JP6099435B2 - Core-shell particle, photoelectric conversion layer, and photoelectric conversion element - Google Patents

Description

  The present invention relates to a core-shell particle, a photoelectric conversion layer, and a photoelectric conversion element.

  In recent years, a solar cell that directly converts solar energy into electric energy has been rapidly expected as a next-generation energy source particularly from the viewpoint of global environmental problems. There are various types of solar cells such as those using crystalline silicon, amorphous silicon, compound semiconductors, or organic materials. Currently, solar cells using crystalline silicon are the mainstream.

  In general, a solar cell forms a photoelectric conversion layer having a pn junction by diffusing an impurity having a conductivity type opposite to that of a crystalline silicon wafer on a light receiving surface of a single crystal or polycrystalline crystal silicon wafer. And it is produced by forming an electrode in the light-receiving surface of a photoelectric converting layer, and the back surface on the opposite side to a light-receiving surface.

  Research and development are also underway for solar cells in which electrodes are not formed on the light receiving surface of the photoelectric conversion layer, but electrodes are formed only on the back surface of the photoelectric conversion layer.

  In the conventional solar cell, light having energy smaller than the band gap energy of the photoelectric conversion layer is not absorbed by the photoelectric conversion layer, so that a large photoelectric conversion loss occurs. Therefore, for example, Non-Patent Document 1 proposes an intermediate band solar cell including an intermediate band in the band gap of the photoelectric conversion layer.

  Since the solar cell described in Non-Patent Document 1 has an intermediate band in the band gap of the photoelectric conversion layer, it absorbs photons having energy higher than the band gap energy and absorbs the valence band as in the conventional solar cell. Electrons can be excited into the conduction band. Furthermore, the solar cell described in Non-Patent Document 1 is based on absorption of a photon having an energy greater than the energy difference between the valence band upper end and the intermediate band, and absorption of a photon greater than the energy difference between the intermediate band and the conduction band lower end. The electrons in the valence band can be excited to the conduction band through the intermediate band. Thereby, the solar cell described in Non-Patent Document 1 is said to be able to reduce photoelectric conversion loss and improve photoelectric conversion efficiency by photoelectrically converting light in a wavelength region that is not suitable for photoelectric conversion. .

Antonio Luque and Antonio Marti, Physical Review Letters, Volume 78, Number 26, pp.5014-5017 (1997)

  However, since the intermediate-band solar cell described in Non-Patent Document 1 is very difficult to produce a photoelectric conversion layer having a high-quality intermediate band, photogenerated electron / hole pairs are easily generated. There was a problem that recombination would occur and high photoelectric conversion efficiency could not be obtained.

  In view of the above circumstances, the object of the present invention is to absorb carriers generated by absorbing energy smaller than the band gap energy of the photoelectric conversion layer in addition to light having energy equal to or higher than the band gap energy of the photoelectric conversion layer. An object of the present invention is to provide a core-shell particle, a photoelectric conversion layer, and a photoelectric conversion element that can improve photoelectric conversion efficiency by efficiently collecting with an electrode.

The present invention includes a semiconductor core and a semiconductor shell provided on the surface of the semiconductor core, and the semiconductor core includes a first semiconductor including Cu, at least one of Ga and In, and at least one of S and Se. see contains an impurity for forming the intermediate band in the band gap of the first semiconductor, a semiconductor shell, Cu and, at least one of Ga and in, including core-shell a second semiconductor containing at least one of S and Se Particles. With such a configuration, carriers generated using electronic excitation via an intermediate band due to incidence of long-wavelength light on the semiconductor core and carriers generated in the semiconductor shell due to incidence of short-wavelength light Thus, the photoelectric conversion efficiency of the photoelectric conversion element having the photoelectric conversion layer produced using the core-shell particles of the present invention can be improved. In order to form an intermediate band in the semiconductor band gap, when a high concentration impurity is introduced into the semiconductor bulk, a semiconductor having a high quality intermediate band is formed by, for example, segregation of the impurity. In contrast, when impurities are introduced into the semiconductor core of the core-shell particle, the volume of the semiconductor core is so small that problems such as segregation of impurities hardly occur and a high-quality intermediate band is provided. Easy to manufacture semiconductors.

Moreover, this invention is a photoelectric converting layer containing said core-shell particle . With such a configuration, the carriers generated by utilizing electron excitation via the intermediate band by incident light with a long wavelength to a half-conductor core, carriers generated in the semiconductor shell by the incident of short-wavelength light Thus, the photoelectric conversion efficiency of the photoelectric conversion element having the photoelectric conversion layer of the present invention can be improved.

Furthermore, this invention is a photoelectric conversion element containing said photoelectric conversion layer and the electrode electrically connected with the photoelectric conversion layer . With such a configuration, carriers generated using electronic excitation via an intermediate band due to incidence of long-wavelength light on the semiconductor core and carriers generated in the semiconductor shell due to incidence of short-wavelength light Can be taken out from the electrode through the semiconductor shell, so that the photoelectric conversion efficiency of the photoelectric conversion element can be improved.

