Member for photoelectric conversion element

The present invention relates to a member for a photoelectric conversion element, and more particularly to a member for a photoelectric conversion element capable of improving the photoelectric conversion efficiency.

Various methods have been proposed for photoelectric conversion elements for photodetectors, solar cells, etc., particularly for photoelectric conversion elements for solar cells, in order to use sunlight more inexpensively and efficiently. For example, Patent Documents 1 to 3 disclose photoelectric conversion elements using localized surface plasmon resonance. According to the technology, a plurality of metal nanoparticles are arranged on one surface side of a photoelectric conversion layer (semiconductor), and the shape of the plurality of metal nanoparticles is controlled to absorb desired light from white light to generate electricity. Can be made to.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2009-71147</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2012-38541</text></patcit><patcit num="3"><text>International Publication No. 2011/27830</text></patcit></p>

<p num="0004"> However, the photoelectric conversion element is required to further improve the photoelectric conversion efficiency.</p><p num="0005"> The present invention has been made in order to meet the above-mentioned requirements, and an object of the present invention is to provide a member for a photoelectric conversion element capable of improving the photoelectric conversion efficiency.</p>

Means for Solving Problems and Effects of Invention

0006In order to achieve this object, according to the member for a photoelectric conversion element according to claim 1, the semiconductor portion is formed in a plate shape or a film shape. The incident light is absorbed by the metal body and converted into electrical energy by the plasmon resonance of a plurality of fine metal bodies arranged on one surface side of the semiconductor portion. Further, by introducing Cr as an impurity element into the semiconductor portion, the mechanism is under study, but there is an effect that the photoelectric conversion efficiency can be improved.

0007According to the member for a photoelectric conversion element according to claim 2, the semiconductor portion has a maximum value of the concentration distribution of the introduced impurity element at a depth position of 20 nm or more and 150 nm or less from the one surface side on which the metal body is arranged. doing. As a result, in addition to the effect of claim 1, there is an effect that the impurity concentration on one side of the semiconductor portion on which the metal body is arranged can be increased, and the photoelectric conversion efficiency can be improved by the synergistic effect with the metal body.

0008According to the member for a photoelectric conversion element according to claim 3, since the impurity element is introduced with the lattice defect of the semiconductor portion by ion implantation, the amount and depth of the impurity element introduced into the semiconductor portion can be accurately determined. Can be controlled. Further, since the semiconductor portion is annealed, the concentration of lattice defects generated by ion implantation can be reduced, and the introduced impurity elements can be activated. As a result, in addition to the effect of claim 1 or 2, there is an effect that the photoelectric conversion efficiency can be improved with good reproducibility.

<figref num="1">(A) is a front view of a member for a photoelectric conversion element according to an embodiment of the present invention, and (b) is a cross-sectional view of a member for a photoelectric conversion element in line Ib-Ib of the arrow Ib-Ib of FIG. 1 (a).</figref><figref num="2">This is the calculation result of the concentration distribution of impurity elements in the depth direction.</figref><figref num="3">It is the concentration distribution in the depth direction of the impurity element measured by the secondary ion mass spectrometry.</figref><figref num="4">It is a schematic diagram which shows the measurement circuit of the photoelectric conversion efficiency of the member for a photoelectric conversion element.</figref><figref num="5">It is a figure which shows the relationship between the impurity element introduced into the semiconductor part, and the spectral sensitivity characteristic (IPCE).</figref>

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1A is a front view of the photoelectric conversion element member 1 according to the embodiment of the present invention, and FIG. 1B is a photoelectric conversion element member 1 in the arrow Ib-Ib line of FIG. 1A. It is a cross-sectional view of. As shown in FIGS. 1A and 1B, the photoelectric conversion element member 1 is two-dimensionally arranged on one surface of a semiconductor portion 2 formed of a metal oxide semiconductor in a plate shape and the semiconductor portion 2. It is mainly composed of a plurality of fine metal bodies 3 formed therein.

