Tandem solar cell

Abstract

The present invention relates to a tandem solar cell, and more particularly, to a tandem solar cell in which a plurality of solar cells are electrically connected. The tandem solar cell according to an embodiment of the present invention includes a first solar cell unit having a first upper electrode and a first lower electrode that are arranged apart from each other, a second solar cell unit provided below the first solar cell unit and having a second upper electrode and a second lower electrode that are arranged apart from each other, a first output terminal unit connected to the first upper electrode, a second output terminal unit connected to the second lower electrode, and a third output terminal unit commonly connected to the first lower electrode and the second upper electrode.

Description

Technical Field

[0001] The present invention relates to a tandem solar cell, and more particularly, to a tandem solar cell in which a plurality of solar cells are electrically connected.

Background Art

[0002] A solar cell is a device that converts solar energy, i.e., sunlight, into electrical energy and outputs it using the properties of semiconductors.

[0003] A solar cell has a P-N junction structure in which a P (positive) type semiconductor and an N (negative) type semiconductor are joined. When sunlight is incident on a solar cell having such a structure, holes and electrons are generated in the semiconductor by the energy of the incident light. At this time, due to the electric field generated in the P-N junction, the holes move to the P-type semiconductor side and the electrons move to the N-type semiconductor side, generating a potential, thereby making it possible to produce electrical energy, i.e., electric power.

[0004] Recently, in order to improve the efficiency of solar cells, efforts have been actively made to develop tandem solar cells formed by stacking and electrically connecting a plurality of solar cells. However, in tandem solar cells, since the amount of light incident on each solar cell is different from each other, it is very difficult to achieve current matching between solar cells, and thus there is a problem of low photoelectric conversion efficiency.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention provides a tandem solar cell that can utilize the idle current generated from a plurality of solar cells.

Means for Solving the Problems

[0007] The tandem solar cell according to an embodiment of the present invention includes a first solar cell unit having a first upper electrode and a first lower electrode that are arranged apart from each other, a second solar cell unit provided below the first solar cell unit and having a second upper electrode and a second lower electrode that are arranged apart from each other, a first output terminal unit connected to the first upper electrode, a second output terminal unit connected to the second lower electrode, and a third output terminal unit commonly connected to the first lower electrode and the second upper electrode.

[0008] A first load may be connected between the first output terminal unit and the second output terminal unit, a second load may be connected between the first output terminal unit and the third output terminal unit, and a third load may be connected between the second output terminal unit and the third output terminal unit.

[0009] The tandem solar cell may further include a first current adjustment unit provided between the first output terminal unit and the third output terminal unit, a second current adjustment unit provided between the second output terminal unit and the third output terminal unit, and a control unit for controlling the operations of the first current adjustment unit and the second current adjustment unit.

[0010] The tandem solar cell may further include a first light amount sensing unit for sensing the amount of sunlight incident on the first solar cell unit and a second light amount sensing unit for sensing the amount of sunlight incident on the second solar cell unit, and the control unit may selectively operate the first current adjustment unit and the second current adjustment unit according to the amount of sunlight sensed by the first light amount sensing unit and the second light amount sensing unit.

[0011] When the amount of light detected by the first light amount detection unit is greater than a first reference light amount that has already been set, or when the amount of light detected by the second light amount detection unit is less than a second reference light amount that has already been set, the control unit may operate the first current adjustment unit. When the amount of light detected by the first light amount detection unit is less than the first reference light amount, or when the amount of light detected by the second light amount detection unit is greater than the second reference light amount, the control unit may operate the second current adjustment unit.

[0012] The tandem solar cell further includes a current detection unit provided between the first output terminal unit and the second output terminal unit. The control unit may control the operation of at least one of the first current adjustment unit and the second current adjustment unit according to the amount of current detected by the current detection unit.

[0013] At least one of the first current adjustment unit and the second current adjustment unit may include a switch element.

[0014] When there is no change in the amount of current detected by the current detection unit within a set time period, the control unit may switch the switch element in the off state to the on state.

[0015] After the control unit switches the switch element to the on state, if the amount of current detected by the current detection unit decreases, the control unit may switch the switch element in the on state to the off state.

[0016] At least one of the first current adjustment unit and the second current adjustment unit may include a variable resistance element.

[0017] When there is no change in the amount of current detected by the current detection unit within a set time, the control unit may decrease the resistance value of the variable resistance element set to the maximum resistance value.

[0018] While decreasing the resistance value of the variable resistor element, if the amount of current sensed by the current sensing unit decreases, the control unit may hold the decreased resistance value of the variable resistor element.

[0019] The first solar cell unit may include a first transparent substrate for transmitting sunlight incident from above, and the second solar cell unit may include a second transparent substrate for transmitting sunlight incident from below.

[0020] The tandem solar cell may further include a junction layer provided between the first lower electrode and the second upper electrode.

[0021] At least one of the first load, the second load, and the third load may include a secondary battery.

