PHOTOELECTRIC CONVERSION ELEMENT MATERIAL, METHOD FOR PRODUCING PHOTOELECTRIC CONVERSION ELEMENT MATERIAL, AND INK IN WHICH SEMICONDUCTOR NANOPARTICLES ARE DISPERSED

Abstract

The present invention relates to a photoelectric conversion element material provided with a base material and a light-receiving layer including a semiconductor film formed on the base material. The semiconductor film that forms this light-receiving layer includes Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1) and has a crystallite diameter of 10 nm or more and 40 nm or less. The light-receiving layer can be produced by applying an ink containing the semiconductor nanoparticles dispersed in a dispersion medium to a base material and then firing the ink at 200 C. or higher and 350 C. or lower. The photoelectric conversion element material of the present invention has an absorption property with respect to light with wavelengths in the near infrared region and excellent photoresponsivity.

Claims

1. A photoelectric conversion element material comprising: a base material; and a light-receiving layer comprising a semiconductor film formed on the base material, wherein the semiconductor film comprises Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1), and the semiconductor film has a crystallite diameter of 10 nm or more and 40 nm or less.

2. The photoelectric conversion element material according to claim 1, wherein the semiconductor film has a crystallite diameter of 10 nm or more and 25 nm or less.

3. The photoelectric conversion element material according to claim 1, wherein the semiconductor film has a surface roughness of 2 nm or more and 15 nm or less.

4. The photoelectric conversion element material according to claim 1, wherein the photoelectric conversion element material has responsiveness to light having wavelengths of 700 nm or more and 1200 nm or less.

5. An ink comprising semiconductor nanoparticles dispersed in a dispersion medium, wherein the semiconductor nanoparticles comprise Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1) and have a crystallite diameter of 5 nm or more and 20 nm or less, the semiconductor nanoparticles are protected by a protective agent comprising at least any one of a long-chain alkylamine, a long-chain carboxylic acid and a thiol, and the dispersion medium is an organic solvent with a low polarity.

6. A method for producing the photoelectric conversion element material defined in claim 1, the method comprising: applying the ink comprising semiconductor nanoparticles dispersed in a dispersion medium, wherein the semiconductor nanoparticles comprise Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1) and have a crystallite diameter of 5 nm or more and 20 nm or less, the semiconductor nanoparticles are protected by a protective agent comprising at least any one of a long-chain alkylamine, a long-chain carboxylic acid and a thiol, and the dispersion medium is an organic solvent with a low polarity to a base material to form a semiconductor layer; and firing the semiconductor layer to form a light-receiving layer, wherein a firing temperature in the step of firing the semiconductor layer is 200 C. or higher and 350 C. or lower.

7. The photoelectric conversion element material according to claim 2, wherein the semiconductor film has a surface roughness of 2 nm or more and 15 nm or less.

8. The photoelectric conversion element material according to claim 2, wherein the photoelectric conversion element material has responsiveness to light having wavelengths of 700 nm or more and 1200 nm or less.

9. The photoelectric conversion element material according to claim 3, wherein the photoelectric conversion element material has responsiveness to light having wavelengths of 700 nm or more and 1200 nm or less.

10. A method for producing the photoelectric conversion element material defined in claim 2, the method comprising: applying the ink comprising semiconductor nanoparticles dispersed in a dispersion medium, wherein the semiconductor nanoparticles comprise Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1) and have a crystallite diameter of 5 nm or more and 20 nm or less, the semiconductor nanoparticles are protected by a protective agent comprising at least any one of a long-chain alkylamine, a long-chain carboxylic acid and a thiol, and the dispersion medium is an organic solvent with a low polarity to a base material to form a semiconductor layer; and firing the semiconductor layer to form a light-receiving layer, wherein a firing temperature in the step of firing the semiconductor layer is 200 C. or higher and 350 C. or lower.

11. A method for producing the photoelectric conversion element material defined in claim 3, the method comprising: applying the ink comprising semiconductor nanoparticles dispersed in a dispersion medium, wherein the semiconductor nanoparticles comprise Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1) and have a crystallite diameter of 5 nm or more and 20 nm or less, the semiconductor nanoparticles are protected by a protective agent comprising at least any one of a long-chain alkylamine, a long-chain carboxylic acid and a thiol, and the dispersion medium is an organic solvent with a low polarity to a base material to form a semiconductor layer; and firing the semiconductor layer to form a light-receiving layer, wherein a firing temperature in the step of firing the semiconductor layer is 200 C. or higher and 350 C. or lower.