  According to the present invention, in addition to light having energy equal to or higher than the band gap energy of the photoelectric conversion layer, carriers generated by absorbing energy smaller than the band gap energy of the photoelectric conversion layer are efficiently collected by the electrode. Thus, a core-shell particle, a photoelectric conversion layer, and a photoelectric conversion element that can improve the photoelectric conversion efficiency can be provided.

It is typical sectional drawing of an example of the core-shell particle of this invention. It is a figure which shows a preferable example of the correlation diagram of the band gap of the semiconductor core of the core-shell particle of this invention, and a semiconductor shell. (A) And (b) is typical sectional drawing illustrated about an example of the manufacturing method of the core-shell particle of this invention. It is a figure which shows the change of the lattice constant and band gap energy by the change of the composition of a semiconductor shell. It is typical sectional drawing of an example of the photoelectric conversion element of this invention. It is a figure which shows the relationship between the band gap of a photoelectric converting layer when the band gap of a semiconductor shell is narrower than the band gap of a semiconductor core, and the energy of the carrier which moves in the said photoelectric converting layer. It is a figure which shows the relationship between the band gap of a photoelectric converting layer when the band gap of a semiconductor shell and the band gap of a semiconductor core are the same width, and the energy of the carrier which moves in the said photoelectric converting layer. It is a typical side view illustrating the manufacturing method of the semiconductor core of an Example. It is a typical side view illustrating the preparation method of the semiconductor fine particle of an Example. (A)-(c) is typical sectional drawing illustrated about the manufacturing method of the photoelectric conversion element of an Example.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<Core shell particles>
In FIG. 1, typical sectional drawing of an example of the core-shell particle | grains of this invention is shown. A core-shell particle 3 shown in FIG. 1 includes a semiconductor core 1 and a semiconductor shell 2 provided on the surface of the semiconductor core 1. When the core-shell particle 3 having such a configuration is used for the photoelectric conversion layer of the photoelectric conversion element, carriers generated in the semiconductor core 1 and the semiconductor shell 2 can be taken out by the incidence of light on the photoelectric conversion layer. Therefore, the photoelectric conversion efficiency of the photoelectric conversion element can be improved.

<Semiconductor core>
The semiconductor core 1 includes a semiconductor and an impurity including an impurity that forms an intermediate band in the band gap of the semiconductor. Thereby, when light enters the semiconductor core 1 of the core-shell particle 3, electrons in the valence band can be excited to the conduction band through the intermediate band.

The semiconductor constituting the semiconductor core 1 is preferably a semiconductor containing copper (Cu), at least one of gallium (Ga) and indium (In), and at least one of sulfur (S) and selenium (Se). . For example, a semiconductor represented by the formula CuGa _1-x1 In _x1 S _2-2y1 Se _2y1 (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) is preferable, and in particular, a semiconductor represented by the formula CuCuS _2. More preferably. In this case, the carrier generation efficiency in the semiconductor core 1 due to the incidence of light can be further improved.

  Further, as impurities forming an intermediate band in the semiconductor band gap constituting the semiconductor core 1, carbon (C), silicon (Si), germanium (Ge), titanium (Ti), iron (Fe), and chromium ( It is preferable to use at least one selected from the group consisting of Cr). In this case, since the semiconductor core 1 with few crystal defects can be formed, electrons can be efficiently excited in the semiconductor core 1 by the incidence of excitation light, and carriers in the semiconductor core 1 due to the incidence of light. The generation efficiency can be further improved.

  The average particle size of the semiconductor core 1 is preferably 5 nm or more and 25 nm or less, and more preferably 8 nm or more and 15 nm or less. When the average particle size of the semiconductor core 1 is 5 nm or more and 25 nm or less, particularly when the semiconductor core 1 is 8 nm or more and 15 nm or less, even when an impurity forming an intermediate band is introduced into the semiconductor constituting the semiconductor core 1, the impurity Since it is difficult for abnormalities such as segregation of atoms to occur, it is easy to form the semiconductor core 1 with few crystal defects. For this reason, electrons can be efficiently excited in the semiconductor core 1 due to the incidence of excitation light, carrier generation efficiency in the semiconductor core 1 can be further improved, and generated in the semiconductor core 1 due to the incidence of light. More carriers can flow out into the semiconductor shell 2.

  The average particle diameter of the semiconductor core 1 can be calculated using, for example, a transmission electron microscope. More specifically, the core-shell particles 3 of the present invention are dispersed on a mesh for observation with a transmission electron microscope, and the cross-section of the dispersed core-shell particles 3 is observed at an appropriate magnification. 100 semiconductor cores 1 of the core-shell particles 3 are selected at random, the sum of the cross-sectional areas is obtained, and the value converted to the diameter of a circle having the same area as the area obtained by dividing the sum by 100 is the average of the semiconductor cores 1 The particle size.

