KR20140015180A - Organic solar cell - Google Patents

Abstract

The present invention relates to an organic solar cell. According to one embodiment of the present invention, the organic solar cell includes a sub cell including a first active layer and a second sub cell including a second active layer. The first active layer or/and the second active layer include(s) electron accepters. An optical accepter is an optical asymmetry structure.

Description

Organic solar cell {ORGANIC SOLAR CELL}

It relates to an organic solar cell.

An organic solar cell is a photoelectric conversion element that converts solar energy into electrical energy, and has been spotlighted as a next generation energy source without pollution.

The organic solar cell includes a photoactive layer including an p-type semiconductor and an n-type semiconductor, which are organic semiconductors, and when the solar energy is absorbed by the photoactive layer, an electron-hole pair (EHP) is generated inside the semiconductor. The electrons and holes generated here are moved to the n-type semiconductor and the p-type semiconductor, respectively, and they are collected by the electrodes, which can be used as electrical energy from the outside.

However, since the organic semiconductor absorbs only light in a predetermined wavelength region according to the intrinsic properties of the material, it is disadvantageous in absorbing light in a wide wavelength region.

In order to solve this problem, a tandem organic solar cell including a plurality of sub solar cells (hereinafter, referred to as 'sub cells') that absorb light in different wavelength ranges has been proposed. Tandem organic solar cells can absorb light in a wide wavelength range, thereby increasing light absorption.

However, since the total output current of the tandem organic solar cell is determined based on the subcell with the lower output current among the plurality of subcells, surplus charges of the subcell with the high output current do not contribute to the output and degrade the performance of the tandem organic solar cell. You can.

According to one embodiment, a tandem organic solar cell capable of preventing performance degradation due to surplus charge is provided.

According to one embodiment, a first sub-cell comprising a first active layer and a second sub-cell comprising a second active layer, wherein at least one of the first active layer and the second active layer is at least different in light absorption An organic solar cell including two kinds of electron acceptors is provided.

The first active layer includes a first electron donor that absorbs light in a first wavelength region, and a first electron acceptor, and the second active layer absorbs light in a second wavelength region having a longer wavelength than the first wavelength region. And a second electron donor, and a second electron acceptor and a third electron acceptor having different light absorbances.

The second electron acceptor and the third electron acceptor may absorb light in substantially the same wavelength region.

The second electron acceptor and the third electron acceptor may absorb light in a wavelength region different from that of the second electron donor.

The second electron acceptor and the third electron acceptor may be included in a weight ratio of about 1:99 to 99: 1.

The second electron acceptor may include a compound having a light absorption moiety in an optical symmetry structure, and the third electron acceptor includes a compound having a light absorption moiety in an optical asymmetry structure. can do.

The second electron acceptor may include a fullerene derivative having a fullerene core having an optically symmetric structure, and the third electron acceptor may include a fullerene derivative having a fullerene core having an optical asymmetric structure.

The second electron acceptor and the third electron acceptor may be selected from a fullerene derivative having a common functional group.

The second electron acceptor may comprise C ₆₀ , PC ₆₀ BM, IC ₆₀ BA or a combination thereof, and the third electron acceptor may comprise C ₇₀ , PC ₇₀ BM, IC ₇₀ BA or a combination thereof. have.

The first electron donor may comprise a first compound having a bandgap of about 1.6 to 2.2 eV, and the second electron donor may comprise a second compound having a bandgap of about 0.6 to 2.0 eV.

The first wavelength region may be about 200 nm to 780 nm, and the second wavelength region may be about 400 nm to 2000 nm.

The first subcell and the second subcell may be connected in series.

According to another embodiment, a first electrode, a first active layer located on one surface of the first electrode, an interconnection part formed on one surface of the first active layer, and formed on one surface of the intermediate connection part A second active layer including at least two kinds of electron acceptors having different absorbances, and a second electrode formed on the second active layer, wherein the first electrode, the first active layer, and the intermediate connection part have a first output A current is generated, and the second electrode, the second active layer, and the intermediate connection portion adjust a composition ratio of at least two kinds of electron acceptors having different light absorbances to obtain a second output current that is substantially equal to the first output current. Provide organic solar cells to produce.

The first active layer may include a first electron donor that absorbs light in a first wavelength region, and a first electron acceptor, and the second active layer absorbs light in a second wavelength region having a longer wavelength than the first wavelength region. And a second electron donor, and a second electron acceptor and a third electron acceptor having different light absorbances.

The first wavelength region may be about 200 nm to 780 nm, and the second wavelength region may be about 400 nm to 2000 nm.