12. A method for producing the photoelectric conversion element material defined in claim 4, the method comprising: applying the ink comprising semiconductor nanoparticles dispersed in a dispersion medium, wherein the semiconductor nanoparticles comprise Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1) and have a crystallite diameter of 5 nm or more and 20 nm or less, the semiconductor nanoparticles are protected by a protective agent comprising at least any one of a long-chain alkylamine, a long-chain carboxylic acid and a thiol, and the dispersion medium is an organic solvent with a low polarity to a base material to form a semiconductor layer; and firing the semiconductor layer to form a light-receiving layer, wherein a firing temperature in the step of firing the semiconductor layer is 200 C. or higher and 350 C. or lower.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is TEM photographs of AgBiS.sub.2 nanoparticles produced in First Embodiment;

[0037] FIG. 2 is a view showing an XRD diffraction pattern of the AgBiS.sub.2 nanoparticles produced in First Embodiment;

[0038] FIG. 3 is a view showing the result of a DSC analysis of the AgBiS.sub.2 nanoparticles produced in First Embodiment;

[0039] FIG. 4 is a view showing the light absorption characteristic of a AgBiS.sub.2 ink produced in First Embodiment;

[0040] FIG. 5 is a view showing XRD diffraction patterns of light-receiving layer surfaces of photoelectric conversion elements produced in First Embodiment;

[0041] FIG. 6 is photographs showing the observation results of the surface morphologies with AFM of the light-receiving layer surfaces of the photoelectric conversion elements produced in First Embodiment;

[0042] FIG. 7 is a view showing the PL measurement result of each photoelectric conversion element produced in First Embodiment;

[0043] FIG. 8 is graphs showing the result of an evaluation test of photoresponsivity of each photoelectric conversion element produced in First Embodiment;

[0044] FIG. 9 is a graph showing the comparison of the PL measurement results of the photoelectric conversion elements produced at firing temperatures of 200 C. and 500 C.;

[0045] FIG. 10 is graphs showing the comparison of the photoresponsivity of the photoelectric conversion elements produced at firing temperatures of 200 C. and 500 C.;

[0046] FIG. 11 is graphs showing the comparison among the photoelectric conversion elements (200 C. and 300 C.) produced in First Embodiment and a light-receiving layer including PbS;

[0047] FIG. 12 is graphs showing the result (high bias) of an evaluation test of photoresponsivity of each photoelectric conversion element produced in First Embodiment;

[0048] FIG. 13 is a TEM photograph of Ag.sub.2S nanoparticles produced in Second Embodiment;

[0049] FIG. 14 is a view showing an XRD diffraction pattern of the Ag.sub.2S nanoparticles produced in Second Embodiment;

[0050] FIG. 15 is a view showing the light absorption characteristic of a Ag.sub.2S ink produced in Second Embodiment;

[0051] FIG. 16 is a view showing XRD diffraction patterns of light-receiving layer surfaces of photoelectric conversion elements produced in Second Embodiment;

[0052] FIG. 17 is photographs showing the observation results of the surface morphologies with AFM of the light-receiving layer surfaces of the photoelectric conversion elements produced in Second Embodiment;

[0053] FIG. 18 is a view showing the PL measurement result of each photoelectric conversion element produced in Second Embodiment;

[0054] FIG. 19 is graphs showing the result of an evaluation test of photoresponsivity of each photoelectric conversion element produced in Second Embodiment;

[0055] FIG. 20 is a graph showing the comparison of the PL measurement results of the photoelectric conversion elements produced at firing temperatures of 200 C. and 500 C.;

[0056] FIG. 21 is graphs showing the comparison of the photoresponsivity of the photoelectric conversion elements produced at firing temperatures of 200 C. and 500 C.; and

[0057] FIG. 22 is graphs showing the comparison among the photoelectric conversion elements (200 C. and 300 C.) produced in Second Embodiment and a light-receiving layer including PbS.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] First Embodiment: Hereinafter, an embodiment of the present invention will be described. In the present embodiment, a photoelectric conversion element material provided with a light-receiving layer including AgBiS.sub.2 as a semiconductor material was produced. Semiconductor nanoparticles of AgBiS.sub.2 were synthesized to produce an ink, this ink was applied to and fired on a base material to form a light-receiving layer, thereby producing a photoelectric conversion element material. Subsequently, the morphology of a thin film, which served as the light-receiving layer, was observed and the photoresponse characteristic of a photoelectric conversion element was evaluated.