The semiconductor unit 2 is a member for photoelectric conversion when irradiated with light such as sunlight. In this embodiment, TiO_２The semiconductor portion 2 is formed by the single crystal substrate of. However, the present invention is not limited to this, and ZnO and SnO are not limited to this._２, ZrO_２, Ta_２O_５, Nb_２O_５, SrTIO_３, BaTIO_３, CaTIO_３, KTaO_３, WO_３Other metal oxide semiconductors such as, composite semiconductors of these metal oxides, TiO_２Various metal oxide semiconductors such as semiconductors of the composite system with and can be used.

Further, the semiconductor portion 2 is not limited to one formed of a single crystal substrate, for example, one formed into a plate shape by sintering, or one formed on the surface of a substrate made of glass or the like and sintered to form a film. It also includes those formed in. It is also possible to form a film on the surface of a flexible substrate such as a film for production. When the semiconductor portion 2 is formed by sintering, it can be formed on a substrate by a wet process such as spin coating, doctor blade, or screen printing. Dry processes such as sputtering, CVD, vapor deposition, electron layer deposition, and pulse laser deposition can be adopted, and processes such as electrodeposition method, hydrothermal treatment method, and sol-gel method can also be adopted.

Further, the metal oxide semiconductor (semiconductor portion 2) can have a hollow structure such as a nanotube or a porous body structure. Since the surface area of the semiconductor portion 2 can be increased by forming the metal oxide semiconductor into a hollow structure such as a nanotube or a porous body structure, the photoelectric conversion efficiency can be improved.

The semiconductor portion 2 can be made to transmit visible light by being formed of a single crystal substrate. Further, visible light can be transmitted by forming a film on the surface of a substrate such as a glass substrate or a film. The semiconductor portion 2 is not limited to the metal oxide semiconductor, and it is possible to use a polycrystalline or single crystal silicon-based semiconductor, a compound semiconductor, an organic semiconductor, or the like. Further, the present invention is not limited to n-type semiconductors, and it is naturally possible to adopt p-type semiconductors such as GaP and NiO. When the photoelectric conversion element member 1 is applied to a solar cell, when a p-type semiconductor is used for the semiconductor part 2, the semiconductor part 2 functions as a cathode, and when an n-type semiconductor is used for the semiconductor part 2, the semiconductor part 2 functions as an anode. To do.

The metal body 3 is composed of a plurality of metal nanoparticles and is arranged on one side of the semiconductor portion 2. The metal body 3 is formed by a method of heat-treating a metal thin film formed on the surface of the semiconductor portion 2. By forming the metal body 3 by this method, the metal body 3 having a substantially spherical shape or a spheroidal shape can be easily formed.

Of course, it is possible to form the metal body 3 by using the semiconductor microfabrication technique. By forming the metal body 3 using the semiconductor microfabrication technique, the metal body 3 can be formed into a controlled shape such as a substantially spherical shape, a spheroidal shape, a weight shape, or a rod shape. For example, when gold (Au) nanorods having a short side of about 100 nm, a long side of about 200 nm, and a height of about 40 nm are arranged on the surface of the semiconductor portion 2 at intervals of about 100 nm, infrared rays having a wavelength of 800 nm or more are absorbed (for electrical energy). (Conversion) becomes possible. It is speculated that the absorption of infrared rays by the metal body 3 is due to localized surface plasmon resonance.

According to the localized surface plasmon resonance, when the wavelength of the irradiated wavelength of light satisfies the resonance condition, the free electrons on the surface of the metal body 3 move collectively, and the energy of the light is used as electromagnetic energy. store. The stored strong electromagnetic field excites the electrons in the metal, which induces electron injection into the semiconductor and charge separation based on it, resulting in conversion into electrical energy. Since the wavelength showing localized surface plasmon resonance depends on the shape and size of the metal body 3, for example, by appropriately setting these, light in an extremely wide wavelength range of 450 to 1300 nm can be converted into electrical energy. Is possible.

The material of the metal body 3 is not limited to Au, and it is naturally possible to use other metals such as Ag, Cu, and Al that exhibit localized surface plasmon resonance. Further, the shape, size, pitch, etc. of the metal nanostructure are not limited, and these can be appropriately set according to the wavelength of light.

