JP5204079B2 - Dye-sensitized solar cell and method for producing the same - Google Patents

Description

  The present invention relates to a dye-sensitized solar cell and a method for producing the same.

Conventionally, as a dye-sensitized solar cell, a photoelectrode provided with an electron transport layer coated with a light absorbing layer containing a sensitizing dye on a transparent conductive substrate, and a counter electrode disposed so as to face the photoelectrode There is known a structure in which a hole transport layer is interposed therebetween. As sensitizing dyes, in addition to organic sensitizers represented by ruthenium complexes and the like, inorganic sensitizers represented by cadmium sulfide (CdS), copper indium disulfide (CuInS), tin sulfide (SnS) and the like. It has been known. Among these, SnS has a photoabsorption coefficient of 10 ⁵ cm ⁻¹ and a band gap of 1.1 to 1.4 eV, and therefore has suitable optoelectronic properties as a sensitizer for use in a dye-sensitized solar cell. . For example, Patent Document 1 discloses an all-solid-state dye-sensitized solar cell using SnS as an inorganic sensitizer and CuSCN as a p-type semiconductor as a hole transport layer.

JP 2006-216958 A

  However, the all-solid dye-sensitized solar cell using SnS as an inorganic sensitizer described in Patent Document 1 has a low short-circuit current density Isc and an open-circuit voltage Voc, and as a result, only a very low conversion efficiency is obtained. Absent. The reason is not clear, but is considered as follows. That is, the electrons (carriers) generated by the absorption of light by SnS must be carried out to the electron transport layer, but since the level density at the interface between SnS and the CuSCN that is the hole transport layer is high, This is probably because electrons and holes in the hole transport layer are recombined.

  The present invention has been made to solve such problems, and in a dye-sensitized solar cell using an inorganic sensitizer, the current and voltage generated by absorbing light are increased as compared with the prior art. The main purpose.

  In order to achieve the above-described object, the present inventors formed a metal sulfide film as a sensitizing dye on an electron transport layer formed on a transparent substrate when producing a dye-sensitized solar cell. Then, when heated under specified conditions, the surface of the metal sulfide is modified with an element having a higher electronegativity than sulfur (for example, oxygen or nitrogen), so that the dye-sensitized solar cell has diode characteristics (rectifying action). ), And found that the current and voltage generated by light absorption are higher than those of the prior art, and completed the present invention.

That is, the dye-sensitized solar cell of the present invention is
Dye in which a hole transport layer is interposed between a photoelectrode provided with an electron transport layer coated with a light absorbing layer containing a sensitizing dye on a transparent conductive substrate and a counter electrode arranged to face the photoelectrode A sensitized solar cell,
The light absorption layer includes a metal sulfide in which an element having higher electronegativity than sulfur is adsorbed on the surface on the hole transport layer side, and the element has an atomic concentration on the outermost surface of the metal sulfide. The maximum atomic concentration is in the range of 18 to 31%.

Moreover, the method for producing the dye-sensitized solar cell of the present invention is as follows:
Dye in which a hole transport layer is interposed between a photoelectrode provided with an electron transport layer coated with a light absorbing layer containing a sensitizing dye on a transparent conductive substrate and a counter electrode arranged to face the photoelectrode A method for producing a sensitized solar cell, comprising:
Forming the electron transport layer on the transparent conductive substrate, forming a metal sulfide film as the sensitizing dye on the electron transport layer, and then in an atmosphere containing an element having a higher electronegativity than sulfur; The element is adsorbed on the surface of the metal sulfide by heating so that the temperature of the metal sulfide is 180 to 210 ° C., and then the hole transport layer and the counter electrode are formed on the surface of the metal sulfide. They are stacked in this order.

  According to the dye-sensitized solar cell of the present invention, the current and voltage generated by light absorption are higher than conventional ones, and the conversion efficiency is also improved. The reason is not clear, but is considered as follows. That is, by heating a metal sulfide in an atmosphere containing an element having a higher electronegativity than sulfur, the element is adsorbed on the surface of the metal sulfide. Thus, interface polarization is formed at the interface between the light absorption layer containing the metal sulfide in which the element having high electronegativity is adsorbed at an appropriate atomic concentration and the hole transport layer. Due to the interfacial polarization, electrons generated in the light absorption layer and diffused to the hole transport layer are driven back to the light absorption layer, and holes generated in the hole transport layer and diffused to the light absorption layer are transferred to the hole transport layer. Be repulsed. For this reason, the hole of a positive hole transport layer and the electron of the light absorption layer produced by light absorption do not recombine in the interface vicinity. As a result, the dye-sensitized solar cell has a diode characteristic in which almost no current flows with respect to the reverse bias voltage, and the current rapidly increases with respect to the forward bias voltage. It is thought that it was higher than before.

  According to the method for producing the dye-sensitized solar cell of the present invention, by a simple process of heating the metal sulfide to 180 to 210 ° C. in an atmosphere containing an element having a higher electronegativity than sulfur, A dye-sensitized solar cell having the above-described diode characteristics can be easily produced.

