Patent Application
20120073639
This application claims priority to Korean Patent Application No. 10-2009-0023048 filed on Mar. 18, 2009 and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are incorporated by reference in their entirety.
The present disclosure relates to a solar cell and manufacturing method thereof, and more particularly, to an organic solar cell and manufacturing method thereof, where two or more photoelectric conversion layers are stacked.
While fossil fuels are used, environmental pollution such as those contributing to global warming becomes an issue. Uranium that replaces fossil fuels has limitations in terms of radioactive contamination and the need for a nuclear waste facility. The demand for alternative energy sources, such as solar cells which convert solar energy to electrical energy, is growing, and thus research is being conducted in this field.
In the related art, single crystalline or polycrystalline silicon solar cells have been widely used. However, there are limitations in that their manufacturing costs are high and they are difficult to apply to flexible boards. To solve these limitations, research has being conducted on organic solar cells in recent years. Organic solar cells can be manufactured by a simple process and at low cost. Moreover, when using organic solar cells, large areas can be coated, and thin layers can be formed at low temperature. Furthermore, solar cells can be manufactured using almost all kinds of substrates from glass to plastic, and can be manufactured with various cross-sectional shapes such as a curved or spherical shape as with plastic molds, and can be bent and folded to be portable. Accordingly, organic solar cells can be attached to clothes, bags, and portable electronic and electrical equipment and used. Polymer blend thin films have high transparency to light, and thus can generate power while attached to a glass window of a building or vehicle. Accordingly, polymer blend thin films may have broader applications than opaque silicon solar cells.
However, despite these advantages, organic solar cells have a low power conversion efficiency and short life, and thus are not suitable for practical applications. That is, the efficiency of organic solar cells has been about 1% up to the late 1990s, and after 2000, their performance has been significantly enhanced due to the development of the morphology of polymer blend structures. For example, in 2003, an efficiency of about 3.5% was accomplished using P3HT (poly(3-hexylthiophene) and PCBM ([6,6]-phenyl-C61 butyric acid methyl ester) blend thin films, and using a thin LiF layer in a contact interface with an Al electrode [F. Padinger, R. S. Rittberger, N. S. Sariciftci, Adv. Func. Mater., 13, 85 (2003)].
However, polymer solar cells still have efficiency less than other thin film solar cells and require further improvement.
The present disclosure provides a solar cell and manufacturing method thereof, which lead to the enhancement of efficiency.
The present invention also provides a solar cell and manufacturing method thereof, in which first and second photoelectric conversion layers are stacked, and a tunneling layer and transflective conductive layer are formed between the first and second photoelectric conversion layers, leading to the enhancement of efficiency.
In accordance with an exemplary embodiment, a solar cell includes: first and second electrodes, at least one of the first and second electrodes having light transmittance; two or more photoelectric conversion layers positioned between the first and second electrodes; and a transflective conductive layer positioned between the photoelectric conversion layers.
Each of the photoelectric conversion layers may include a donor material and an acceptor material.
The photoelectric conversion layers may further include a blocking layer.
The solar cell may further include a tunneling layer positioned between the transflective conductive layer and photoelectric conversion layer.
The tunneling layer may include a metal oxide.
The tunneling layer may be a natural oxide layer.
The metal oxide may include Al2O3.
The solar cell may further include an electron injection layer positioned between the tunneling layer and photoelectric conversion layers.
The transflective conductive layer may have short-wavelength reflectivity and long-wavelength reflectivity which differ, in a visible light region.
The transflective conductive layer may include Au, Cu, or alloy thereof.
In accordance with another exemplary embodiment, a method of manufacturing a solar cell includes: forming a first electrode layer on a substrate; forming two or more photoelectric conversion layers on the first electrode layer, and tunneling layer and transflective conductive layer between the photoelectric conversion layers; and forming a second electrode layer on the photoelectric conversion layer.
The method may further include annealing each of the photoelectric conversion layers after each of the photoelectric conversion layers is formed.
The method may further include annealing all of the photoelectric conversion layers after all of the photoelectric conversion layers are formed.
The tunneling layer may be formed by depositing and oxidizing a metal material.
Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawing. The present disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. In the figures, the dimensions of layers and regions may be exaggerated for clarity of illustration, and like reference numerals refer to like elements throughout. In the specification, it will be understood that when a layer (or film), a region, or a plate is referred to as being ‘on’ another layer, region, or plate, it can be directly on the other layer, region, or plate, or intervening layers, regions, or plates may also be present.
Referring to
A substrate 100 uses a transparent material with the light transmittance ratio of at least 110% or more, preferably, 80% or more in the wavelength of visible light. That is, the substrate 100 may use a transparent inorganic material such as quartz or glass, or a transparent plastic material such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polystyrene (PS), polypropylene (PP), polyimide (PI), polyethylenesulfonate (PES), polyoxymethylene (POM), acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, and triacetyl cellulose (TAC).
The first electrode layer 200 may be used as an anode, and use a conductive material with a high work function of about 4.5 eV or more and low resistance. The first electrode layer 200 uses a material with a high transparency because the first electrode layer 200 is a path through which light passing the substrate 100 reaches the first photoelectric conversion layer 300. Accordingly, the first electrode layer 200 may use a transparent conductive material such as indium tin oxide (ITO), zinc oxide (ZnO), indium-doped ZnO (IZO), gallium-doped ZnO (GZO), and aluminum-doped ZnO (AZO). The first electrode layer 200 may be formed using the thermal evaporation, electron-beam evaporation, RF or magnetron sputtering, or chemical deposition.
The first photoelectric conversion layer 300 includes the first hole transport layer 310, first donor/acceptor layer 320, and first blocking layer 330. The donor/acceptor layer 320 absorbs light to generate excitons. The hole transport layer 310 delivers holes separated from the excitons to the first electrode layer 200. The blocking layer 330 prevents the holes which has been separated from the excitons and excitons form which holes are not separated, from moving to the tunneling layer 400 and enables electrons to move to the tunneling layer 400.
The first hole transport layer 310 is formed of a conductive polymer material. For example, a conductive polymer such as poly(3,4-ethylene dioxythiopene) (PEDOT), poly(styrene sulphonate) (PSS), polyaniline, phtalocyanine, pentacene, poly(diphenylacetylene), poly(t-butyl)diphenylacetylene, poly(trifluoromethyl)diphenylacetylene, CuPc (Copper Phthalocyanine), poly(bistrifluoromethyl)acetylene, polybis(T-butildiphenyl)acetylene, poly(trimethylsilyl)diphenylacetylene, poly(carbazole)diphenylacetylene, polydiacetylene, polyphenylacetylene, polypyridineacetylene, polymethoxyphenylacetylene, polymethylphenylacetylene, poly(t-butil)phenylacetylene, polynitrophenylacetylene, poly(trifluoromethyl)phenylacetylene, poly(trimethylsilyl)phenylacetylene and derivatives thereof may be used in one or more mixtures. A mixture of PEDOT and PSS may be used. The conductive polymer materials may be formed using a common coating method, for example, spraying, spin coating, dipping, printing, doctor blading, or sputtering.
The first donor/acceptor layer 320 may be formed by blending donor and acceptor materials. A conductive polymer material including a π-electron may be used as the donor materials. For example, one of conductive polymers such as poly(3-hexylthiophene), polysiloxane carbazole, polyaniline, polyethylene oxide, poly(1-methoxy-4-(0-disperse red1)-2,5-phenylene-vinylene), polyindole, polycarbazole, polypyridazine, polyisothianaphthene, polyphenylene sulfide, polyvinylpyridine, polythiophene, polyfluorene, polypyridine and their derivatives or a mixture thereof may be used. The first donor/acceptor layer 320 uses a mixture of P3HT as the donor material and PCBM ([6,6]-phenyl-C61 butyric acid methyl ester) being a derivative of fullerene as the acceptor material. Herein, P3HT and PCBM may be mixed at a weight ratio (wt %) of 1:0.1 to 1:2.-20 wt % or 1 to 20 wt % The first donor/acceptor layer 320 also may be formed using a common coating method, for example, spraying, spin coating, dipping, printing, doctor blading, or sputtering.