The second electron acceptor and the third electron acceptor may be included in a weight ratio of about 1:99 to 99: 1.

The second electron acceptor and the third electron acceptor may absorb light in substantially the same wavelength region, and the second electron acceptor and the third electron acceptor may emit light in a wavelength region different from that of the second electron donor. It can absorb.

The second electron acceptor may include a fullerene derivative having a fullerene core having an optically symmetric structure, and the third electron acceptor may include a fullerene derivative having a fullerene core having an optical asymmetric structure.

The second electron acceptor and the third electron acceptor may be selected from a fullerene derivative having a common functional group.

The intermediate connection part may include a plurality of layers including a conductive polymer, an insulating polymer, a ferroelectric polymer, a metal oxide, or a combination thereof.

The intermediate connector may include a conductive thin film layer positioned between the plurality of layers.

The second output current may be about 0.9 to 1.1 times the first output current.

In tandem organic solar cells in which a plurality of sub-cells are stacked, current matching between sub-cells can be implemented without controlling the thickness of the active layer, thereby reducing the occurrence of surplus charges due to the difference in output current, thereby reducing the occurrence of surplus charges. It can reduce the adverse effect on performance.

1 is a cross-sectional view showing an organic solar cell according to one embodiment;
2 is a cross-sectional view showing an organic solar cell according to another embodiment;
3 is a graph showing the light absorption of the solar cell according to Example 1 and Comparative Examples 1 and 2,
4 is a graph showing current densities of solar cells according to Example 1 and Comparative Examples 1 and 2;
5 is a graph showing an external quantum efficiency (EQE) according to the wavelength of the organic solar cell according to Examples 2-1 to 2-5,
6 is a graph showing the cumulative light absorbance of the organic solar cells according to Examples 2-1 to 2-5,
7 is a graph showing the light absorption of the lower subcell and the upper subcell in the tandem organic solar cell according to Example 3,
8 and 9 are graphs showing the external quantum efficiency (EQE) and the cumulative light absorbance according to the wavelength when the tandem organic solar cell according to Example 3 is the point 'A' of FIG. 7, respectively.

Hereinafter, exemplary embodiments of the present invention will be described in detail 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 the drawings, the thickness is enlarged to clearly represent the layers and regions. Like parts are designated with like reference numerals throughout the specification. Whenever a portion of a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case where it is "directly on" 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.

Hereinafter, an organic solar cell according to an embodiment will be described with reference to the drawings.

1 is a cross-sectional view illustrating an organic solar cell according to an embodiment.

Referring to FIG. 1, an organic solar cell according to an embodiment includes a first subcell C1 and a second subcell C2 that are sequentially stacked, and include a first subcell C1 and a second subcell. C2 is connected to an intermediate connection part 130.

The first sub cell C1 includes the first electrode 110, the first active layer 120, and the first intermediate connector 130a, and the second sub cell C2 includes the second intermediate connector 130b and the first intermediate cell 130. And an active layer 140 and a second electrode 150.

The substrate (not shown) may be located at the side of the first electrode 110 or the second electrode 120 and may be made of, for example, a light transmissive material. The light transmissive material may include an inorganic material such as glass or an organic material such as polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyethersulfone or a combination thereof.

One of the first electrode 110 and the second electrode 150 may be an anode and the other may be a cathode. When the first electrode 110 is an anode, the first intermediate connector 130a may serve as a cathode, and when the first electrode 110 is a cathode, the first intermediate connector 130a may serve as an anode. Similarly, when the second electrode 150 is an anode, the second intermediate connector 130b may serve as a cathode, and when the second electrode 150 is a cathode, the second intermediate connector 130b may serve as an anode. .

One of the first electrode 110 and the second electrode 150 is, for example, indium tin oxide (ITO), indium doped ZnO (IZO), tin oxide (SnO ₂ ), aluminum doped zinc oxide ( made of transparent conductors such as conductive oxides such as aluminum doped ZnO, AZO), gallium doped ZnO, GZO, and conductive carbon composites such as carbon nanotubes (CNT) or graphene. The other may be made of an opaque conductor such as aluminum (Al), silver (Ag), gold (Au), lithium (Li), or the like.

The intermediate connector 130 includes a first intermediate connector 130a of the first subcell C1 and a second intermediate connector 130b of the second subcell C2, and includes the first intermediate connector 130a and the first intermediate connector 130a. The interface of the two intermediate connectors 130b may be a recombination center of the charges of the first intermediate connector 130a and the charges of the second intermediate connector 130b.

