KR20150014298A - Compound semiconductor solar cell - Google Patents

Abstract

The present invention relates to a compound semiconductor solar cell. The compound semiconductor solar cell according to the present invention includes at least one light absorption layer which includes a base layer doped with a first thickness of a first conductivity type impurity and an emitter layer doped with a second thickness of a second conductivity type impurity which is thinner than the first thickness - the second conductivity type impurity is opposite to the first conductivity type impurity-; a first electrode located in the front side of the light entering surface of at least one light absorption layer; and a second electrode located to the back surface which is opposite to the light entering surface of at least one light absorption layer. The emitter layer is located in the back surface of the base layer in the light absorption layer.

Description

COMPOUND SEMICONDUCTOR SOLAR CELL [0002]

The present invention relates to a compound semiconductor solar cell.

A compound semiconductor is a compound that is not a single element such as silicon or germanium but is operated as a semiconductor by combining two or more elements. Various kinds of compound semiconductors are currently being developed and used in various fields. Typically, a compound semiconductor is used for a light emitting device such as a light emitting diode or a laser diode using a photoelectric conversion effect, a solar cell, and a thermoelectric conversion device using a Peltier effect.

Environmentally friendly solar cells that do not require a separate energy source other than natural sunlight are being actively studied as a future alternative energy source. Solar cells are roughly classified into a silicon solar cell using a single element of silicon and a compound semiconductor solar cell using a compound semiconductor.

Among these, a compound semiconductor solar cell uses a compound semiconductor for a light absorbing layer (PV) that absorbs sunlight to generate electron-hole pairs, and is a compound semiconductor such as a III-V compound semiconductor such as GaAs, InP, GaAlAs, or GaInAs, II-VI group compound semiconductors such as CdTe and ZnS, and I-III-VI group compound semiconductors such as CuInSe2.

The photovoltaic layer (PV) of a solar cell is required to have excellent long-term electrical and optical stability, high photoelectric conversion efficiency, and easy control of band gap energy or conduction type by compositional change or doping. In addition, for commercialization, requirements such as manufacturing cost and yield must be satisfied. The above-described various compound semiconductors do not satisfy all of these requirements together, and depending on their advantages and disadvantages, they are suitably used according to the application.

An object of the present invention is to provide a compound semiconductor solar cell having improved photoelectric conversion efficiency.

A compound semiconductor solar cell according to the present invention comprises a base layer doped with impurities of a first conductivity type by a first thickness, an impurity of a second conductivity type opposite to the first conductivity type doped with a second thickness less than the first thickness At least one light absorbing layer comprising an emitter layer; A first electrode located on a front surface, which is an incident surface of at least one light absorbing layer; And a second electrode located on the rear surface opposite to the incident surface of the at least one light absorbing layer, wherein the emitter layer is located on the rear surface of the base layer.

Here, the at least one light absorbing layer may further include a rear front layer in which impurities of the second conductivity type are doped at a higher concentration than the emitter layer.

Here, the rear whole layer may be located on the back side of the emitter layer.

Further, the thickness of the base layer may be between 1 탆 and 5 탆, and the thickness of the emitter layer may be between 0.1 탆 and 1 탆.

The energy bandgap of the base layer and the emitter layer may be between 1.35 eV and 1.45 eV.

In addition, a passivation layer doped with an impurity of the first conductivity type may be further included between the at least one light absorbing layer and the first electrode.

Here, the energy band gap of the passivation layer may be higher than the energy band gap of the base layer. For example, the energy band gap of the passivation layer may be between 1.8 eV and 1.9 eV.

In addition, the passivation layer may further include an antireflection film, and the antireflection film may be formed to cover at least a portion of the first electrode and the passivation layer.

The first electrode may include a plurality of finger electrodes formed in a first direction and a bus bar electrode formed in a second direction to connect the plurality of finger electrodes to each other.

Further, between each finger electrode and the passivation layer, the first cap layer may be further doped with impurities of the first conductivity type at a higher concentration than the passivation layer.

Here, an antireflection film may be formed on the plurality of finger electrodes, and an antireflection film may not be formed on the bus bar electrode.

In addition, a substrate may be further included between the at least one light absorbing layer and the second electrode, and the substrate and the light absorbing layer may be formed to include the same compound, and the passivation layer and the light absorbing layer may be formed to include different compounds.

In one example, the substrate and the light absorbing layer include a GaAs compound, and the passivation layer may include an InGap compound.

In addition, a plurality of at least one light absorbing layer may be formed, and a tunnel junction layer may be formed between each of the plurality of light absorbing layers.

