KR101495764B1 - Inverted organic solar cell containing quantum dot single layer in electron transfer layer and method for fabricating the same - Google Patents

Abstract

Provided are an organic solar cell capable of increasing light absorption and an electron transfer layer by forming a quantum dot single layer, and a method for fabricating the same. An inverted organic solar cell includes a first electrode, an electrode transfer layer, a photoactive layer, a hole transfer layer and a second electrode which are successively formed on the substrate. The electron transfer layer is made of semiconductor having quantum dots, thereby increasing photoelectric conversion efficiency and providing a supplier inverted organic solar cell.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverse-structured organic solar cell having a single-layer quantum dot electron transporting layer and a fabrication method thereof,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell, and more particularly, to a solar cell device and a manufacturing method thereof by sequentially stacking organic solar cells.

Recently, fossil fuel depletion and renewable energy are attracting attention, and many researches on clean energy technology of solar cells are being conducted. A solar cell converts light energy directly into electric energy by using photovoltaic effect. Organic solar cell has a high absorptivity of organic molecules used as a photoactive layer and can be manufactured as a thin device, Diversity, and low unit price, it is possible to realize a simple and inexpensive manufacturing cost.

The conventional organic solar cell structure is composed of a substrate / first electrode / hole transport layer / photoactive layer / electron transport layer / second electrode, and an ITO (indium tin oxide) electrode having a high work function as a first electrode And Al or Ca having a low work function is used as the second electrode material. The photoactive layer includes a bulk heterojunction (BHJ) structure formed by mixing a bilayer structure of an electron donor and an electron acceptor or an electron donor material and an electron acceptor material, ≪ / RTI >

When an organic solar cell receives light, the electrons and holes generated in the photoactive layer made of organic semiconductor materials are separated from each other due to the electric field due to the difference in work function between the upper and lower electrodes. do. At this time, the work function difference between the photoactive layer and the upper and lower electrodes is large, so that generated electrons and holes can not be smoothly transferred. As an alternative to decrease the work function difference, electrons and holes are smoothly transported by using a semiconductor material having an n-type / p-type property and having a solubility function value of the work function difference between the photoactive layer and the two electrodes, The need for research on the buffer layer, which plays a role in reducing the number of microbes, has been emphasized and many studies have been made.

Further, in the case of conventional solar cells, poly (3,4-ethylenedixythiophene): poly (styrenesulfonate), which is commonly used as a hole transport layer material, has strong acidity and the lower electrode And low work function materials such as Al, which is mainly used as an upper electrode (second electrode), forms an oxide film at the contact interface with air, thereby adversely affecting the lifetime and efficiency of the device. Furthermore, inverted organic solar cells have been proposed as a solution to this problem.

In addition, since the metal oxide used as the electron transporting layer in the reverse-structured organic solar cell is mainly prepared by the sol-gel method, the drying process is necessarily included, In addition, since the metal oxide used as the electron transporting layer is crystalline, it is practically impossible to form a high-quality thin film having few defects in the electron transporting layer due to the formation of the metal oxide crystals, due to the nature of the sol-gel process requiring subsequent heat treatment.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a process for producing a high-quality thin film having few defects of a metal oxide upon heat treatment when an electron transport layer is used as a crystalline metal oxide, It is practically impossible.

Also, in the case of forming the electron transport layer of the mixed layer, it is difficult to produce a high quality mixed layer in the process of manufacturing the mixed layer, and the light scattering and light transmittance are remarkably reduced. A semiconductor single layer having quantum dots is simply formed to improve the scattering of light and the absorption of light with the electron transporting layer.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: preparing a substrate having a first electrode; and sequentially stacking an electron transport layer, a photoactive layer, a hole transport layer, and a second electrode on the first electrode, And the electron transport layer comprises a semiconductor quantum dots as a single layer.

Semiconductor materials including semiconductor quantum dots of all kinds of solar regions (visible light) may include a core structure and a core-shell structure.