  The content of impurities forming the intermediate band in the semiconductor core 1 is preferably 0.1 atomic percent or more and 10 atomic percent or less of the entire semiconductor core 1, and is 0.2 atomic percent or more and 2 atomic percent or less. Is more preferable. When the content of impurities forming the intermediate band in the semiconductor core 1 is 0.1 atomic percent or more and 10 atomic percent or less of the entire semiconductor core 1, particularly when the content is 0.2 atomic percent or more and 2 atomic percent or less. The carrier generation efficiency in the semiconductor core 1 can be further improved by the incidence of light.

<Semiconductor shell>
As the semiconductor shell 2, a semiconductor whose band gap of the semiconductor shell 2 is narrower than that of the semiconductor core 1 is used. Thus, carriers generated in the semiconductor core 1 when light enters the core-shell particles 3 can flow out to the semiconductor shell 2. Since the semiconductor shell 2 is a semiconductor, the semiconductor shell 2 itself generates carriers by the incidence of light.

  The lower end of the conduction band and the upper end of the valence band of the semiconductor shell 2 are preferably positioned closer to the intermediate band than the lower end of the conduction band and the upper end of the valence band of the semiconductor constituting the semiconductor core 1. This makes it easy for carriers generated in the semiconductor core 1 to flow out to the semiconductor shell 2 due to the incidence of light, and effectively prevents carriers from flowing back from the semiconductor shell 2 to the semiconductor core 1. Therefore, more carriers generated in the semiconductor core 1 when light enters can be taken out to the outside through the semiconductor shell 2, so that the photoelectric conversion of the photoelectric conversion element having the photoelectric conversion layer manufactured using the core-shell particles 3 Efficiency can be improved.

The semiconductor shell 2 is preferably a semiconductor containing Cu, at least one of Ga and In, and at least one of S and Se. For example, CuGa _1-x2 In _x2 S is more preferably a semiconductor represented by the formula _{2-2y2 Se 2y2 (0 ≦ x2 ≦} 1,0 ≦ y2 ≦ 1), CuGaS 2, CuInS 2, CuGa 1-x2 The semiconductor is particularly preferably a semiconductor represented by at least one formula selected from the group consisting of In _x2 S ₂ (0 <x2 <1) and CuGaS _2-2y2 Se _2y2 (0 <y2 <1). Since these semiconductors are direct transition semiconductors, their light emission efficiency is high. In particular, when a semiconductor containing copper (Cu), at least one of gallium (Ga) and indium (In), and at least one of sulfur (S) and selenium (Se) is used as the semiconductor core 1. Since the lattice mismatch hardly occurs at the interface between the semiconductor core 1 and the first semiconductor shell 2, carrier recombination at the interface can be remarkably suppressed. Therefore, since more carriers generated in the semiconductor core 1 and the semiconductor shell 2 can be taken out by the incidence of light, the photoelectric conversion element having the photoelectric conversion layer manufactured using the core-shell particles 3 of the present invention. The photoelectric conversion efficiency can be further improved. Since it is not necessary to form an intermediate band in the semiconductor shell 2 unlike the semiconductor core 1, it is not necessary to add an impurity for forming the intermediate band.

The semiconductor constituting the semiconductor core 1 and the semiconductor shell 2 are CuGa _1-x1 In _x1 S _2-2y1 Se _2y1 (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1) and CuGa _1-x2 In _x2 S _{2−, respectively. In} the case of a semiconductor represented by the formula _2y2 Se _2y2 (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1), the content ratio of In and / or Se is higher in the semiconductor shell 2 than in the semiconductor constituting the semiconductor core 1. (Atom%) is preferably high (x2> x1 and / or y2> y1). In this case, the band gap of the semiconductor shell 2 is narrower than the band gap of the semiconductor constituting the semiconductor core 1, and the lower end of the conduction band and the upper end of the valence band of the semiconductor shell 2 are each of the semiconductor constituting the semiconductor core 1. Since it is located on the intermediate band side from the lower end of the conduction band and the upper end of the valence band, the carriers generated in the semiconductor core 1 are likely to flow out to the semiconductor shell 2, and the backflow of carriers from the semiconductor shell 2 to the semiconductor core 1 is further increased. It can be effectively deterred.

<Photoelectric conversion mechanism>
FIG. 2 shows a preferred example of a band gap correlation diagram between the semiconductor core 1 and the semiconductor shell 2 of the core-shell particle 3 of the present invention. Here, the band gap 2 a of the semiconductor shell 2 is narrower than the band gap 1 a of the semiconductor constituting the semiconductor core 1, and the lower end of the conduction band and the upper end of the valence band of the semiconductor shell 2 are each of the semiconductor constituting the semiconductor core 1. It is located closer to the intermediate band 4a than the lower end of the conduction band and the upper end of the valence band.

  As shown in FIG. 2, when light 5 (long wavelength light) having energy smaller than the band gap energy of the semiconductor constituting the semiconductor core 1 is incident on the semiconductor core 1, the energy of the light 5 is absorbed. The electrons in the semiconductor constituting the semiconductor core 1 excited by this release holes first into the valence band of the semiconductor constituting the semiconductor core 1 and are added to the semiconductor constituting the semiconductor core 1. Is excited by the intermediate band 4a formed by the above.