The first blocking layer 330 is formed of a material having a great Highest Occupied Molecular Orbital (HOMO) level so as to prevent movement of the holes which has been separated from the excitons and excitons form which holes are not separated and allow movement of electrons. For example, the first blocking layer 330 is formed using bathocuproine (BCP). The first blocking layer 330 may be formed in the evaporation.
The tunneling layer 400 enables an electron delivered through the first blocking layer 330 to smoothly move to the transflective conductive layer 500. The tunneling layer 400 may be formed using a metal oxide. For example, Al2O3 may be used. The tunneling layer 400 may be formed depositing a metal material at low speed such that the metal material is naturally oxidized during the deposition. In addition, the tunneling layer 400 may be formed in various methods such as an oxidation using oxygen plasma.
The transflective conductive layer 500 delivers electrons that are delivered from the first photoelectric conversion layer 300 through the tunneling layer 400, to the second photoelectric conversion layer 600. That is, the transflective conductive layer 500 may be formed of at least a transflective conductive material such that light can be transmitted to the second photoelectric conversion layer 600. The transflective conductive layer 500 may be formed using at least one of Ag, Au, Mg, Ca, Li, Cu, and alloy thereof. For example, a material where the reflectivity in the short wavelength of 300-400 nm is different from the reflectivity in the long wavelength of 700-800 nm in the visible light region may be used. That is, as shown in a graph showing metal materials and their reflectivities of
The second photoelectric conversion layer 600 includes a second hole transport layer 610, second donor/acceptor layer 620, and second blocking layer 630, which are stacked on the transflective conductive layer 500. The second donor/acceptor layer 620 absorbs light which is lost in the first photoelectric conversion layer 300 to generate excitons. The second hole transport layer 610 delivers holes separated from the excitons of the second donor/acceptor layer 620, to the transflective conductive layer 500. The first blocking layer 630 prevents the holes which have been separated from the excitons and excitons from which holes are not separated, from moving to the second electrode layer 700 and enables electrons to move to the second electrode layer 700. That is, in the light incident through the first electrode 200, the light reflected by the transflective conductive layer 500 is absorbed in the first photoelectric conversion layer 300, but the light passing the transflective conductive layer 500 is absorbed in the second photoelectric conversion layer 600 to generate electrons and holes. In this case, the second photoelectric conversion layer 600 is formed in the same structure as the first photoelectric conversion layer 300. However, the second photoelectric conversion layer 600 and first photoelectric conversion layer 300 may be formed of different materials. For example, a donor material of the first photoelectric conversion layer 300 may be different from that of the second photoelectric conversion layer 600 in the band-gap energy. That is, donor materials of the first and second photoelectric conversion layer 300 and 600 each have a light absorption spectrum and one more peak wavelengths. Herein, at least one of the peak wavelengths may be different from that of the other donor material. For example, when the transflective conductive layer 500 is formed of Au, in the light incident through a first photoelectric conversion layer 300, the light in a long wavelength region is reflected by the transflective conductive layer 500. Thus, the first photoelectric conversion layer 300 may be formed to include a donor material having a peak wavelength in the red region. Since the light in a short wavelength region is incident to the second photoelectric conversion layer 600 through the transflective conductive layer 500, the second photoelectric conversion layer 600 may be formed to include a donor material having a peak wavelength in the blue or green region.
The second electrode layer 700 is used as a cathode and formed of a material having a work function less than the first electrode layer 200. For example, the second electrode layer 700 may be formed of a metal such as Mg, Al, or Ag or alloy thereof. Preferably, the second electrode layer 700 may be formed of Al with a high reflectivity.
Referring to
That is, the solar cell according to another embodiment of the present invention has a structure where the electron injection layer 800 is added to the structure of
The electron injection layer 800 injects electrons separated from the first photoelectric conversion layer 300 into the tunneling layer 400, thereby enhancing the interface property. The electron injection layer 800 may be formed of a material such as LiF and Liq. Also, the electron injection layer may be further formed between the second blocking layer 630 and second electrode 700.
