KR20130037569A - Inverted organic solar cell and method for fabricating the same - Google Patents

Abstract

PURPOSE: An inverted organic solar cell and a manufacturing method thereof are provided to improve the mobility of electrons by using a high quality thin film electron transport layer formed by atomic layer deposition. CONSTITUTION: A substrate(210) including a first electrode(220) is prepared. An electron transport layer(230) is formed on the first electrode. The electron transport layer is a thin metal oxide layer which is formed by using an atomic layer deposition method. An organic light active layer(240) is formed on the electron transport layer. A hole transport layer(250) and a second electrode(260) are sequentially formed on the organic light active layer.

Description

Inverted organic solar cell and method for fabricating the same

The present invention relates to an inverted organic solar cell and a method for manufacturing the same, and more particularly, to an inverted organic solar cell including a metal oxide thin film formed by an atomic layer deposition method as an electron transport layer and a method for manufacturing the same.

A solar cell is a semiconductor device that converts light energy directly into electrical energy using a photovoltaic effect. Recently, many studies have been conducted as part of clean alternative energy technologies in the face of environmental problems and high oil price problems. Among them, the organic solar cell has a high absorption coefficient of the organic molecules used as the photoactive layer can be manufactured in a thin device, can be manufactured with a simple manufacturing method and low equipment cost, due to the nature of the organic material is good because of the bendability and processability There are several advantages that can be applied in the field.

Conventional organic solar cell (conventional organic solar cell) structure is a substrate 110 / first electrode 120 / hole transport layer 150 / photoactive layer 140 / electron transport layer 130 as shown in Figure 1a The second electrode 160, an indium tin oxide (ITO) electrode, which is a transparent electrode having a high work function, as the first electrode 120, and an Al or Ca having a low work function; (160, cathode) Used as a material.

The photoactive layer 140 is largely a bulk heterojunction formed by mixing a bi-layer structure of an electron donor and an electron acceptor or by mixing an electron donor and an electron acceptor. heterojunction (BHJ) structure. However, in order to generate photocurrent in a solar cell, an exciton generated by absorption of light in the photoactive layer 140 must be separated into electrons and holes at the junction between the electron donor material and the electron acceptor material. However, since the diffusion distance of excitons is about 10 nm, the BHJ structure having a wide bonding interface inside the photoactive layer 140 is advantageous for the separation of electrons and holes of excitons.

Meanwhile, the hole transport layer 150 inserted between the first electrode 120 and the photoactive layer 140 and the electron transport layer 130 inserted between the cathode 160 and the photoactive layer 140 are separated from each other. It serves as a buffer layer that can improve transfer and collection efficiency.

However, in the conventional solar cell illustrated in FIG. 1, since PEDOT: PSS (poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate)) commonly used as a material of the hole transport layer 130 has a strong acidity, The lower work function materials such as Al, which are used to corrode the lower electrode (first electrode) 120 and are mainly used as the upper electrode (second electrode, 160), form an oxide film at the contact interface with air, thereby increasing the lifetime of the device. There is a problem that adversely affects the efficiency.

Inverted organic solar cell (inverted organic solar cell) has been proposed as part of the research to solve this problem, as shown in Figure 1b substrate 110 / first electrode 120 / electron transport layer 130 / The photoactive layer 140 / hole transport layer 150 / second electrode 160 has a structure.

Currently, the metal oxide used as the electron transport layer 130 in the reverse structure organic solar cell is mainly manufactured by a sol-gel method. In this case, subsequent heat treatment is required to form a crystalline metal oxide. However, it is practically impossible to form a high quality thin film with few defects due to the nature of the sol-gel process. Formation of high quality thin films is an essential technique for improving photoelectric conversion efficiency because defects in the film inhibit the movement of charges and promote recombination of charges.

Another method is to prepare the electron transport layer 130 by spin coating, doctor blade coating or spray coating a dispersion solution of metal oxide nanoparticles, which is also difficult to remove defects occurring at the interface of the nanoparticles.

Therefore, in order to implement a high efficiency organic solar cell, a technology capable of forming an electron transport layer into a high quality thin film will be required.

The technical problem to be solved by the present invention is to provide an inverse structure organic solar cell including a high-quality thin film electron transport layer formed by an atomic layer deposition method and a method of manufacturing the same.

In order to solve the above technical problem, an aspect of the present invention provides a method of preparing a substrate including a first electrode, and sequentially stacking an electron transport layer, an organic photoactive layer, a hole transport layer, and a second electrode on the first electrode. It includes, The electron transport layer provides an inverse structure organic solar cell manufacturing method of forming a metal oxide thin film using an atomic layer deposition method.