[Production of AgBiS.SUB.2 .Ink]

[0059] 133.5 mg of silver acetate (Ag(OAc)), 386 mg of bismuth acetate (Bi(OAc).sub.3) and 5.5 mL of oleic acid were mixed together, the inside of a mixing container was substituted with a N.sub.2 gas, and then the liquid mixture was stirred at 100 C. for one hour. A solution containing 33 mg of sulfur dissolved in 5 mL of oleylamine was added to this liquid mixture and reacted. During the reaction, the liquid mixture was left to stand and cooled. Subsequently, AgBiS.sub.2 nanoparticles were separated and extracted with acetone, and the extraction liquid was centrifuged to collect the AgBiS.sub.2 nanoparticles. Furthermore, the collected nanoparticles were mixed with toluene, again, extracted and centrifuged with acetone, thereby collecting the AgBiS.sub.2 nanoparticles. These were added to toluene, which was a dispersion medium, to produce an ink (nanoparticle concentration: 0.04 M). This ink was black.

[Measurement of Particle Diameters and Crystallite diameter of AgBiS.sub.2 Nanoparticles]

[0060] The particle diameters and crystallite diameter of the AgBiS.sub.2 nanoparticles in the ink produced above were studied. In this study, the AgBiS.sub.2 nanoparticles were observed with a transmission electron microscope (TEM) to measure the particle diameters (average particle diameter). In addition, the AgBiS.sub.2 nanoparticles were supported by a SiO.sub.2 powder from the ink and measured in a dry state. An XRD analyzer was Ultima IV produced by Rigaku Corporation, CuK rays were used as characteristic X rays, and 0.1/m in. was set as an analysis condition.

[0061] FIG. 1 is TEM images of the AgBiS.sub.2 nanoparticles produced in the present embodiment. It was confirmed that nanoparticles having uniform particle diameters could be produced, and, as a result of an image analysis (binarized image analysis using ImageJ software), the average particle diameter was 8.75 nm. In addition, FIG. 2 shows the XRD diffraction pattern of the AgBiS.sub.2 nanoparticles. The crystallite diameter of these AgBiS.sub.2 nanoparticles was calculated to be 7.2 nm based on the diffraction peak at 2=near 31 from the full-width at half maximum of the peak.

[Thermal Behaviors of AgBiS.SUB.2 .Nanoparticles]

[0062] Next, the differential scanning calorimetry (DSC) of the AgBiS.sub.2 nanoparticles was performed. The result is shown in FIG. 3. Heat peaks derived from the volatilization of the residual solvent at near 110 C. and the detachment of the protective agent at neat 160 C. were observed. That is, it is suggested that the excessive protective agent sufficiently volatilized at lower than 200 C. In addition, a large endothermic peak was detected at near 250 C. to 260 C. This can be considered to be a peak derived from the three-phase eutectic point of AgBiS.sub.2.

[Light Absorption Characteristic of AgBiS.SUB.2 .Nanoparticles]

[0063] In order to confirm the optical semiconductor characteristic of the AgBiS.sub.2 nanoparticles produced in the present embodiment, the light absorption characteristic was evaluated. The light absorption characteristic of a solution obtained by diluting the above ink 100 times was analyzed with a UV-Vis-NIR Spectrophotometer (UV-3600i Plus produced by Shimadzu Corporation).

[0064] The absorption spectrum of the AgBiS.sub.2 ink is shown in FIG. 4. In this AgBiS.sub.2 ink, it was confirmed that the absorption end extends up to a region exceeding a wavelength of 1000 nm and light absorption in the near infrared region is possible.

[Formation of Light-Receiving Layer]

[0065] After a variety of characteristics of the above AgBiS.sub.2 nanoparticles and ink were confirmed, this ink was applied to a base material to form a light-receiving layer, thereby producing a photoelectric conversion element material. As the base material, a silicon wafer (dimensions: 2525, thickness: 0.6 mm) was prepared, and the above ink was applied to this base material. The application of the ink was performed by the spin coating method, the ink was dropped and applied onto the base material at a rotation speed of 2000 rpm (30 seconds) to form a semiconductor layer. In the present embodiment, this application step was repeated three times, and the amount of the ink applied per step was set to 0.1 mL (the mass of the nanoparticles: 2.8 mg).