Impurity elements are introduced into the semiconductor portion 2 in order to improve the photoelectric conversion efficiency before the metal body 3 is formed on one surface side. As the impurity element, an element other than the element doped in the semiconductor portion 2 as a donor or acceptor, particularly Cr, is adopted. In the present embodiment, the impurity element (Cr) is introduced by ion implantation from the one side on which the metal body 3 is arranged. When the impurity element is introduced into the semiconductor portion 2 by ion implantation, the amount and depth of the impurity element in the semiconductor portion 2 can be accurately controlled. Thereby, the reproducibility of the introduction effect of the impurity element can be improved.

In the case of ion implantation, once the impurity element and the material of the semiconductor portion 2 are determined, the implantation conditions are determined by the implantation energy and the dose amount. Although it depends on the material of the semiconductor part 2, the injection energy is preferably 80 keV or more and 400 keV or less, and the dose amount is 5 × 10.^１１Pieces / cm^２Above 5x10^１４Pieces / cm^２The following are suitable.

When the injection energy is smaller than 80 keV, the injection depth of the impurity element (Cr) becomes shallow, and the interaction between the introduced impurity element and the semiconductor portion 2 decreases, so that it becomes difficult to improve the photoelectric conversion efficiency. On the other hand, when the implantation energy is larger than 400 keV, the concentration of lattice defects in the semiconductor portion 2 formed by ion implantation increases, and the man-hours required for annealing to restore the crystal lattice of the semiconductor portion 2 increase. In addition, since the ion implantation device becomes large and the equipment cost becomes high, it becomes unreasonable in terms of industry.

Also, the dose amount is 5 x 10^１１Pieces / cm^２When the amount is smaller, the photoelectric conversion efficiency tends to vary. On the other hand, the dose amount is 5 × 10.^１４Pieces / cm^２If the number is larger, the processing man-hours will be larger and the industrial rationality will be lost. Further, since the structure of the semiconductor portion 2 is destroyed, it is expected that the photoelectric conversion efficiency will rather decrease.

The semiconductor portion 2 into which the impurity element (Cr) has been introduced by ion implantation has a concentration distribution of the impurity element formed so as to have a maximum value at a depth position of 20 nm or more and 150 nm or less from the one-sided side where the metal body 3 is arranged. It is desirable to be done. This is because the impurity concentration on one side of the semiconductor portion 2 on which the metal body 3 is arranged can be increased, and the photoelectric conversion efficiency can be efficiently improved by the synergistic effect with the metal body 3.

The mass concentration of the impurity element (Cr) at the depth position showing the maximum value of the concentration distribution of the impurity element depends on the type of the semiconductor portion 2, but is 0.0001 wt% or more and 0.1 wt% or less, preferably 0. It is desirable that it is 001 wt% or more and 0.01 wt% or less. As the mass concentration becomes smaller than 0.001 wt%, the photoelectric conversion efficiency tends to vary easily. As the mass concentration becomes larger than 0.01 wt%, the structure of the semiconductor portion 2 is destroyed, and the photoelectric conversion efficiency tends to decrease. In particular, when the mass concentration is smaller than 0.0001 wt% or larger than 0.1 wt%, these tendencies become remarkable.

The impurity element (Cr) can be injected into the semiconductor portion 2 in multiple stages by a plurality of different injection energies of 80 keV or more and 400 keV or less. Since the injection depth of the impurity element injected into the semiconductor portion 2 is determined by the injection energy, the injection region having a wide distribution in the depth direction is formed by injecting in multiple stages by changing the injection energy. By injecting ions of 80 keV or more and 400 keV or less in multiple stages, impurity elements are widely dispersed in a depth range of 10 to 150 nm from the surface (one surface) of the semiconductor portion 2 on which the metal body 3 is arranged. As a result, the impurity concentration on one side of the semiconductor portion 2 can be increased, and the photoelectric conversion efficiency can be improved by the synergistic effect of the metal body 3 and the impurity element. However, since the proportion of impurity elements that do not contribute to the improvement of photoelectric conversion efficiency increases, the profitability decreases.

