Method for improving short wavelength sensitivity of photoelectric conversion element

Abstract

To provide a method with which, when light energy density-wavelength characteristics (photon energy-wavelength characteristics) of a spectrum of a light source (sunlight, etc.) deviate significantly from a design standard value, a high conversion efficiency tandem-type photoelectric conversion element (tandem solar cell) can avoid significant drop in output current.SOLUTION: A photoelectric conversion element includes a first semiconductor region of a first conductivity type, the first semiconductor region having a first energy gap EG1, and a third semiconductor region of a second conductivity type inverse to the first conductivity type, the third semiconductor region having a third energy gap EG3 larger than the first energy gap EG1. An energy band edge in the third semiconductor region forms, with an energy band edge in the first semiconductor region, band edge discontinuity ΔES (also called as band edge offset) to first conductivity type carriers, and energy |ΔES| of ΔES is larger than the first energy gap EG1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for improving the short wavelength sensitivity of a photoelectric conversion element that converts light into electricity. [Background technology]

[0002] Photoelectric conversion elements include photoresistors, whose element resistance changes as a result of changes in the intensity or wavelength of the light source, photodiodes, whose element current or voltage changes, phototransistors, whose element current changes as it is amplified by the photodiode, and solar cells, whose output current, voltage, or power changes. Known electronic structures that make up photodiodes and solar cells include homojunction, heterojunction, and MIS structure.

[0003] A homojunction is a pn junction formed by joining a p-type semiconductor and an n-type semiconductor of the same semiconductor material. A heterojunction is a junction formed by joining different semiconductor materials together; when one of the dissimilar semiconductors is p-type and the other is n-type, it becomes a pn junction, and is called an anisotype heterojunction. This heterojunction has been used as a means to realize highly efficient solar cells using compound semiconductors. On the other hand, isotype heterojunctions, in which dissimilar semiconductors of the same conductivity type are in contact with each other, have also been used as photoelectric conversion elements. (For example, see Non-Patent Document 1, Fig. 5)

[0004] Homojunctions are often used to realize photodiodes and phototransistors with silicon semiconductors, but heterojunction solar cells using pn junctions of hydrogenated amorphous silicon and crystalline silicon have been developed with the aim of achieving high efficiency (see, for example, Non-Patent Document 2).

[0005] To achieve even higher efficiency, a "tandem" solar cell has been developed in which junction H, which has sensitivity to short wavelengths and a high open circuit voltage, is connected in series with junction L, which has sensitivity to long wavelengths. FIG. 2 is a cross-sectional view of the tandem solar cell shown in FIG. 9.11(a) of Non-Patent Document 3 with reference numbers added to each component. 2, 101 is a first semiconductor having a first conductivity type (e.g., p-type), and 102 is a first semiconductor having a second conductivity type (e.g., n-type), which are in contact with each other to form a junction L. 101, 102, and 103 (described later) are collectively referred to as a first semiconductor region 100. Reference numeral 201 denotes a second semiconductor having a first conductivity type, and 202 denotes a second semiconductor having a second conductivity type, which are in contact with each other to form a junction H. 201, 202, and 203 (described later) are collectively referred to as a second semiconductor region 200. 103 is a first semiconductor of the second conductivity type having a high impurity concentration, 203 is a second semiconductor of the first conductivity type having a high impurity concentration, and the junction between 103 and 203 forms a low resistance tunnel junction, connecting in series the long wavelength range solar cell element of the tandem solar cell formed by 101 and 102 and the short wavelength range solar cell element of the tandem solar cell formed by 201 and 202. The tandem solar cell has a short wavelength region photocurrent value I generated in the short wavelength region solar cell element for the standard spectrum of sunlight (expressed as a function of light energy density or photon density of light as a function of light wavelength). phH and the long wavelength region photocurrent I generated in the long wavelength region solar cell element phL The band gap and thickness of the second semiconductor are adjusted so that the voltage V of the junction H is approximately the same as that of the first semiconductor. H and the voltage V of the junction L L and the photocurrent (I phH ≒I phL ) and is designed to be highly efficient. Incidentally, reference numeral 104 denotes an ohmic electrode provided on the first semiconductor 101 , and reference numeral 204 denotes an ohmic electrode provided on the second semiconductor 202 .

[0006] However, when the spectrum of sunlight deviates from the standard spectrum, the conversion efficiency of the tandem solar cell decreases significantly, and the output power obtained is lower than the output power change proportional to the change in the solar energy density. For example, when the solar energy in the short wavelength region is extremely reduced and approaches zero, the I phLEven if there is almost no change in I, the output current of the tandem solar cell will be close to zero. Conversely, if the solar energy in the long wavelength range drops drastically and approaches zero, I phH Even if there is almost no change in the output current of the tandem solar cell, the output current approaches zero. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Y, Hayashi, M. Yamanaka and Jin Murayama, “SnO2 / nSi SOLAR CELL”, 1981 IEDM Digest of Technical Papers, 6.4, p140. [Non-Patent Document 2] M. Taguchi, M. Tanaka, T. Matsuyama, T. Matsuoka, S. Tsuda, S. Nakano, Y. Kishi and Y. Kuwano, “Improvement of the conversion efficiency of polycrystalline silicon thin film solar cell”, Technical Digest of the International PVSEC-5, Paper No. C-IIIa-1, p. 689, Kyoto, Japan, 1990. [Non-Patent Document 3] Masashi Yamaguchi, MA Green, Yoshio Ohshita, and Nobuaki Kojima, "Fundamentals and Applications of Solar Cells," July 30, 2010, published by Maruzen Co., Ltd. Summary of the Invention [Problem to be solved by the invention]

[0008] As explained in the case of solar cells above, when the optical wavelength characteristics of the spectrum of sunlight (generally a light source) deviate significantly from the design standard value, the output current of a high conversion efficiency tandem solar cell (tandem type photoelectric conversion element) drops significantly. A method is needed to avoid this phenomenon and realize a photoelectric conversion element that has an output current greater than that of a conventional single junction solar cell (photoelectric conversion element). The challenge is how to realize a high efficiency photoelectric conversion element that can be used in environments where the light source spectrum changes significantly, such as on a mobile vehicle or installed on a structure that is shaded by trees or other buildings depending on the time. [Means for solving the problem]

[0009] The present invention has been made in view of these problems, and has an object to provide a method for improving the efficiency of conversion of one photon in the short wavelength region into an electron-hole pair to a value greater than 1 in a photoelectric conversion element.