[0066] After the application of the AgBiS.sub.2 ink, the semiconductor layer was made into a light-receiving layer by a firing treatment. The firing treatment was performed in a nitrogen atmosphere at seven patterns of the treatment temperature set to 150 C., 200 C., 250 C., 300 C., 350 C., 400 C. and 500 C. The treatment time was set to 0.5 hours.

[Measurement of Crystallite Diameter and Surface Roughness of Light-Receiving Layer (XRD and AFM)]

[0067] For seven photoelectric conversion elements produced by the above-described seven patterns of firing, XRD analyses were performed on semiconductor thin films that configured the light-receiving layers, and the crystallite diameters were calculated. In the XRD analyses, the thin films on the silicon wafers were measured as they were. The XRD analyses were performed with the same device under the same conditions as those in the analysis of the nanoparticles. In addition, the images of the surface morphologies of the light-receiving layers were captured and the surface roughness was measured with an atomic force microscope (AFM: NANOCUTE produced by Hitachi High-Tech Science Corporation).

[0068] FIG. 5 shows the XRD diffraction patterns of the light-receiving layer surfaces of the above-described seven photoelectric conversion elements. When diffraction peaks of this diffraction pattern at near 27 are observed, it is confirmed that, as the firing temperature increases, the peak intensity becomes higher, and a sharp peak having a narrower full-width at half maximum is developed. From this fact, it can be seen that, when the firing temperature is set to be high, the crystallinity improves. Therefore, as a result of calculating crystallite diameters based on diffraction peaks at near 31, the following values were obtained. In addition, FIG. 6 is the observation results of the light-receiving layer surface morphologies with AFM. The measurement results of the surface roughness with AFM are shown in Table 1.

TABLE-US-00001 TABLE 1 No. Firing temperature Crystallite diameter Surface roughness 1 150 C. 8.26 nm 2.44 nm 2 200 C. 13.77 nm 1.60 nm 3 250 C. 19.21 nm 9.99 nm 4 300 C. 22.32 nm 9.05 nm 5 350 C. 21.29 nm 2.42 nm 6 400 C. 47.74 nm 12.48 nm 7 500 C. *.sup.1 9.88 nm *.sup.1No peaks are clearly observed at near 31 and thus calculation is not possible.

[0069] From Table 1, it can be seen that, as the temperature of the firing treatment increases, the crystallite diameter of the thin film becomes larger.

[0070] Particularly, at 200 C. or higher, improvement in the crystallinity is shown. However, when the firing temperature reaches 500 C., from the fact that the peak at near 31 vanishes in smoke and a Ag-derived peak near pure 38.3 becomes clear, it can be seen that the decomposition of AgBiS.sub.2 occurs at this firing temperature.

[0071] In addition, when the relationship between the firing temperature and the surface roughness of the thin film is observed, the surface roughness does not change at firing temperatures of up to 200 C., the surface roughness increases at 250 C. to 300 C., and the surface roughness once returns to the original at 300 C. to 350 C.

[0072] This is considered to be related to the fact that, during the firing at a temperature exceeding the three-phase eutectic point of AgBiS.sub.2, which was confirmed in the DSC analysis of the AgBiS.sub.2 nanoparticles (near 250 C. to 260 C.), the AgBiS.sub.2 nanoparticles once dissolve. Therefore, it is deemed that there is no complete proportional relationship between the firing temperature and the surface roughness. However, when the firing temperature exceeds 400 C., the surface roughness increases at once, and the AgBiS.sub.2 particles coarsen. This point matches the fact that, in the XRD diffraction profiles, the diffraction peaks at near 27 rapidly increase at 400 C. In addition, during the firing at 500 C., even when the surface roughness decreases owing to the decomposition of AgBiS.sub.2, the AgBiS.sub.2 particles become islands.

[Measurement of Photoluminescence]

[0073] After the configurations of the light-receiving layers were confirmed as described above, as a preliminary evaluation of the optical semiconductor characteristics of the photoelectric conversion element materials produced in the present embodiment, the photoluminescence (PL) was measured. Here, the measurement was performed using the photoelectric conversion element materials produced by the firing treatments performed at 150 C., 200 C. and 300 C. The PL measurement was conducted using LabRam Aramis produced by Horiba, Ltd. as the measurement device within a range of 500 to 1000 nm as a measurement condition.