1 is a schematic cross-sectional view showing a configuration of a dye-sensitized solar cell 10. FIG. FIG. 4 is a schematic diagram showing a state of an interface between the light absorption layer 18 and the hole transport layer 22. 2 is a schematic cross-sectional view showing a configuration of a battery module 100. FIG. It is a schematic diagram in case the structure of the electron carrying layer 16, the light absorption layer 18, and the positive hole transport layer 22 is a nanostructure. It is a schematic sectional drawing which shows the structure of the laminated | stacked dye-sensitized solar cell produced in Experimental Examples 1-15. It is a graph which shows the relationship between the heating time in the tubular furnace of a 2nd intermediate substrate, and the temperature of a 2nd intermediate substrate. It is a graph which shows the solar cell characteristic of Experimental example 1,4,13. It is a graph which shows the solar cell characteristic of Experimental example 14 and 15. It is a graph which shows the spectral sensitivity characteristic of Experimental example 1 and 4. It is a graph which shows the diode characteristic of Experimental Examples 1-8. It is a graph which shows the diode characteristic of Experimental example 1, 9-12. It is a X-ray-diffraction pattern of the SnS film | membrane for every heating temperature. 5 is a graph showing the oxygen atom concentration depth distribution of Experimental Examples 1, 4, and 6. It is a graph which shows the relationship between heat processing temperature and oxygen atom concentration.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the configuration of the dye-sensitized solar cell 10 of the present embodiment, and FIG. 2 is a schematic diagram showing the state of the interface between the light absorption layer 18 and the hole transport layer 22. a) shows the case where interface polarization occurs, and (b) shows the case where interface polarization does not occur.

  The dye-sensitized solar cell 10 has a photoelectrode 12 provided with an electron transport layer 16 covered with a light absorption layer 18 containing an inorganic sensitizer on a transparent conductive substrate 14, and faces the photoelectrode 12. The hole transport layer 22 is interposed between the counter electrode 20 and the counter electrode 20. The outer periphery of the region between the transparent conductive substrate 14 and the counter electrode 20 in the dye-sensitized solar cell 10 is covered with a sealing material 24.

The transparent conductive substrate 14 has a configuration in which a transparent conductive film 14b is laminated on the electron transport layer 16 side in a transparent substrate 14a such as a glass substrate. Examples of the material of the transparent conductive substrate 14 include fluorine-doped SnO ₂ coated glass, ITO coated glass, ZnO: Al coated glass, and antimony doped tin oxide (SnO ₂ —Sb). In addition, tin oxide or indium oxide doped with cations or anions with different valences, or a metal electrode with a structure capable of transmitting light, such as a mesh or stripe, provided on a glass substrate is also transparent. It can be used as the substrate 14. As the transparent substrate 14a, in addition to a transparent glass substrate, a substrate that transmits light, such as a glass substrate semi-transparent glass substrate that prevents light reflection by appropriately roughening the surface of the glass substrate, transparent Although a plastic plate, a transparent plastic film, an inorganic transparent crystal, etc. can be used, a transparent glass substrate is preferable.

The electron transport layer 16 is a layer that transports electrons generated in the light absorption layer 18 to the transparent conductive substrate 14. Examples of the material for the electron transport layer 16 include n-type semiconductor materials typified by TiO ₂ , ZnO, SnO _{2 and the} like, and among these, TiO ₂ is preferable. Examples of the crystal structure of TiO ₂ include a rutile type and an anatase type, and among these, the anatase type is preferable. The reason is that the band gaps of the anatase type and the rutile type are 3.2 eV and 3.0 eV, respectively, and the anatase type has a higher energy level at the lower end of the conduction band and a higher open end voltage. This is because there is a report that the anatase type is more efficient than the rutile type in the sensitized solar cell (Chem. Mater., Vol. 14, p2930 (2002)). As the TiO ₂ particles, anatase type particles may be used alone, or mixed particles of anatase type and rutile type may be used. The particle diameter of the TiO ₂ particles is preferably 5 nm to 500 nm. When the particle diameter of the TiO ₂ particles is less than 5 nm, the pore diameter of the electron transport layer 16 becomes too small compared with the case where the particle diameter is in the above range, and the adsorption time of the inorganic sensitizer in the light absorption layer 18 increases. Or diffusion of the hole transport layer 22 becomes difficult and the diffusion resistance tends to increase. On the other hand, when the particle diameter exceeds 500 nm, the amount of adsorption of the inorganic sensitizer is reduced as compared with the case where the particle diameter is in the above range, and the stress in the electron transport layer 16 increases due to the coarse particles, which is mechanical. There is a tendency that the strength is insufficient and the electron transport layer 16 is easily peeled off. In order to keep the diffusion resistance lower and make the electron transport layer 16 more difficult to peel off, the particle diameter of the TiO ₂ particles is preferably 10 nm to 100 nm. Furthermore, as described in JP-A-2000-106222, TiO ₂ particles having a large particle size (10 nm to 300 nm) and TiO ₂ particles having a small particle size (10 nm or less) may be mixed. In this case, since the incident light incident on the electron transport layer 16 is scattered inside the electron transport layer 16 by large particles, the energy conversion efficiency is improved. Further, in the photoelectrode 12 having the electron transport layer 16, a light reflection layer made of rutile TiO ₂ particles may be provided on the electron transport layer 16 as described in JP-A-2003-142171. In this case, the electron transport layer 16 may be a mixture of TiO ₂ particles having an average particle diameter of 70 nm or less and TiO ₂ particles having an average particle diameter of 150 nm or more, and the light reflection layer is a rutile type TiO _2. Particles (average particle diameter of 150 nm or more and refractive index of 2.4 or more) and SiO ₂ particles (refractive index of 1.8 or less) may be mixed.