The first intermediate connector 130a and the second intermediate connector 130b may include, for example, a conductive polymer, an insulating polymer, a ferroelectric polymer, a metal oxide, or a combination thereof, and may each be a single layer or a plurality of layers. The conductive polymer may be, for example, PEDOT: PSS and the metal oxide is, for example, nickel (Ni), ruthenium (Ru), tungsten (W), molybdenum (Mo), vanadium (V), iridium (Ir), titanium (Ti) , Zinc (Zn) or an oxide of a combination thereof, but is not limited thereto.

The intermediate connector 130 may further include a conductive thin film (not shown) positioned between the central connectors 130a and 130b of the plurality of layers. The conductive thin film can serve as an effective recombination center of charges. The conductive thin film may be, for example, a light transmissive conductor that does not affect the transmission of light, and may be a conductive oxide layer such as indium tin oxide and / or a thin metal layer.

 The first active layer 120 and the second active layer 140 may each include a photoactive material including an electron acceptor made of an n-type semiconductor material and an electron donor made of a p-type semiconductor material.

The electron acceptor and the electron donor may have a bulk heterojunction structure, for example. In the bulk heterojunction structure, an electron-hole pair excited by light absorbed by the first photoactive layer 120 and the second active layer 140 is diffused to form an electron acceptor and an electron donor. When the interface is reached, electrons and holes are separated by the difference in electron affinity between the two materials forming the interface, electrons move to the cathode through the electron acceptor, and holes move to the anode through the electron donor, thereby generating photocurrent. Generate.

The first active layer 120 and the second active layer 150 include electron donors that absorb light in different wavelength regions.

The first active layer 120 may include, for example, a first electron donor that absorbs light in a relatively short wavelength region of about 200 nm to 780 nm. The first electron donor, which absorbs light in a relatively short wavelength region, may include, for example, a first compound having a bandgap of about 1.6 to 2.2 eV, examples of which include polyaniline; Polypyrrole; Polythiophene; Poly (p-phenylenevinylene); Benzodithiophene; Thienothiophene; MEH-PPV (poly [2-methoxy-5- (2'-ethyl-hexyloxy) -1,4-phenylene vinylene); MDMO-PPV (poly (2-methoxy-5- (3,7-dimethyloctyloxy) -1,4-phenylene-vinylene); pentacene; perylene; poly (3,4-ethylenedioxythiophene) ( PEDOT), poly (3-alkylthiophene); polytriphenylamine; phthalocyanine; tin (II) phthalocyanine (SnPc); copper phthalocyanine; triarylamine Bezidine; pyrazoline; styrylamine; hydrazone; carbazole; thiophene; 3,4-ethylenedioxythiophene (3,4 ethylenedioxythiophene (EDOT); pyrrole; phenanthrene; tetracene; natraceene; rubrene; 1,4,5,8-naphthalene-tetracarboxylic dianhydride Ride (1,4,5,8-naphthalene-tetracarboxylic dianhydride, NTCDA); poly (3-hexylthiophene) (poly (3-hexylthiophene, P3HT)), but is not limited thereto.

The first active layer 120 may include a first electron acceptor forming a bulk heterojunction structure with the first electron donor. The first electron acceptor may be selected from a material having a lower level of lower unoccupied molecular orbital (LUMO) than the first electron donor. For example, fullerene (C60, C70, C74, C76, C78, C82, C84, C720, C860 and the like); 1- (3-methoxy-carbonyl) propyl-1-phenyl (6,6) C61 (1- (3-methoxy-carbonyl) propyl-1-phenyl (6,6) C61), C71-PCBM, C84 And fullerene derivatives such as -PCBM, bis-PCBM.

The second active layer 140 may include, for example, a second electron donor that absorbs light in a relatively long wavelength region of about 400 nm to 2000 nm. The second electron donor, which absorbs light in a relatively long wavelength region, may include a second compound having a bandgap of about 0.6 to 2.0 eV, and examples of the second compound include poly ((4,8-bis (octyl) Oxy) benzo [1,2- b : 4,5- b ' ] dithiophene) -2,6-diyl-alt- (2-((dodecyloxy) carbonyl) thieno [3,4- b ] thiophene) -3,6-diyl) (poly ((4,8-bis (octyloxy) benzo (1,2- b: 4,5- b ') dithiophene) -2,6-diyl- alt - (2 -((dodecyloxy) carbonyl) thieno (3,4- b ) thiophenediyl) -3,6-diyl), PTB1), poly ((4,8-bis (2-ethylhexyloxy) benzo [1,2- b : 4,5- b ' ] dithiophene) -2,6-diyl-alt- (2-((2-ethylhexyloxy) carbonyl) -3-fluorothieno [3,4- b ] Thiophene) -3,6-diyl) (poly ((4,8-bis (2-ethylhexyloxy) benzo [1,2- b : 4,5- b ' ] dithiophene) -2,6-diyl-alt- (2-((2-ethylhexyloxy) carbonyl) -3-fluorothieno [3,4- b ] thiophenediyl) -3,6-diyl)), PTB7), cyclopenta [2,1- b : 3,4- b '] dithiophene-based polymer (cyclopenta [2,1- b: 3,4- b '] dithiophene-based polymers), La fluorene-based polymer (silafluorene-based polymer), Carbazole compounds, fluorene compounds, halogenated fused thiophene, dieteno [3,2-b: 2'3'-d] silol (dithieno [3,2-b: 2'3] '-d] silole) -based compounds, but is not limited thereto.