[0074] The PL measurement result of each photoelectric conversion element material is shown in FIG. 7. When the PL measurement results are observed in consideration of the previous XRD measurement results, it can be seen that the firing treatments at 200 C. or higher improve the crystallinity of the thin films and increase PL.

[Evaluation of Photoresponse Characteristic]

[0075] For the photoelectric conversion element materials produced in the present embodiment, the photoresponse characteristics were evaluated. In this evaluation test, the photoelectric conversion element materials produced by the firing treatments at 150 C., 200 C. and 300 C. were used, and an electrode was formed on the light-receiving layer surface of each material by patterning a Ti film (film thickness: 5 nm) and a Au film (film thickness: 40 nm) in this order in a comb shape by a thermal deposition method, thereby producing a sample. In addition, a bias voltage of 0.5 V was loaded with a multimeter connected to the electrode, and a photocurrent owing to pulse irradiation of a near infrared light source was measured. The wavelengths of near infrared rays were set to 740 nm, 850 nm and 940 nm, and the pulse irradiation with the near infrared rays was performed in a manner of 20-second ON/40-second OFF.

[0076] These photocurrent measurement results are shown in FIG. 8. In the AgBiS.sub.2 thin films for which the firing treatment at 200 C. or higher was performed and the crystallite diameter of the thin film was adjusted, it can be seen that improvement in photoresponsivity was shown. In the case of this test, a particularly favorable increase in photocurrent was shown in the sample for which, particularly, the firing treatment at 200 C. was performed (crystallite diameter: 13.77 nm).

[0077] Furthermore, in order to confirm the influence of the firing temperature of higher than 350 C., PL measurement and photoresponsivity evaluation were performed on the light-receiving layer produced by the firing treatment at 500 C. These results are shown in FIG. 9 and FIG. 10 while being compared with those of the light-receiving layer produced by firing at 200 C. From the PL measurement results of FIG. 9, it can be seen that the light-emitting peak almost disappeared in the AgBiS.sub.2 thin film fired at 500 C. In addition, from the photocurrent measurement results of FIG. 10, it was confirmed that a photoresponse is rarely exhibited in the AgBiS.sub.2 thin film fired at 500 C. As a result of analyzing this AgBiS.sub.2 thin film fired at 500 C. by SEM-EDS, the crystal structure of AgBiS.sub.2 collapsed and the presence of particles was confirmed.

[0078] Here, in the present embodiment, comparison with photoelectric conversion elements including a PbS thin film, which has been conventionally known as a metal chalcogenide thin film having responsiveness in the near infrared region, as a light-receiving layer was performed. An ink in which commercially available PbS particles (Sigma-Aldrich) had been dispersed was produced, and this was applied to the same base material as in the present embodiment. In addition, the evaluation test of photoresponsivity was performed in the same manner as described above.

[0079] The results are shown in FIG. 11 together with the photoelectric conversion elements of the present embodiment (firing temperatures: 150 C., 200 C. and 300 C.). In the photoelectric conversion elements including PbS in the light-receiving layer, it was recognized that a photocurrent was once generated, but the photoelectric conversion elements (200 C. and 300 C.) including the AgBiS.sub.2 thin film as the light-receiving layer of the present embodiment emit a higher photocurrent than that from this related art. Therefore, it has been clarified that the photoelectric conversion element of the present invention has superiority to the related art.

[0080] Next, as the photoresponse characteristic evaluation of the photoelectric conversion element, evaluation was performed when the bias during photocurrent measurement was set to a high bias. In this evaluation, a commercially available Ag nanopaste was applied to the light-receiving layer surface by screen printing, and a wire having a thickness of approximately 1 m was formed in a comb shape, thereby producing a sample. In addition, a bias voltage of 2.0 V was loaded with a multimeter connected to an electrode, and a photocurrent owing to pulse irradiation of the near infrared light source was measured. The wavelengths of near infrared rays were set to 850 nm and 940 nm, and the pulse irradiation with the near infrared rays was performed in a manner of 10-second ON/10-second OFF.

[0081] The results of these photoresponsivity evaluation tests are shown in FIG. 12. From FIG. 12, regarding the photoresponsivity under a high bias, significant increases in the photocurrent were shown particularly in the thin films fired at 300 C. and 350 C. (crystallite diameters: 22.32 nm and 21.29 nm).