[0010] In order to achieve the above object, the present invention provides the following method. (1) [Aspect 1] First energy gap E G1 a first semiconductor region having a first conductivity type; The first energy gap E G1 Larger third energy gap E G3 and a third semiconductor region having a second conductivity type opposite to the first conductivity type, the first semiconductor region has opposing first and second surfaces; the third semiconductor region has opposing third and fourth surfaces; the third semiconductor region is disposed at the fourth surface opposite the first surface of the first semiconductor region; The first conductive type carriers photogenerated in the third semiconductor region are transported by the light irradiated on the third semiconductor region. The energy band edge of the third semiconductor region is at a fourth surface with respect to the energy band edge of the first semiconductor region and the band edge discontinuity ΔE S Forming The band edge discontinuity ΔES Energy |ΔE S | is the first energy gap E G1 Bigger, The first surface and the fourth surface are in contact with each other, or the distance between the first surface and the fourth surface is such that the first conductive type carriers lose their energy |ΔE S |―E G1 is the distance that can be transported without loss, The first conductive type carriers photogenerated in the third semiconductor region by light irradiated from the third surface side to the third semiconductor region are guided to the first energy gap E G1 A method for improving the short wavelength sensitivity of a photoelectric conversion element, comprising: injecting a larger amount of energy into the first semiconductor region while maintaining the larger amount of energy, thereby generating further electron-hole pairs in the first semiconductor region.

[0011] The above operation will now be described with reference to the energy band diagram of FIG. When light is incident from the third surface side, the wavelength λ corresponding to the energy gap of the third semiconductor is EG3 =1240 / E G3 (Unit: nm, E G3 (unit is eV) longer wavelength λ L The incident light passes through the third semiconductor and is absorbed in the first semiconductor, generating electron-hole pairs. EG3 =1240 / E G3 (Unit: nm, E G3 (unit is eV) shorter wavelength λ S The light is absorbed by the third semiconductor and generates electron (e1)-hole (h1) pairs. Among them, the first conductivity type carriers (electrons e1 in the illustrated example) move (drift, diffuse) toward the first semiconductor region as shown by the arrows in the figure, resulting in the band edge discontinuity ΔE S (also called the band edge offset, hereafter referred to as such) gives the energy ΔE S The electrons are then injected into the first semiconductor region, some of which further generate electron (e2)-hole (h2) pairs within the first semiconductor region. In the figure, E C1 and EV1 are the conduction band edge and the valence band edge of the first semiconductor region 100, respectively, and E C3 and E V3 are the conduction band edge and the valence band edge of the third semiconductor region 300, respectively, and FIG. 1 shows an energy offset ΔE S If there is (ΔE in (2) below) CS E F is the Fermi level when the first semiconductor region and the second semiconductor region are in a zero bias state. The first semiconductor region 100 faces the fourth surface of the third semiconductor region at its first surface. They face each other via a vacuum, contact, or an intermediate layer 400 described below.

[0012] (2) [Aspect 2] A first conduction band edge and a first valence band edge, and a first energy gap E G1 a first semiconductor region having a first conductivity type; A third conduction band edge and a third valence band edge, and a third energy gap E G3 and a third semiconductor region having a second conductivity type opposite to the first conductivity type, the first semiconductor region has opposing first and second surfaces; the third semiconductor region has opposing third and fourth surfaces; the third semiconductor region is disposed at the fourth surface opposite the first surface of the first semiconductor region; the first conductivity type is n-type, The third conduction band edge at the fourth surface of the third semiconductor region is closer to the vacuum energy level in its energy level than the first conduction band edge at the first surface of the first semiconductor region, and has a band edge offset ΔE CS Forming The band edge offset ΔE CS Absolute value of |ΔE CS | is the first energy gap E G1 Bigger, The distance between the first surface and the fourth surface is the distance at which the first conductive type carriers transfer their energy |ΔE CS|-E G1 is the distance that can be transported without loss, The first conductive type carriers photogenerated in the third semiconductor region by light irradiated from the third surface side to the third semiconductor region are guided to the first energy gap E G1 The method for improving the short wavelength sensitivity of a photoelectric conversion element according to embodiment 1, further comprising generating electron-hole pairs in the first semiconductor region by injecting a larger amount of energy into the first semiconductor region while maintaining the larger amount of energy. (3) [Aspect 3] A first conduction band edge and a first valence band edge, and a first energy gap E G1 a first semiconductor region having a first conductivity type; A third conduction band edge and a third valence band edge, and a third energy gap E G3 and a third semiconductor region having a second conductivity type opposite to the first conductivity type, the first semiconductor region has opposing first and second surfaces; the third semiconductor region has opposing third and fourth surfaces; the third semiconductor region is disposed at the fourth surface opposite the first surface of the first semiconductor region; the first conductivity type is p-type, A third valence band edge at the fourth surface of the third semiconductor region is farther from the vacuum energy level at its energy level than the first valence band edge at the first surface of the first semiconductor region, and has a band edge offset ΔE VS Forming The band edge offset ΔE VS Absolute value of |ΔE VS | is the first energy gap E G1 Bigger, The distance between the first surface and the fourth surface is the distance at which the second conductive type carriers transfer their energy |ΔE VS |-E G1 is the distance that can be transported without loss, The first conductive type carriers photogenerated in the third semiconductor region by light irradiated from the third surface side to the third semiconductor region are guided to the first energy gap E G1 The method for improving the short wavelength sensitivity of a photoelectric conversion element according to embodiment 1, further comprising generating electron-hole pairs in the first semiconductor region by injecting a larger amount of energy into the first semiconductor region while maintaining the larger amount of energy.