The light absorption layer 18 is a layer covering the electron transport layer 16 and contains a metal sulfide as an inorganic sensitizer. This metal sulfide has absorption in the visible light region and / or the infrared light region, for example, a group consisting of SnS, Sb ₂ S ₃ , Cu ₂ S, ZnS, FeS ₂ , TiS ₂ , MoS _2. At least one selected from the above. Of these, SnS is preferable. This is because SnS has a light absorption coefficient of 10 ⁵ cm ⁻¹ and a band gap of 1.1 to 1.4 eV, and has optoelectronic properties suitable as a sensitizer for use in a dye-sensitized solar cell. . Further, in the metal sulfide, an element (for example, O, N, F, Cl, or Br) having a higher electronegativity than sulfur is adsorbed on the surface on the hole transport layer 22 side. The atomic concentration of the element is maximum on the outermost surface when the depth distribution of the metal sulfide is seen, and the maximum value is 18 to 31%, preferably 21 to 23%. In addition, as a method for adsorbing an element having a higher electronegativity than sulfur on the surface of the metal sulfide, for example, a predetermined state in which a metal sulfide layer is formed on the electron transport layer 16 formed on the transparent conductive substrate 14 is used. Although it is mentioned to heat on these conditions, it mentions later in detail. As described above, in the dye-sensitized solar cell including the metal sulfide having an element having a high electronegativity adsorbed on the surface, almost no current flows with respect to the reverse bias voltage, and the current rapidly increases with respect to the forward bias voltage. Has diode characteristics.

  The counter electrode 20 is a conductive layer through which electrons can pass. For example, a metal thin film such as Au or Pt or a porous carbon thin film can be used, and the counter electrode 20 has the same configuration as the above-described transparent conductive substrate 14 ( In this case, the transparent conductive film is disposed so as to be in contact with the hole transport layer 22).

The hole transport layer 22 receives electrons from the counter electrode 20 in a state where loads are connected to both electrodes of the dye-sensitized solar cell 10, and on the other hand, the metal sulfide cation generated in the light absorption layer 18 by absorbing light. Is a layer that returns to the original neutralized state with electrons received from the counter electrode 20. Examples of the material of the hole transport layer 22 include p-type semiconductor materials typified by CuI, CuSCN, Li-doped NiO, and the like, as well as redox species (I ³⁻ / I ⁻ -based electrolyte, Br ³⁻ / Br ^- based electrolyte include hydroquinone / quinone electrolyte redox electrolyte) laden electrolyte or a known gelling agent such as (polymer or low molecular gelling agent) gel electrolyte with the addition of the.

  The sealing material 24 is for preventing the electron transport layer 16, the light absorption layer 18, and the hole transport layer 22 from coming into contact with outside air. For example, a thermoplastic resin film such as polyethylene or an epoxy adhesive can be used as the sealing material 24.

  Next, the operation of the dye-sensitized solar cell 10 will be described. When the transparent conductive substrate 14 is irradiated with sunlight in a state where loads are connected to both electrodes of the dye-sensitized solar cell 10, the metal sulfide of the light absorption layer 18 that has been exposed to sunlight emits electrons. Become a cation. The emitted electrons move to the transparent conductive film 14b of the transparent conductive substrate 14 via the electron transport layer 16 and flow to the load. The hole transport layer 22 receives electrons passing through the load from the counter electrode 20, and returns the metal sulfide cation generated in the light absorption layer 18 to the original neutralized state by the received electrons. As a result of such a series of reactions, when the dye-sensitized solar cell 10 is irradiated with sunlight, a current flows through the load.

Here, with respect to the interface between the hole transport layer 22 and the light absorption layer 18 containing a metal sulfide, the case where the metal sulfide in the light absorption layer 18 is SnS and the hole transport layer 22 is CuI is taken as an example. I will explain. SnS adsorbs an element having a higher electronegativity than sulfur on the surface on the hole transport layer 22 side, and the atomic concentration of the element is maximum on the outermost surface when the distribution of SnS in the depth direction is seen. The maximum value is 18 to 31%. Such a layer on which an element having a high electronegativity is adsorbed is referred to as a surface modified layer. Since this surface modification layer exists, an interface polarization 26 is formed at the interface between SnS and CuI, as shown in FIG. Due to the interface polarization 26, electrons (e ⁻ ) generated in the light absorption layer 18 and diffused to the hole transport layer side are driven back to the light absorption layer 18, generated in the hole transport layer 22, and diffused to the light absorption layer side. Holes (h ⁺ ) are driven back to the hole transport layer 22. For this reason, it is considered that the holes of the hole transport layer 22 and the electrons of the light absorption layer 18 generated by light absorption do not recombine near the interface. On the other hand, when the light absorption layer 18 includes a metal sulfide that does not have the above-described surface modification layer (that is, a metal sulfide that has not been subjected to heat treatment), the interface as shown in FIG. Since polarization is not formed, it is considered that electrons generated in the light absorption layer 18 and diffused to the hole transport layer side recombine with holes generated in the hole transport layer 22 and diffused to the light absorption layer side. . Therefore, in the present embodiment in which the light absorption layer 18 is made of a metal sulfide having a surface modification layer, the light absorption layer 18 is generated by light absorption compared to the case where the light absorption layer 18 is made of a metal sulfide having no surface modification layer. Current and voltage to be increased.

  Next, a method for producing the dye-sensitized solar cell 10 will be described. First, the transparent conductive substrate 14 is obtained by forming the transparent conductive film 14b on the transparent substrate 14a such as a glass substrate using a known thin film manufacturing technique such as spray coating.