[0082] Second Embodiment: In the present embodiment, a photoelectric conversion element material provided with a light-receiving layer including Ag.sub.2S as a semiconductor thin film was produced. After semiconductor nanoparticles of Ag.sub.2S were synthesized and an ink was produced in the same manner as in First Embodiment, the ink was applied to and fired on a base material to manufacture a photoelectric conversion element material.

[Production of Ag.SUB.2.S Ink]

[0083] 134 mg of silver acetate, 30.5 mg of thiourea, 11.8 mL of oleylamine and 0.2 mL of dodecanethiol were mixed together, and a liquid mixture was stirred and reacted at 200 C. for 10 minutes. After the reaction, the liquid mixture was left to stand and cooled. Subsequently, Ag.sub.2S nanoparticles were separated and extracted with methanol, and the extraction liquid was centrifuged to collect the Ag.sub.2S nanoparticles. Furthermore, the collected nanoparticles were mixed with toluene, again, extracted and centrifuged with methanol, thereby collecting the Ag.sub.2S nanoparticles. These were added to toluene, which was a dispersion medium, to produce an ink (nanoparticle concentration: 0.04 M). This ink was light brownish transparent.

[Measurement of Particle Diameters and Crystallite Diameters of Ag.SUB.2.S Nanoparticles]

[0084] The particle diameters and crystallite diameters of the Ag.sub.2S nanoparticles in the ink produced above were studied. Particle diameter (average particle diameter) measurement and XRD analysis were performed with TEM under the same conditions as in First Embodiment.

[0085] FIG. 13 is a TEM image of the Ag.sub.2S nanoparticles produced in the present embodiment. In this case as well, it was confirmed that nanoparticles having uniform particle diameters could be produced, and the average particle diameter was 14.86 nm. In addition, FIG. 14 shows the XRD diffraction pattern of the AgBiS.sub.2 nanoparticles. The crystallite diameter of these Ag.sub.2S nanoparticles was calculated to be 17.2 nm based on the diffraction peak at 2=near 38 from the full-width at half maximum of the peak.

[Light Absorption Characteristic of Ag.SUB.2.S Nanoparticles]

[0086] The measurement result of the light absorption characteristic of the Ag.sub.2 S ink by the same method as in First Embodiment is shown in FIG. 15. In the Ag.sub.2S ink as well, it was confirmed that the absorption end extends up to a region exceeding a wavelength of 1000 nm and light absorption in the near infrared region is possible.

[Formation of Light-Receiving Layer]

[0087] After the above-described studies were performed, the Ag.sub.2S ink was applied to a base material to form a light-receiving layer, thereby producing a photoelectric conversion element material. The Ag.sub.2S ink was applied to a silicon wafer, which was the base material, in the same manner as in First Embodiment. A method for applying the ink was the same as that in First Embodiment. After the application of the Ag.sub.2S ink, a firing treatment was performed in the same manner as in First Embodiment, thereby forming a light-receiving layer. The firing treatment was performed in a nitrogen atmosphere at treatment temperatures set to 150 C., 200 C., 250 C., 300 C., 350 C., 400 C. and 500 C.

[Measurement of Crystallite Diameter and Surface Roughness of Light-Receiving Layer (XRD and AFM)]

[0088] For seven photoelectric conversion element materials of the present embodiment, XRD analyses were performed on semiconductor thin films that configured the light-receiving layers, and the crystallite diameters were calculated. In addition, the images of the surface morphologies of the light-receiving layers were captured and the surface roughness was measured with an atomic force microscope.

[0089] FIG. 16 shows the XRD diffraction pattern of the light-receiving layer surface of each photoelectric conversion element material. In addition, FIG. 17 is the observation results of the light-receiving layer surface morphologies with AFM. The values of the crystallite diameter and the surface roughness calculated based on the diffraction peaks at near 38 in the XRD diffraction pattern are shown in Table 2.

TABLE-US-00002 TABLE 2 No. Firing temperature Crystallite diameter Surface roughness 1 150 C. *.sup.1 11.06 nm 2 200 C. 13.26 nm 5.85 nm 3 250 C. 13.26 nm 10.15 nm 4 300 C. 17.97 nm 14.56 nm 5 350 C. 24.82 nm 15.92 nm 6 400 C. 11.59 nm 14.91 nm 7 500 C. 17.70 nm 9.88 nm *.sup.1Peaks at near 38 are extremely small and thus calculation is not possible.