[0013] Due to the above-mentioned mutual relationship of electronic structures, in the third semiconductor region, the minority carriers among the photogenerated carriers are in the first energy gap E G1 When a photon with greater energy is injected from the third semiconductor region into the first semiconductor region, more electron-hole pairs are generated with a certain probability. That is, one photon first generates one pair of electron-hole pairs in the third semiconductor region, and among them, the minority carrier (first conductivity type carrier) for the third semiconductor is E G1 When the electron is injected into the first semiconductor region with a larger energy, it generates another electron-hole pair. The probability of this generation is |ΔE CS |-E G1 or |ΔE VS |-E G1 The larger the value, the larger the

[0014] Here, even if the fourth surface and the first surface are opposed to each other with a distance therebetween, if there is a vacuum between them, for example, carriers of the first conductivity type that fly out of the fourth surface toward the first surface are injected into the first semiconductor region through the first surface without losing energy. (4) [Aspect 4] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of aspects 1, 2, and 3, wherein a space between the fourth surface and the first surface is a vacuum.

[0015] On the other hand, when the fourth surface and the first surface are in contact with each other, the first conductive type carriers are disposed in a region E G1 The electrons are injected into the first semiconductor region with a larger energy, and the effects of the present invention can be obtained. Therefore, the following (5) is an effective configuration of the present invention. (5) [Aspect 5] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of embodiment 1, embodiment 2, and embodiment 3, wherein the fourth surface and the first surface are in contact with each other.

[0016] However, when the photoelectric conversion element of the present invention is used as a solar cell, the output power may decrease due to electronic defects formed on the first surface or the fourth surface. Alternatively, when a third semiconductor region is formed in contact with the first surface of the first semiconductor region via the fourth surface, an interface layer is formed by bonding at the interface between the constituent materials, resulting in Fermi level pinning. A phenomenon called Fermi level pinning (Fermi level pinning) occurs, and when the photoelectric conversion element of the present invention is used as a solar cell, the output voltage may drop. In this case, as shown in Figure 3, a measure can be taken to prevent this phenomenon from occurring by opposing the first semiconductor region and the third semiconductor region through an intermediate film 400 made of a material different from the first semiconductor and the third semiconductor. However, when this intermediate film is interposed, the above-mentioned E G1 If most of the first conductive type carriers having a larger energy collide with the lattice or defects of the intermediate film and lose their energy, the operation of the present invention will not be realized. In Fig. 3, 100 is a first semiconductor region, 300 is a third semiconductor region, 400 is an intermediate layer, 105 is an ohmic contact electrode provided on the first semiconductor region, and 304 is an ohmic contact electrode provided on the first semiconductor. The first semiconductor region 100 faces the fourth surface 340 of the third semiconductor region 300 through the intermediate layer 400 at its first surface 110. Note that 120 indicates a second surface facing the first surface 110 of the first semiconductor region 100, and 330 indicates a third surface facing the fourth surface 340 of the third semiconductor region 300.

[0017] When an intermediate film 400 is provided between the first semiconductor region and the third semiconductor region, if the intermediate film has a thickness such that scattering of the first conductive type carriers in the intermediate film is negligible, when the first conductive type carriers are injected from the second semiconductor region into the intermediate film, the first conductive type carriers are injected into the first semiconductor region with only a small energy loss. As an example of the intermediate film, a hydrogenated amorphous silicon-based film (hydrogenated amorphous silicon, hydrogenated amorphous silicon-carbon, hydrogenated amorphous silicon-oxygen, etc.) can be used. It is more preferable that the thickness of this hydrogenated amorphous silicon-based semiconductor film is 15 nm or less. A silicon oxide film having a thickness of 1 nm or less can also be used as the intermediate film. This is particularly suitable when the first semiconductor region 100 is silicon. Furthermore, it is also preferable that the intermediate film is a compound semiconductor having a thickness of 10 nm or less and having a lattice constant that is approximately matched with that of the first semiconductor. That is, the operation of the present invention can be realized with the following configuration. (6) [Aspect 6] Between the fourth surface of the third semiconductor region and the first surface of the first semiconductor region, the energy loss of the first conductive type carriers is equal to the band edge offset ΔE S Absolute value of |ΔE S | to the energy gap E of the first semiconductor G1 The method for improving the short wavelength sensitivity of a photoelectric conversion element according to embodiment 1, further comprising providing an intermediate film having a thickness equal to or less than the value obtained by subtracting (7) [Aspect 7] The first conductive type carriers photogenerated in the third semiconductor region between the fourth surface and the first surface have their energy expressed as |ΔE CS |-E G1 The thickness of the intermediate film is limited to the thickness required for the material to be transported without loss. 3. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to aspect 2. (8) [Aspect 8] The first conductive type carriers photogenerated in the third semiconductor region between the fourth surface and the first surface have their energy expressed as |ΔE VS |-E G1The thickness of the intermediate film is limited to the thickness required for the material to be transported without loss. 4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to aspect 3. (9) [Aspect 9] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 6, 7, 8, and 9, wherein the intermediate film is a hydrogenated amorphous silicon semiconductor film. (10) [Aspect 10] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to Aspect 9, wherein the intermediate film is a hydrogenated amorphous silicon-based semiconductor film having a thickness of 15 nm or less. (11) [Aspect 11] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 6, 7, 8, and 9, wherein the intermediate film is a silicon oxide film having a thickness of 1 nm or less. (12) [Aspect 12] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 6, 7, 8, and 8, wherein the intermediate film is a compound semiconductor film having a thickness of 10 nm or less and having a lattice constant that is approximately matched to that of the first semiconductor.