The second active layer 140 may include at least two kinds of electron acceptors forming a bulk heterojunction structure with the second electron donor. The electron acceptor may be selected from a material having a lower LUMO level than the second electron donor.

The electron acceptor may be selected from electron acceptors having different light absorbances in substantially the same wavelength region, for example, a second electron acceptor having a low light absorbance and a third electron acceptor having a high light absorbance in substantially the same wavelength region. It may include.

The second electron acceptor and the third electron acceptor may absorb light in a wavelength region different from that of the second electron donor. Here, the term light of different wavelength regions is meant the difference between the second electron acceptor and the third maximum absorption wavelength of an electron acceptor (λ _max) and the maximum absorption wavelength (λ _max) of the second electron donor at least about 70nm do.

The light absorption may be determined according to the compound structure. The second electron acceptor may include a compound having a light absorbing moiety having a low light absorbing structure, and the third electron acceptor has a light absorbing moiety having a high light absorbing structure. It may include a compound. For example, the second electron acceptor may include a compound having a light absorption moiety having an optical symmetry structure, and the third electron acceptor may include a compound having a light absorption moiety having an optical asymmetry structure. It may include.

The light absorbing moiety can be, for example, fullerene, the second electron acceptor can be a fullerene derivative having, for example, a fullerene core of optically symmetrical structure and the third electron acceptor has for example an optically asymmetrical fullerene core. It may be a fullerene derivative.

Meanwhile, when the second electron acceptor and the third electron acceptor have side chains, the side chains may have a common functional group. As such, the morphology of the second active layer 140 may be improved by having a common functional group between the second electron acceptor and the third electron acceptor.

For example, the second electron acceptor may be C60 represented by Chemical Formula 1, and the third electron acceptor may be C70 represented by Chemical Formula 2.

[Formula 1] [Formula 2]

For example, the second electron acceptor may be [6,6] -phenyl-C60-butyric acid methyl ester ([6,6] -phenyl-C60-butyric acid methyl ester, PC ₆₀ BM) represented by Formula 3, wherein The third electron acceptor may be [6,6] -phenyl-C70-butyric acid methyl ester ([6,6] -Phenyl-C70-butyric acid methyl ester, PC ₇₀ BM) represented by Formula 4 below.

[Formula 3] [Formula 4]

For example, the second electron acceptor may be, for example, Indene C60 bis-adduct (IC ₆₀ BA) represented by the following Chemical Formula 5, and the third electron acceptor may be represented by the following Chemical Formula 6 Duct (Indene C70 bis-adduct, IC ₇₀ BA).

[Formula 5] [Formula 6]

The second electron acceptor and the third electron acceptor may be included at a predetermined blending ratio, and the desired output of the second subcell C2 including the second active layer 140 may be adjusted by adjusting the blending ratio. It can be controlled to produce a current.

The second electron acceptor and the third electron acceptor may be included, for example, in a weight ratio of about 1:99 to 99: 1, and the specific mixing ratio is a current between the first subcell C1 and the second subcell C2. It may be determined according to current matching.

 This will be described in detail.

The organic solar cell according to the present exemplary embodiment includes a plurality of subcells absorbing light in different wavelength regions, thereby increasing light absorption by widening the absorption wavelength region. For example, as described above, by including a subcell that absorbs light in the short wavelength region and a subcell that absorbs light in the long wavelength region, light absorption may be increased by absorbing both light in the short wavelength region and the long wavelength region.

However, since the plurality of subcells are connected in series, the total output current of the organic solar cell may be determined by the output current of the subcell having the lower output current among the plurality of subcells. In this case, surplus charges of a subcell having a high output current do not contribute to the output and accumulate inside, which may affect the performance of the organic solar cell.

The output current of the subcell may be determined according to the light absorbance of the active layer. In particular, in a subcell including an electron donor which absorbs light in a relatively long wavelength region, the light absorbance of the electron acceptor may have a large influence on the output current of the subcell. Can be.

