had a crystal grain size of about 0.45 μm and a thickness of about 14.6 μm. The sample had an average absorbance of 0.96 and an average optical reflectivity of about 10.92% in a wavelength range of 450 nm to 5,000 nm, and a band gap of about 0.30 eV.

[0085] The above are only some typical examples of the present invention, and are not intended to limit the present invention. Any modifications, changes, and transformations of equivalent elements made to the above examples according to the technical essence of the present invention are still within the protection scope of the technical solutions of the present invention.