In the compound semiconductor solar cell according to the present invention, by moving the emitter layer of the light absorption layer on the rear surface of the base layer, the movement distance of the minority carriers can be shortened as compared with the movement distance of the majority carriers, .

1 and 2 are views for explaining a first embodiment of a compound solar cell according to the present invention.
3 is a comparative example 1 for comparison with the first embodiment of the present invention.
4 is a diagram for explaining the effect of the first embodiment according to the present invention in comparison with Comparative Example 1. Fig.
5 is a view for explaining a second embodiment of a compound solar cell according to the present invention.
6 is a comparison example 2 for comparison with the second embodiment of the present invention.
7 is a diagram for explaining the effect of the second embodiment according to the present invention in comparison with the second comparative example.
8 is a view for explaining a third embodiment of the compound solar cell according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. When a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case directly above another portion but also the case where there is another portion in between. Conversely, when a part is "directly over" another part, it means that there is no other part in the middle. Also, when a part is formed "entirely on another part", it means that it is formed not only on the entire surface (or the front surface) of the other part but also on the edge part.

In the following description, the front surface means a surface positioned in a direction in which direct light is incident, not the reflected light, and the rear surface means a surface located on the opposite surface of the front surface.

1 and 2 are views for explaining a first embodiment of a compound solar cell according to the present invention.

2 (a) is a plan view of the first embodiment, and FIG. 2 (b) is a cross-sectional view taken along line IIB-II in the first embodiment, Fig.

A first embodiment of a compound solar cell according to the present invention includes a first electrode 120, a first cap layer 150, an antireflection film 130, a passivation layer 110, a light absorbing layer PV, a substrate 100, And may include a second electrode 140. Here, at least one of the passivation layer 110 and the substrate 100 may be omitted, but when the passivation layer 110 is included, the efficiency of the solar cell is further improved. When the substrate 100 is included, The process efficiency and yield of the battery are further improved, so that a case where the battery is provided as shown in Figs. 1 and 2 (b) will be described as an example.

1 and 2 (b), the light absorbing layer PV is shown as including a base layer BL, an emitter layer EL and a rear front layer BSF, May be omitted.

However, when the back front layer (BSF) is included, since the efficiency of the solar cell is further improved, a case where the solar cell is provided as shown in FIGS. 1 and 2B will be described as an example.

The light absorbing layer PV may be entirely positioned between the first electrode 120 and the second electrode 140. For example, as shown in FIGS. 1 and 2, when the passivation layer 110 is disposed on the rear surface of the first electrode 120, the passivation layer 110 may be disposed on the rear surface of the passivation layer 110.

The light absorbing layer PV may be formed on the entire surface of the substrate 100 by an epitaxial growth method using an organic metal chemical vapor deposition (MOCVD) method.

At this time, as the epitaxial growth method, a lattice method of growing the lattice constant of the substrate 100 and the lattice constant of the light absorption layer (PV) formed on the substrate 100 may be used .

As such, the light absorbing layer PV may be formed including the base layer BL, the emitter layer EL, and the back front layer BSF. In this case, since the back surface front layer (BSF) may be omitted, the efficiency of the solar cell can be further improved when the light absorbing layer PV includes the back front layer (BSF) The case of including the rear whole layer (BSF) will be described as an example.

In addition, such a light absorbing layer (PV) may be formed including a III-V semiconductor compound. For example, an InGaP compound containing indium (In), gallium (Ga) and phosphorus (P), or a GaAs compound containing gallium (Ga) and arsenic (As). However, it is not necessarily limited to such a semiconductor compound, but may be formed by including other semiconductor compounds. Hereinafter, a case where a light absorbing layer (PV) is formed by including a GaAs compound as an example will be described as an example.

The light absorbing layer PV may be one as described in the first embodiment, but a plurality of the light absorbing layers may be formed. An example in which a plurality of light absorbing layers PV are formed will be described with reference to FIG.

The base layer BL may be located on the front surface of the light absorbing layer PV. 1 and 2, the base layer BL may be formed in contact with the rear surface of the passivation layer 110 when the light absorbing layer PV is one, Unlike the first embodiment, when there are a plurality of light absorbing layers PV, each base layer BL in each light absorbing layer PV is located closest to the front surface of each light absorbing layer PV, that is, the passivation layer 110 .

The base layer BL may be doped with impurities of the first conductivity type by a first thickness, for example, a GaAs compound. However, it is not necessarily limited to the GaAs compound, but other kinds of compounds may be used.

The base layer BL can generate electrons and holes, which are carriers, in response to incident light.

The emitter layer EL may be doped with a second thickness of impurities of the second conductivity type opposite to the first conductivity type and being in contact with the backside of the base layer BL to a second thickness less than the first thickness, May comprise the same GaAs compound as layer (BL). However, it is not necessarily limited to the GaAs compound, and other kinds of compounds having a lattice constant similar to or the same as the base layer BL may be used.