Advantages of the Invention

[0022] According to the tandem solar cell according to the embodiment of the present invention, in addition to the first output terminal portion and the second output terminal portion for supplying power to the main load, a third output terminal portion for supplying power to the auxiliary load is provided, and the idle current generated by the difference in the amount of current generated in each solar cell can be further supplied to the auxiliary load.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be embodied in various different forms. These embodiments are merely provided to make the disclosure of the present invention complete and to fully inform those with ordinary knowledge of the scope of the invention.

[0025] Throughout the specification, when referring to one component such as a film, region, or substrate being "on" another component, it is to be interpreted that the one component may be in direct contact "on" the other component or there may be other components intervening between them.

[0026] Also, relative terms such as "upper" or "lower" may be used herein to describe the relative relationship of one element to another as shown in the drawings. It is to be understood that relative terms are intended to include other directions of the element in addition to the directions depicted in the figures. Here, the drawings may be shown exaggerated for the purpose of explaining the present invention in detail, and in the figures, the same reference numerals indicate the same elements.

[0027] FIG. 1 is a diagram schematically showing a tandem solar cell according to an embodiment of the present invention.

[0028] Referring to FIG. 1, a tandem solar cell according to an embodiment of the present invention includes a first solar cell unit 100 having a first upper electrode 120 and a first lower electrode 140 disposed apart from each other, a second solar cell unit 200 provided below the first solar cell unit 100 and having a second upper electrode 240 and a second lower electrode 220 disposed apart from each other, a first output terminal portion T1 connected to the first upper electrode 120, a second output terminal portion T2 connected to the second lower electrode 220, and a third output terminal portion T3 commonly connected to the first lower electrode 140 and the second upper electrode 240.

[0029] Here, a first load 310 may be connected between the first output terminal portion T1 and the second output terminal portion T2, a second load 320 may be connected between the first output terminal portion T1 and the third output terminal portion T3, and a third load 330 may be connected between the second output terminal portion T2 and the third output terminal portion T3.

[0030] The first solar cell unit 100 absorbs sunlight incident from above and converts it into electrical energy. Such a first solar cell unit 100 may include a crystalline solar cell, an amorphous solar cell, a thin film solar cell, a dye-sensitized solar cell, an organic solar cell, a quantum dot solar cell, or a perovskite solar cell. Hereinafter, an exemplary structure in which the first solar cell unit 100 includes a first substrate 110, a first upper electrode 120 provided below the first substrate 110, a first light absorbing layer 130 provided below the first upper electrode 120, and a first lower electrode 140 provided below the first light absorbing layer 130 will be described. However, the present invention is not limited thereto, and it goes without saying that the present invention is applicable to various well-known solar cells.

[0031] The first substrate 110 may include a transparent substrate for transmitting sunlight incident from above. When the first substrate 110 includes a transparent substrate, the first substrate 110 may be made of glass.

[0032] The first upper electrode 120 is provided on the lower side of the first substrate 110. The first upper electrode 120 may be made of a transparent conductive material in order to transmit the sunlight that has passed through the first substrate 110 to the first light absorption layer 130 provided on the lower side of the first upper electrode 120. Such a transparent conductive material may include a material having high light transmittance and excellent electrical conductivity, such as ZnO:Al, ZnO:B, or ZnO:Ga (GZO).

[0033] The first output terminal portion T1 may be provided in connection with the first upper electrode 120. Such a first output terminal portion T1 may be electrically connected to the first upper electrode 120 by a conducting wire or wiring and connected to one terminal of a first load 310 that receives the power generated from the tandem solar cell. At this time, the first load 310 may include a secondary battery that stores the power generated from the tandem solar cell and can supply it to the outside, but the present invention is not limited thereto at all, and may include various electrical devices capable of receiving the power generated from the tandem solar cell.

[0034] The first light absorption layer 130 is provided on the lower side of the first upper electrode 120. The first light absorption layer 130 may be made of a silicon-based material such as amorphous silicon or crystalline silicon, but the present invention is not limited thereto at all, and it goes without saying that it may be made of various materials that generate holes and electrons from the incident sunlight.

[0035] For example, the first light absorption layer 130 may be formed in an NIP structure including an N (negative) type semiconductor layer, a P (positive) type semiconductor layer, and an I (intrinsic) type semiconductor layer provided between the N type semiconductor layer and the P type semiconductor layer. In this way, if the light absorption layer 115 is formed in an NIP structure, the I type semiconductor layer is depleted by the P type semiconductor layer and the N type semiconductor layer, and an internal electric field is generated. As a result, holes and electrons generated by incident sunlight can be drifted by the electric field and collected in the P type semiconductor layer and the N type semiconductor layer, respectively.

[0036] The first lower electrode 140 is provided below the first light absorption layer 130. The first lower electrode 140 may be made of a transparent conductor in order to transmit sunlight that has passed through the first light absorption layer 130 or sunlight that has passed through the second solar cell unit 200 described later. As described above, such a transparent conductor may include a material having high light transmittance and excellent electrical conductivity, such as ZnO:Al, ZnO:B, or ZnO:Ga (GZO).