It is also possible to adopt a method in which the synthesis of the film-like semiconductor portion 2 on the surface of the substrate (not shown) and the ion implantation of the impurity element are alternately repeated a plurality of times. In the case of this method, the injection depth is not limited, and an impurity element injection phase having an arbitrary thickness can be formed.

After ion implantation, the semiconductor portion 2 is annealed. Annealing is performed to fix the implanted impurity elements in the crystal lattice and activate them by reducing the lattice defects of the semiconductor portion 2 generated by the ion implantation. Annealing is performed by a method of heating the semiconductor portion 2 in the furnace, a method of irradiating the semiconductor portion 2 with a laser beam, or the like. The annealing temperature is set to 400 to 800 ° C., although it depends on the material of the semiconductor portion 2. Annealing can be performed in various atmospheres such as in vacuum, in the atmosphere, and in an inert gas.

Annealing is usually performed after ion implantation, but ion implantation and annealing can be performed at the same time. When ion implantation and annealing are performed at the same time, ion implantation is performed while maintaining the semiconductor portion 2 at a predetermined annealing temperature. It is also possible to perform ion implantation and annealing at the same time by irradiating the site where the ions are implanted with a laser beam at the same time as the ion implantation.

In the present embodiment, the case where the impurity element (Cr) is intentionally introduced into the semiconductor portion 2 by ion implantation has been described, but the present invention is not necessarily limited to this, and the impurity element (Cr) is introduced by another method. Of course, it is possible to intentionally introduce it into the semiconductor unit 2. Other methods include, for example, a thermal diffusion method (a method in which a gas containing an impurity element is heated to a high temperature and diffused by spraying it onto the semiconductor portion 2), a method using plasma or a laser, and an impurity element as a starting material constituting the semiconductor portion 2. Examples thereof include a method of mixing and preparing the semiconductor portion 2 by a liquid phase method such as a gas phase method or a solgel method.

As described above, by intentionally introducing an impurity element into the semiconductor portion 2, it is possible to make it less susceptible to the influence of unavoidable impurities and the like, and the photoelectric conversion efficiency can be stably improved. Further, according to the vapor phase method or the liquid phase method, the semiconductor portion 2 can be prepared while controlling the amount (concentration) of the impurity element. In particular, according to the vapor phase method, the impurity element and the element constituting the semiconductor portion 2 can be laminated to prepare the semiconductor portion 2, so that the concentration of the impurity element at the depth position from the surface of the semiconductor portion 2 Control is also possible.