  Subsequently, the electron transport layer 16 is formed on the transparent conductive film 14 b of the transparent conductive substrate 14. Specifically, a dispersion liquid in which n-type semiconductor particles having a predetermined size (for example, a particle diameter of about 20 to 400 nm) are dispersed is prepared, and this dispersion liquid is applied to the transparent conductive film 14b by a bar coater method or a printing method. The electron transporting layer 16 may be formed by coating by drying, etc., and baking after drying. Alternatively, a thin film electron made of an n-type semiconductor is formed on the transparent conductive film 14b by a physical vapor deposition method such as electron beam vapor deposition, resistance heating vapor deposition, sputter vapor deposition, or cluster ion beam vapor deposition, or a chemical vapor deposition method such as chemical vapor deposition (CVD). The transport layer 16 may be formed.

  Subsequently, the light absorption layer 18 is formed on the electron transport layer 16. Specifically, it is made of a metal sulfide on the electron transport layer 16 by physical vapor deposition such as electron beam vapor deposition, resistance heating vapor deposition, sputter vapor deposition, cluster ion beam vapor deposition, or chemical vapor deposition such as CVD or CBD (Chemical Bath Deposition). After forming a thin film, the light absorption layer 18 is formed by heating under predetermined conditions. The vapor deposition may be repeated a plurality of times. Here, the predetermined condition is set so that the metal sulfide has a surface modification layer. A metal sulfide with a surface modification layer is one in which an element having a higher electronegativity than sulfur is adsorbed on the surface of the metal sulfide, and the atomic concentration of the element has a distribution in the depth direction of the metal sulfide. When viewed, the maximum is at the outermost surface, and the maximum value is in the range of 18 to 31%. Predetermined conditions are good also as heating so that the temperature of a metal sulfide may become 180-210 degreeC in the atmosphere containing the element whose electronegativity is higher than sulfur, for example. In this case, a thin film made of a metal sulfide is placed in a heating furnace at 180 to 210 ° C., and after the time required for the temperature of the thin film to be substantially the same as the temperature of the heating furnace has elapsed, You may make it take out from. Alternatively, a thin film made of a metal sulfide is placed in a heating furnace at a temperature exceeding 210 ° C. (for example, 400 ° C. or 500 ° C.), and a time has elapsed so that the temperature of the thin film falls within 180 to 210 ° C. You may make it take out from a heating furnace later.

  Subsequently, the hole transport layer 22 is formed on the light absorption layer 18. Specifically, a dispersion in which p-type semiconductor particles having a predetermined size (for example, a particle diameter of about 20 to 400 nm) are dispersed is prepared, and this dispersion is applied to the light absorption layer 18 by a bar coater method or a printing method. Alternatively, the hole transport layer 22 may be formed by applying, for example, and baking after drying. Alternatively, a thin hole transport layer 22 made of a p-type semiconductor is formed on the light absorption layer 18 by physical vapor deposition such as electron beam vapor deposition, resistance heating vapor deposition, sputter vapor deposition, cluster ion beam vapor deposition, or chemical vapor deposition such as CVD. It may be formed.

  Thereafter, the counter electrode 20 is formed on the hole transport layer 22. Specifically, a counter electrode made of a metal thin film such as Au or Pt on the hole transport layer 22 by physical vapor deposition such as electron beam vapor deposition, resistance heating vapor deposition, sputter vapor deposition, or cluster ion beam vapor deposition, or chemical vapor deposition such as CVD. 20 may be formed. Or the same board | substrate as the transparent conductive substrate 14 mentioned above may be prepared, and it may laminate | stack so that the transparent conductive film 14b may contact the hole transport layer 22. FIG. Finally, the side surfaces of the electron transport layer 16, the light absorption layer 18, and the hole transport layer 22 are covered with the sealing material 24, thereby completing the dye-sensitized solar cell 10.

  In addition, when using the electrolyte solution containing redox species as the hole transport layer 22, the step of forming the hole transport layer 22 on the light absorption layer 18 and the counter electrode 20 are formed on the hole transport layer 22. The forming step is not performed. Instead, the electrolytic solution is injected through the step of forming the sealing material 24 in a state where the counter electrode 20 is disposed on the light absorption layer 18 with a gap formed therein or through the injection port leading to the gap. A step of closing the inlet after the injection is performed.

  Since the dye-sensitized solar cell 10 of the present embodiment described in detail above includes the light absorption layer 18 made of a metal sulfide having a surface modification layer, almost no current flows with respect to the reverse bias voltage. It has a diode characteristic in which the current rapidly increases with respect to the forward bias voltage. For this reason, the electric current and voltage which generate | occur | produce by light absorption become high compared with the past, and conversion efficiency improves by extension. Moreover, according to the manufacturing method of this embodiment, the dye-sensitized solar cell 10 is obtained by a simple process in which the temperature of the metal sulfide is heated to 180 to 210 ° C. in an atmosphere containing an element having a higher electronegativity than sulfur. Can be easily manufactured. Furthermore, when a p-type semiconductor such as CuI is used as the hole transport layer 22 instead of the electrolyte, there is no risk of liquid leakage because it becomes an all-solid solar cell.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, one dye-sensitized solar cell 10 has been described, but a battery in which a plurality of dye-sensitized solar cells (hereinafter referred to as single cells) 110 are connected in series as shown in FIG. The module 100 may be used. The single cell 110 is a portion surrounded by a one-dot chain line in FIG. In the single cell 110, the electron transport layer 16, the light absorption layer 18 and the hole transport of the dye-sensitized solar cell 10 of the above-described embodiment are disposed between the transparent conductive film 114b of the transparent conductive substrate 114 and the counter electrode 120. The electron transport layer 116, the light absorption layer 118, and the hole transport layer 122 are the same as the layer 22. The counter electrode 120 of one single cell 110 is bent in the thickness direction of the cell and is electrically connected to the transparent conductive film 114b of one adjacent single cell 110, but the transparent conductive property of the other adjacent single cell 110 is transparent. The membrane 114b and the counter electrode 120 of both adjacent unit cells 110 are electrically insulated by a sealing material 124. Of the transparent conductive substrate 114, the transparent substrate 114 a is a member common to all the single cells 110, but the transparent conductive film 114 b is formed for each single cell 110. This battery module 100 is effective when high output is required. Further, it can be arranged in a planar space. Depending on the space in which the batteries are arranged, a plurality of dye-sensitized solar cells 10 may be stacked in the vertical direction and connected in series. Of course, parallel connection is also possible.