[0037] The second solar cell unit 200 absorbs sunlight and converts it into electrical energy. The second solar cell unit 200 may also include a crystalline solar cell, an amorphous solar cell, a thin film solar cell, a dye-sensitized solar cell, an organic solar cell, a quantum dot solar cell, a perovskite solar cell, or the like. Hereinafter, an exemplary structure in which the second solar cell unit 200 includes a second substrate 210, a second lower electrode 220 provided above the second substrate 210, a second light absorption layer 230 provided above the second lower electrode 220, and a second upper electrode 240 provided above the second light absorption layer 230 will be described. However, the present invention is not limited thereto, and it goes without saying that the present invention is applicable to various well-known solar cells.

[0038] Here, the second solar cell unit 200 can absorb the sunlight that has passed through the first solar cell unit 100 described above and convert it into electrical energy, and can also absorb the sunlight incident from below and convert it into electrical energy. That is, the tandem solar cell according to the embodiment of the present invention may be a tandem solar cell of a single-sided light receiving type in which the second solar cell unit 200 absorbs the sunlight that has passed through the first solar cell unit 100 and converts it into electrical energy, or together with the first solar cell unit 100 that absorbs the sunlight incident from above and converts it into electrical energy, the second solar cell unit 200 may be a tandem solar cell of a double-sided light receiving type that absorbs the sunlight incident from below and converts it into electrical energy.

[0039] The second substrate 210 may include an opaque substrate or a transparent substrate. That is, the second substrate 210 may include an opaque substrate in the case of the single-sided light receiving type, and may include a transparent substrate in the case of the double-sided light receiving type. However, it goes without saying that the second substrate 210 may include a transparent substrate even in the case of the single-sided light receiving type. When the second substrate 210 includes a transparent substrate, the second substrate 210 may be made of glass in order to transmit the sunlight incident from below.

[0040] The second lower electrode 220 is provided on the upper side of the second substrate 210. Further, the second light absorption layer 230 is provided on the upper side of the second lower electrode 220 and can absorb the sunlight that has passed through the first solar cell unit 100, or can absorb the sunlight incident from below and passing through the second substrate 210. Further, the second upper electrode 230 may be provided on the upper side of the second light absorption layer 230. Regarding the second lower electrode 220, the second light absorption layer 230, and the second upper electrode 240, since the structures of the electrodes and the light absorption layer described above regarding the first solar cell unit 100 are similarly applicable, redundant descriptions are omitted.

[0041] The second output terminal portion T2 may be provided connected to the second lower electrode 220. Such a second output terminal portion T2 may be electrically connected to the second lower electrode 220 by a conducting wire or wiring and connected to the other terminal of a first load 310 that receives the supply of electric power generated from the tandem solar cell.

[0042] The tandem solar cell according to an embodiment of the present invention may further include a bonding layer 800 for bonding the first solar cell portion 100 and the second solar cell portion 200. Such a bonding layer 800 is provided between the second upper electrode 240 located on the upper side of the second solar cell portion 200 and the first lower electrode 140 located on the lower side of the first solar cell portion 100, and can be bonded so that the first solar cell portion 100 is laminated on the second solar cell portion 200. Such a bonding layer 800 may contain a light-transmissive substance, and the light-transmissive substance may include a polyolefin elastomer (POE), a thermosetting resin, a photocurable resin, and the like.

[0043] On the other hand, the second upper electrode 240 located on the upper side of the second solar cell portion 200 and the first lower electrode 140 located on the lower side of the first solar cell portion 100 may be electrically connected to each other. In this way, when the second upper electrode 240 and the first lower electrode 140 are electrically connected, the power generation efficiency of the solar cell can be improved. However, since the first solar cell portion 100 and the second solar cell portion 200 are connected in series, it is necessary to perform current matching to match the current output from the first solar cell portion 100 and the current output from the second solar cell portion 200.

[0044] For current matching, in the tandem solar cell according to an embodiment of the present invention, at least one of the first light absorption layer 130 and the second light absorption layer 230 is patterned as a plurality of unit cells, and the second upper electrode 240 and the first lower electrode 140 can connect the unit cells in which the first light absorption layer 130 is patterned and the unit cells in which the second light absorption layer 230 is patterned by combining a series structure and a parallel structure. For example, when it is expected that sunlight with a first reference light amount is incident on the first solar cell unit 100 and sunlight with a second reference light amount is incident on the second solar cell unit 200, at least one of the first light absorption layer 130 and the second light absorption layer 230 is patterned as a plurality of unit cells so that the current output from the first solar cell unit 100 when sunlight with the first reference light amount is incident and the current output from the second solar cell unit 200 when sunlight with the second reference light amount is incident have the same value, and the second upper electrode 240 and the first lower electrode 140 can connect each patterned unit cell by combining a series structure and a parallel structure.