Such an emitter layer EL can collect a small number of carriers in electrons and holes, which are carriers generated in the base layer BL.

In addition, the rear front layer BSF is located in contact with the rear surface of the emitter layer EL, and impurities of the second conductivity type can be doped at a higher concentration than the emitter layer EL. For example, And the like. However, it is not necessarily limited to the GaAs compound, and other kinds of compounds having lattice constants similar to or the same as the emitter layer (EL) may be used.

The impurity of the first conductivity type may be, for example, any one of a p-type impurity and an n-type impurity. The impurity of the p-type may be boron (B), gallium (In), or the like, and the n-type impurity may be an impurity of a pentavalent element such as phosphorus (P), arsenic (As), antimony (Sb), or the like.

In addition, the impurity of the second conductivity type may be an impurity opposite to the first conductivity type. Therefore, when the impurity of the first conductivity type is a p-type impurity, the impurity of the second conductivity type may be an n-type impurity. When the impurity of the first conductivity type is an n-type impurity, May be a p-type impurity.

In the first embodiment, as an example, the case where the impurity of the first conductivity type is an n-type impurity and the impurity of the second conductivity type is a p-type impurity will be described as an example.

Therefore, the base layer BL may be formed of an n-GaAs compound doped with an n-type impurity, and the emitter layer EL may be formed of a p-GaAs compound doped with a p-type impurity, The back front layer (BSF) may be formed of p + -GaAs in which p-type impurities are heavily doped than the emitter layer (EL).

The n-type base layer BL may be in contact with the p-type emitter layer EL to form an electrical PN junction. If light is incident on the base layer BL, Electrons and holes can be generated. Here, the former becomes a majority carrier and the hole becomes a minority carrier.

Electrons which are majority carriers generated in the base layer BL can be collected into the first electrode 120 through the passivation layer 110. Holes which are minority carriers generated in the base layer BL are collected in the emitter layer EL, The backside front layer (BSF), and the substrate 100, as shown in FIG.

The thickness (TBL) of the base layer (BL) may be between 1 탆 and 5 탆 and the thickness (TEL) of the emitter layer (EL) To about 1 mu m.

In addition, the energy bandgap of each of the base layer BL and the emitter layer EL may be between 1.35 eV and 1.45 eV.

The thickness TBSF of the backside front layer BSF may be between 0.5 μm and 2 μm and the energy band gap of the back front layer BSF may be equal to or lower than the energy band gap of the emitter layer EL .

The substrate 100 may be positioned between the light absorbing layer PV and the second electrode 140 and may include a III-V semiconductor compound. For example, gallium (Ga) and arsenic (As) May be formed. In addition, the substrate 100 may be doped with an impurity of the second conductivity type, which is the same type as the emitter layer EL or the back front layer BSF.

Thus, for example, in FIG. 1 and FIG. 2, the substrate 100 may be formed to include a p-GaAs compound doped with a p-type impurity.

The thickness T100 of the substrate 100 is equal to the total thickness T110 + TBL + TEL + TBSF of the passivation layer 110, the base layer BL, the emitter layer EL, For example, between 300 [mu] m and 500 [mu] m.

In FIG. 1, the substrate 100 is provided between the light absorbing layer PV and the second electrode 140. However, the substrate 100 may be omitted.

The passivation layer 110 may be formed between the light absorbing layer PV and the first electrode 120 and may be formed by doping impurities of the same conductivity type as the base layer BL in contact with the passivation layer 110 .

1 and 2B, when the impurity of the first conductivity type of the base layer BL is n-type, the n-type impurity may be doped into the passivation layer 110 .

Such a passivation layer 110 serves to passivate the front surface of the light absorbing layer PV, that is, the front surface of the base layer BL. Therefore, when many carriers (electrons) move to the surface of the light absorbing layer PV, the passivation layer 110 can prevent the carriers from recombining at the surface of the light absorbing layer PV.

In addition, the passivation layer 110 may be formed of a material having the same or similar lattice constant as the compound contained in the base layer BL among the III-V semiconductor compounds. As an example, the passivation layer 110 may be formed comprising an InGaP compound. Accordingly, as shown in FIGS. 1 and 2 (b), the passivation layer 110 may be formed to include an n-InGaP compound.

Since the passivation layer 110 is disposed on the incident surface of the light absorbing layer PV, the energy band gap of the passivation layer 110 may be set to be less than the energy band gap of the base layer BL of the second conductivity type. In one example, the energy band gap of the passivation layer 110 may be between 1.8 eV and 1.9 eV. Accordingly, the light absorptance in the passivation layer 110 can be minimized.