<p> Hereinafter, the present invention will be specifically described with reference to Examples. The present invention is not limited to these examples.</p><p> TiO with a thickness of 0.5 mm as a semiconductor part_２A single crystal (n-type semiconductor) was used. Using an ion implanter, ion implantation was performed on one side of each semiconductor portion at room temperature under the conditions shown in Table 1, and an impurity element (Cr, Fe or Au) was introduced into each semiconductor portion.</p><p><tables num="1"></tables> The concentration distribution of the ion-implanted impurity elements in the depth direction under this condition was calculated by a calculation method called Stopping and Range of Ions in Matter (SRIM). FIG. 2 shows the calculation result of the concentration distribution of impurity elements in the depth direction by SRIMM. As shown in FIG. 2, Cr, Fe and Au all have a maximum concentration distribution (peak concentration) at a depth position (peak depth) of about 60 nm from the surface of the semiconductor portion. As shown in Table 1, since the dose amount of Fe is about 1/10 of the dose amount of other impurity elements (Cr, Au), the peak concentration of Fe at a depth of about 60 nm shown in FIG. 2 is Cr. , Au is about 1/10 of the peak concentration.</p><p> After introducing an impurity element into the semiconductor portion by ion implantation, the semiconductor portion was heated to 450 ° C. in nitrogen gas for annealing. FIG. 3 shows the concentration distribution of impurity elements (Cr, Fe) in the depth direction measured by secondary ion mass spectrometry (SIMS) in the semiconductor portion after annealing.</p><p> As shown in FIG. 3, the calculation results show that Cr and Fe have peak concentrations at a depth of about 60 nm, and that the peak concentration of Fe is about 1/10 of the peak concentration of Cr (see FIG. 2). Consistent with. Although the concentration distribution in the depth direction of Au has not been measured, the peak depth of Au and the calculation result of the peak concentration of Cr and Fe (Fig. 2) are almost the same as the actual measurement result (Fig. 3). And the peak concentration is also estimated to be almost the same as the calculation result.</p><p> In the concentration distribution of Fe shown in FIG. 3, the measured concentration value in the deep part of about 100 nm or more shows a substantially constant value because the actual concentration of Fe in the deep part is Fe by SIMS used in this experiment. It is presumed that this is because it was below the detection limit of.</p><p> Next, Au was formed on one surface side of the annealed semiconductor portion (the side where the ions were implanted) so as to have a thickness of 3 nm by sputtering. The semiconductor portion on which the Au film was formed was heated to 800 ° C. in nitrogen gas in a furnace. By this heating, Au atoms move on the surface of the substrate (semiconductor part), and the Au film changes to a shape such as a substantially spherical shape or a spheroid due to surface tension, and a plurality of fine metal bodies are formed on one surface side of the semiconductor part. Was placed. As a result, a member for a photoelectric conversion element in which a metal body is arranged in a semiconductor portion into which an impurity element has been introduced has been obtained.</p><p> Next, the photoelectric conversion efficiency of the photoelectric conversion element using the obtained member for the photoelectric conversion element was measured. A method for measuring the photoelectric conversion efficiency will be described with reference to FIG. FIG. 4 is a schematic diagram showing a measurement circuit of photoelectric conversion efficiency of a photoelectric conversion element for a solar cell using a member 1 for a photoelectric conversion element.</p><p> As shown in FIG. 4, an electrode 4 made of a Cu plate is provided on the back surface of the semiconductor portion 2 (the opposite surface on one side on which the metal body 3 is arranged). Between the electrode 4 and the semiconductor part 2, an In-Ga alloy rubbed against the semiconductor part 2 to ensure ohmic contact, and an Ag paste applied to the electrode 4 to make contact with the In-Ga alloy. Is provided.</p><p> A transparent liquid container 5 is arranged on one surface side (metal body 3 side) of the semiconductor portion 2. An electrode 6 made of Pt is arranged in the liquid container 5, and an electrolytic solution (0.1 mol / L KClO) is provided._４Aqueous solution) is filled. The one side of the semiconductor portion 2 and the space between the electrodes 6 are immersed in the electrolytic solution. The photoelectric conversion element member 1 and the electrode 4 are used as a working electrode, the electrode 6 is used as a counter electrode, and a saturated calomel electrode (not shown) is used as a reference electrode. This is a photoelectric conversion efficiency measurement circuit.</p><p> When the light emitted from the xenon light source (not shown) is incident on the liquid container 5 through a bandpass filter (wavelength 600 nm, half-value full width is about 10 nm), the light passes through the liquid container 5 and reaches the semiconductor portion 2. Then, the light is absorbed by the metal body 3 and converted into electric energy. The electrons of the semiconductor part 2 generated by the photoelectric conversion move from the electrode 4 to the electrode 6, while the semiconductor part 2 passes through the electrolytic solution from the electrode 6 due to the electrochemical redox reaction generated in the electrolytic solution in the liquid container 5. Move to. The photoelectric conversion efficiency can be calculated by measuring the current (short-circuit current) between the electrode 4 (working electrode) and the electrode 6 (counter electrode) using an electrochemical analyzer.