  Next, when light 5 (long wavelength light) having energy smaller than the band gap energy of the semiconductor constituting the semiconductor core 1 is further incident on the semiconductor core 1, electrons located in the intermediate band are emitted from the light 5. Furthermore, energy is absorbed and excited to the conduction band of the semiconductor constituting the semiconductor core 1.

  The electrons excited to the conduction band of the semiconductor constituting the semiconductor core 1 and the holes in the valence band of the semiconductor are respectively in the conduction band and valence band of the low-bandgap semiconductor shell 2 adjacent to the semiconductor core 1. leak. Then, these leaked electrons and holes are taken out through the semiconductor shell 2, and electrons and holes are also generated in the semiconductor shell 2 itself by the incidence of light having a wavelength shorter than that of the light 5. Holes are extracted outside. Thereby, the photoelectric conversion efficiency of the photoelectric conversion element in which the photoelectric conversion layer was formed using the core-shell particle 3 of the present invention can be improved.

<Method for producing core-shell particles>
Hereinafter, an example of the method for producing the core-shell particle 3 of the present invention will be described with reference to the schematic cross-sectional views of FIGS. First, as shown in FIG. 3A, the semiconductor core 1 is manufactured. Here, the semiconductor core 1 can be obtained, for example, as a precipitate that is precipitated by reacting and purifying the semiconductor constituting the semiconductor core 1 and impurity raw material powder in a predetermined liquid phase.

  Next, as shown in FIG. 3B, the surface of the semiconductor core 1 is covered with the semiconductor shell 2. The coating of the surface of the semiconductor core 1 with the semiconductor shell 2 is performed, for example, by adding a liquid obtained by reacting the raw material powder of the semiconductor shell 2 in a predetermined liquid phase to the above-described dispersion of the precipitate of the semiconductor core 1. And can be precipitated. That is, the precipitate becomes particles in which the surface of the semiconductor core 1 is covered with the semiconductor shell 2.

4, the composition of the semiconductor shell 2 when the semiconductor shell 2 is composed of a semiconductor represented by the formula _{CuGa 1-x2 In x2 S 2-2y2} Se 2y2 (0 ≦ x2 ≦ 1,0 ≦ y2 ≦ 1) The change of the lattice constant and band gap energy by the change of is shown. As shown in FIG. 4, by changing the composition of the semiconductor shell 2 to CuGaS ₂ , CuGaSe ₂ , CuInS ₂ and CuInSe ₂ , the band gap energy of the semiconductor shell 2 is changed to CuGaS ₂ (2.43 eV), CuGaSe ₂ ( 1.68 eV), CuInS ₂ (1.53 eV), and CuInSe ₂ (1.04 eV) can be sequentially reduced.

Note that when the hatched portion in FIG. 4, the semiconductor shell 2 is composed of a semiconductor represented by the formula _{CuGa 1-x2 In x2 S 2-2y2} Se 2y2 (0 ≦ x2 ≦ 1,0 ≦ y2 ≦ 1) The range of the lattice constant and the band gap energy that the semiconductor shell 2 can take is shown.

<Photoelectric conversion layer and photoelectric conversion element>
In FIG. 5, typical sectional drawing of an example of the photoelectric conversion element of this invention is shown. As shown in FIG. 5, an example of the photoelectric conversion element of the present invention includes a photoelectric conversion layer 15, a buffer layer 13 provided on the light receiving surface side of the photoelectric conversion layer 15, and a light receiving surface side of the buffer layer 13. The transparent electrode layer 14 provided on the front surface and the back side electrode 11 provided on the back side of the photoelectric conversion layer 15 are provided.

  The photoelectric conversion layer 15 has a structure in which a plurality of semiconductor cores 1 are embedded in the semiconductor shell 2. Here, the photoelectric conversion layer 15 is prepared, for example, by preparing a dispersion in which the core-shell particles 3 manufactured as described above are dispersed in a predetermined liquid, and applying the dispersion on the surface of the back-side electrode 11. It can be formed by bonding the semiconductor shells 2 of the core-shell particles 3 by drying and then sintering.

  The thickness of the photoelectric conversion layer 15 is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 4 μm or less. When the thickness of the photoelectric conversion layer 15 is 0.5 μm or more and 10 μm or less, particularly when the thickness is 1 μm or more and 4 μm or less, carriers that have flowed from the semiconductor core 1 to the semiconductor shell 2 are efficiently collected by the electrodes. Therefore, the photoelectric conversion efficiency of the photoelectric conversion element can be improved.

  The buffer layer 13 is formed by, for example, laminating zinc sulfide (ZnS or ZnS (O, OH)) on the surface of the photoelectric conversion layer 15 by a sputtering method or a CBD (Chemical Bath Deposition) method. Can do. The transparent electrode layer 14 can be formed, for example, by laminating zinc oxide (ZnO) on the surface of the buffer layer 13 by a sputtering method. In addition, as the back surface side electrode 11, metals, such as molybdenum (Mo), can be used, for example.