In addition, the thickness (T110) of the passivation layer 110 may be between 0.1 μm and 1 μm.

A quantum dot (not shown) having a diameter of 100 nm or less may be formed on the incident surface of the passivation layer 110, that is, on the front surface thereof, in order to scatter and disperse incident light.

When the light is incident on the quantum dot 110QD, the incident light can be scattered by a plurality of paths by the quantum dot 110QD and refracts the incident angle of light to further increase the light path in the light absorbing layer PV And the light absorbing layer (PV) absorbs a larger amount of light.

The first electrode 120 may be positioned on the front surface of the light absorbing layer PV as shown in FIG. 1 and FIG. 2B. In the case where the passivation layer 110 is provided, 110).

2 (a), the first electrode 120 may include a plurality of finger electrodes 120F formed in a first direction and a plurality of finger electrodes 120F formed in a second direction And a bus bar electrode 120B formed on the bus bar electrode 120B.

The bus bar electrode 120B may be electrically and physically connected to the ends of the plurality of finger electrodes 120F. The plurality of finger electrodes 120F may be spaced apart from each other and may be formed in a stripe shape in a predetermined first direction. So that they can be formed in a stripe shape in the second direction.

Here, each of the plurality of finger electrodes 120F serves to collect carriers, and the bus bar electrode 120B collects all the carriers collected by each of the plurality of finger electrodes 120F and supplies them to an external electric circuit do. For this purpose, a ribbon (not shown) electrically connected to an external electric circuit may be formed on the bus bar electrode 120B.

At this time, the width WF of each finger electrode 120F may be smaller than the width WB of the bus bar electrode 120B. For example, the width WB of the bus bar electrode 120B may be several tens times greater than the width WF of the finger electrode 120F.

In addition, the distance DF between the finger electrodes 120F may be between 1 mm and 2 mm, which is several hundred times larger than the thickness T110 of the light absorption layer PV and the passivation layer 110.

The first electrode 120 may include an electrically conductive material. The first electrode 120 may include at least one of gold (Au), germanium (Ge), and nickel (Ni).

The first cap layer 150 may be positioned between the passivation layer 110 and the first electrode 120 and may have a doping concentration higher than that of the dopant doped in the passivation layer 110.

The first cap layer 150 may form an ohmic contact between the passivation layer 110 and the first electrode 120. That is, when the first electrode 120 is formed in direct contact with the passivation layer 110, the impurity of the passivation layer 110 is relatively small, and the ohmic contact with the first electrode 120 is not well formed, The carrier moved to the layer 110 can not easily move to the first electrode 120 and can be destroyed.

However, when the first cap layer 150 is formed between the first electrode 120 and the passivation layer 110 as in the present invention, the first cap layer 150 forming the ohmic contact with the first electrode 120 So that the short circuit current Jsc of the compound semiconductor solar cell can be improved.

In order to form an ohmic contact with the first electrode 120, the doping concentration of the doped impurity in the first cap layer 150 may be higher than that of the dopant doped in the passivation layer 110.

The first cap layer 150 may be doped with the same impurity of the first conductivity type as the passivation layer 110 and may include a compound that is the same as or similar to the lattice constant of the passivation layer 110. For example, the first cap layer 150 may be formed to include an n + -GaAs compound.

The antireflection film 130 may be disposed on the front surface of the light absorbing layer PV and on a part of the first electrode 120. When the passivation layer 110 is provided as shown in FIG. 120) and the passivation layer (110).

Specifically, the antireflection film 130 may be formed on the plurality of finger electrodes 120F, but not on the bus bar electrode 120B, as shown in FIG.

1, the second electrode 140 may be positioned entirely on the rear surface of the light absorbing layer PV. When the substrate 100 is positioned on the rear surface of the light absorbing layer PV, Lt; RTI ID = 0.0 > a < / RTI >

In the compound semiconductor solar cell according to the present invention, a light absorbing layer (PV), a passivation layer (not shown) are formed on the entire surface of a GaAs compound substrate 100 manufactured in advance by using MOCVD (Metal Organic Chemical Vapor Deposition) 110 and the first cap layer 150 may be sequentially formed by an epitaxial growth method.

At this time, as the epitaxial growth method, a lattice method of growing the lattice constant of the substrate 100 and the lattice constant of the light absorption layer (PV) formed on the substrate 100 may be used .

The operation of a compound semiconductor solar cell having such a structure is as follows.