[0018] Built-in fields In order to increase the probability that the first conductive type carriers photogenerated in the third semiconductor region are injected from the fourth surface through the first surface into the first semiconductor region, it is desirable to provide an internal electric field in the vicinity of the fourth surface of the third semiconductor region for accelerating the first conductive type carriers toward the first semiconductor region. The following configurations can be used to form this accelerating electric field. (13) [Embodiment 13] A method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of embodiments 1, 2, and 3, characterized in that a portion having a low impurity concentration is provided in the third semiconductor region near the fourth surface. (14) [Aspect 14] A method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 1, 2, and 3, characterized in that a fourth semiconductor region is provided facing the first surface, the fourth surface having an energy band edge, through which first conductivity type carriers are transported, closer to the first semiconductor than to the third semiconductor. By carrying out the above process, an internal electric field that accelerates first conductive type carriers toward the first semiconductor region can be formed in the vicinity of the fourth surface of the second semiconductor region.

[0019] Voc Although the above configuration and operation can increase the photocurrent, there are also applications in which it is necessary to ensure a photovoltage. To increase the photovoltage, the built-in voltage of the junction between the third semiconductor region and the first semiconductor region must be large. To achieve this, (15) [Aspect 15] A method for improving the short wavelength sensitivity of a photoelectric conversion element according to Aspect 2, wherein a third valence band edge of the third semiconductor region is located in a direction farther from the vacuum energy level than the first valence band edge of the first semiconductor region. (16) [Aspect 16] The third conduction band edge of the third semiconductor region is closer to the vacuum energy level than the first conduction band edge of the first semiconductor region. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to embodiment 3, wherein the short wavelength sensitivity is located in a closer direction. would be desirable.

[0020] front surface field & passivation In order to prevent the first conductive type carriers generated by light incident on the third semiconductor region from recombining and disappearing at the third surface of the third semiconductor region and to help the first conductive type carriers to be pushed back from the third surface and transported to the fourth surface, a fifth semiconductor region having a conduction band closer to the vacuum energy level than the third semiconductor region can be provided on the third surface of the third semiconductor region when the third semiconductor region is p-type, and a fifth semiconductor region having a valence band closer to the vacuum energy level than the third semiconductor region can be provided on the third surface of the third semiconductor region when the third semiconductor region is n-type. That is, (17) [Aspect 17] A method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 1, 2, and 3, characterized in that a fifth semiconductor region is provided on the third surface of the third semiconductor when the third semiconductor region is p-type, the fifth semiconductor region having a conduction band edge closer to the vacuum energy level than the third semiconductor region, and when the third semiconductor region is n-type, the fifth semiconductor region having a valence band edge farther from the vacuum energy level than the third semiconductor region.

[0021] Transparent electrode &texture In the photoelectric conversion element of the present invention, light is incident on the third surface side of the third semiconductor region. Therefore, an anti-reflection film is often provided on the third surface of the third semiconductor region or the fifth surface of the fifth semiconductor region described in (17). When the sheet resistance of the third semiconductor region or the parallel sheet resistance of the third semiconductor region and the fifth semiconductor region is large, it is necessary to deposit a transparent electrode on the third surface of the third semiconductor region or on the fifth surface of the fifth semiconductor region described in (17) in order to extract current or voltage from the third semiconductor region with minimal effect of series resistance. Furthermore, it is desirable that the third surface of the third semiconductor region or the fifth surface of the fifth semiconductor region described in (17) have irregularities with planar dimensions of at least ¼ of the wavelength of incident light in order to prevent reflection of the incident light. That is, (18) [Aspect 18] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 1, 2, and 3, further comprising providing a transparent electrode on a third surface of the third semiconductor. (19) [Aspect 19] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to Aspect 17, further comprising providing a transparent electrode on a fifth surface of the fifth semiconductor. As for the transparent conductive film, indium oxide (InOx), indium oxide hydride (InOx:H), indium tin oxide (ITO), zinc oxide (ZnOx) and its aluminum (Al) additive or boron (B) additive, nanocarbon such as graphene, etc. are used. (20) [Aspect 20] A method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 1, 2, and 3, characterized in that the third surface of the third semiconductor region has irregularities with planar dimensions of at least 1 / 4 of the wavelength of incident light. (21) [Aspect 21] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to Aspect 17, wherein the fifth surface of the fifth semiconductor region has irregularities with planar dimensions of at least ¼ of the wavelength of incident light. (22) [Aspect 22] A method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 18 and 19, characterized in that the transparent electrode is zinc oxide and has a surface having irregularities with planar dimensions of at least 1 / 4 of the wavelength of incident light. Zinc oxide deposited by CVD technology can form an uneven structure on its surface depending on the deposition conditions. Effect of the Invention

[0022] According to the method for improving the short wavelength sensitivity of a photoelectric conversion element of the present invention, This will realize a photoelectric conversion element that avoids the significant drop in output current seen in high-conversion-efficiency tandem solar cells (tandem photoelectric conversion elements) when the photon number-wavelength characteristics of a light source such as sunlight deviate significantly from the standard value, and has an output current greater than that of conventional single-junction photoelectric conversion elements. This will contribute to the realization of a highly efficient photoelectric conversion element that can be used in environments where the light source spectrum changes significantly, such as when mounted on a mobile vehicle or installed on a structure or wall that is shaded by other buildings or trees depending on the time of day. [Brief description of the drawings]