  When light is incident on the photoelectric conversion layer 15 from the light receiving surface side of the photoelectric conversion element shown in FIG. 5, long wavelength light of the incident light is used for generation of carriers through the intermediate band in the semiconductor core 1. Of the incident light, light having a short wavelength is used to generate carriers in the semiconductor shell 2 by entering the semiconductor shell 2. Then, carriers generated in the semiconductor core 1 due to incidence of long wavelength light are taken out from the back surface side electrode 11 and the transparent electrode layer 14 through the semiconductor shell 2. Further, the carriers generated in the semiconductor shell 2 by the incidence of short-wavelength light are also taken out from the back surface side electrode 11 and the transparent electrode layer 14. Thereby, when the photoelectric conversion layer is formed using the core-shell particles 3 of the present invention, the carrier generation efficiency through the intermediate band in the semiconductor core 1 is high, and the carriers generated in the semiconductor core 1 are effectively removed. Since it can take out in the direction of the semiconductor shell 2, the carrier recombination in the semiconductor core 1 which has an intermediate | middle band can be suppressed, and the photoelectric conversion efficiency of a photoelectric conversion element can be made high.

  FIG. 6 shows the relationship between the band gap of the photoelectric conversion layer 15 when the band gap of the semiconductor shell 2 is narrower than the band gap of the semiconductor core 1 and the energy of carriers moving in the photoelectric conversion layer 15. FIG. 7 shows the relationship between the band gap of the photoelectric conversion layer 15 when the band gap of the semiconductor shell 2 and the band gap of the semiconductor core 1 are the same, and the energy of carriers moving through the photoelectric conversion layer 15. Show the relationship. 6 and 7, the solid line indicates the band gap where the semiconductor core 1 is present, the broken line indicates the band gap where the semiconductor core 1 is not present, and the one-dot chain line indicates the carrier energy.

  As shown in FIG. 6, in the photoelectric conversion layer 15 when the band gap of the semiconductor shell 2 is narrower than the band gap of the semiconductor core 1, the portion where the band gap energy due to the semiconductor core 1 is large is localized. Therefore, carriers moving through the photoelectric conversion layer 15 are not easily captured by the semiconductor core 1. On the other hand, as shown in FIG. 7, in the photoelectric conversion layer 15 when the band gap of the semiconductor shell 2 and the band gap of the semiconductor core 1 are the same width, the band gap energy caused by the semiconductor core 1 is large. Since the part which has become does not exist locally, the carrier which moves in the photoelectric converting layer 15 is easy to be capture | acquired by the semiconductor core 1 compared with the case where it shows in FIG.

  Accordingly, by making the band gap of the semiconductor shell 2 narrower than the band gap of the semiconductor core 1, not only can the carriers generated in the semiconductor core 1 be transported smoothly to the semiconductor shell 2, but also the photoelectric conversion element from the semiconductor shell 2 It is possible to carry out transportation smoothly until it is taken out.

  Hereinafter, specific examples of the core-shell particles, the photoelectric conversion layer, and the photoelectric conversion element of the present invention will be described in the Examples section, but it is needless to say that the present invention is not limited to the configurations of the Examples.

<Fabrication of semiconductor core>
First, as shown in the schematic side view of FIG. 8, in an argon atmosphere, 0.5 mmol (mmol) of CuCl, 0.47 mmol of GaCl ₃ , 1 mmol of S, 0.03 mol of bis (2 , 4-pentanedionato) tin (IV) dichloride and 15 ml of oleylamine with a concentration of 70% were added to prepare a solution 20 for preparing a semiconductor core.

  Next, the flask 26 was installed in the mantle heater 24 and connected to a Schlenk line (not shown) via the cooler 21. At this time, air was prevented from entering the flask 26.

  Next, evacuation of the flask 26 and replacement with a nitrogen atmosphere were alternately repeated three times using a vacuum pump and a nitrogen gas supply pipe connected to the Schlenk line.

  Next, while stirring the solution 20 with the magnetic stirrer 23, while watching the thermometer 22, the temperature of the solution 20 is raised using the mantle heater 24 until it reaches 130 ° C., and kept in that state for 1 hour. did.

  Next, using the mantle heater 24, the temperature of the solution 20 was slowly raised to 265 ° C. at a heating rate of about 2.5 ° C./min, and kept in that state for 1.5 hours. Thereby, the semiconductor core grew in the solution 20. Thereafter, the flask 26 was immersed in a water bath (not shown) and rapidly cooled.

Next, purification was performed by adding 1 ml of oleylamine, toluene and ethanol in this order to the flask 26, centrifuging, and discarding the supernatant. This purification was repeated three times. Thus, a Sn as an impurity for forming the intermediate band to the band gap of the semiconductor and the semiconductor of the formula of CuGaS ₂ CuGaS _2: semiconductor core of the formula of Sn was obtained as a precipitate. When the average particle size of the semiconductor core thus obtained was calculated using a transmission electron microscope, it was confirmed to be 11 nm.

<Production of semiconductor shell>
First, a solution for producing a semiconductor shell was prepared by dissolving 0.5 mmol of CuCl, 0.5 mmol of GaCl ₃ and 1 mmol of S in 15 ml of oleylamine having a concentration of 70% in an argon atmosphere.