Specifically, in the case of the nucleus structure, a cadmium compound such as cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe) and the like may be formed into a single layer by a reverse structure method in the form of a quantum dot .

The core-shell structure is composed of zinc sulfide (ZnS), zinc selenide (ZnSe), cadmium sulfide (ZnSe), zinc sulfide ) Or the like to form a single layer with a quantum dot structure.

As a reverse-structured solar cell device, a single-layer semiconductor quantum dot can be used to provide a solar cell that increases light scattering and light absorption while serving as an electron transport layer.

In addition, the electron transport layer of the mixed layer significantly reduces light scattering and light transmittance. To overcome this disadvantage, a single layer of electron transport layer is formed to overcome the conventional problems.

In addition, in the case of a single-layer electron transport layer having a core structure and a core-shell structure using a semiconductor material including semiconductor quantum dots, the charge mobility is further improved, thereby enhancing the electron transporting ability and improving the charge recombination probability The efficiency of the solar cell can be increased. As a result, the efficiency of transporting electrons is improved as compared with that of the organic reverse structure solar cell, so that the current conversion efficiency is increased and the efficiency of the solar cell is improved.

Finally, when a single-layer QD electron transport layer is used, the conventional sol-gel drying process is not required, thereby reducing time and cost. Accordingly, it is possible to overcome the conventional problems that it is difficult to produce a high-quality thin film according to the crystallinity of the electron transport layer using a metal oxide through a sol-gel process.

FIG. 1A is a schematic diagram of a reverse structure organic solar cell in which quantum dots according to the present invention are formed into a single layer electron transport layer and light scattering and light absorption are increased.
FIG. 1B is a schematic diagram showing an enlarged view of light scattering and light absorption in a single layer of a quantum dot.
FIGS. 2A and 2B are cross-sectional transmission electron microscope images of a reverse-structured solar cell device that increases the scattering and absorption of light by an electron transport layer and a quantum dot having a single-layer nucleus structure and a nucleus-shell structure shown in FIG.
FIGS. 3A and 3B are schematic diagrams showing that the charge mobility of a CdSe core structure and a CdSe-ZnS core-shell quantum dot structure is improved.
FIG. 4 is a graph showing the absorption of CdSe (core) QD / P3HT: PCBM or CdSe (core) -ZnS (shell) QD / P3HT: PCBM according to the present invention.
5 shows the current density-voltage (JV) characteristics of the reverse-structured organic solar cell device using CdSe (core) QD / P3HT: PCBM or CdSe (core) -ZnS (shell) QD / P3HT: PCBM according to the present invention Fig.
6 is a graph of an incident photon-to-current conversion efficiency (IPCE) of an organic solar cell using the single-layer quantum dot electron transporting layer of the present invention.

Embodiments of the present invention will now be described with reference to the accompanying drawings. It is to be understood, however, that the present invention is not limited to the embodiments described herein, but may be embodied and practiced in other forms and includes all equivalents and substitutions.

1 is a cross-sectional view of a solar cell in which a quantum dot size is simply formed as a single layer to increase light scattering and light absorption with the electron transport layer 13. In the case of the substrate 10 and the first electrode 11 of ITO, a light-transmissive material is used for laminating in order, and in the case of the electron-transporting layer 13, a single layer having quantum dots is laminated. Thereafter, a light absorbing layer composed of a polymer is laminated. And a hole transport layer 15 and a second electrode 16 are sequentially stacked thereon to constitute a solar cell.

In FIG. 1B, light reaches the photoactive layer 14 to form an electron transport layer 13, a quantum dot; It is a scatter diagram by absorption of light.

 The substrate 10 may be a light-transmissive inorganic substrate 10 or an organic substrate 10, or may be a substrate 10 of the same type or differently stacked. For example, the substrate 10 may be formed of glass, quartz, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polycarbonate (PC) , Plastic substrates (e.g., polyethylene terephthalate), polystyrene (PS), polyoxyethylene (POM), acrylonitile styrene copolymer (AS resin) and triacetyl cellulose 10).