When light is incident on the front surface of a compound semiconductor solar cell, incident light generates electron-hole pairs in the base layer (BL) in the light absorbing layer (PV). These electron-hole pairs are separated into electrons and holes by the pn junction of the base layer BL and the emitter layer EL and electrons which are majority carriers in the base layer BL pass through the passivation layer 110 and the first cap layer And the holes which are minority carriers in the base layer BL are transferred to the second electrode 140 through the emitter layer EL, the back front layer BSF and the substrate 100, .

At this time, if the first electrode 120 and the second electrode 140 are connected to each other by a lead wire, a current flows and it is moved from outside to the outside.

On the other hand, in such a structure, the compound semiconductor solar cell according to the present invention can improve the efficiency of the solar cell overall by placing the emitter layer EL on the rear surface of the base layer BL.

This will be described below in comparison with the comparative example shown in Fig.

3 is a comparative example 1 for comparison with the first embodiment of the present invention.

The greatest difference between Comparative Example 1 according to FIG. 3 and the first embodiment is that the emitter layer EL 'is located on the front surface of the base layer BL', unlike the first embodiment.

Accordingly, impurities doped in the passivation layer 110 'may be the same impurities as the impurities doped in the emitter layer EL', and impurities doped to the back front layer BSF 'may also be doped into the base layer BL' May be the same as the impurity to be doped.

Therefore, in Comparative Example 1, the base layer BL 'is an n-GaAs compound, the emitter layer EL' is a p-GaAs compound, the passivation layer 110 'is a p-InGaP compound, n + -GaAs compound.

Therefore, in Comparative Example 1, since the base layer BL 'is formed of the n-GaAs compound, the holes become the minority carriers collecting in the emitter layer EL', and the electrons become the majority carriers.

Here, the thicknesses T110 ', TEL', TBL ', and TBSF of the passivation layer 110', the emitter layer EL ', the base layer BL', the back whole layer BSF ' ', T100') may be the same as the thicknesses (T110, TEL, TBL, TBSF, T100) of each layer in the first embodiment.

Typically, the short circuit current Jsc in the solar cell is determined according to the amount of carriers collected in the first electrode 120 'and the second electrode 140', and in the case of Comparative Example 1, the base layer BL ' The emitter layer EL 'is formed toward the first electrode 120', and the minority carriers are collected by the first electrode 120 'and the majority carriers are collected by the second electrode 140' Collected.

Here, theoretically, the amount of the minority carriers collected by the first electrode 120 'and the amount of the majority carriers collected by the second electrode 140' may always be the same. However, the carrier which is more sensitive to the short circuit current (Jsc) of the solar cell may be a minority carrier.

This is because the minority carriers can be recombined and disappeared for a variety of reasons during the movement. If the minority carriers disappear during the movement, the amount of minority carriers collected by the first electrode 120 'can be reduced accordingly. , The number of carriers collected by the second electrode 140 'also has to be reduced. In this case, the short circuit current of the solar cell can also be reduced.

The problem is that the majority carriers generated in the base layer BL 'have a relatively large amount of majority carriers even though the traveling distance is long, so that even if some are recombined, they do not significantly affect the short circuit current of the solar cell, ) May have a relatively large influence on the short circuit current of the solar cell because the amount of minority carrier is relatively small when the moving distance is long.

Therefore, when the moving distance of the minority carriers is shorter than the moving distance of the majority carriers, the efficiency of the solar cell can be more advantageous.

3, the emitter layer EL 'is positioned closer to the incident surface of the light absorbing layer PV' than the base layer BL '. In this case, the minority carriers (here, Hole) is longer than several carriers by a few hundred mu m or more.

That is, the minority carriers moving to the first electrode 120 of the solar cell not only move the solar cell in the vertical direction parallel to the light incidence direction (or in a direction parallel to the thickness direction of each layer), but also the emitter layer EL ' (Or in a direction perpendicular to the thickness direction of each layer) parallel to the plane forming direction of the layer 110 '. In this case, the moving distance in the horizontal direction is longer than the moving distance in the vertical direction by several hundred micrometers have.

The distance DF 'between the finger electrodes 120F' formed on the front surface of the solar cell is greater than the distance DF 'between the light absorption layer PV' and the passivation layer 110 ' of the thickness T110 '.

For example, the maximum distance between the finger electrodes 120F 'is 2 mm and the base layer BL' (maximum thickness 5 μm), emitter layer EL '(maximum thickness 1 μm), passivation layer 110' Maximum thickness 1 占 퐉) may be 7 占 퐉.

Therefore, in Comparative Example 1, the distance of movement of the minority carriers collected by the first electrode 120 'may be approximately 2 mm (negligible since 7 탆 is minus 2 mm).