In the above-described embodiment, the detailed structures of the electron transport layer 16, the light absorption layer 18, and the hole transport layer 22 have not been described. For example, these layers are formed using a film formation technique such as sputtering or vacuum evaporation. When sequentially formed, a structure in which three layers of films are stacked. On the other hand, the electron transport layer 16 is formed as a fine particle thin film by screen printing and subsequent heat treatment, the light absorption layer 18 is formed by the CBD method, and the hole transport layer 22 is formed by using a film forming technique such as vacuum deposition. In such a case, the nanostructure shown in FIG. 4 is obtained. The nanostructure of FIG. 4 is a structure in which a fine particle array thin film (electron transport layer 16) of an n-type semiconductor carrying the light absorption layer 18 is formed, and the hole transport layer 22 penetrates between the fine particle arrays. The fine particle array thin film has a structure in which adjacent fine particles are in contact with each other to form 20-400 nm pores. The inorganic sensitizer of the light absorption layer 18 is coated on the surface of the fine particles with a thickness of 1-150 nm. An example of a specific procedure for producing such a nanostructure is shown below. First, an ITO glass substrate is prepared as the transparent conductive substrate 14, a TiO ₂ fine particle thin film is formed as the electron transport layer 16 by screen printing on the ITO glass substrate, heated at 150 ° C. in the atmosphere for 10 minutes, and similarly in the atmosphere. Heat at 450 ° C. for 2 hours. Thereafter, an SnS thin film is produced as the light absorption layer 18 by the CBD method. CBD is performed as follows. (1) The ITO glass substrate on which the TiO ₂ fine particle thin film is formed is immersed in an SnCl ₂ .2H ₂ O aqueous solution (0.025M) for 10 seconds, and then the excess chemical adsorbed on the surface is washed with water. (2) Similarly, the substrate is immersed in an aqueous Na ₂ S.9H ₂ O solution (0.025M) for 10 seconds and then washed with water. (3) The above (1) and (2) are set as one cycle, and the film thickness is changed by changing the number of cycles. Thereafter, CuI is deposited as a hole transport layer by a vacuum deposition method, whereby the nanostructure of FIG. 4 can be obtained. In addition to the method of forming a film of CuI by vacuum vapor deposition, the nanostructure of FIG. 4 can also be formed by dropping CuI in acetonitrile and drying it to form CuI. Actually, when the change in the color of the film with respect to the number of cycles of the CBD process was observed, the TiO ₂ fine particle thin film was transparent at 0 cycle, and only the region of the TiO ₂ fine particle thin film was discolored by the CBD process, and the number of cycles increased. The color got darker. Further, when the XRD spectrum was measured corresponding to the number of cycles of the CBD process, a peak attributable to orthorhombic SnS crystals was observed at the number of cycles of 2 or more.

[1] Preparation / Experimental Examples 1 to 8 of dye-sensitized solar cell (hereinafter also referred to as element)
The stacked element shown in FIG. 5 was manufactured according to the following procedure. First, an electron transport layer (TiO ₂ film) having a thickness of 50 nm was formed on a transparent conductive substrate (ITO substrate) under the film formation condition A in Table 1 to obtain a first intermediate substrate. Subsequently, the first intermediate substrate was inserted into a tubular furnace and heated at 500 ° C. for 30 minutes in the atmosphere. Next, a light absorption layer (SnS film) having a thickness of 20 nm was formed on the TiO ₂ film of the first intermediate substrate under the film formation condition B in Table 1 to obtain a second intermediate substrate. Next, the surface modification of the SnS film of the second intermediate substrate was performed. Specifically, the second intermediate substrate was inserted into a tubular furnace that was previously heated to a predetermined temperature and that the predetermined temperature was stable. In this state, the second intermediate substrate was left in a tubular furnace for 15 minutes and then taken out. Since both ends of the tube of the tubular furnace were open at this time, it was considered that the SnS film of the second intermediate substrate was heated in the atmosphere. In performing the surface modification of the SnS film of the second intermediate substrate, in the experimental example 1, the SnS film is not heated, and in the experimental examples 2 to 8, the SnS film is 150 ° C., 180 ° C., 200 ° C., 220 ° C., respectively. Heated at 250 ° C, 300 ° C and 350 ° C. Next, a hole transport layer (CuI film) having a thickness of 50 nm is formed on the SnS film of the second intermediate substrate after the surface modification in this manner under the film formation condition C in Table 1. Three intermediate substrates were used. Thereafter, a counter electrode (Au film) having a thickness of 100 nm was formed on the CuI film of the third intermediate substrate under the film formation condition D shown in Table 1 to obtain an element.