</p><p> The photoelectric conversion efficiency per monochromatic light is obtained from the number of electrons obtained with respect to the amount of irradiation light. The wavelength dependence is shown by the spectral sensitivity characteristic (IPCE), which can be expressed by Equation 1 in accordance with JIS C8936.</p><p> IPCE (%) = 1240 x J_ph/ (Λ × Φ) × 100... Equation 1 However, J shown in Equation 1_phIs the short-circuit current density (mA / cm) under monochromatic light irradiation.^２), Which is obtained by dividing the short-circuit current by the effective light receiving area. Further, λ is the wavelength (nm), and Φ is the intensity of the irradiated monochromatic light (mW / cm).^２). Here, the spectral sensitivity characteristic (IPCE) 5 seconds after irradiating the semiconductor portion with light is calculated, and the photoelectric conversion efficiency is evaluated by evaluating the IPCE.</p><p> FIG. 5 is a diagram showing the relationship between the impurity element introduced into the semiconductor unit 2 and the spectral sensitivity characteristic (IPCE). In FIG. 5, the horizontal axis shows the types (Cr, Fe, Au) of impurity elements introduced into the semiconductor portion by ion implantation. However, "None" indicates a member for a photoelectric conversion element in a comparative example in which an impurity element is not introduced.</p><p> The member for the photoelectric conversion element in the comparative example is a TIO having a thickness of 0.5 mm._２An Au film having a thickness of 3 nm was formed on a single crystal by sputtering, and then heated to 800 ° C. in nitrogen gas in a furnace to melt and solidify the Au film. The member for the photoelectric conversion element in the comparative example is prepared in the same manner as the member for the photoelectric conversion element in the example except that it is not ion-implanted and annealed.</p><p> The vertical axis of FIG. 5 is the ratio of IPCE in each example when the average value of IPCE of the photoelectric conversion element member (sample number is 7) in the comparative example is 1. The number of each sample of the photoelectric conversion element member in the examples is 3 to 5.</p><p> As shown in FIG. 5, the spectral sensitivity characteristics (IPCE) in the examples were 1.8 times that of Comparative Example (None) by introducing Cr, 1.5 times by introducing Fe, and 1.3 times by introducing Au. It has doubled. As described above, in the member for the photoelectric conversion element in the examples, the increase in IPCE is remarkable as compared with the comparative example in which the impurity element is not introduced. Therefore, according to this embodiment, it is clear that the photoelectric conversion efficiency can be improved by introducing a predetermined impurity element into the semiconductor portion. This mechanism is under consideration.</p><p> In particular, it was found that by introducing Cr into the semiconductor portion, the IPCE can be increased 1.8 times as compared with the comparative example in which the impurity element is not introduced. Further, by introducing Fe into the semiconductor portion, the material cost of the member for the photoelectric conversion element can be reduced and the environmental load can be reduced, and the IPCE is 1.5 times higher than that of the comparative example in which the impurity element is not introduced. I also found that I could do it. Further, it was confirmed that Fe can improve IPCE with a dose amount of about 1/10 of the dose amount when Cr is ion-implanted. However, it was found that the introduction of Cr is the most effective in improving IPCE.</p><p> Although the description is omitted in this embodiment, TiO_２In addition to single crystals, TiO synthesized by the vapor phase method_２It is predicted that the IPCE of the photoelectric conversion element member can be improved by introducing the impurity element (Cr) even in polycrystals. In addition, TiO_２Besides, other metal oxide semiconductors (ZnO, SnO)_２, Nb_２O_５Etc.), it is predicted that the IPCE can be improved by introducing the impurity element (Cr).</p><p> Although the present invention has been described above based on the embodiments and examples, the present invention is not limited to the above-described embodiments and examples, and various improved modifications are made without departing from the spirit of the present invention. It is easy to infer that is possible. Further, the numerical values given in the above-described embodiments and examples are examples, and it is naturally possible to adopt other numerical values.</p><p> In the above embodiment, the member for the photoelectric conversion element is evaluated by measuring the spectral sensitivity characteristic (IPCE) of the solar cell, but the member for the photoelectric conversion element is not limited to the one applied to the solar cell. .. For example, it is naturally possible to apply it to a member for a photoelectric conversion element for which another photoelectric conversion element such as a photodetector is intended.</p>

1 Photoelectric conversion element member 2 Semiconductor section 3 Metal body