The first electrode 11 is preferably a light-transmissive material such that the light passing through the substrate 10 reaches the photoactive layer 14. The first electrode 11 receives electrons generated in the photoactive layer 14, Can play a role. The first electrode 11 may be formed of an indium tin oxide (ITO) film, a fluorinated tin oxide (FTO) film, an indium zinc oxide (IZO) film, an aluminum doped oxide a light-transmitting film such as a doped zinc oxide (AZO) film, a zinc oxide (ZnO) film, and an indium zinc tin oxide (IZTO) film. However, the present invention is not limited thereto.

The first electrode may be formed by applying a transparent electrode material on one side of the substrate 10 or by coating it with a film using sputtering, E-beam, thermal evaporation, spin coating, screen printing, inkjet printing, doctor blade or gravure printing The coating layer 12 can be formed.

In order to construct a reverse-structured organic solar cell, a step of lowering the work function of the first electrode is required. The work function reducing film is formed by depositing a polyethyleneimine ethoxylated (PEIE) polymer by spin coating to form a coating layer 12 on the surface of the first electrode 11 to lower the work function.

Referring to FIG. 1A, an organic photoactive layer 14 is formed on the electron transport layer 13. The organic photoactive layer 14 may be formed through a solution process in which a mixed solution of an electron donor and an electron donor is coated on the electron transport layer 13 and then the solvent is dried. The coating may be performed by a conventional coating method such as spin coating, spray coating, doctor blade coating, and inkjet printing, preferably by spin coating.

In the case of the electron transporting layer 13, the electron transporting layer is composed of single-layer quantum dots by adjusting the thickness of the electron transporting layer to a nano-sized thickness, and is composed of a semiconductor containing quantum dots. In the case of the quantum dot, it is a nanocrystal and has a diameter of 2 to 10 nm. Since quantum dots have a small number of orbits and the energy that electrons can have is fixed, the wavelength is fixed. However, because Qtots only emit specific light, energy efficiency is good. Recently, LEDs, TVs, and signals using quantum dots have been utilized.

Semiconductor materials including semiconductor quantum dots may include a core structure and a core-shell structure.

Specifically, in the case of the nucleus structure, a cadmium compound such as cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe) and the like may be formed into a single layer by a reverse structure method in the form of a quantum dot .

A _{2 ·} 2.5H ₂ 0 and Se CdCl powder for the production of CdSe nanoparticles, for example by the method of example, if CdSe from Ⅱ- Ⅵ group semiconductor compound aqueous solution of a Na ₂ SO ₃ 0.2M Na ₂ SeSO ₃ solution refluxed at 90 ° C for 1 hour was used with the aqueous solution. 0.4567 g (1.9 mmol) of CdCl ₂ was added to 90 ml of distilled water containing 10 ml DEA (99%), and then 10 ml of Na ₂ SeSO ₃ solution was added to make the total solution 100 ml. CdSe nanoparticles were obtained in a colloidal state by irradiating the mixed aqueous solution obtained at room temperature with a high-power ultrasonic wave for 5 to 30 minutes. The precipitate thus obtained was repeatedly washed with distilled water and alcohol, centrifuged and vacuum-dried for 50 to 120 minutes.

The core-shell structure consists of zinc sulfide (ZnS), zinc selenide (ZnSe), and zinc sulfide (ZnSe) in the core structure of cadmium compounds including cadmium sulfide (CdS), cadmium selenide (CdSe), and cadmium telluride (CdTe) And a method of forming a single layer with a quantum dot structure formed in the form of a shell structure.

For example, cadmium oxide and selenium powder were selected as precursors for CdSe as a core-shell structure. First, 0.45 g of cadmium oxide and 8 g of stearic acid are heated to 150 ° C. and then cooled down to room temperature to prepare a cadmium precursor, and 0.7896 g of selenium powder is dissolved in tri-n-octylphosphine (TOP) to prepare TOP-Se. The prepared precursor is injected into the reactor together with 8 g of trioctylphosophine oxide (TOPO) to be used as a solvent and 12 g of HDA. The nanoparticles are crystallized while maintaining the temperature of the reactor at 110 占 폚. Crystallization was continued for 40 minutes while maintaining the temperature at 110 캜. Crystallization at 150 캜 for 60 minutes was continued at 120 캜 for 50 minutes to extract nanoparticles of green luminescence, followed by heating at 190 캜 for 80 minutes and at 220 캜 for 100 Minute crystallization, and the resulting nanoparticle product of red light emission is extracted.