Experimental examples 9-12
A stacked element was obtained in the same manner as in Experimental Examples 1 to 8, except that the conditions for modifying the surface of the SnS film on the second intermediate substrate were changed. The surface modification of the SnS film was performed as follows. That is, the second intermediate substrate was inserted into a tubular furnace heated in advance and stabilized at 400 ° C. In this state, the second intermediate substrate was left in the tubular furnace for a predetermined heating time and then taken out. Since both ends between the tubular furnaces were open at this time, it was considered that the SnS film of the second intermediate substrate was heated in the atmosphere as in Experimental Examples 1-8. FIG. 6 shows the relationship between the heating time of the second intermediate substrate in the tubular furnace and the temperature of the second intermediate substrate. As apparent from FIG. 6, the temperature of the second intermediate substrate is raised to 210 ° C. 1 minute after insertion into the tube furnace, 290 ° C. after 2 minutes, 360 ° C. after 5 minutes, and about 370 ° C. after 15 minutes. . Here, in Experimental Example 9, the heating time was 1 minute, and in Experimental Examples 10 to 12, the heating time was 2 minutes, 5 minutes, and 15 minutes, respectively.

Experimental example 13
A stacked element was obtained in the same manner as in Experimental Examples 1 to 8, except that the conditions for modifying the surface of the SnS film on the second intermediate substrate were changed. The surface modification of the SnS film was performed as follows. That is, after the second intermediate substrate was placed in the tube of the tubular furnace, the tube was sealed, and N ₂ gas was allowed to flow in at a flow rate of ₂ L / min for 30 minutes at room temperature. As a result, it was considered that the atmosphere in the tube was completely replaced with N ₂ gas. In this state, the second intermediate substrate was heated to 200 ° C. at a temperature increase rate of 6.7 ° C./minute, held in that state for 30 minutes, and then the heating was terminated and the second intermediate substrate was taken out.

Experimental examples 14 and 15
In Experimental Example 14, the element was fabricated in the same manner as in Experimental Example 4 except that the thickness of the light absorption layer when forming the light absorption layer (SnS film) under the film formation condition B was changed from 20 nm to 50 nm. Produced. In Experimental Example 15, the element was formed in the same manner as in Experimental Example 1 except that the thickness of the light absorption layer when forming the light absorption layer (SnS film) under the film formation condition B was changed from 20 nm to 50 nm. Was made.

[2] Evaluation of solar cell characteristics The solar cell characteristics (current-voltage characteristics during simulated sunlight irradiation) of the elements obtained in Experimental Examples 1, 4 and 13 were measured with a solar simulator. The measurement was performed at room temperature in the air. The solar cell characteristics when the device is irradiated with AM1.5 simulated sunlight are shown in FIG. In FIG. 7, the horizontal axis represents the bias voltage applied to the element (in FIG. 1, the potential of the terminal on the counter electrode side with respect to the terminal on the transparent conductive substrate side, the same applies hereinafter), and the vertical axis represents the current density generated from the element. . The short-circuit current density Isc of the element of Experimental Example 1 in which the SnS film was not heat-treated was 0.26 mA / cm ² , and when the bias voltage was increased thereafter, no current flowed at 0.04 V (open voltage Voc). . The fill factor (FF), which is the ratio of the maximum output defined by the ratio of the product of the optimum operating voltage and the optimum operating current to the product of the short-circuit current density Isc and the open circuit voltage Voc, was 0.26. On the other hand, the short-circuit current density Isc of the element of Experimental Example 4 in which the SnS film was heated in the atmosphere at 200 ° C. was 1.2 mA / cm ² , the open circuit voltage Voc was 0.11 V, and the FF was 0.23. From the above results, when the SnS film was heat-treated at 200 ° C. in the atmosphere, the short-circuit current density Isc and the open-circuit voltage Voc were improved three times as compared with the case where the heat treatment was not performed. In addition, the short-circuit current density Isc of the element of Experimental Example 13 in which the SnS film was heated in an N ₂ atmosphere at 200 ° C. was 1.7 mA / cm ² , the open-circuit voltage Voc was 0.12 V, and FF was 0.19. From the above results, when the SnS film was heated in an N ₂ atmosphere at 200 ° C., the short-circuit current density Isc of the device was improved 7 times and the open circuit voltage Voc was improved 3 times compared to the case where the heat treatment was not performed.

Similarly, the solar cell characteristics of the elements obtained in Experimental Examples 14 and 15 were measured with a solar simulator. The solar cell characteristics when the element is irradiated with AM1.5 simulated sunlight are shown in FIG. The short-circuit current density Isc of the element of Experimental Example 15 in which the SnS film was not heat-treated was 1.6 mA / cm ² , the open circuit voltage Voc was 0.04 V, and FF was 0.24. The short-circuit current density Isc of the element of Experimental Example 14 in which the SnS film was heat-treated at 200 ° C. in the atmosphere was 6.3 mA / cm ² , the open-circuit voltage Voc was 0.10 V, and the FF was 0.29. From the above results, when the SnS film was heated in the atmosphere at 200 ° C., the short-circuit current density Isc of the device was improved by a little less than 4 times and the open-circuit voltage Voc was improved by a factor of 2 or more compared to the case where the heat treatment was not performed.