In this embodiment, the light absorption is adjusted to produce a substantially equivalent output current to a subcell having a low output current by mixing a plurality of types of electron acceptors in an active layer of a subcell having a high output current and adjusting a mixing ratio therebetween. Can be. Herein, 'adjusting to have substantially the same level of output current' may mean adjusting the output current of a subcell having a high output current to be about 0.9 to 1.1 times that of a subcell having a low output current. May vary from case to case.

As described above, the organic solar cell according to the present embodiment may implement a plurality of subcells capable of generating substantially equivalent output currents, thereby reducing the occurrence of surplus charges due to the difference in the output currents between the subcells, and thus surpluses. Accumulation of charge can reduce the adverse effects on the performance of the organic solar cell.

On the other hand, by implementing a plurality of sub-cells capable of generating a substantially equivalent output current as described above, it is not necessary to adjust the thickness of the active layer to balance the output current between the sub-cells. Therefore, not only a separate means for controlling the thickness of the active layer of each subcell is required, but also a process that is difficult to control thin film thickness, such as a roll-to-roll process, is applicable.

Hereinafter, an organic solar cell according to another embodiment will be described with reference to FIG. 2.

2 is a cross-sectional view illustrating an organic solar cell according to another embodiment.

Referring to FIG. 2, an organic solar cell according to another embodiment may include a first sub cell C1 including a first electrode 110 and a first active layer 120, as in the above-described embodiment; A second sub cell C2 including a second active layer 140 and a second electrode 150; And an intermediate connector 130.

However, in the organic solar cell according to the present embodiment, unlike the above-described embodiment, the intermediate connector 130 is positioned between them in addition to the first intermediate connector 130a and the second intermediate connector 130b. More). The third intermediate connector 135 may be interposed between the first intermediate connector 130a and the second intermediate connector 130b, and may be, for example, a metal thin film layer.

In addition, unlike the above-described embodiment, the organic solar cell according to the present embodiment further includes an auxiliary layer 115 between the first electrode 110 and the first active layer 120, and the second electrode 150 and the second electrode. The auxiliary layer 145 is further included between the active layers 140. The auxiliary layer 115 may serve to increase charge mobility between the first active layer 120 and the first electrode 115, and the buffer layer 145 may be disposed between the second active layer 140 and the second electrode 150. It may serve to increase charge mobility. The auxiliary layers 115 and 145 may be one or more selected from, for example, an electron injection layer, an electron transport layer, a hole injection layer, a hole transport layer, and a hole blocking layer, but are not limited thereto. Either one of the auxiliary layers 115 and 145 may be omitted and both may be omitted in some cases.

In the above description, a solar cell including two subcells has been exemplarily described for convenience of description, but the present invention is not limited thereto, and the same can be applied to a solar cell including three or more subcells.

Examples and comparative examples of the present invention will be described below. However, the following examples are only examples of the present invention, and the present invention is not limited by the following examples.

Manufacturing of Organic Solar Cells-1

Example  One

A 150 nm thick ITO anode is formed on a 1 mm thick transparent glass substrate by sputtering. Then, on the ITO anode, an electron donor (Mn = 25,000) The active layer is formed by applying a mixture of PC ₆₀ BM / PC ₇₀ BM electron acceptors dissolved in chlorobenzene. At this time, the electron donor represented by the formula (A) : PC ₆₀ BM: PC ₇₀ BM = 10: 7.5: 7.5 (w / w) in a ratio of mixing. Subsequently, an aluminum (Al) cathode having a thickness of 80 nm is formed on the active layer to manufacture a solar cell.

(A)

Comparative Example  One

An electron donor represented by Chemical Formula A : PC ₆₀ BM: PC ₇₀ BM = 10: 15: 0 (w / w) A solar cell was manufactured in the same manner as in Example 1, except that it was used.

Comparative Example  2

An electron donor represented by Chemical Formula A : PC ₆₀ BM: PC ₇₀ BM = 10: 0: 15 A solar cell was prepared in the same manner as in Example 1 except that it was used as (w / w).

Evaluation 1: Light Absorption

The light absorption of the solar cell according to Example 1 and Comparative Examples 1 and 2 is evaluated.

The results are shown in FIG.

3 is a graph showing light absorbance of the solar cells according to Example 1 and Comparative Examples 1 and 2. FIG.

Referring to FIG. 3, it can be seen that the solar cells according to Example 1 and Comparative Examples 1 and 2 exhibit substantially the same light absorption in the long wavelength region, while the light absorption in the short wavelength region is significantly different.