The electron donor material refers to a material that absorbs sunlight to form an electron-hole pair (exciton), and moves the hole separated from the pn junction interface of the electron donor material and the electron acceptor material to the anode direction .

The electron donor may be a conjugated polymer usable as a p-type semiconductor, and may be a polythiophene type, a polyfluorene type, a polyaniline type, a polycarbazole type, a polyvinyl carbazole type, Polyvinylcarbazole type, polyphenylene type, polyphenylenevinylene type, polysilane type, polythiazole type, or a copolymer thereof.

The electron acceptor material refers to a material that moves electrons separated from the p-n junction interface in the photoactive layer 14 toward the cathode. For example, the electron acceptor material may be fullerene and PC61BM ([6,6] -phenyl-C61-butyric acid methyl ester), PC71BM ([6,6] -phenyl- butyric acid methyl ester, PC81BM ([6,6] -phenyl-C81-butyric acid methyl ester).

The hole transport layer 15 is a p-type buffer layer for allowing holes generated in the organic photoactive layer 14 to be easily transferred to the anode. The p-type buffer layer is formed of a conductive organic material such as PEDOT: PSS or a conductive metal oxide such as WO3, V2O3, and MoO3 As shown in FIG.

The second electrode 16 may be any one selected from the group consisting of a metal, an alloy, a conductive polymer and other conductive compounds, and a combination thereof, which serves as an anode for finally collecting holes and transferring the holes to an external circuit. For example, when the metal is a metal, the second electrode 16 may be formed of a material having a high work function such as Cu, Ag, Au, W, Ni and Ti. Is preferably used.

Each of the layers may be formed by a thermal evaporation method, an electron beam evaporation method, a sputtering method, an ion plating method, or a chemical vapor deposition method. The electrodes may be formed by applying an electrode forming paste containing a metal and then heat-treating the paste.

≪ Example 1 >

In the case of the first electrode 11 and the substrate 10, the first electrode 11 and the substrate 10 are washed with ethanol, acetone, isopropyl alcohol, etc. for 20 minutes through an ultrasonic washing machine, Thereby modifying the interface. Next, a polyethyleneimine ethoxylated (PEIE) polymer is deposited to a thickness of about 7 nm by spin coating to form a coating layer 12 on the surface of the first electrode 11 to lower the work function. Thereafter, an electron transport layer 13 of a single layer of quantum dots having a nucleus structure is formed by a spin coating method. The photoactive layer 14 is formed on the quantum dot electron transport layer 13 of a single layer of quantum dots formed by a single layer by a spin coating method and then the hole transport layer 15 and the second electrode 16 are sequentially deposited by using an evaporation method can do.

≪ Example 2 >

In the case of the first electrode 11 and the substrate 10, the first electrode 11 and the substrate 10 are washed with ethanol, acetone, isopropyl alcohol, etc. for 20 minutes through an ultrasonic washing machine, Thereby modifying the interface. Next, a polyethyleneimine ethoxylated (PEIE) polymer is deposited to a thickness of about 7 nm by spin coating to form a coating layer 12 on the surface of the first electrode 11 to lower the work function. Thereafter, an electron transport layer 13 of a single layer of quantum dots having a nucleus structure is formed by a spin coating method. The photoactive layer 14 is formed on the quantum dot electron transport layer 13 of a single layer of quantum dots formed by a single layer by a spin coating method and then the hole transport layer 15 and the second electrode 16 are sequentially deposited by using an evaporation method can do.

≪ Comparative Example 1 &

An organic solar cell was manufactured by the same method and conditions as in Example 1, except that a single layer organic reverse structure solar cell having no quantum dot was prepared.