[3] Spectral Sensitivity Characteristic Evaluation Spectral sensitivity characteristics of the elements obtained in Experimental Examples 1 and 4 (photoelectric conversion characteristics of solar cell elements with respect to light of a specific wavelength) were measured with a spectral sensitivity measuring device. The measurement was performed at room temperature in the air. FIG. 9 shows spectral sensitivity characteristics of the element of Experimental Example 1 in which the SnS film was not heat-treated and the element of Experimental Example 4 in which heat-treatment was performed at 200 ° C. in the atmosphere. In FIG. 9, the wavelength of light applied to the device is plotted on the horizontal axis, and the external quantum yield (the number of electrons generated from the device with respect to the number of photons of incident light) is plotted on the vertical axis. The quantum yield reached its maximum value at a wavelength of 400 nm, and was 0.05 for the device of Experimental Example 1 and 0.17 for the device of Experimental Example 4. Since any element performs photoelectric conversion in a wavelength region of 400 nm or more, the sensitizing action by SnS could be confirmed. When the SnS film was heated in the atmosphere at 200 ° C. because the external quantum yield of the device of Experimental Example 4 exceeded the external quantum yield of the device of Experimental Example 1 in the wavelength range of 300 to 600 nm, heat treatment was performed. It was determined that the photoelectric conversion characteristics of the device were improved as compared with the case where the test was not performed.

[4] Evaluation of diode characteristics The diode characteristics (current-voltage characteristics in a dark environment) of the elements obtained in Experimental Examples 1 to 8 were measured with a prober. The measurement was performed at room temperature in the air. FIG. 10 shows the diode characteristics of each element. In FIG. 10, the horizontal axis represents the bias voltage applied to the element, and the vertical axis represents the current flowing through the element. In the element of Experimental Example 1 where the SnS film was not heat-treated (FIG. 10A) and the element of Experimental Example 2 where the SnS film was heat-treated at 150 ° C. (FIG. 10B), the current was uniform with respect to the bias voltage. It did not show rectifying action. On the other hand, in the element of Experimental Example 3 (FIG. 10C) in which the SnS film was heat-treated at 180 ° C. and the element of Experimental Example 4 in which the SnS film was heat-treated at 200 ° C. (FIG. 10D), the forward bias voltage (V > 0 [V]), the current increases sharply, whereas almost no current flows for the reverse bias voltage (V <0 [V]). all right. In addition, in the element of Experimental Example 5 (FIG. 10E) in which the SnS film was heated at 220 ° C. and the element of Experimental Example 6 in which the SnS film was heated at 250 ° C. (FIG. 10F), an increase in current with respect to the forward bias voltage. And the amount of current also increased with respect to the reverse bias voltage, so it was determined that no rectifying action was exhibited. In the element of Experimental Example 7 (FIG. 10 (g)) in which the SnS film was heated at 300 ° C. and the element of Experimental Example 8 (FIG. 10 (h)) in which the SnS film was heated at 350 ° C., almost no current was applied to the forward bias voltage. Although it does not flow, the current amount suddenly increases with respect to the reverse bias voltage.

  The diode characteristics of the elements obtained in Experimental Examples 9 to 12 are shown in FIG. The horizontal axis and the vertical axis are the same as those in FIG. Moreover, the result of Experimental Example 1 is also shown in FIG. In the element of Experimental Example 9 (FIG. 11B) that was heated to 400 ° C. for 1 minute and heated until the element temperature reached 210 ° C., the current rapidly increased with respect to the forward bias voltage (V> 0 [V]). On the other hand, almost no current flowed with respect to the reverse bias voltage (V <0 [V]). Further, in the element of Experimental Example 10 (FIG. 11 (c)) that was heated at 400 ° C. for 2 minutes and heated until the element temperature reached 290 ° C., the increase in current with respect to the forward bias voltage was small, and the current was bias voltage. Increased uniformly and showed no rectifying effect. An experiment in which the SnS film was allowed to stand at 400 ° C. for 5 minutes and heated until the element temperature reached 360 ° C. and the element of Experimental Example 11 (FIG. 11D) was left for 15 minutes and heated until the element temperature reached 370 ° C. In the element of Example 12 (FIG. 11 (e)), almost no current flows with respect to the forward bias voltage, but the amount of current increases with respect to the reverse bias voltage.

[5] Structural Evaluation of SnS Film For the structural evaluation of the SnS film, a SnS film formed on a glass substrate under the same conditions as the film forming conditions B in Table 1 was used. The produced SnS film was heat-treated in the atmosphere under the same conditions as in Experimental Examples 1, 4, and 6, and then the diffraction pattern was measured with an X-ray diffractometer. FIG. 12 shows X-ray diffraction patterns of the SnS film according to the heat treatment temperature. The diffraction patterns of the unheated SnS film, the SnS film heated at 200 ° C. as in Experimental Example 4, and the SnS film heated at 250 ° C. as in Experimental Example 6 are diffracted around 2θ = 31.5 °. A line is shown. This diffraction line is considered to be a diffraction line from the SnS (111) plane. By the heat treatment of the SnS film, the position of the diffraction line is 31.32 ° (the film not heat-treated (FIG. 12A) to 31.66 ° (heat-treated at 250 ° C. (FIG. 12C)). However, this diffraction line was not lost by the heat treatment, and no new diffraction line was shown in the diffraction pattern.From the above, even if the SnS film was heat treated, crystals other than SnS were formed. It is considered that the orthorhombic crystal of SnS was retained.