Specifically, it can be seen that the solar cells according to Example 1 and Comparative Examples 1 and 2 exhibit substantially the same light absorbance in the wavelength region of about 600 to 780 nm by commonly applied electron donors. On the other hand, in the wavelength region of about 380 to 600nm, the solar cell according to Example 1 using PC ₆₀ BM and PC ₇₀ BM together as the electron acceptor has a light absorption degree of the solar cell according to Comparative Example 1 using only PC ₆₀ BM as the electron acceptor. It can be seen that the light absorbency of the medium of the solar cell according to Comparative Example 2 using only PC ₇₀ BM as the electron acceptor is shown.

Accordingly, the light absorption of the solar cell according to Comparative Example 1 using only PC ₆₀ BM as the electron acceptor by adjusting the mixing ratio of PC ₆₀ BM and PC ₇₀ BM of the solar cell according to Comparative Example 2 using only PC ₇₀ BM as the electron acceptor It can be seen that it is possible to implement a solar cell having a desired light absorption between the light absorption.

Evaluation 2: current density

The current density of the solar cells according to Example 1 and Comparative Examples 1 and 2 is evaluated.

A xenon lamp (Oriel, 01193) was used as the light source, and the solar condition (AM 1.5) of the xenon lamp was a standard solar cell (Frunhofer Institute Solare Engeriessysteme, Certificate No. C-ISE369, Type of material: Mono-). Si + KG filter) to calibrate.

The result is shown in Fig.

4 is a graph showing current densities of solar cells according to Example 1 and Comparative Examples 1 and 2. FIG.

Referring to FIG. 4, it can be seen that the solar cell according to Example 1 has a current density that is about the middle of the current density of the solar cell according to Comparative Example 1 and the current density of the solar cell according to Comparative Example 2.

Accordingly, by adjusting the mixing ratio of PC ₆₀ BM and PC ₇₀ BM, the current density of the solar cell according to Comparative Example 1 using only PC ₆₀ BM as the electron acceptor and the solar cell according to Comparative Example 2 using only PC ₇₀ BM as the electron acceptor It can be seen that a solar cell having a desired current density can be implemented between current densities.

Manufacturing of Organic Solar Cells-2

Example  2-1

A 180 nm thick ITO anode is formed on a 1 mm thick transparent glass substrate by sputtering. PEDOT: PSS is then spin coated onto the ITO anode to form a 30 nm thick lower auxiliary layer. Subsequently, on the lower auxiliary layer, the electron donor (Mn = 34,000) and the PC ₆₀ BM / PC ₇₀ BM electron acceptor represented by the following Chemical Formula B are 1: 2 (w / w) in ratio: A mixture dissolved in chlorobenzene: 1,8-diiodooctane (97: 3, v / v) was applied to form an 85 nm thick active layer. Here, the electron acceptor PC ₆₀ BM and PC ₇₀ BM are mixed in a ratio of 99: 1 (w / w). Subsequently, TiO ₂ is coated on the active layer by spin coating to form an upper auxiliary layer having a thickness of 5 nm. Subsequently, an aluminum (Al) cathode having a thickness of 150 nm is formed on the upper auxiliary layer to manufacture an organic solar cell.

[Formula B]

Example  2-2

An organic solar cell was manufactured in the same manner as in Example 2-1, except that the electron acceptor PC ₆₀ BM and PC ₇₀ BM were mixed in a ratio of 9: 1 (w / w).

Example  2-3

An organic solar cell was manufactured in the same manner as in Example 2-1, except that the electron acceptor PC ₆₀ BM and PC ₇₀ BM were mixed at a ratio of 8: 2 (w / w).

Example  2-4

An organic solar cell was manufactured in the same manner as in Example 2-1, except that the electron acceptor PC ₆₀ BM and PC ₇₀ BM were mixed in a ratio of 7: 3 (w / w).

Example  2-5

An organic solar cell was manufactured in the same manner as in Example 2-1, except that the electron acceptor PC ₆₀ BM and PC ₇₀ BM were mixed at a ratio of 6: 4 (w / w).

Rating 3

The external quantum efficiency (EQE) and cumulative light absorption of the organic solar cells according to Examples 2-1 to 2-5 are evaluated.

The results are shown in FIGS. 5 and 6. FIG.

5 is a graph showing external quantum efficiency (EQE) according to the wavelength of the organic solar cells according to Examples 2-1 to 2-5, Figure 6 is a graph of the organic solar cells according to Examples 2-1 to 2-5 A graph showing cumulative light absorbance.

5 and 6, the organic solar cells according to Examples 2-1 to 2-5 have an external quantum efficiency (EQE) and cumulative light absorption according to the mixing ratio of the electron acceptor of the active layer while maintaining the absorption wavelength region. It can be seen that the degree can be finely adjusted.