[0023] [Figure 1] 1 is an energy band diagram illustrating an operation for realizing a method for improving the short wavelength sensitivity of a photoelectric conversion element according to the present invention. [Diagram 2] 1 is an example of a cross-sectional view of a conventional tandem solar cell. [Diagram 3] 1 shows an example of the structure of a photoelectric conversion element provided with an intermediate layer, which can be used to implement the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] ZnS x Se (1-x) An embodiment in which the first semiconductor region is made of crystalline Si and the third semiconductor region is made of a ZnSe-based compound semiconductor will be described below. (23) [Aspect 23] The method for improving the short-wavelength sensitivity of the photoelectric conversion element according to Aspect 12, wherein the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of zinc selenide (ZnSe), and the intermediate region is formed of zinc sulfide (ZnS). The first-conductivity-type carriers injected from ZnSe to Si are given energy by the valence-band-edge offset E VS (1.6 - 1.7 eV) between ZnSe and Si, and generate electron-hole pairs as high-energy first-conductivity-type carriers. Since ZnS has a lattice constant close to that of Si and can reduce the generation of lattice defects on the first surface of Si, the recombination at the interface of the high-energy first-conductivity-type carriers (holes in this case) injected from ZnSe to Si can be reduced. Therefore, the generation of electron-hole pairs by the high-energy holes after injection into Si is ensured. The valence-band-edge barrier of ZnS as seen from the valence band edge of ZnSe is about 0.3 eV, but since the thickness of ZnS is 10 nm or less, which is a distance through which holes can tunnel, there is no problem. When the third semiconductor region is formed as a mixed crystal ZnS x Se (1-x) (0 < x < 1), the absolute value |E VS | of the band offset of the valence band edge changes between 1.7 - 1.9 eV. As |E VS | increases, the probability of electron-hole pair generation by the high-energy first-conductivity-type carriers injected into the first semiconductor region Si increases. On the other hand, since the energy gap E G3 increases, the wavelength range in the short-wavelength region of the light source corresponding to the energy gap E G3 becomes smaller, and the number of high-energy first-conductivity-type carriers injected into the first semiconductor region Si decreases. Therefore, the optimal value of x is selected according to the spectrum of the light source. On the other hand, when the lattice matching at the interface with Si grows well, when x decreases close to 0, the absolute value |ΔE CS | of the band offset of the conduction band edge increases to ~1.9 eV. Therefore, the optimal value of x can be selected according to the spectrum of the light source in the same way as above. In this case, ZnS x Se(1-x) The high energy first conductivity type carriers injected from ZnS into Si become electrons. x Se (1-x) is designed to be p-type and Si is designed to be n-type. (24) [Aspect 24] The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of mixed crystal ZnS x Se (1-x) The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of the first, second and third aspects, (25) It is preferable to provide an internal electric field for accelerating the first conductive type carriers from the vicinity of the fourth surface of the third semiconductor region toward the first semiconductor region. The accelerating internal electric field is generated when the third semiconductor region is a mixed crystal ZnS x Se (1-x) In the case where the third semiconductor region is formed as above, this can be realized by providing, in at least a part of the third semiconductor region, a semiconductor region in which x increases with increasing distance to the third surface of the third semiconductor region. [Aspect 25] The third semiconductor region is made of mixed crystal ZnS x Se (1-x) and providing, in at least a portion of the third semiconductor region, a semiconductor region in which x increases with increasing distance from a third surface of the third semiconductor region. (26) The third semiconductor region is a mixed crystal of ZnS x Se (1-x) The effect of the ZnS intermediate layer is also effective when the ZnS intermediate layer is formed. [Aspect 26] The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of mixed crystal ZnS x Se (1-x) The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of aspects 12 and 25, wherein the intermediate region is formed from zinc sulfide (ZnS). (27) Furthermore, ZnSe or ZnS x Se (1-x) The sheet resistance of ZnSe or ZnS is large to improve the output power loss of the photoelectric conversion element. x Se (1-x)It is necessary to provide a transparent electrode on the third surface side of the transparent electrode, and in this case, an indium tin oxide (ITO) film is suitable as the transparent electrode. [Aspect 27] A method for improving the short wavelength sensitivity of a photoelectric conversion element described in Aspect 23, characterized in that the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of ZnSe, and a transparent electrode made of an indium tin oxide (ITO) film is provided on a third surface (light-receiving surface) of the ZnSe. (28) [Aspect 28] The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of ZnS x Se (1-x) The ZnS x Se (1-x) The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of aspects 24, 25, and 26, characterized in that a transparent electrode made of an indium tin oxide (ITO) film is provided on the third surface (light-receiving surface).