[0045] Thus, at least one of the first light absorption layer 130 and the second light absorption layer 230 is patterned as a plurality of unit cells, and the second upper electrode 240 and the first lower electrode 140 are connected by combining the series structure and the parallel structure of each patterned unit cell, so that when sunlight with a reference light amount is incident, current matching between the first solar cell unit 100 and the second solar cell unit 200 can be achieved. However, when sunlight exceeding the reference light amount or sunlight less than the reference light amount is incident on at least one of the first solar cell unit 100 and the second solar cell unit 200, the current output from the first solar cell unit 100 and the current output from the second solar cell unit 200 are limited to currents having relatively small values, and the photoelectric conversion efficiency of the tandem solar cell decreases. In the case where the tandem solar cell is a double-sided light receiving type in which the first solar cell unit 100 absorbs sunlight incident from above and converts it into electrical energy, and the second solar cell unit 200 absorbs sunlight incident from below and converts it into electrical energy, it is almost impossible to keep the sunlight incident from above and below at the reference light amount, so such a problem occurs more seriously.

[0046] Therefore, the tandem solar cell according to an embodiment of the present invention forms a third output terminal portion T3 so as to be commonly connected to the first lower electrode 140 and the second upper electrode 240, and utilizes the idle current generated by the difference between the current output from the first solar cell portion 100 and the current output from the second solar cell portion 200. For this purpose, the third output terminal portion T3 may be electrically connected to the first lower electrode 140 and the second upper electrode 240 by conductors or wirings, respectively. When the third output terminal portion T3 is formed, the first output terminal portion T1 may be connected to one terminal of a second load 320 provided separately from the first load 310, and the third output terminal portion T3 may be connected to the other terminal of the second load 320. Also, the third output terminal portion T3 may be connected to one terminal of a third load 330 provided separately from the first load 310, and the second output terminal portion T2 may be connected to the other terminal of the third load. At this time, the second load 320 and the third load 330 may include a secondary battery capable of storing the power generated from the idle current and supplying it to the outside, but the present invention is not limited thereto, and may include various electric devices capable of receiving the power generated from the idle current.

[0047] Further, the tandem solar cell according to an embodiment of the present invention further includes a first current adjustment unit 170 provided between the first output terminal portion T1 and the third output terminal portion T3, a second current adjustment unit 270 provided between the second output terminal portion T2 and the third output terminal portion T3, and a control unit 400 for controlling the operations of the first current adjustment unit 170 and the second current adjustment unit 270, in order to maximize the utilization of the idle current generated by the difference between the current output from the first solar cell portion 100 and the current output from the second solar cell portion 200. Such first current adjustment unit 170 and second current adjustment unit 270 may include a switch element or a variable resistance element.

[0048] FIG. 2 is a diagram showing a state in which a current adjustment unit is arranged according to an embodiment of the present invention. Here, FIG. 2(a) is a diagram exemplifying a case where the current adjustment unit includes a switch element, and FIG. 2B is a diagram exemplifying a case where the current adjustment unit includes a variable resistance element.

[0049] Referring to FIG. 2(a), the current adjustment unit may include a switch element. That is, at least one of the first current adjustment unit 170 and the second current adjustment unit 270 may include a switch element. For example, the first current adjustment unit 170 may include a first switch element 170a, and the second current adjustment unit 270 may include a second switch element 270a. Here, the second load 320 and the first switch element 170a may be arranged to be connected in series on a path electrically connecting the first output terminal portion T1 and the third output terminal portion T3, that is, on a conducting wire or wiring. At this time, the first switch element 170a may be set to an off state in which the path connecting the first output terminal portion T1 and the third output terminal portion T3 is disconnected, that is, opened, and according to a command of the control unit 400, the path connecting the first output terminal portion T1 and the third output terminal portion T3 is connected, that is, short-circuited, and the path connecting the first output terminal portion T1 and the third output terminal portion T3 is disconnected, that is, opened, and operated in the off state. Further, the third load 330 and the second switch element 270a may be arranged to be connected in series on a path electrically connecting the third output terminal portion T3 and the second output terminal portion T2, that is, on a conducting wire or wiring. At this time, the second switch element 270a may also be set to an off state in which the path connecting the third output terminal portion T3 and the second output terminal portion T2 is disconnected, that is, opened, and according to a command of the control unit 400, the path connecting the third output terminal portion T3 and the second output terminal portion T2 is connected, that is, short-circuited, and the path connecting the third output terminal portion T3 and the second output terminal portion T2 is disconnected, that is, opened, and operated in the off state.