Fabrication of Tandem Organic Solar Cells

Reference example

A 180 nm thick ITO anode is formed on a 1 mm thick transparent glass substrate by sputtering. PEDOT: PSS is then spin coated onto the ITO anode to form a 30 nm thick lower auxiliary layer. Subsequently, a lower active layer is formed on the lower auxiliary layer by applying a mixture obtained by dissolving an electron donor (P3HT) represented by Formula C and an electron acceptor (ICBA) represented by Formula D below in dichlorobenzene. At this time, the electron donor represented by Chemical Formula B and the electron acceptor (ICBA) represented by Chemical Formula C are mixed at a ratio of 1: 1 (w / w). Subsequently, a titanium oxide (TiO 2) is coated on the lower active layer by spin coating to form a lower intermediate connection portion of 5 nm to prepare a lower sub cell.

Subsequently, tungsten oxide (WO ₃ ) is vacuum deposited on the lower intermediate interconnection to form an upper intermediate interconnection of 7 nm. Subsequently, the electron donor (Mn = 34,000) PC ₇₀ BM electron acceptor at 1: 1.5 (w / w) A mixture dissolved in chlorobenzene: 1,8-dioodooctane (97: 3, v / v) is applied to form the top active layer. Subsequently, TiO ₂ is coated on the upper active layer by spin coating to form an upper auxiliary layer having a thickness of 5 nm. Subsequently, a 150 nm thick aluminum (Al) cathode is formed on the upper auxiliary layer to prepare an upper subcell. Accordingly, a tandem organic solar cell including a lower subcell and an upper subcell is manufactured.

≪ RTI ID = 0.0 &

[Chemical Formula D]

 (E)

Example  3

Instead of using the electron acceptor of the upper subcell alone as PC ₇₀ BM alone, PC ₆₀ BM and PC ₇₀ BM are used as 99: 1 (w / w), 9: 1, 8: 2, 7: 3, 6: 4, A tandem organic solar cell was manufactured in the same manner as the reference example, except that a mixture including the ratio of 5: 5, 4: 6, 3: 7, 2: 8, 1: 9, and 1:99 was used.

Rating 4

The light absorbency of the tandem organic solar cell according to Example 3 is evaluated.

7 is a graph showing light absorbance of the lower subcell and the upper subcell in the tandem organic solar cell according to Example 3. FIG.

As shown in FIG. 7, the lower subcell shows a relatively low light absorbency and thus has a low output current, and the upper subcell shows a relatively high light absorbency and thus has a high output current.

Referring to FIG. 7, the tandem organic solar cell according to Example 3 is applied to the mixing ratio of PC ₆₀ BM / PC ₇₀ BM of the upper subcell, starting from the light absorbance and current amount of the tandem organic solar cell according to the reference example. Accordingly, it can be seen that the difference between the light absorbance and the current amount of the upper subcell and the lower subcell can be reduced, and a point where the light absorbance and the current amount of the upper subcell and the lower subcell are substantially equally matched can be found. 'A' of FIG. 7 indicates a point where the light absorbance and the current amount of the lower subcell and the upper subcell are equally matched.

From this, by controlling the mixing ratio of the electron acceptor of the upper subcell, the upper subcell and the lower subcell are controlled to have substantially the same light absorbance and current amount, so that the lower subcell and the upper subcell have substantially the same output current. It can be implemented to have As a result, the excess charges of the upper subcell having the high output current may be accumulated inside the organic solar cell, thereby affecting the performance.

8 and 9 are graphs showing the external quantum efficiency (EQE) and the cumulative light absorbance according to the wavelength when the tandem organic solar cell according to Example 3 is the point 'A' of FIG. 7, respectively.

8 and 9, in the tandem organic solar cell according to Example 3, the lower subcell and the upper subcell absorb light in a wide wavelength region while absorbing light in a short wavelength region and a long wavelength region, respectively. At the same time, by controlling the cumulative light absorbance of the lower subcell and the upper subcell to be substantially equal, it is possible to reduce the surplus charges generated in the high light absorbing subcell to prevent performance degradation due to the surplus charges. Can be.

In addition, since the above effects can be expected only by adjusting the mixing ratio of the electron acceptor of the subcell having a high output current, it is necessary to artificially control the thickness of the photoactive layer in order to balance the output current among the plurality of subcells. Can improve the fairness of the tandem organic solar cell.

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, but, on the contrary, And it goes without saying that the invention belongs to the scope of the invention.