A method of manufacturing the solar cells according to embodiments of the present invention will be described with reference to
Referring to
To generate the material forming a hole transport layer, a mixture of PEDOT and PSS is melted in an organic solvent such as isopropyl alcohol (IPA) and dispersed for at least 24 hours. The material forming a hole transport layer may be generated by mixing PEDOT and PSS with organic solvents, respectively, and then mixing the organic solvents. Also, the material forming a hole transport layer may be generated by mixing PEDOT and PSS. That is, the material forming a hole transport layer may be generated by mixing PEDOT and PSS without an organic solvent. To generate a material forming a donor/acceptor layer, P3HT and PCBM are mixed at a weight ratio (wt %) of 1:0.1 to 2:1. The mixture is melted in an organic solvent and dispersed for at least 72 hours. To remove macro particles make a problem in coating, the mixture is filtered with, for example, a 5 μm filter. Herein, chlorobenzene, benzene, chloroform, and THF may be used as an organic solvent. Also, a mixture thereof may be used. The material forming a donor/acceptor layer may be generated by mixing PEDOT and PSS with organic solvents, respectively, and then mixing the organic solvents.
Referring to
Referring to
Referring to
Referring to
The second hole transport layer 620 is formed by spin-coating the material forming a hole transport layer in which PEDOT and PSS are melted in an organic solvent, for example, at 1000 rpm for approximately 60 seconds and annealing the material in a nitrogen atmosphere at approximately 125° C. for 10 minutes. For example, the second hole transport layer 610 and second donor/acceptor layer 620 may be formed of materials different from the first hole transport layer 310 and first donor/acceptor layer 320, respectively. In particular, the second donor/acceptor layer 620 may be formed of another material which absorbs light with a wavelength different from the first donor/acceptor layer 320. For example, the second donor/acceptor layer 620 may be formed of a material which absorbs light with a wavelength longer than the first donor/acceptor layer 320. The second blocking layer 630 is formed by depositing BCP on the second donor/acceptor layer 620 in the evaporation. The second hole transport layer 610, second donor/acceptor layer 620, and second blocking layer 630 may be formed to a thickness of approximately 5 to 50 nm, approximately 10 to 150 nm, and approximately 5 to 30 nm.
Referring to
It has been described above that annealing process is performed after the first hole transport layer 310, first donor/acceptor layer 320, second hole transport layer 610, and second donor/acceptor layer 620 are each formed. However, the annealing process may be performed not after the first hole transport layer 310 and first donor/acceptor layer 320 are formed, but only after the second hole transport layer 610 and second donor/acceptor layer 620 are formed.
In a solar cell according to an embodiment of the present invention with reference to
A solar cell is manufactured by stacking a 100 nm first electrode layer of ITO, 10 nm first hole transport layer of PEDOT:PSS, 70 nm first donor/acceptor layer of P3HT:PCBM, 12 nm first blocking layer of BCP, 0.5 nm electron injection layer of LiF, 0.5 nm tunneling layer of Al2O3, 10 nm transflective conductive layer of Au, 10 nm second hole transport layer of PEDOT:PSS, 70 nm second donor/acceptor layer of P3HT:PCBM, 12 nm second blocking layer of BCP, and 80 nm second electrode layer of Al on a glass substrate.
The properties of a solar cell are evaluated using an open circuit voltage (Voc), short circuit current (Jsc), fill factor (FF), and efficiency. The open circuit voltage (Voc) is a voltage which is generated when light is emitted without an external electrical load, namely a voltage when a current is zero. The short circuit current (Jsc) is a current which is generated when light is emitted with a short electrical contact, namely a current when a voltage is not applied. The fill factor (FF) is defined as a value that is obtained by dividing the multiplication of a changed current and voltage by the multiplication of the open circuit voltage Voc and short circuit current Jsc. The fill factor (FF) is always less than one because the open circuit voltage (Voc) and short circuit current (Jsc) are not simultaneously obtained. However, the efficiency of a solar cell becomes higher as the fill factor (FF) gets closer to 1. A resistance becomes greater as the fill factor (FF) gets lower. The efficiency is defined as a valued which is obtained by diving the multiplication of the open circuit voltage (Voc), short circuit current (Jsc), and fill factor (FF) by the strength of emitted light, namely as [Equation 1].