[0025] AlP,GaP An embodiment in which the first semiconductor region is made of crystalline Si and the third semiconductor region is made of an AlP (aluminum phosphide) compound semiconductor will be described below. (29) [Aspect 29] A method for improving the short wavelength sensitivity of a photoelectric conversion element described in any one of Aspects 1 and 3, characterized in that the first semiconductor region is made of crystalline silicon (Si) and the third semiconductor region is made of aluminum phosphide (AlP). (30) [Aspect 30] A method for improving the short wavelength sensitivity of a photoelectric conversion element according to aspect 11, characterized in that the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of aluminum phosphide (AlP), and the intermediate region is formed of gallium phosphide (GaP). The first conductive type carriers injected from AlP to Si are offset by the valence band edge E VS(about 1.4 eV) to generate electron-hole pairs as high-energy first-conductivity-type carriers. Since the GaP in the intermediate region does not create a valence band barrier for the AlP, the first-conductivity-type carriers tunnel through the intermediate region and are injected in a high-energy state into the first semiconductor region (crystalline Si). Furthermore, since AlP becomes unstable when exposed to the outside air, a protective film is required on the light-receiving surface side made of GaN or the like. (31) [Aspect 31] The method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of Aspects 29 and 30, further comprising providing a GaN protective film on the third surface of the AlP that forms the third semiconductor region. [Industrial Applicability]

[0026] The photoelectric conversion element embodying the method of the present invention is Highly efficient, yet in light sources or operating environments where the energy density-wavelength (photon density-wavelength) characteristics vary greatly. Unlike conventional tandem photovoltaic conversion elements (tandem solar cells), the conversion efficiency does not change significantly. This is suitable for applications where the spectrum of the light source changes over time due to shadows from buildings, trees, walls, etc., and for installation on moving objects where the spectrum of the light source changes over time. [Explanation of symbols]

[0027] 100: First semiconductor region (general term including 101, 102, and 103 below) 101: a first semiconductor region having a first conductivity type 102: a first semiconductor region having a second conductivity type 103: A first semiconductor region of a first conductivity type having a high impurity concentration 104: an ohmic electrode provided on the first semiconductor region 101 having a first conductivity type 105: Ohmic electrode provided on the first semiconductor region 100 110: First surface of a first semiconductor region 120: second surface of the first semiconductor region 200: Second semiconductor region (general term including 201, 202, and 203 below) 201: a second semiconductor region having a first conductivity type 202: a second semiconductor region having a second conductivity type 203: A first semiconductor region of a first conductivity type having a high impurity concentration 204: an ohmic electrode provided on the second semiconductor region 202 having the second conductivity type 300: Third semiconductor region 304: Ohmic electrode provided on the third semiconductor region 300 330: a third surface of a third semiconductor region 340: A fourth surface of the third semiconductor region 400: Interlayer I phH :Short wavelength range photocurrent I phL :Long wavelength photocurrent E G1 : First energy gap (energy gap of the first semiconductor region) E G3 :Third energy gap (energy gap of the third semiconductor region) E C1 : Conduction band edge of the first semiconductor region 100 E V1 : valence band edge of the first semiconductor region 100 E C3 : Conduction band edge of the third semiconductor region 300 E V3 : Valence band edge of the third semiconductor region 300 E F Fermi level when the first semiconductor region and the second semiconductor region are in a zero bias state ΔE S : Band edge discontinuity (band edge offset) for first conductivity type carriers ΔE CS : the band edge offset that the third conduction band edge (of the third semiconductor region) forms with the first conduction band edge (of the first semiconductor region) ΔE VS : The band edge offset that the third valence band edge (of the third semiconductor region) forms with the first valence band edge (of the first semiconductor region) λ EG3 : The wavelength of light corresponding to the energy gap of the third semiconductor, λ EG3=1240 / E G3 (Unit: nm, E G3 (unit is eV) λ S :λ EG3 Shorter wavelengths of light λ L :λ EG3 Longer wavelengths of light e1: short wavelength λ S The light is absorbed by the third semiconductor, generating electron-hole pairs. h1: short wavelength λ S The light is absorbed by the third semiconductor, generating electron-hole pairs. e2: short wavelength λ S When light is absorbed in the third semiconductor, the first conductivity type carriers among the electron (e1)-hole (h1) pairs are generated, and the band edge discontinuity ΔE S from energy ΔE S The electrons in the electron-hole pairs that are generated by being injected into the first semiconductor region are h2: short wavelength λ S When light is absorbed in the third semiconductor, the first conductivity type carriers among the electron (e1)-hole (h1) pairs are generated, and the band edge discontinuity ΔE S from energy ΔE S The holes among the electron-hole pairs that are generated by being injected into the first semiconductor region

Claims

1. First energy gap E Ｇ１ a first semiconductor region having a first conductivity type; The first energy gap E Ｇ１ Larger third energy gap E Ｇ３ and a third semiconductor region having a second conductivity type opposite to the first conductivity type, the first semiconductor region has opposing first and second surfaces; the third semiconductor region has opposing third and fourth surfaces; the third semiconductor region is disposed at the fourth surface opposite the first surface of the first semiconductor region; The energy band edge of the third semiconductor region to which the first conductive type carriers photogenerated in the third semiconductor region by the light irradiated to the third semiconductor region are transported is A band edge discontinuity ΔE between the energy band edge of the first semiconductor region and the first conductive type carriers at the fourth surface. Ｓ Forming The band end discontinuity ΔE Ｓ Energy |ΔE Ｓ | is the first energy gap E Ｇ１ Bigger, The first surface and the fourth surface are in contact with each other, or the distance between the first surface and the fourth surface is such that the first conductive type carriers lose their energy |ΔE Ｓ |―E Ｇ１ is the distance that can be transported without loss, The third semiconductor region is photogenerated in response to light irradiated from a third surface side of the third semiconductor region, and the first conductive type carriers are photogenerated in the third semiconductor region through a first energy gap E Ｇ１ A method for improving the short wavelength sensitivity of a photoelectric conversion element, comprising the steps of: injecting light into the first semiconductor region while maintaining a larger energy, thereby generating further electron-hole pairs in the first semiconductor region.