[0050] Referring to FIG. 2B, the current adjustment unit may include a variable resistor element. That is, at least one of the first current adjustment unit 170 and the second current adjustment unit 270 may include a variable resistor element. For example, the first current adjustment unit 170 may include a first variable resistor element 170b, and the second current adjustment unit 270 may include a second variable resistor element 270b. Here, the second load 320 and the first variable resistor element 170b may be arranged to be connected in series on a path that electrically connects the first output terminal portion T1 and the third output terminal portion T3, that is, on a conducting wire or wiring. At this time, the first variable resistor element 170b may be set to have a maximum resistance value and may be operated so that the resistance value decreases according to a command from the control unit 400. Also, the third load 330 and the second variable resistor element 270b may be arranged to be connected in series on a path that electrically connects the third output terminal portion T3 and the second output terminal portion T2, that is, on a conducting wire or wiring. At this time, the second variable resistor element 270b may also be set to have a maximum resistance value and may be operated so that the resistance value decreases according to a command from the control unit 400.

[0051] Further, the tandem solar cell according to the embodiment of the present invention may further include a first light amount sensing unit 500 for sensing the amount of sunlight incident on the first solar cell unit 100 and a second light amount sensing unit 600 for sensing the amount of sunlight incident on the second solar cell unit 200.

[0052] As described above, the tandem solar cell may be a tandem solar cell with a double-sided light receiving method in which the second solar cell unit 200 absorbs sunlight incident from below and converts it into electrical energy, together with the first solar cell unit 100 that absorbs sunlight incident from above and converts it into electrical energy. At this time, the first light quantity sensing unit 500 can sense the light quantity of sunlight incident from above, and the second light quantity sensing unit 600 can sense the light quantity of sunlight incident from below. However, the present invention is not limited thereto, and it goes without saying that the second light quantity sensing unit 600 can also sense the light quantity absorbed by the second solar cell unit 200 in the case of a tandem solar cell with a single-sided light receiving method. Such a first light quantity sensing unit 500 and second light quantity sensing unit 600 may be provided with a sensor for sensing the light quantity, and such a sensor can adopt various known configurations for sensing the light quantity.

[0053] On the other hand, the tandem solar cell according to an embodiment of the present invention may further include a current sensing unit 700 provided between the first output terminal portion T1 and the second output terminal portion T2.

[0054] The current sensing unit 700 may be disposed so as to be connected in series with the first load 310 on a path that electrically connects the first output terminal portion T1 and the second output terminal portion T2, that is, on a conducting wire or wiring. Thereby, the current sensing unit 700 can measure the amount of current flowing along the path that electrically connects the first output terminal portion T1 and the second output terminal portion T2. Such a current sensing unit 700 may be provided with a sensor for sensing the current, and such a sensor can adopt various known configurations for sensing the current.

[0055] As described above, the control unit 400 controls the operations of the first current adjustment unit 170 and the second current adjustment unit 270. At this time, the control unit 400 can selectively operate the first current adjustment unit 170 and the second current adjustment unit 270 described above according to the amount of sunlight detected by the first light amount detection unit 500 and the second light amount detection unit 600. In addition, the control unit 400 can control the operation of at least one of the first current adjustment unit 170 and the second current adjustment unit 270 described above according to the amount of current detected by the current detection unit 700.

[0056] Hereinafter, based on FIGS. 3 to 5, specific details of the control unit 400 controlling the operations of the first current adjustment unit 170 and the second current adjustment unit 270 will be described in detail.

[0057] FIG. 3 is a diagram showing the flow of current when sunlight of a reference light amount is incident on the first solar cell and the second solar cell, respectively.

[0058] In the tandem solar cell according to the embodiment of the present invention, a case is set in which sunlight of a first reference light amount A is incident on the first solar cell unit 100 and sunlight of a second reference light amount B is incident on the second solar cell unit 200, and current matching between the first solar cell unit 100 and the second solar cell unit 200 is performed.

[0059] When the amount of light detected by the first light amount detection unit 500 has the same value as the already set first reference light amount A, and the amount of light detected by the second light amount detection unit 600 has the same value as the already set second reference light amount B, the current I output from the first solar cell unit 100 a and the current I output from the second solar cell unit 200 a have the same current amount, and no idle current is generated.

[0060] Therefore, the control unit 400 does not activate the first switch element 170a and the second switch element 270a. As described above, the first switch element 170a is initially set to an off state that opens the path connecting the first output terminal portion T1 and the third output terminal portion T3, and the second switch element 270a is also initially set to an off state that opens the path connecting the third output terminal portion T3 and the second output terminal portion T2. Therefore, the current I output from the first solar cell unit 100 and the second solar cell unit 200 a is supplied to both the first load 310, and no current is supplied to the second load 320 and the third load 330.

[0061] Although not shown in the figure, the first current adjustment unit 170 and the second current adjustment unit 270 may each include a first variable resistor element 170b and a second variable resistor element 270b. Also in this case, the control unit 400 does not activate the first variable resistor element 170b and the second variable resistor element 270b. As described above, the first variable resistor element 170b is initially set to have a maximum resistance value, and the second variable resistor element 270b is also initially set to have a maximum resistance value. Therefore, the current I output from the first solar cell unit 100 and the second solar cell unit 200 a is almost entirely supplied to the first load 310, and almost no current is supplied to the second load 320 and the third load 330.

[0062] FIG. 4 is a diagram showing the flow of current when sunlight having a light amount exceeding the reference light amount is incident on the first solar cell unit.