  Next, oleylamine was added to the semiconductor core obtained as a precipitate as described above to prepare dispersion A in which the semiconductor core was dispersed in oleylamine, and the dispersion A was transferred to a syringe.

  Next, Dispersion A was placed in a flask, and the flask was placed on a mantle heater and connected to a Schlenk line. Next, using a vacuum pump connected to the Schlenk line and a nitrogen gas supply pipe, evacuation of the flask and replacement with a nitrogen atmosphere were alternately repeated three times.

  Next, the solution for producing the semiconductor shell produced as described above is dropped into the flask containing the dispersion A heated to 265 ° C. by a mantle heater, and then the temperature of the solution in the flask is set to room temperature ( 25 ° C).

Next, 1 ml of oleylamine, toluene and ethanol were added to the flask in this order, followed by centrifugation, and purification was performed by discarding the supernatant. This purification was repeated three times. Thus, CuGaS _2: particle structure semiconductor shell is formed of the formula in CuGaS ₂ on the surface of the semiconductor core of the formula of _{Sn (CuGaS 2: Sn / CuGaS} 2) was obtained as a precipitate.

In addition, (i) substitution of at least part of GaCl ₃ with InCl ₃ or the like, (ii) substitution of at least part of S with Se, and (iii) any of both (i) and (ii) above By performing one of these, the band gap of the semiconductor shell can be made narrower than the band gap of the semiconductor core. That is, when a part of Ga in CuGaS ₂ is replaced with In, the lower end of the conduction band of the semiconductor shell can be shifted to the intermediate band side of the semiconductor core, and a part of S in CuGaS ₂ is replaced with Se. In this case, the upper end of the valence band of the semiconductor shell can be shifted to the intermediate band side of the semiconductor core. As a result, carriers generated in the semiconductor core due to the incidence of light can smoothly flow out to the semiconductor shell, and carriers do not easily flow back from the semiconductor shell to the semiconductor core.

<Preparation of semiconductor fine particles>
First, as shown in the schematic side view of FIG. 9, in an argon atmosphere, a flask 26 was charged with 0.5 mmol (mmol) CuCl, 0.5 mmol GaCl ₃ , 1 mmol S, and oleylamine 15 ml with a concentration of 70%. Then, a solution 30 for producing semiconductor fine particles was produced.

  Next, the flask 26 was installed in the mantle heater 24 and connected to a Schlenk line (not shown) via the cooler 21. At this time, air was prevented from entering the flask 26.

  Next, evacuation of the flask 26 and replacement with a nitrogen atmosphere were alternately repeated three times using a vacuum pump and a nitrogen gas supply pipe connected to the Schlenk line.

  Next, while stirring the solution 30 with the magnetic stirrer 23, while watching the thermometer 22, the temperature of the solution 30 is increased using the mantle heater 24 until it reaches 130 ° C., and this state is maintained for 1 hour. did.

  Next, using the mantle heater 24, the temperature of the solution 30 was slowly raised to 265 ° C. at a heating rate of about 2.5 ° C./min, and kept in that state for 1.5 hours. Thereby, semiconductor fine particles grew in the solution 20. Thereafter, the flask 26 was immersed in a water bath (not shown) and rapidly cooled.

Next, purification was performed by adding 1 ml of oleylamine, toluene and ethanol in this order to the flask 26, centrifuging, and discarding the supernatant. This purification was repeated three times. Thereby, the semiconductor fine particle represented by the formula of CuGaS ₂ was obtained as a precipitate.

<Production of photoelectric conversion element>
Hereinafter, with reference to the schematic cross-sectional views of FIGS. 10A to 10C, a method for manufacturing the photoelectric conversion element of the example will be described. First, as shown in FIG. 10A, a Mo film 42 is laminated on a glass substrate 41 by, for example, sputtering or vapor deposition.

  Next, the first semiconductor layer precursor 43 is formed by applying the dispersion liquid C in which the semiconductor fine particles 51 produced as described above are dispersed in toluene on the Mo film 42 and drying it.

  Next, the dispersion B, in which the semiconductor core 1 covered with the semiconductor shell 2 manufactured as described above is dispersed in toluene, is applied onto the first semiconductor layer precursor 43 and dried to thereby form the second semiconductor. A layer precursor 44 is formed. Here, the second semiconductor layer precursor 44 may be formed using a mixed liquid of the dispersion B and the dispersion C. In this case, by making the particle size of the semiconductor fine particles 51 in the dispersion C smaller than the particle size of the core-shell particles 3 in the dispersion B, the photoelectric conversion layer after the second semiconductor layer precursor 44 is sintered. 15 can be suppressed.

  Next, the dispersion liquid C produced as described above is applied onto the second semiconductor layer precursor 44 and dried to form the third semiconductor layer precursor 45.