2. A first conduction band edge and a first valence band edge, and a first energy gap E between the first conduction band edge and the first valence band edge. Ｇ１ a first semiconductor region having a first conductivity type; A third conduction band edge and a third valence band edge, and a third energy gap E between the third conduction band edge and the third valence band edge. Ｇ３ and a third semiconductor region having a second conductivity type opposite to the first conductivity type, the first semiconductor region has opposing first and second surfaces; the third semiconductor region has opposing third and fourth surfaces; the third semiconductor region is disposed at the fourth surface opposite the first surface of the first semiconductor region; the first conductivity type is n-type, A third conduction band edge at the fourth surface of the third semiconductor region is closer to the vacuum energy level in its energy level than the first conduction band edge at the first surface of the first semiconductor region, and has a band edge offset ΔE between the third conduction band edge and the first conduction band edge. ＣＳ Forming The band edge offset ΔE ＣＳ Absolute value of |ΔE ＣＳ | is the first energy gap E Ｇ１ Bigger, The distance between the first surface and the fourth surface is the distance at which the first conductive type carriers lose their energy |ΔE ＣＳ |-E Ｇ１ is the distance that can be transported without loss, The third semiconductor region is photogenerated in response to light irradiated from a third surface side of the third semiconductor region, and the first conductive type carriers are photogenerated in the third semiconductor region through a first energy gap E Ｇ１ 2. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, further comprising the step of generating electron-hole pairs in said first semiconductor region by injecting light into said first semiconductor region while maintaining a larger energy.

3. A first conduction band edge and a first valence band edge, and a first energy gap E between the first conduction band edge and the first valence band edge. Ｇ１ a first semiconductor region having a first conductivity type; A third conduction band edge and a third valence band edge, and a third energy gap E between the third conduction band edge and the third valence band edge. Ｇ３ and a third semiconductor region having a second conductivity type opposite to the first conductivity type, the first semiconductor region has opposing first and second surfaces; the third semiconductor region has opposing third and fourth surfaces; the third semiconductor region is disposed at the fourth surface opposite the first surface of the first semiconductor region; the first conductivity type is p-type, A third valence band edge at the fourth surface of the third semiconductor region is farther from the vacuum energy level at its energy level than the first valence band edge at the first surface of the first semiconductor region, and has a band edge offset ΔE ＶＳ The mold is The band edge offset ΔE ＶＳ Absolute value of |ΔE ＶＳ | is the first energy gap E Ｇ１ Bigger, The distance between the first surface and the fourth surface is the distance at which the second conductive type carriers lose their energy |ΔE ＶＳ |-E Ｇ１ is the distance that can be transported without loss, The third semiconductor region is photogenerated in response to light irradiated from a third surface side of the third semiconductor region, and the first conductive type carriers are photogenerated in the third semiconductor region through a first energy gap E Ｇ１ 2. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, further comprising the step of generating electron-hole pairs in said first semiconductor region by injecting light into said first semiconductor region while maintaining a larger energy.

4. 4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, wherein a space between said fourth surface and said first surface is a vacuum.

5. 4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, wherein the fourth surface and the first surface are in contact with each other.

6. Between the fourth surface of the third semiconductor region and the first surface of the first semiconductor region, the energy loss of the first conductive type carriers photogenerated in the third semiconductor region is equal to the band edge offset ΔE Ｓ Absolute value of |ΔE Ｓ | to the energy gap E of the first semiconductor Ｇ１ 4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, further comprising providing an intermediate film having a thickness equal to or less than the value obtained by subtracting

7. Between the fourth surface and the first surface, first conductive type carriers photogenerated in the third semiconductor region transfer their energy |ΔE ＣＳ |-E Ｇ１ The thickness of the intermediate film is limited to the thickness required for the film to be transported without loss.

3. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 2.

8. Between the fourth surface and the first surface, first conductive type carriers photogenerated in the third semiconductor region transfer their energy |ΔE ＶＳ |-E Ｇ１ The thickness of the intermediate film is limited to the thickness required for the film to be transported without loss.

4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 3.

9. 7. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 6, wherein the intermediate film is a hydrogenated amorphous silicon based semiconductor film.

10. 8. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 7, wherein the intermediate film is a hydrogenated amorphous silicon based semiconductor film.

11. 9. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 8, wherein the intermediate film is a hydrogenated amorphous silicon based semiconductor film.

12. 10. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 9, wherein the intermediate film is a hydrogenated amorphous silicon semiconductor film having a thickness of 15 nm or less.

13. 11. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 10, wherein the intermediate film is a hydrogenated amorphous silicon-based semiconductor film having a thickness of 15 nm or less.

14. 12. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 11, wherein the intermediate film is a hydrogenated amorphous silicon-based semiconductor film having a thickness of 15 nm or less.

15. 7. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 6, wherein the intermediate film is a silicon oxide film having a thickness of 1 nm or less.

16. 8. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 7, wherein the intermediate film is a silicon oxide film having a thickness of 1 nm or less.

17. 9. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 8, wherein the intermediate film is a silicon oxide film having a thickness of 1 nm or less.

18. 7. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 6, wherein the intermediate film is a compound semiconductor film having a thickness of 10 nm or less and having a lattice constant substantially matching that of the first semiconductor.

19. 8. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 7, wherein the intermediate film is a compound semiconductor film having a thickness of 10 nm or less and having a lattice constant substantially matching that of the first semiconductor.

20. 9. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 8, wherein the intermediate film is a compound semiconductor film having a thickness of 10 nm or less and having a lattice constant substantially matching that of the first semiconductor.

21. 4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, wherein a portion having a low impurity concentration is provided in said third semiconductor region near said fourth surface.

22. 4. A method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, further comprising providing a fourth semiconductor region facing the first surface, the fourth semiconductor region having an energy band edge, through which the first conductivity type carriers are transported to the fourth surface, closer to the first semiconductor than the third semiconductor.

23. 3. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 2, wherein a third valence band edge of the third semiconductor region is located in a direction farther from the vacuum energy level than a first valence band edge of the first semiconductor region.