The metal oxide thin film may be a titanium oxide thin film, a zinc oxide thin film, or a tin oxide thin film.

Specifically, the formation of the metal oxide thin film using the atomic layer deposition method,

Placing a substrate with the first electrode in an atomic layer deposition reactor and introducing a metal oxide precursor into the reactor; Purging the reactor into which the metal oxide precursor is introduced; Introducing an oxidant into the purged reactor; And purging the reactor into which the oxidant is introduced.

The metal oxide precursor may be tetrakis dimethyl amido titanium, tetrakis diethyl amido titanium, tetrakis ethyl methyl amido titanium, diethyl zinc, tin chloride, tetrakis dimethyl amido tin, tetrakis diethyl amido tin and Tetrakis ethylmethylamido may also be selected from tin.

On the other hand, according to an embodiment of the present invention, the reverse structure organic solar cell manufacturing method may further include forming a nanoparticle thin film on the first electrode before forming the metal oxide thin film.

The nanoparticle thin film may be formed by coating a dispersion solution of nanoparticles on the first electrode.

The nanoparticle thin film may include metal oxide nanoparticles, and the metal oxide nanoparticles may be titanium oxide, zinc oxide, or tin oxide.

In order to solve the above technical problem, another aspect of the present invention includes a first electrode, an electron transport layer, a photoactive layer, a hole transport layer, and a second electrode sequentially stacked on a substrate, wherein the electron transport layer is a metal formed by atomic layer deposition. Provided is an inverse structure organic solar cell that is an oxide thin film.

Meanwhile, according to one embodiment of the present invention, the inverse structure organic solar cell may further include a nanoparticle thin film positioned between the first electrode and the metal oxide thin film.

As described above, according to the present invention, since the high-quality thin film electron transport layer formed by the atomic layer deposition method is used, the movement of the separated electrons can be promoted, thereby improving the photoelectric conversion efficiency.

In addition, when the electron transport layer is composed of a double layer of the nanoparticle thin film (first electron transport layer) and the thin film (second electron transport layer) formed by the atomic layer deposition method, the surface area of the electron transport layer is increased by the nanoparticle thin film and the electron transport layer and The contact area of the photoactive layer can be widened and the separation of the electron-hole pairs can be facilitated. In addition, since contact bonds that may occur between nanoparticles can be removed by a thin film formed by atomic layer deposition, separated electrons can be collected without loss to the first electrode.

In addition, since the material having excellent oxidation stability can be used as the upper electrode, it is possible to provide an organic solar cell having excellent atmospheric stability.

However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1A and 1B are cross-sectional views illustrating a conventional general organic solar cell and an inverse structure organic solar cell, respectively.
2A through 2D are cross-sectional views illustrating a method of manufacturing an inverse structure organic solar cell according to an exemplary embodiment of the present invention.
3 is a graph showing current-voltage characteristics of the reverse structure organic solar cells prepared in Preparation Examples 1 to 5 and Comparative Examples.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms and should be understood to include all equivalents and substitutes included in the spirit and scope of the present invention. In the drawings, the thicknesses of the layers and regions may be exaggerated or omitted for the sake of clarity. Like reference numerals designate like elements throughout the specification. In addition, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2A through 2D are cross-sectional views illustrating a method of manufacturing an inverse structure organic solar cell according to an exemplary embodiment of the present invention.

Referring to FIG. 2A, first, a substrate 210 having the first electrode 220 is prepared.

The substrate 210 may be a light-transmitting inorganic substrate or an organic substrate, or may be a substrate in which two or more of them are stacked in the same or different types. For example, the substrate 210 may be an inorganic substrate selected from glass, quartz, Al ₂ O ₃ , and SiC, or PC (polycarbonate), PMMA (polymethylmethacrylate), PET (polyethylene terephthalate), PES (polyethersulfone), PS ( It may be a plastic substrate selected from polystyrene, polyimide (PI), polyethylene naphthalate (PEN) and polyarylate (PAR).

The first electrode 220 is preferably a light transmissive material so that light passing through the substrate 210 reaches the photoactive layer, and serves as a cathode that receives electrons generated in the photoactive layer and delivers the electrons to an external circuit. Can be. The first electrode 220 may be an indium tin oxide (ITO) film, a fluorinated tin oxide (FTO) film, an indium zinc oxide (IZO) film, an Al-doped Zinc Oxide (AZO) film, a zinc oxide (ZnO) film, or an IZTO film. It may be a light transmissive film such as (Indium Zinc Tin Oxide) film. However, it is not limited thereto.