Next, by sintering the first semiconductor layer precursor 43, the second semiconductor layer precursor 44, and the third semiconductor layer precursor 45 in a hydrogen sulfide (H ₂ S) or selenium (Se) atmosphere, The semiconductor fine particles 51 or the core-shell particles 3 in the precursor can be bonded to each other. Thus, as shown in FIG. 10B, the first semiconductor layer 43a formed by sintering the semiconductor fine particles 51 in the first semiconductor layer precursor 43 on the Mo film 42, and the second semiconductor layer precursor. The photoelectric conversion layer 15 formed by sintering the core-shell particles 3 in 44 and the third semiconductor layer 45a formed by sintering the semiconductor fine particles 51 in the third semiconductor layer precursor 45 are laminated in this order. Is done. The photoelectric conversion layer 15 has a structure in which a plurality of semiconductor cores 1 are embedded in the semiconductor shell 2.

  Next, as shown in FIG. 10C, the buffer layer 46 is formed on the third semiconductor layer 45a. Here, the band gap energy of the buffer layer 46 is preferably larger than the band gap energy of the third semiconductor layer 45a. The lower end of the conduction band of the buffer layer 46 is located on the higher energy side than the lower end of the conduction band of the third semiconductor layer 45a, and the upper end of the valence band of the buffer layer 46 is the valence of the third semiconductor layer 45a. It is preferable that it is located on the lower energy side of the upper end of the electron band or coincides with the upper end of the valence band of the third semiconductor layer 45a. In these cases, the open circuit voltage of the photoelectric conversion element can be increased.

  As the buffer layer 46, a ZnS film can be laminated by, for example, the CBD method. The ZnS film may contain oxygen (O) and / or hydroxyl group (OH).

  Next, the high resistance layer 47 and the transparent conductive layer 48 are laminated on the buffer layer 46 in this order. Here, as the high resistance layer 47, a high resistance ZnO layer can be formed by sputtering, for example. Further, as the transparent conductive layer 48, an ITO (Indium Tin Oxide) layer, a ZnO layer, or a layer in which ZnO is doped with impurities such as aluminum (Al) and / or boron (B) is formed by, for example, sputtering. Can do.

  Thereafter, a silver paste or an aluminum paste is screen-printed on the surface of the transparent conductive layer 48 and then fired to form the light-receiving surface side electrode 49. Thereby, the photoelectric conversion element of an Example is produced.

<Summary>
The present invention includes a semiconductor core and a semiconductor shell provided on the surface of the semiconductor core, and the semiconductor core is a core-shell particle including a semiconductor and an impurity that forms an intermediate band in the band gap of the semiconductor. With such a configuration, carriers generated using electronic excitation via an intermediate band due to incidence of long-wavelength light on the semiconductor core and carriers generated in the semiconductor shell due to incidence of short-wavelength light Thus, the photoelectric conversion efficiency of the photoelectric conversion element having the photoelectric conversion layer produced using the core-shell particles of the present invention can be improved.

  Here, in the core-shell particles of the present invention, the lower end of the conduction band and the upper end of the valence band of the first semiconductor shell are located closer to the intermediate band side than the lower end of the conduction band and the upper end of the valence band of the semiconductor core, respectively. Is preferred. By adopting such a configuration, it becomes easier for carriers generated in the semiconductor core to flow out to the semiconductor shell due to the incidence of light, and effectively prevent the carriers from flowing back from the semiconductor shell to the semiconductor core. it can. Therefore, the photoelectric conversion efficiency of a photoelectric conversion element having a photoelectric conversion layer produced using the core-shell particles of the present invention can be improved.

  In the core-shell particle of the present invention, the semiconductor core semiconductor includes copper, at least one of gallium and indium, and at least one of sulfur and selenium, and the semiconductor core impurity includes carbon, silicon, germanium, titanium, It is preferable to include at least one selected from the group consisting of iron and chromium. With such a configuration, the carrier generation efficiency in the semiconductor core due to the incidence of light can be further improved.

  In the core-shell particle of the present invention, the semiconductor shell preferably contains copper, at least one of gallium and indium, and at least one of sulfur and selenium. With such a configuration, the interface state density at the interface between the semiconductor core and the semiconductor shell is reduced to suppress carrier recombination, and the efficiency of carrier generation in the semiconductor core due to light incidence and the semiconductor core Carrier extraction efficiency to the semiconductor shell can be improved.

  In the core-shell particles of the present invention, the semiconductor shell preferably has a higher content ratio of indium or selenium than the semiconductor core. By adopting such a configuration, the band gap of the semiconductor shell is narrower than the band gap of the semiconductor constituting the semiconductor core, and the lower end of the conduction band and the upper end of the valence band of the semiconductor shell are each of the semiconductor constituting the semiconductor core. Because it is located on the middle band side from the lower end of the conduction band and the upper end of the valence band, carriers generated in the semiconductor core are likely to flow out to the semiconductor shell, and the backflow of carriers from the semiconductor shell to the semiconductor core is more effectively suppressed. can do.