24. 4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 3, wherein a third conduction band edge of the third semiconductor region is located in a direction closer to the vacuum energy level than a first conduction band edge of the first semiconductor region.

25. A method for improving the short wavelength sensitivity of a photoelectric conversion element described in any one of claims 1, 2 and 3, characterized in that a fifth semiconductor region is provided on the third semiconductor third surface when the third semiconductor region is p-type, the fifth semiconductor region having a conduction band edge closer to the vacuum energy level than the third semiconductor region, and when the third semiconductor region is n-type, the fifth semiconductor region is provided on the third surface of the third semiconductor.

26. 4. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, 2 or 3, further comprising providing a transparent electrode on a third surface of said third semiconductor.

27. 26. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 25, further comprising providing a transparent electrode on a fifth surface of the fifth semiconductor.

28. A method for improving the short wavelength sensitivity of a photoelectric conversion element described in any one of claims 1, 2 and 3, characterized in that the third surface of the third semiconductor region has irregularities with planar dimensions of at least 1 / 4 of the wavelength of incident light.

29. 26. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 25, wherein the fifth surface of the fifth semiconductor region has irregularities with planar dimensions of at least 1 / 4 of the wavelength of incident light.

30. 27. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 26, wherein the transparent electrode is made of zinc oxide and has a surface having irregularities with a planar dimension of at least 1 / 4 of the wavelength of incident light.

31. 28. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 27, wherein the transparent electrode is made of zinc oxide and has a surface having irregularities with a planar dimension of at least 1 / 4 of the wavelength of incident light.

32. 20. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 18, wherein the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of zinc selenide (ZnSe), and the intermediate region is formed of zinc sulfide (ZnS).

33. 20. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 19, wherein the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of zinc selenide (ZnSe), and the intermediate region is formed of zinc sulfide (ZnS).

34. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 20, characterized in that the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of zinc selenide (ZnSe), and the intermediate region is formed of zinc sulfide (ZnS).

35. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of mixed crystal ZnS ｘ Se （1－ｘ） 4. A method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 1, 2 or 3, wherein the photoelectric conversion element is formed of

36. The third semiconductor region is a mixed crystal of ZnS. ｘ Se （1－ｘ） and providing a semiconductor region in at least a portion of the third semiconductor region in which x increases with increasing distance from a third surface of the third semiconductor region.

37. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of mixed crystal ZnS ｘ Se （1－ｘ） 20. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 18, wherein the intermediate region is made of zinc sulfide (ZnS).

38. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of mixed crystal ZnS ｘ Se （1－ｘ） 20. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 19, wherein the intermediate region is made of zinc sulfide (ZnS).

39. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of mixed crystal ZnS ｘ Se （1－ｘ） 21. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 20, wherein the intermediate region is made of zinc sulfide (ZnS).

40. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 32, characterized in that the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of ZnSe, and a transparent electrode made of an indium tin oxide (ITO) film is provided on a third surface (light-receiving surface) of the ZnSe.

41. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 33, characterized in that the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of ZnSe, and a transparent electrode made of an indium tin oxide (ITO) film is provided on a third surface (light-receiving surface) of the ZnSe.

42. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 34, characterized in that the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of ZnSe, and a transparent electrode made of an indium tin oxide (ITO) film is provided on a third surface (light-receiving surface) of the ZnSe.

43. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of ZnS ｘ Se （1－ｘ） The ZnS ｘ Se （1－ｘ） 36. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 35, further comprising providing a transparent electrode made of an indium tin oxide (ITO) film on the third surface (light receiving surface).

44. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of ZnS ｘ Se （1－ｘ） The ZnS ｘ Se （1－ｘ） 37. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 36, further comprising providing a transparent electrode made of an indium tin oxide (ITO) film on the third surface (light receiving surface).

45. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of ZnS ｘ Se （1－ｘ） The ZnS ｘ Se （1－ｘ） 38. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 37, further comprising providing a transparent electrode made of an indium tin oxide (ITO) film on the third surface (light receiving surface).

46. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of ZnS ｘ Se （1－ｘ） The ZnS ｘ Se （1－ｘ） 39. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 38, further comprising providing a transparent electrode made of an indium tin oxide (ITO) film on the third surface (light receiving surface).

47. The first semiconductor region is made of crystalline silicon (Si), and the third semiconductor region is made of ZnS ｘ Se （1－ｘ） The ZnS ｘ Se （1－ｘ） 40. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 39, further comprising providing a transparent electrode made of an indium tin oxide (ITO) film on the third surface (light receiving surface).

48. A method for improving the short wavelength sensitivity of a photoelectric conversion element according to any one of claims 1 and 3, characterized in that the first semiconductor region is made of crystalline silicon (Si) and the third semiconductor region is made of aluminum phosphide (AlP).

49. 20. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 18, wherein the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of aluminum phosphide (AlP), and the intermediate region is formed of gallium phosphide (GaP).

50. 20. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 19, wherein the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of aluminum phosphide (AlP), and the intermediate region is formed of gallium phosphide (GaP).

51. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 20, characterized in that the first semiconductor region is made of crystalline silicon (Si), the third semiconductor region is made of aluminum phosphide (AlP), and the intermediate region is formed of gallium phosphide (GaP).

52. 49. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 48, further comprising providing a protective film of GaN on a third surface of the AlP forming said third semiconductor region.

53. 50. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 49, further comprising providing a protective film of GaN on a third surface of the AlP forming said third semiconductor region.

54. 51. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 50, further comprising providing a protective film of GaN on a third surface of the AlP forming the third semiconductor region.

55. 52. The method for improving the short wavelength sensitivity of a photoelectric conversion element according to claim 51, further comprising providing a protective film of GaN on a third surface of the AlP forming said third semiconductor region.

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