In addition, in Comparative Example 1, the distance by which the majority carriers collected by the second electrode 140 'move is divided into a base layer BL (maximum thickness 5 mu m), a back front layer BSF (maximum thickness 2 mu m) 100 ") (maximum thickness 500 mu m), it can be approximately 500 mu m (7 mu m is negligible as compared with 500 mu m).

Therefore, in Comparative Example 1, the minority carriers must move about 1500 占 퐉 more than the majority carriers.

In such a case, the minority carrier having a relatively larger moving distance is more likely to disappear by recombination during the movement, which may result in lowering the efficiency of the solar cell.

However, in the first embodiment according to the present invention, the emitter layer EL is formed toward the second electrode 140 with respect to the base layer BL, so that the minority carriers are collected in the second electrode 140 And a plurality of carriers may be collected at the first electrode 120. [

Therefore, in the case of the first embodiment according to the present invention, the maximum distance that the minority carriers can move decreases from 2 mm to 500 탆, although the moving distance of the majority carriers increases from 500 탆 to 2 mm as compared with Comparative Example 1.

Thus, the probability that the minority carriers can recombine can be greatly reduced.

In addition, in Comparative Example 1, since the hole having a relatively small mobility is a minority carrier, the short-circuit current of the solar cell can be further lowered due to a large increase in the resistance component. However, in the present invention, Since the relatively large electrons are the minority carriers, the resistance component can be largely reduced, and the shortcircuit current can be further improved.

In the comparative example 1, since the emitter layer EL 'is located on the front surface of the base layer BL', the amount of light absorbed by the emitter layer EL 'may be relatively large and the emitter layer EL' The amount of electrons generated due to light absorption can be relatively increased.

Therefore, in Comparative Example 1, the probability that the minority carriers (holes) passing through the emitter layer EL 'are recombined with the electrons generated in the emitter layer EL' during traveling can be greatly increased.

However, in the first embodiment according to the present invention, since the emitter layer EL is located on the rear surface of the base layer BL, the amount of light absorbed in the emitter layer EL can be relatively small and the emitter layer EL ) May be relatively small. Thus, in the present invention, the probability that recombination of electrons generated in the emitter layer (EL) during the movement of the minority carriers (holes) passing through the emitter layer (EL) can be greatly reduced.

Therefore, the compound solar cell according to the first embodiment of the present invention can greatly increase the efficiency of the solar cell as compared with the comparative example 1.

4 is a diagram for explaining the effect of the first embodiment according to the present invention in comparison with Comparative Example 1. Fig.

4 (a) is a graph comparing the comparative open-circuit voltage (Voc) with that of the first embodiment and FIG. 4 (b) , and (d) are graphs comparing efficiency.

4, the first embodiment of the present invention is different from the first comparative example in that (a) the open-circuit voltage is improved by 0.05 V, (b) the short-circuit current is improved by 0.8 mA, (c) (D) efficiency was improved from 21.1% to 23.5%, as a whole.

Here, as compared with Comparative Example 1, the open-circuit voltage of the first embodiment is further improved because the open-circuit voltage Voc is proportional to the log Jsc value.

Although the case where the base layer BL is an n-type has been described as an example in the first embodiment so far, the present invention can also be applied to the case where the base layer BL is p-type.

5 is a view for explaining a second embodiment of a compound solar cell according to the present invention.

5, the positions of the passivation layer 110, the base layer BL, the emitter layer EL, the back front layer BSF, and the substrate 100 may be the same as in the first embodiment, May be the same as that of the first embodiment, and the compound contained in each layer may be the same as that of the first embodiment.

Therefore, the description of the position of each layer, the material of the compound, and the thickness is omitted.

However, as shown in FIG. 5, the second embodiment of the present invention differs from the first embodiment in that the impurity of the first conductivity type doped in the base layer BL may be a p-type impurity.

Therefore, in the base layer BL according to the second embodiment, holes become majority carriers and electrons become minor carriers.

The impurity of the second conductive type doped in the emitter layer EL may be an n-type impurity. Therefore, the passivation layer 110 located on the front surface of the base layer BL is also doped with the p- .

In addition, the rear front layer (BSF) located on the rear surface of the emitter layer EL can be doped with the impurity of the same n-type type as that of the emitter layer EL at a higher concentration than the emitter layer EL.

Therefore, in the second embodiment of the present invention, the passivation layer 110 is formed of a p-InGaP compound, the base layer BL is formed of a p-GaAs compound, the emitter layer EL is formed of an n-GaAs compound, ) May be formed including an n + -GaAs compound.

Accordingly, in the second embodiment according to the present invention, the holes, which are the majority carriers, can be collected by the first electrode 120 and the electrons which are the minor carriers can be collected by the second electrode 140, Which is shorter than 2 mm, which is the maximum moving distance of the carrier.