[0063] When the light amount detected by the first light amount detection unit 500 is greater than the already set first reference light amount A (A'>A), and the light amount detected by the second light amount detection unit 600 has the same value as the already set second reference light amount B, the current I a +I b output from the first solar cell unit 100 a has a larger current amount than the current I bThis occurs when the light amount detected by the first light amount detection unit 500 is the same as the first reference light amount A that has already been set, and the light amount detected by the second light amount detection unit 600 is smaller than the second reference light amount B that has already been set (B’ < B), or when the increase rate of the light amount detected by the first light amount detection unit 500 is larger than the increase rate of the light amount detected by the second light amount detection unit 600, or when the decrease rate of the light amount detected by the first light amount detection unit 500 is smaller than the decrease rate of the light amount detected by the second light amount detection unit 600. The same applies in these cases.

[0064] In this case, the control unit 400 activates only the first switch element 170a and does not activate the second switch element 270a. As described above, since the second switch element 270a is initially set to the off state that opens the path connecting the third output terminal portion T3 and the second output terminal portion T2, no current is supplied to the third load 330.

[0065] At this time, when activating the first switch element 170a, the control unit 400 controls the operation of the first switch element 170a according to the amount of current detected by the current detection unit 700. That is, the first switch element 170a is initially set to the off state that opens the path connecting the first output terminal portion T1 and the third output terminal portion T3. Here, if there is no change in the amount of current detected by the current detection unit 700 during the set time, the control unit 400 switches the first switch element 170 in the off state to the on state. After that, after the control unit 400 switches the first switch element 170 to the on state, if the amount of current detected by the current detection unit 700 decreases, the control unit 400 switches the first switch element 170a in the on state to the off state.

[0066] That is, even when the light amount detected by the first light amount detector 500 is greater than the previously set first reference light amount A (A’>A), and the light amount detected by the second light amount detector 600 has the same value as the previously set second reference light amount B, since the first solar cell unit 100 and the second solar cell unit 200 are connected in series, there is no change in the current amount detected by the current detector 700. However, if there is a difference in the detected light amount, but there is no change in the current amount detected by the current detector 700 during the set time, the control unit 400 switches the first switch element 170a from the off (OFF) state to the on (ON) state to supply the idle current I b to the second load 320. At this time, since the second load 320 and the first switch element 170a have a low resistance value, there is a possibility that a current having a current amount greater than the idle current I b is supplied to the second load 320 and the current amount supplied to the first load 310 decreases. In this case, if the current amount detected by the current detector 700 decreases after the control unit 400 switches the first switch element 170a to the on (ON) state, the control unit 400 switches the first switch element 170a to the off (OFF) state. Then, a constant current is supplied to the first load 310 again, and if there is no change in the current amount detected by the current detector 700 during the set time, the control unit 400 switches the first switch element 170a from the off (OFF) state to the on (ON) state. Therefore, the first switch element 170a continues to be switched between the off (OFF) state and the on (ON) state, and the second load 320 can be intermittently supplied with current when the first switch element 170a is in the on (ON) state.

[0067] Although not shown in the figure, the first current adjustment unit 170 and the second current adjustment unit 270 may each include a first variable resistor element 170b and a second variable resistor element 270b. Even in this case, the control unit 400 operates only the first variable resistor element 170b and does not operate the second variable resistor element 270b. As described above, since the second variable resistor element 270b is initially set to have the maximum resistance value, almost no current is supplied to the third load 330.

[0068] At this time, when the control unit 400 operates the first variable resistor element 170b, it controls the operation of the first variable resistor element 170b according to the amount of current sensed by the current sensing unit 700. That is, the first variable resistor element 170b is initially set to have the maximum resistance value. Here, further, if there is no change in the amount of current sensed by the current sensing unit 700 during the set time, the control unit 400 gradually decreases the resistance value of the first variable resistor element 170b set to the maximum resistance value. After that, if the amount of current sensed by the current sensing unit 700 decreases while the control unit 400 decreases the resistance value of the first variable resistor element 170b, the control unit 400 holds the resistance value of the first variable resistor element 170b in the decreased state.

[0069] That is, even when the amount of light sensed by the first light amount sensing unit 500 is greater than the first reference light amount A that has already been set (A’>A) and the amount of light sensed by the second light amount sensing unit 600 has the same value as the second reference light amount B that has already been set, since the first solar cell unit 100 and the second solar cell unit 200 are connected in series, there is no change in the amount of current sensed by the current sensing unit 700. However, although there is a difference in the sensed light amount, if there is no change in the amount of current sensed by the current sensing unit 700 during the set time, the control unit 400 decreases the resistance value of the first variable resistor element 170b to supply the idle current I b to the second load 320. At this time, since the first variable resistor element 170b is initially set to the maximum resistance value, the idle current I bA current having a smaller current amount than that is supplied, and the amount of current supplied to the first load 310 may not change. In this case, the control unit 400 continues to decrease the resistance value of the first variable resistor element 170b, and if the amount of current sensed by the current sensing unit 700 decreases, the control unit 400 holds the resistance value of the first variable resistor element 170b. In this situation, the second load 320 is supplied with the idle current I a +I b corresponding to the difference between the current I a output from the first solar cell unit 100 and the current I b output from the second solar cell unit 200 as it is.