The first electrode 220 may be formed on the substrate 210 by thermal image deposition, electron beam deposition, sputtering, chemical vapor deposition, or the like.

Referring to FIG. 2B, an electron transport layer 230 is formed on the first electrode 220.

The electron transport layer 230 is an n-type buffer layer that allows electrons generated in the photoactive layer to be easily transferred to the cathode, and is a single layer or a double layer in which the first electron transport layer 232 and the second electron transport layer 234 are sequentially stacked. It may have a structure of.

For convenience of description, in FIG. 2B, only the case where the electron transport layer 230 is configured as a double layer is illustrated, and the case where the electron transport layer 230 is configured as a single layer will be apparent to those skilled in the art from the following description.

The first electron transport layer 232 may be a nanoparticle thin film made of a plurality of nanoparticles, the diameter of the nanoparticles may be 1nm to 500nm, the thickness of the nanoparticle thin film may be 1nm to 200nm.

The nanoparticle thin film 232 may be formed through a conventional solution process in which the nanoparticle-dispersed solution is applied to the first electrode 220 and then volatilized the dispersion solvent at an appropriate temperature. For example, the nanoparticle thin film 232 may be formed by spin coating, doctor blade coating, spray coating, or the like, and preferably by spin coating.

The nanoparticles included in the nanoparticle thin film 232 may be n-type semiconductor materials such as metal oxides, for example, titanium oxide, zinc oxide, tin oxide, or the like. Can be.

Subsequently, a second electron transport layer 234 is formed on the nanoparticle thin film, which is the first electron transport layer 232, using atomic layer deposition (ALD). The second electron transport layer 234 may be a thin film made of a metal oxide such as titanium oxide, zinc oxide, and tin oxide, and may be formed to a thickness of 1 nm to 50 nm.

Specifically, the process of forming the metal oxide thin film using the atomic layer deposition method, after placing the substrate 210 with the first electrode 220 in the atomic layer deposition reactor, the step of introducing a metal oxide precursor into the reactor ; Purging the reactor into which the metal oxide precursor is introduced; Introducing an oxidant into the purged reactor; And purging the reactor into which the oxidant is introduced.

The metal oxide precursor used in the atomic layer deposition process may be an organometallic compound, a metal chloride, or the like. For example, the titanium oxide precursor can be selected from tetrakis dimethylamido titanium, tetrakis diethylamido titanium, and tetrakis ethylmethylamido titanium, , Zinc oxide precursor may be diethyl zinc, tin oxide precursor is tin chloride, tetrakis dimethylamido tin, tetrakis diethylamido tin ) And tetrakis ethylmethylamido tin.

The bubbler temperature for heating the precursor may be appropriately selected from a temperature range of 25 to 100 ° C. according to the kind of precursor, and maintains a constant temperature at the selected temperature.

The reaction gas used as the oxidant may be selected from among O ₂ , O ₃ , H ₂ O, H ₂ O _2, and a mixture thereof, and the reaction gas may be more effectively activated by activating the reaction gas using plasma. have. The temperature of the substrate for film formation is to maintain a constant temperature within the range of 25 ~ 300 ℃, the pressure inside the reactor (chamber) is to be 0.001 ~ 760 Torr.

Meanwhile, when the electron transport layer 230 has a single layer structure, the electron transport layer 230 may be a single metal oxide thin film directly formed on the first electrode 220 (not shown). Here, the metal oxide thin film may be formed using the same material and method (atomic layer deposition method) as described in the process of forming the second electron transport layer 234 of the double layer structure.

Referring to FIG. 2C, an organic photoactive layer 240 is formed on the electron transport layer 230. The organic photoactive layer 240 may be formed by applying a mixed solution of an electron donor material and an electron acceptor material on the electron transport layer 230 and then drying the solvent. The coating process may use a known coating method such as spin coating, spray coating, doctor blade coating, and inkjet printing, and may be preferably performed by spin coating.

The electron donor material absorbs sunlight incident from the outside to form electron-hole pairs (excitons), and moves holes separated at the pn junction interface between the electron donor material and the electron acceptor material toward the anode. Mean material. For example, the electron donor material may be a conjugated polymer that can be used as a p-type semiconductor, polythiophene-based, polyfluorene-based, polyaniline-based, polycarbazole-based , Polyvinylcarbazole-based, polyphenylene-based, polyphenylenevinylene-based, polysilane-based, polythiazole-based, or copolymers thereof .