[0090] The behaviors of the particles by the firing treatment of the light-receiving layer including the Ag.sub.2S thin film of the present embodiment are basically the same as those in the light-receiving layer including the AgBiS.sub.2 thin film of First Embodiment. That is, as the temperature of the firing treatment increases, the crystallite diameter of the thin film becomes larger; however, when the firing temperature becomes a high temperature, the decomposition of Ag.sub.2S occurs. In the present embodiment, the peak of Ag.sub.2S at near 38 when fired at 150 C. was too small to calculate the crystallite diameter. In addition, in the relationship between the firing temperature and the surface roughness of the thin film as well, the surface roughness does not change at firing temperatures of relatively low temperatures, but it is observed that the surface roughness increases during the firing at 250 C. or higher and it is presumed that the crystal structure changes in this firing as well. During the firing at 500 C., Ag.sub.2S decomposes, and Ag.sub.2S particles become islands.

[Measurement of Photoluminescence]

[0091] Furthermore, the PL measurement results of the photoelectric conversion element materials provided with the light-receiving layer including Ag.sub.2S produced in the present embodiment are shown in FIG. 18. In the present embodiment as well, it can be seen that the firing treatments improve the crystallinity of the thin films and increase PL.

[Evaluation of Photoresponse Characteristic]

[0092] In addition, for the photoelectric conversion element materials provided with the light-receiving layer including Ag.sub.2S produced in the present embodiment, the photoresponse characteristics were evaluated. Here, photocurrents were measured from photoelectric conversion elements produced by the firing treatments at 150 C., 200 C. and 300 C. with the same samples under the same measurement conditions as in the photocurrent measurement under a low bias condition (0.5 V) in First Embodiment.

[0093] The photocurrent measurement results of the photoelectric conversion elements provided with the light-receiving layer including Ag.sub.2S are shown in FIG. 19. In the present embodiment as well, a particularly favorable increase in photocurrent is shown in the sample for which, particularly, the firing treatment at 200 C. was performed (crystallite diameter: 13.26 nm). It was confirmed that the light-receiving layers fired at 200 C. or higher exhibited clear photoresponsivity with respect to the light-receiving layer fired at 150 C., which was also the same as in the light-receiving layers including AgBiS.sub.2 of First Embodiment.

[0094] Furthermore, in the present embodiment as well, PL measurement and photoresponsivity evaluation were performed on the light-receiving layers including Ag.sub.2S produced by the firing treatment at 500 C. These results are shown in FIG. 20 and FIG. 21. From the PL measurement results of FIG. 20, it can be seen that the light-emitting peak disappeared in the Ag.sub.2S thin film fired at 500 C. In addition, from the photoresponsivity evaluation results of FIG. 21, it was confirmed that a photoresponse is rarely exhibited in the Ag.sub.2S thin film fired at 500 C. In the present embodiment as well, as a result of analyzing this Ag.sub.2S thin film fired at 500 C. by SEM-EDS, it was confirmed that the composition of Ag.sub.2S collapsed.

[0095] In addition, comparison between the light-receiving layers including Ag.sub.2S of the present embodiment and the light-receiving layer including PbS, which is the related art, is shown in FIG. 22. When compared with AgBiS.sub.2 of First Embodiment, Ag.sub.2S is not superior to PbS as much as AgBiS.sub.2. However, at 740 nm and 850 nm, the photocurrent value becomes higher in Ag.sub.2 S than PbS. Regarding this fact, since AgBiS.sub.2 of First Embodiment exhibits a far more favorable photoresponse than PbS in a region of 940 nm, the possibility of applying AgBiS.sub.2 as a near infrared light-receiving element is further expected.

INDUSTRIAL APPLICABILITY

[0096] As described above, the photoelectric conversion element material of the present invention is provided with a semiconductor film including Ag.sub.2xBi.sub.xS.sub.x+1 (x is an integer of 0 or 1), which is a metal chalcogenide, as a light-receiving layer. This light-receiving layer exhibits excellent responsiveness to light in the near infrared region by being imparted with appropriate crystallinity. The present invention is particularly useful as a photoelectric conversion thin film for a light-receiving element for a variety of optical semiconductor devices and is expected to contribute to the size reduction or performance improvement of LIDAR or image sensors as a light-receiving element therefor.