Efficiency=Vos×Jsc×FF/the strength of emitted light [Equation 1]
A solar cell is manufactured by stacking a 100 nm first electrode layer of ITO, 10 nm hole transport layer of PEDOT:PSS, 70 nm donor/acceptor layer of P3HT:PCBM, 12 nm blocking layer of BCP, 0.5 nm electron injection layer of LiF, and 80 nm second electrode layer of Al on a glass substrate. That is, the solar cell according to the comparison example 1 is manufactured by forming a photoelectric conversion layer in a single layer, unlike the present invention.
A solar cell is manufactured by stacking a 100 nm first electrode layer of ITO, 10 nm first hole transport layer of PEDOT:PSS, 70 nm first donor/acceptor layer of P3HT:PCBM, 12 nm first blocking layer of BCP, 10 nm second hole transport layer of PEDOT:PSS, 70 nm second donor/acceptor layer of P3HT:PCBM, 12 nm second blocking layer of BCP, and 80 nm second electrode layer of Al on a glass substrate. That is, the solar cell according to the comparison example 2 is manufactured by stacking two photoelectric conversion layers without forming an electron injection layer, tunneling layer, and transflective conductive layer, unlike the present invention. For the comparison example 2, the first blocking layer may be damaged when the second hole transport layer of PEDOT:PSS is spin-coated on the first blocking layer of BCP in a manufacturing process.
Also,
A solar cell is manufactured by stacking a 100 nm first electrode layer of ITO, 10 nm first hole transport layer of PEDOT:PSS, 70 nm first donor/acceptor layer of P3HT:PCBM, 12 nm first blocking layer of BCP, 3 nm transflective conductive layer of Al, 10 nm second hole transport layer of PEDOT:PSS, 70 nm second donor/acceptor layer of P3HT:PCBM, 12 nm second blocking layer of BCP, and 80 nm second electrode layer of Al on a glass substrate. That is, the solar cell according to the comparison example 3 is manufactured by using a transflective conductive layer of Al instead of Au without forming an electron injection layer and tunneling layer unlike embodiments of the present invention.
For the comparison example 3, the transflective conductive layer is formed of Al with a high reflectivity and to a thickness of 3 nm, considering the reflectivity of Al. However, the layer of Al is so thin that the resistance is significantly increased, thereby functioning as not a transflective layer but a resistance. That is, as shown in
A solar cell is manufactured by stacking an 100 nm thick first electrode layer of ITO, 10 nm first hole transport layer of PEDOT:PSS, 70 nm first donor/acceptor layer of P3HT:PCBM, 12 nm first blocking layer of BCP, 10 nm transflective conductive layer of Au, 10 nm second hole transport layer of PEDOT:PSS, 70 nm second donor/acceptor layer of P3HT:PCBM, 12 nm second blocking layer of BCP, and 80 nm second electrode layer of Al on a glass substrate. That is, a solar cell according to the comparison example 4 is manufactured without forming electron injection layer and tunneling layer, unlike the present invention.
The results of the above experiment examples and comparison examples are as the following Table 1.
From the above-described, it can be seen that the solar cell according to an embodiment of the present invention has the open circuit voltage (Voc) and short circuit current (Jsc) higher than the solar cells. Accordingly, the fill factor (FF) is enhanced, and thus the efficiency can be significantly enhanced.
As described above, the technical idea of the present invention has been specifically described with respect to the above embodiments, but it should be noted that the foregoing embodiments are provided only for illustration while not limiting the present invention. Various embodiments may be provided to allow those skilled in the art to understand the scope of the preset invention.
The present invention provides the solar cell with first and second photoelectric conversion layers between first and second electrode layers, and tunneling layer and transflective conductive layer between the first and second photoelectric conversion layers. Also, an electric injection layer is further provided between the first photoelectric conversion layer and tunneling layer.
The tunneling layer and transflective conductive layer enable electrons to smoothly move and enable the second photoelectric conversion layer to absorb light which is not absorbed in the firs photoelectric conversion layer, thereby enhancing the efficiency of the solar cell.
Although a solar cell and manufacturing method thereof have been described with reference to the specific embodiments, it is not limited thereto. Therefore, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the present invention defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2009-0023048 | Mar 2009 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2010/001685 | 3/18/2010 | WO | 00 | 12/10/2011 |