  The present invention also includes a semiconductor core and a semiconductor shell provided so as to surround the semiconductor core, and the semiconductor core includes a semiconductor and an impurity that forms an intermediate band in the semiconductor band gap. Is a layer. With such a configuration, carriers generated using electronic excitation via an intermediate band due to incidence of long-wavelength light on the semiconductor core and carriers generated in the semiconductor shell due to incidence of short-wavelength light Thus, the photoelectric conversion efficiency of the photoelectric conversion element having the photoelectric conversion layer of the present invention can be improved.

  In the photoelectric conversion layer of the present invention, the band gap of the semiconductor shell is preferably narrower than the band gap of the semiconductor core. With such a configuration, not only can the carrier generated in the semiconductor core be smoothly transported to the semiconductor shell, but also the transport from the semiconductor shell to the outside of the photoelectric conversion element can be performed smoothly.

  In the photoelectric conversion layer of the present invention, it is preferable that the lower end of the conduction band and the upper end of the valence band of the semiconductor shell are positioned closer to the intermediate band than the lower end of the conduction band and the upper end of the valence band of the semiconductor core, respectively. By adopting such a configuration, it becomes easier for carriers generated in the semiconductor core to flow out to the semiconductor shell due to the incidence of light, and effectively prevent the carriers from flowing back from the semiconductor shell to the semiconductor core. it can. Therefore, the photoelectric conversion efficiency of the photoelectric conversion element having the photoelectric conversion layer of the present invention can be improved.

  Furthermore, this invention is a photoelectric conversion element containing said photoelectric conversion layer and the electrode provided on the surface of the photoelectric conversion layer. With such a configuration, carriers generated using electronic excitation via an intermediate band due to incidence of long-wavelength light on the semiconductor core and carriers generated in the semiconductor shell due to incidence of short-wavelength light Can be taken out from the electrode through the semiconductor shell, so that the photoelectric conversion efficiency of the photoelectric conversion element can be improved.

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICABILITY The present invention can be used for core-shell particles, photoelectric conversion layers, and photoelectric conversion elements, and is particularly preferably used for core-shell particles for solar cells, photoelectric conversion layers for solar cells, and solar cells using these. be able to.

  DESCRIPTION OF SYMBOLS 1 Semiconductor core, 1a The band gap of the semiconductor which comprises a semiconductor core, 2 Semiconductor shell, 2a The band gap of a semiconductor shell, 3 Core shell particle | grains, 4a Intermediate band, 5 Light, 11 Back side electrode, 13 Buffer layer, 14 Transparent electrode layer , 15 photoelectric conversion layer, 20, 30 solution, 21 cooler, 22 thermometer, 23 magnetic stirrer, 24 mantle heater, 26 flask, 41 glass substrate, 42 Mo film, 43 first semiconductor layer precursor, 43a first Semiconductor layer, 44 Second semiconductor layer precursor, 45 Third semiconductor layer precursor, 45a Third semiconductor layer, 46 Buffer layer, 47 High resistance layer, 48 Transparent conductive layer, 49 Light receiving surface side electrode, 51 Semiconductor fine particles.

Claims (13)

A semiconductor core;
A semiconductor shell provided on the surface of the semiconductor core,
The semiconductor core is seen containing a Cu, at least one of Ga and In, and the first semiconductor and at least one of S and Se, an impurity for forming the intermediate band in the band gap of the first semiconductor,
The semiconductor shell, Cu and, at least one of Ga and In, including a second semiconductor containing at least one of S and Se, core-shell particles. 2. The core-shell particle according to claim 1, wherein a band gap of the second semiconductor is narrower than a band gap of the first semiconductor. 3. The core-shell particle according to claim 1, wherein a lower end of the conduction band of the second semiconductor is located closer to the intermediate band than a lower end of the conduction band of the first semiconductor. The core-shell particle according to any one of claims 1 to 3, wherein an upper end of the valence band of the second semiconductor is located closer to the intermediate band than an upper end of the valence band of the first semiconductor. The core-shell particle according to any one of claims 1 to 4, wherein a concentration of the impurity is 0.1 atomic percent or more and 10 atomic percent or less. The core-shell particle according to any one of claims 1 to 5, wherein the impurity includes at least one selected from the group consisting of C, Si, Ge, Ti, Fe, and Cr. The core-shell particle according to any one of claims 1 to 6, wherein the impurity includes Sn. The core-shell particle according to any one of claims 1 to 7, wherein the first semiconductor is a direct transition semiconductor. 9. The method according to claim 1, wherein (Ga atom% / In atom%) contained in the first semiconductor is larger than (Ga atom% / In atom%) contained in the second semiconductor. The core-shell particle described in 1. 10. The semiconductor device according to claim 1, wherein (S atom% / Se atom%) contained in the first semiconductor is larger than (S atom% / Se atom%) contained in the second semiconductor. The core-shell particle described in 1. 11. The core-shell particle according to claim 1, wherein the second semiconductor has a higher content ratio of In or Se than the first semiconductor. The photoelectric converting layer containing the core-shell particle of any one of Claims 1-11. The photoelectric conversion layer according to claim 12,
A photoelectric conversion element comprising an electrode electrically connected to the photoelectric conversion layer.

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