Accordingly, in the second embodiment according to the present invention, the moving distance of the minority carriers is significantly shortened as compared with the moving distance of the majority carriers, so that the overall efficiency of the solar cell can be further improved.

6 is a comparison example 2 for comparison with the second embodiment of the present invention.

The greatest difference between Comparative Example 2 and Second Embodiment according to FIG. 6 is that the emitter layer EL 'is on the front surface of the base layer BL', unlike the second embodiment.

Accordingly, impurities doped in the passivation layer 110 'may be impurities of the second conductivity type that are the same as impurities doped in the emitter layer EL', and impurities doped to the back front layer BSF ' (BL ').

Therefore, in Comparative Example 2, the n-InGaP compound and the back front layer BSF 'are formed in the base layer BL', the emitter layer EL ', and the passivation layer 110' p < + > -GaAs compound.

Therefore, in Comparative Example 2, since the base layer BL 'is formed of the p-GaAs compound, the electrons become the minority carriers that are collected by the emitter layer EL', and the holes become the majority carriers.

Here, the thicknesses of the passivation layer 110 ', the emitter layer EL', the base layer BL ', the back whole front layer BSF' and the substrate 100 'are the same as the thicknesses of the respective layers of the second embodiment can do.

Therefore, in the same manner as in Comparative Example 2, the emitter layer EL 'is formed toward the first electrode 120' with respect to the base layer BL ', and the minority carriers are collected by the first electrode 120' And a plurality of carriers are collected at the second electrode 140 '.

Therefore, like the above-described Comparative Example 1, the movement distance of the minority carriers is longer than the movement distance of the majority carriers, and the probability that the minority carriers are recombined is relatively large.

In the case of using the p-type base layer BL 'as in Comparative Example 2, the mobility of electrons as minority carriers is very high, but the electron mobility in the p-type base layer BL' due to the relatively low doping efficiency The number of defects is higher than that of the n-type base layer BL ', and the recombination frequency in the base layer BL' can be relatively high.

Therefore, in the case of Example 2 according to the present invention, the efficiency of the solar cell can be further improved as compared with Comparative Example 2.

7 is a diagram for explaining the effect of the second embodiment according to the present invention in comparison with the second comparative example.

7 (a) is a graph comparing the open-circuit voltage (Voc) of Comparative Example 2 with that of the second embodiment, FIG. 7 (b) , and (d) are graphs comparing efficiency.

As shown in Fig. 7, the second embodiment of the present invention is different from the second comparative example in that (a) the open-circuit voltage is improved by 0.017 V, (b) the short-circuit current is improved by 0.24 mA, (c) Is improved by 0.01, and (d) the efficiency is improved from 19.5% to 20.3% as a whole.

As described above, in the solar cell according to the present invention, the emitter layer EL is located on the rear surface of the base layer BL, so that the moving distance of the minority carriers can be made shorter than the moving distance of the majority carriers. Thus, the efficiency of the solar cell can be further improved.

Up to now, only one light absorbing layer (PV) of a compound semiconductor solar cell has been described as an example, but the same can be applied to a case where a plurality of light absorbing layers (PV) exist.

8 is a view for explaining a third embodiment of the compound solar cell according to the present invention.

8A shows an example of a compound semiconductor solar cell having a plurality of light absorbing layers PV and FIG. 8B shows a detailed configuration of each of the plurality of light absorbing layers PV1, PV2, PV3, and PV4 It is an example.

8, except that a plurality of light absorbing layers PV are formed (PV1, PV2, PV3, and PV4) and tunnel junction layers TJ1, TJ2, and TJ3 are formed between the respective light absorbing layers PV. The materials and thicknesses of the base layer BL, the emitter layer EL and the back front layer BSF in the photovoltaic cell PV are the same as those of the first embodiment or the second embodiment described above, and the passivation layer 110, The substrate 100, the first electrode 120, and the second electrode 140 are also the same as in the first embodiment, and a description thereof will be omitted.

8 (a), even when a plurality of light absorbing layers PV are provided, each light absorbing layer PV is formed by laminating the emitter layer EL on the base layer < RTI ID = 0.0 > (BL), and the back front layer (BSF) may be located on the back side of the emitter layer (EL).

In addition, as shown in FIG. 8A, a tunnel junction layer (TJ1, TJ2, TJ3) may be formed between the respective light absorbing layers PV.

The tunnel junction layers TJ1, TJ2 and TJ3 form ohmic contacts between the light absorbing layers PV1, PV2, PV3 and PV4 adjacent to each other with respect to the tunnel junction layers TJ1, TJ2 and TJ3, (PV1, PV2, PV3, PV4) to move more smoothly.