[0070] FIG. 5 is a diagram showing the current flow when sunlight having a light amount exceeding the reference light amount is incident on the second solar cell unit.

[0071] When the light amount sensed by the first light amount sensing unit 500 has the same value as the already set first reference light amount A, and the light amount sensed by the second light amount sensing unit 600 is larger than the already set second reference light amount B (B’>B), the current I a +I b output from the second solar cell unit 200 has a larger current amount than the current I a output from the first solar cell unit 100, and an idle current I b is generated. This also applies when the light amount sensed by the first light amount sensing unit 500 is smaller than the already set first reference light amount A (A’<A), the light amount sensed by the second light amount sensing unit 600 is the same as the already set second reference light amount B, or when the increase rate of the light amount sensed by the first light amount sensing unit 500 is smaller than the increase rate of the light amount sensed by the second light amount sensing unit 600, or when the decrease rate of the light amount sensed by the first light amount sensing unit 500 is larger than the decrease rate of the light amount sensed by the second light amount sensing unit 600.

[0072] In this case, the control unit 400 activates only the second switching element 270a and does not activate the first switching element 170a. As described above, since the first switching element 170a is initially set to an off state that opens the path connecting the first output terminal portion T1 and the third output terminal portion T3, no current is supplied to the second load 320.

[0073] At this time, when activating the second switching element 270a, the control unit 400 controls the operation of the second switching element 270a according to the amount of current sensed by the current sensing unit 700. That is, the second switching element 270a is initially set to an off state that opens the path connecting the third output terminal portion T3 and the second output terminal portion T2. Here, if there is no change in the amount of current sensed by the current sensing unit 700 during the set time, the control unit 400 switches the second switching element 270 in the off state to the on state. After that, after the control unit 400 switches the second switching element 270 to the on state, if the amount of current sensed by the current sensing unit 700 decreases, the control unit 400 switches the second switching element 270a in the on state to the off state.

[0074] That is, even when the amount of light sensed by the first light amount sensing unit 500 has the same value as the previously set first reference light amount A and the amount of light sensed by the second light amount sensing unit 600 is greater than the previously set second reference light amount B (B’ > B), since the first solar cell unit 100 and the second solar cell unit 200 are connected in series, there is no change in the amount of current sensed by the current sensing unit 700. However, if there is no change in the amount of current sensed by the current sensing unit 700 during the set time despite the difference in the sensed light amounts, the control unit 400 switches the second switching element 270a from the off state to the on state to supply the idle current I b to the third load 330. At this time, since the third load 330 and the second switching element 270a have a low resistance value, the idle current I bA current having a larger current amount than the above may be supplied, and the amount of current supplied to the first load 310 may decrease. In this case, after the control unit 400 switches the second switching element 270a to the on state, if the amount of current sensed by the current sensing unit 700 decreases, the control unit 400 switches the second switching element 270a to the off state. In this case, a constant current is supplied to the first load 310 again. If there is no change in the amount of current sensed by the current sensing unit 700 during the set time, the control unit 400 switches the second switching element 270a from the off state to the on state. Therefore, the second switching element 270a continues to be switched between the off state and the on state, and current can be intermittently supplied to the third load 330 when the second switching element 270a is in the on state.

[0075] Although not shown in the figure, the first current adjustment unit 170 and the second current adjustment unit 270 may each include a first variable resistance element 170b and a second variable resistance element 270b. Also in this case, the control unit 400 operates only the second variable resistance element 270b and does not operate the first variable resistance element 170b. As described above, since the first variable resistance element 170b is initially set to have the maximum resistance value, almost no current is supplied to the second load 320.

[0076] At this time, when the control unit 400 operates the second variable resistance element 270b, it controls the operation of the second variable resistance element 270b according to the amount of current sensed by the current sensing unit 700. That is, the second variable resistance element 270b is initially set to have the maximum resistance value. Here, if there is no change in the amount of current sensed by the current sensing unit 700 during the set time, the control unit 400 gradually decreases the resistance value of the second variable resistance element 270b set to the maximum resistance value. After that, if the amount of current sensed by the current sensing unit 700 decreases while the control unit 400 decreases the resistance value of the second variable resistance element 270b, the control unit 400 holds the resistance value of the second variable resistance element 270b in the decreased state.