C1: first subcell C2: second subcell
110: first electrode 120: first active layer
130: intermediate connector 130a: first intermediate connector
130b: second intermediate connector 135: third intermediate connector
140: second active layer 115, 145: auxiliary layer
150: second electrode

Claims (22)

A first subcell including a first active layer and a second subcell including a second active layer,
At least one of the first active layer and the second active layer includes at least two kinds of electron acceptors having different light absorbances.
Organic solar cells.
In claim 1,
The first active layer is
A first electron donor that absorbs light in the first wavelength region, and
First electron acceptor
Lt; / RTI >
The second active layer is
A second electron donor that absorbs light in a second wavelength region that is longer than the first wavelength region, and
Second electron acceptor and third electron acceptor having different light absorbances
Organic solar cell comprising a.
3. The method of claim 2,
And the second electron acceptor and the third electron acceptor absorb light in substantially the same wavelength region.
3. The method of claim 2,
And the second electron acceptor and the third electron acceptor absorb light in a wavelength region different from that of the second electron donor.
3. The method of claim 2,
The second electron acceptor and the third electron acceptor is an organic solar cell is included in a weight ratio of 1:99 to 99: 1.
3. The method of claim 2,
The second electron acceptor includes a compound having a light absorption moiety of the optical symmetry structure,
The third electron acceptor includes a compound having a light absorption moiety of an optical asymmetry structure
Organic solar cells.
The method of claim 6,
The second electron acceptor includes a fullerene derivative having a fullerene core of an optical symmetric structure,
The third electron acceptor includes a fullerene derivative having a fullerene core having an optical asymmetric structure.
Organic solar cells.
In claim 7,
And the second electron acceptor and the third electron acceptor are selected from a fullerene derivative having a common functional group.
In claim 7,
The second electron acceptor comprises C ₆₀ , PC ₆₀ BM, IC ₆₀ BA, or a combination thereof,
The third electron acceptor comprises C ₇₀ , PC ₇₀ BM, IC ₇₀ BA or a combination thereof.
Organic solar cells.
3. The method of claim 2,
The first electron donor comprises a first compound having a bandgap of 1.6 to 2.2 eV,
The second electron donor comprises a second compound having a bandgap of 0.6 to 2.0 eV
Organic solar cells.
3. The method of claim 2,
The first wavelength region is 200nm to 780nm, the second wavelength region is 400nm to 2000nm organic solar cell.
In claim 1,
And the first subcell and the second subcell are connected in series.
The first electrode,
A first active layer positioned on one surface of the first electrode,
An intermediate connection part formed on one surface of the first active layer,
A second active layer formed on one surface of the intermediate connector and including at least two kinds of electron acceptors having different light absorbances, and
A second electrode formed on the second active layer
/ RTI >
The first electrode, the first active layer and the intermediate connection portion produces a first output current,
The second electrode, the second active layer, and the intermediate connection part adjust a composition ratio of at least two kinds of electron acceptors having different light absorbances to produce a second output current substantially equal to the first output current.
Organic solar cells.
The method of claim 13,
The first active layer is
A first electron donor that absorbs light in the first wavelength region, and
First electron acceptor
Lt; / RTI >
The second active layer is
A second electron donor that absorbs light in a second wavelength region that is longer than the first wavelength region, and
Second electron acceptor and third electron acceptor having different light absorbances
Organic solar cell comprising a.
The method of claim 14,
The first wavelength region is 200nm to 780nm, the second wavelength region is 400nm to 2000nm organic solar cell.
The method of claim 14,
The second electron acceptor and the third electron acceptor is an organic solar cell is included in a weight ratio of 1:99 to 99: 1.
The method of claim 14,
The second electron acceptor and the third electron acceptor absorb light of substantially the same wavelength region and
The second electron acceptor and the third electron acceptor absorb light in a wavelength region different from that of the second electron donor.
Organic solar cells.
The method of claim 14,
The second electron acceptor includes a fullerene derivative having a fullerene core of an optical symmetric structure,
The third electron acceptor includes a fullerene derivative having a fullerene core having an optical asymmetric structure.
Organic solar cells.
The method of claim 18,
And the second electron acceptor and the third electron acceptor are selected from a fullerene derivative having a common functional group.
The method of claim 13,
The intermediate connecting portion includes a plurality of layers including a conductive polymer, an insulating polymer, a ferroelectric polymer, a metal oxide, or a combination thereof. Organic solar cells.
The method of claim 22,
The intermediate connector includes a plurality of layers,
Containing a conductive thin film located between the plurality of layers
Organic solar cells.
The method of claim 13,
The second output current is 0.9 to 1.1 times the organic solar cell than the first output current.

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