For example, unlike FIG. 8, in the case of two light absorbing layers PV, one tunneling junction layer may be formed between two light absorbing layers PV, and in the case of three light absorbing layers PV, Two tunnel junction layers may be formed between the light absorbing layers PV.

Each of the tunnel junction layers TJ1, TJ2, and TJ3 may include an upper tunnel junction layer (not shown) and a lower tunnel junction layer (not shown) located on the rear surface of the upper tunnel junction layer.

The upper tunnel junction layer may be formed by doping impurities of the second conductivity type, which is the same as the back front layer (BSF) of the light absorbing layer (PV) on the front surface of the upper tunnel junction layer, at a higher concentration than the back front layer have.

In addition, the lower tunnel junction layer may be formed by doping the impurity of the first conductivity type, which is the same as the base layer BL located on the rear surface of the lower tunnel junction layer, at a higher concentration than the base layer BL.

Therefore, for example, when the base layer BL of each light absorbing layer PV is an n-GaAs compound, the emitter layer EL is a p-GaAs compound, and the rear whole layer BSF is a p + -GaAs compound, In the tunnel junction layers (TJ1, TJ2, TJ3) positioned between the absorption layers (PV), the upper tunnel junction layer may be a p ++ - GaAs compound and the lower tunnel junction layer may be an n ++ - GaAs compound.

In addition, the thicknesses of the tunnel junction layers TJ1, TJ2, and TJ3 including the upper tunnel junction layer and the lower tunnel junction layer may be between 0.05 mu m and 0.07 mu m.

Since the emitter layer EL is located on the rear surface of the base layer BL in each of the light absorbing layers PV even when a plurality of the light absorbing layers PV are present, the minority carriers are collected in the second electrode 140, The majority carriers can be collected into the first electrode 120.

Accordingly, the moving distance of the minority carriers can be reduced to a greater extent than the moving distance of the majority carriers, and the efficiency of the solar cell can be further improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

Claims (18)

A base layer doped with an impurity of a first conductivity type by a first thickness, and an emitter layer doped with a second thickness of impurities of a second conductivity type opposite to the first conductivity type, the second thickness being less than the first thickness Of the light absorption layer;
A first electrode located on a front surface of the at least one light absorbing layer which is an incident surface; And
And a second electrode located on a rear surface opposite to the incident surface of the at least one light absorbing layer,
Wherein the emitter layer is located on the rear surface of the base layer in the light absorbing layer. The method according to claim 1,
The at least one light absorbing layer
Wherein the second conductive type impurity is further doped at a higher concentration than the emitter layer. 3. The method of claim 2,
And the rear whole layer is located on the rear surface of the emitter layer. The method according to claim 1,
Wherein the thickness of the base layer is between 1 탆 and 5 탆. The method according to claim 1,
Wherein the thickness of the emitter layer is between 0.1 mu m and 1 mu m. The method according to claim 1,
And each energy band gap of the base layer and the emitter layer is between 1.35 eV and 1.45 eV. The method according to claim 1,
And a passivation layer doped with the impurity of the first conductivity type is further provided between the at least one light absorbing layer and the first electrode. 8. The method of claim 7,
Wherein an energy band gap of the passivation layer is higher than an energy band gap of the base layer. 8. The method of claim 7,
And the energy band gap of the passivation layer is between 1.8 eV and 1.9 eV. 8. The method of claim 7,
Further comprising an antireflection film on the passivation layer,
Wherein the antireflection film is formed to cover at least part of the first electrode and the passivation layer. 8. The method of claim 7,
Wherein the first electrode includes a plurality of finger electrodes formed in a first direction and a bus bar electrode formed in a second direction to connect the plurality of finger electrodes to each other. 12. The method of claim 11,
And a first cap layer doped with impurities of the first conductivity type at a higher concentration than the passivation layer is further disposed between each finger electrode and the passivation layer. 12. The method of claim 11,
Wherein the antireflection film is formed on the plurality of finger electrodes, and the antireflection film is not formed on the bus bar electrode. The method according to claim 1,
Wherein a substrate is further included between the at least one light absorbing layer and the second electrode. 15. The method of claim 14,
Wherein the substrate and the light absorbing layer are formed of the same compound,
Wherein the passivation layer and the light absorbing layer are formed of different compounds. 15. The method of claim 14,
Wherein the substrate and the light absorbing layer comprise a GaAs compound. 8. The method of claim 7,
Wherein the passivation layer comprises an InGaP compound. The method according to claim 1,
A plurality of the at least one light absorbing layer,
And a tunnel junction layer is formed between each of the plurality of light absorbing layers.

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