[0077] That is, even when the light amount detected by the first light amount detection unit 500 has the same value as the first reference light amount A that has already been set, and the light amount detected by the second light amount detection unit 600 is larger than the second reference light amount B that has already been set (B’>B), since the first solar cell unit 100 and the second solar cell unit 200 are connected in series, there is no change in the current amount detected by the current detection unit 700. However, if there is no change in the current amount detected by the current detection unit 700 during the set time even though there is a difference in the detected light amounts, the control unit 400 decreases the resistance value of the second variable resistor element 270b to make the idle current I b be supplied to the third load 320. At this time, since the second variable resistor element 270b is initially set to the maximum resistance value, a current having a current amount smaller than the idle current I b is supplied to the third load 330, and there may be no change in the current amount supplied to the first load 310. In this case, after the control unit 400 continues to decrease the resistance value of the second variable resistor element 270b, if the current amount detected by the current detection unit 700 decreases, the control unit 400 holds the resistance value of the second variable resistor element 270b. In this case, the third load 330 is supplied with the idle current I a +I b equal to the difference between the current I a output from the first solar cell unit 100 and the current I b output from the second solar cell unit 200 as it is.

[0078] As described above, according to the tandem solar cell according to the embodiment of the present invention, in addition to the first output terminal portion and the second output terminal portion for supplying power to the main load, there is a third output terminal portion for supplying power to the auxiliary load. The idle current generated by the difference in the current amounts generated from each solar cell can be further supplied to the auxiliary load.

[0079] Although the preferred embodiments of the present invention have been described and illustrated using specific terms, these terms are merely for the purpose of clearly explaining the present invention. It is obvious that various modifications and changes can be made to the embodiments of the present invention and the described terms without departing from the technical idea and scope of the appended claims. These modified embodiments should not be individually understood as departing from the idea and scope of the present invention, but should be said to fall within the scope of the claims of the present invention.

Claims

1. A first solar cell section having a first upper electrode and a first lower electrode disposed apart from each other; A second solar cell section provided below the first solar cell section and having a second upper electrode and a second lower electrode disposed apart from each other; A first output terminal section connected to the first upper electrode; A second output terminal section connected to the second lower electrode; A third output terminal section commonly connected to the first lower electrode and the second upper electrode; A tandem solar cell comprising:

2. A first load is connected between the first output terminal section and the second output terminal section; A second load is connected between the first output terminal section and the third output terminal section; The tandem solar cell according to claim 1, wherein a third load is connected between the second output terminal section and the third output terminal section.

3. A first current adjustment section provided between the first output terminal section and the third output terminal section; A second current adjustment section provided between the second output terminal section and the third output terminal section; A control section for controlling the operations of the first current adjustment section and the second current adjustment section; The tandem solar cell according to claim 1, further comprising:

4. A first light amount sensing section for sensing the amount of sunlight incident on the first solar cell section; A second light amount sensing section for sensing the amount of sunlight incident on the second solar cell section; Further comprising: The control section selectively operates the first current adjustment section and the second current adjustment section according to the amount of sunlight sensed by the first light amount sensing section and the second light amount sensing section. The tandem solar cell according to claim 3.

5. The control section: Operates the first current adjustment section when the amount of light sensed by the first light amount sensing section is greater than a first reference light amount that has already been set, or when the amount of light sensed by the second light amount sensing section is less than a second reference light amount that has already been set; Operates the second current adjustment section when the amount of light sensed by the first light amount sensing section is less than the first reference light amount, or when the amount of light sensed by the second light amount sensing section is greater than the second reference light amount. The tandem solar cell according to claim 4.

6. Further comprising a current sensing section provided between the first output terminal section and the second output terminal section. The control unit controls the operation of at least one of the first current adjustment unit and the second current adjustment unit according to the amount of current sensed by the current sensing unit. The tandem solar cell according to claim 3.

7. The tandem solar cell according to claim 6, wherein at least one of the first current adjustment unit and the second current adjustment unit includes a switching element.

8. The tandem solar cell according to claim 7, wherein the control unit switches the switching element in the off state to the on state when there is no change in the amount of current sensed by the current sensing unit within a set time period.

9. The tandem solar cell according to claim 8, wherein after the control unit switches the switching element to the on state, if the amount of current sensed by the current sensing unit decreases, the control unit switches the switching element in the on state to the off state.

10. The tandem solar cell according to claim 6, wherein at least one of the first current adjustment unit and the second current adjustment unit includes a variable resistance element.

11. The tandem solar cell according to claim 10, wherein when there is no change in the amount of current sensed by the current sensing unit within a set time, the control unit decreases the resistance value of the variable resistance element set to the maximum resistance value.

12. The tandem solar cell according to claim 10, wherein while the control unit decreases the resistance value of the variable resistance element, if the amount of current sensed by the current sensing unit decreases, the control unit holds the decreased resistance value of the variable resistance element.

13. The first solar cell unit includes a first transparent substrate for transmitting sunlight incident from above. The second solar cell unit includes a second transparent substrate for transmitting sunlight incident from below. The tandem solar cell according to claim 1.

14. The tandem solar cell according to claim 1, further including a bonding layer provided between the first lower electrode and the second upper electrode.

15. The tandem solar cell according to claim 2, wherein at least one of the first load, the second load, and the third load includes a secondary battery.

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