FIG. 5 is a graph showing current density-voltage (J-V) characteristics for a solar cell having the manufacturing processes of Example 1, Example 2, and Comparative Example 1. FIG.

Table 1 below shows the open circuit voltage (V _oc ), the short circuit current density (J _sc ), the fill factor (FF) and the photoelectric conversion efficiency (Eff) of the reverse structure organic solar cell manufactured in Examples and Comparative Examples It is summarized.

J _sc V _oc FF Energy change efficiency Comparative Example 1 9.7 0.62 0.60 3.6 CdSe QD 11.3 0.62 0.63 4.4 CdSe-ZnS QD 10.5 0.64 0.61 4.1

Referring to FIG. 5 and Table 1, in the case of forming a quantum dot single-layer electron transport layer 13, the efficiency of electron transport is increased and the probability of charge recombination is reduced as compared with an organic reverse structure solar cell having no quantum dot, It can be confirmed that the device is improved by 20% or more.

10: substrate
11: first electrode
12: Work function reduction thin film layer
13: electron transport layer
14: photoactive layer
15: hole transport layer
16: second electrode

Claims (17)

A first electrode, a work function reducing film, an electron transporting layer, a photoactive layer, a hole transporting layer and a second electrode sequentially stacked on a substrate, wherein the electron transporting layer is a single layer having a quantum dot in a visible light region, .

delete The method according to claim 1,
The substrate may be made of glass, quartz, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polycarbonate (PC), polystyrene (PS) , Polyoxyethylene (POM), acrylonitile styrene copolymer (AS resin), and triacetyl cellulose (TAC). A single-layer reverse-structured organic solar cell.
The method according to claim 1,
In the case of the first electrode, an indium tin oxide (ITO) film, a fluorinated tin oxide (FTO) film, an indium zinc oxide (IZO) film, an aluminum-doped Wherein the film is one or more selected from the group consisting of a Zinc Oxide (AZO) film, a Zinc Oxide (ZnO) film, and an Indium Zinc Tin Oxide (IZTO) Solar cells.
The method according to claim 1,
Wherein the hole transport layer is any one or more selected from the group consisting of a combination organic material of poly (3,4-ethylenedioxythiophene) [PEDOT] and poly (3-styrenesulfonate) [PSS] Single layer reverse structure organic solar cell.
The method according to claim 1,
Wherein the second electrode is at least one selected from the group consisting of a metal, an alloy, a conductive polymer and other conductive compounds, and a combination thereof.
The method according to claim 1,
Wherein the quantum dot comprises a nucleus structure.
The method according to claim 1,
Wherein the quantum dot comprises a nucleus-shell structure.
8. The method of claim 7,
Wherein the core structure is composed of a cadmium sulfide compound.
9. The method of claim 8,
Wherein the core-shell structure is composed of at least one of zinc sulfide (ZnS) and zinc selenide (ZnSe).
Stacking a first electrode on the substrate;
A step of laminating the work function reducing film of the first electrode
Depositing an electron transport layer composed of a single layer having quantum dots in the visible light region on the first electrode;
Depositing a photoactive layer on the electron transporting layer;
Stacking a hole transport layer on the photoactive layer;
And laminating a second electrode on the hole transport layer.
delete 12. The method of claim 11,
Wherein the quantum dot comprises a nucleus structure.
12. The method of claim 11,
Wherein the quantum dot comprises a nucleus-shell structure.
12. The method of claim 11,
Wherein the work function reducing film is composed of polyethylene imine ethoxylated (PEIE) and a polymer.
14. The method of claim 13,
Wherein the nucleation structure is a cadmium sulfide compound structure and the nucleation structure quantum dots are formed in the step of laminating the electron transport layer.
15. The method of claim 14,
In the step of laminating the electron transporting layer, the nucleus-shell structure may be a single-layer reverse-structured organic solar cell having a structure in which at least one of zinc sulfide (ZnS) and zinc selenide (ZnSe) ≪ / RTI >

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