[6] Composition analysis of SnS film For the composition analysis of the SnS film, an SnS film formed on the Si substrate under the same conditions as the film formation conditions B in Table 1 was used. The prepared SnS film was heat-treated in the atmosphere under the same conditions as in Experimental Examples 1, 4, and 6, and then the photoelectron spectrum was measured by XPS. FIG. 13 shows the O (oxygen) atom concentration depth distribution in the SnS film obtained from the photoelectron spectrum for each heat treatment temperature. The horizontal axis of FIG. 13 shows the depth obtained from the Ar ⁺ ion etching time at the time of spectrum measurement. Since the signal intensity originating from Sn was sufficiently obtained at the point where the spectrum was measured after performing Ar ⁺ ion etching for 1 minute (dotted line portion in FIG. 13), this point was regarded as the outermost surface of the SnS film. The amount of oxygen on the outermost surface was 13% when no heat treatment was performed, but increased with increasing temperature, 20% at 200 ° C. and 32% at 250 ° C. Further, as is apparent from the portion up to a depth of about 3 nm in FIG. 13, the amount of oxygen inside increased with the heat treatment temperature. As described above, it has been clarified that the SnS film is subjected to heat treatment so that oxygen enters and adsorbs on the surface of the SnS film and the oxygen content increases as the heat treatment temperature rises. FIG. 13D is a graph comparing the oxygen atom concentrations of Experimental Examples 1, 4, and 6. From FIG. 13D, it can be seen that the oxygen atom concentration takes the maximum value on the outermost surface of the SnS film and decreases as the depth increases in any of the experimental examples. When the measurement of the amount of oxygen was repeated a plurality of times for the element that was not heat-treated and the element that was heat-treated at 200 ° C., as shown in FIG. The element heat-treated at ° C. was 22 ± 1%. Referring to the evaluation results of the diode characteristics shown in FIG. 9, the element (the outermost surface oxygen atom concentration of 21 to 23%) obtained by heating the SnS film at 200 ° C. in the atmosphere functioned as a diode, but the SnS film was heated. No element (the oxygen atom concentration on the outermost surface of 13 to 17%) or an element heated at 250 ° C. or higher (the oxygen atom concentration on the outermost surface of 32%) did not function as a diode. Is less than 17% or more than 32%, the oxygen atom concentration on the outermost surface is preferably other than that, that is, 18 to 31%, more preferably 21 to 23%. From the result of Experimental Example 4 in FIG. 12D, it is preferable that the oxygen atom concentration be 5 to 23%, particularly 5 to 16% in the range of 1 to 3 nm in depth from the outermost surface. It is preferable that the oxygen atom concentration is 0 to 5% in each region from the surface to the deepest part exceeding the depth of 3 nm.

[7] Summary The above results are summarized in Table 2. Since Experimental Examples 4 and 13 have good solar cell characteristics, and the diode characteristics in which current hardly increases with respect to the reverse bias voltage and current rapidly increases with respect to the forward bias voltage are shown in the examples of the present invention. Equivalent to. Although the solar cell characteristics were not measured in Experimental Examples 3 and 9, since the same diode characteristics as in Experimental Examples 4 and 13 were shown, it is predicted that the solar cell characteristics are good by the same mechanism as these. Therefore, it corresponds to an embodiment of the present invention. Other experimental examples correspond to comparative examples.

  The dye-sensitized solar cell of the present invention can be used, for example, as a power source for various electric appliances for home use, office use, and factory use, batteries for electric vehicles, hybrid vehicles, electric bicycles, and solar panels.

10 Dye-sensitized solar cell, 12 Photoelectrode, 14 Transparent conductive substrate, 14a Transparent substrate, 14b Transparent conductive film, 16 Electron transport layer, 18 Light absorption layer, 20 Counter electrode, 22 Hole transport layer, 24 Sealing material, 26 Interfacial polarization, 100 Battery module, 110 Single cell, 114 Transparent conductive substrate, 114a Transparent substrate, 114b Transparent conductive film, 116 Electron transport layer, 118 Light absorption layer, 120 Counter electrode, 122 Hole transport layer, 124 Sealing material, Isc Short-circuit current density, Voc open circuit voltage

Claims (6)

Dye in which a hole transport layer is interposed between a photoelectrode provided with an electron transport layer coated with a light absorbing layer containing a sensitizing dye on a transparent conductive substrate and a counter electrode arranged to face the photoelectrode A sensitized solar cell,
The light absorption layer includes a metal sulfide in which an element having higher electronegativity than sulfur is adsorbed on the surface on the hole transport layer side, and the element has an atomic concentration on the outermost surface of the metal sulfide. The maximum atomic concentration is in the range of 18-31%,
Dye-sensitized solar cell. The metal sulfide is at least one selected from the group consisting of Sn, Sb, Cu, Zn, Fe, Ti, and Mo as a metal element.
The dye-sensitized solar cell according to claim 1. The maximum atomic concentration is in the range of 21 to 23%.
The dye-sensitized solar cell according to claim 1 or 2. The element is at least one selected from the group consisting of O, N, F, Cl and Br.
The dye-sensitized solar cell according to any one of claims 1 to 3. The electron transport layer is one selected from the group consisting of TiO ₂ , ZnO and SnO ₂ which are n-type semiconductors,
The hole transport layer is one selected from the group consisting of NiO doped with CuI, CuSCN, Li, which is a p-type semiconductor, an electrolyte containing a redox species, and a gel electrolyte added with a gelling agent. is there,
The dye-sensitized solar cell according to any one of claims 1 to 4. Dye in which a hole transport layer is interposed between a photoelectrode provided with an electron transport layer coated with a light absorbing layer containing a sensitizing dye on a transparent conductive substrate and a counter electrode arranged to face the photoelectrode A method for producing a sensitized solar cell, comprising:
Forming the electron transport layer on the transparent conductive substrate, forming a metal sulfide film as the sensitizing dye on the electron transport layer, and then in an atmosphere containing an element having a higher electronegativity than sulfur; The element is adsorbed on the surface of the metal sulfide by heating so that the temperature of the metal sulfide is 180 to 210 ° C., and then the hole transport layer and the counter electrode are formed on the surface of the metal sulfide. Laminate in this order,
A method for producing a dye-sensitized solar cell.

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