On the other hand, the electron acceptor material refers to a material that serves to move the electrons separated at the p-n junction interface in the photoactive layer 240 in the direction of the cathode.

For example, the electron acceptor material 140 may include fullerene, PC ₆₁ BM ([6,6] -phenyl-C ₆₁ -butyric acid methyl ester), PC ₇₁ BM ([6] , 6] -phenyl-C ₇₁ -butyric acid methyl ester), and fullerene derivatives such as PC ₈₁ BM ([6,6] -phenyl-C ₈₁ -butyric acid methyl ester). However, it is not limited thereto.

Referring to FIG. 2D, a hole transport layer 250 and a second electrode 260 are sequentially formed on the organic photoactive layer 240.

The hole transport layer 250 is a p-type buffer layer for easily transferring holes generated in the organic photoactive layer 240 to the anode, PEDOT: conductive organic material such as PSS or WO ₃ , V ₂ O ₃ and MoO ₃ It may be formed using a conductive metal oxide such as.

The second electrode 260 serves as an anode that finally collects holes and delivers the holes to an external circuit. The second electrode 260 may be any one selected from metals, alloys, conductive polymers, other conductive compounds, and combinations thereof. However, the second electrode 260 is preferably a material having high oxidative stability against exposure to the atmosphere. For example, the second electrode 260 may be formed of a material having a high work function such as Cu, Ag, Au, W, Ni, and Ti. It is preferable to use.

The second electrode 260 may be formed by thermal image deposition, electron beam deposition, sputtering, ion plating, or chemical vapor deposition, or by heat treatment after applying an electrode forming paste including a metal. However, it is not limited thereto.

As described above, since the electron transport layer 230 is formed using the atomic layer deposition method, a high quality electron transport layer 230 having a low defect density can be formed. Therefore, it is possible to improve the efficiency of the battery by increasing the transport capacity of the electrons, reducing the probability of recombination of the charge.

In particular, when the electron transport layer 230 is configured in the form of a double layer including the first electron transport layer 232, which is a nanoparticle thin film, the second electron transport layer 234 formed by atomic layer deposition is nano Since the particles are deposited along the morphology of the thin film, the electron transport layer 230 having the uneven surface S may be formed. As a result, the contact area between the electron transport layer 230 and the photoactive layer 240 formed thereon may be widened to promote the separation of the electron-holes.

In addition, contact defects between nanoparticles that may occur in the first electron transport layer 232 formed of an array of nanoparticles may be removed in the second electron transport layer 234 coated by atomic layer deposition. In addition, when the constituent materials of the first electron transport layer 232 and the second electron transport layer 234 are different, the conduction band level of the electron transport layer 230 may be stratified to secure an effective path for electron movement. There is an advantage.

Hereinafter, preferred experimental examples are presented to help understand the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited to the following experimental examples.

<Manufacture example 1>

An ITO film (thickness: 180 nm, Rs: ˜5 μs / □) as a lower electrode was formed on the glass substrate by sputtering. 5 nm diameter TiO ₂ powder was spin-coated on the ITO film to form a thin film of TiO ₂ nanoparticles (first electron transport layer) having a thickness of 15 to 20 nm, and then atomic layer deposition was used (precursor: tetrakis die) Methylamido Titanium, Oxidizers: H ₂ O ₂ , Precursor injection: purge: oxidant injection: purge = 1 second: 10 seconds: 0.5 seconds: 30 seconds (cycle), deposition temperature 200 ° C) to form a TiO ₂ thin film (second electron transport layer) to a thickness of 2.5nm. Subsequently, P3HT (poly (3-hexylthiophene): PCBM ([6,6] -phenyl-C ₆₁ -butyric acid methyl ester) mixed in a 1: 0.6 weight ratio was spin-coated on a TiO ₂ thin film to have a thickness of 180 to 200 nm. Next, a PEDOT: PSS having a thickness of 25 nm was formed by spin coating as a hole transport layer on the photoactive layer, and then an Ag upper electrode having a thickness of 100 nm was formed by thermal image deposition. Was prepared.

<Production Examples 2 to 5>

Except that the TiO ₂ thin film formed in the atomic layer deposition process was formed with a thickness of 5 nm (Preparation Example 2), 10 nm (Preparation Example 3), 20 nm (Preparation Example 4), and 30 nm (Preparation Example 5), respectively. An inverse structure organic solar cell was manufactured in the same manner as in Preparation Example 1.

<Comparative Example>

An inverse structure organic solar cell was manufactured in the same manner as in Preparation Example 1, except that the TiO ₂ thin film formation process by the atomic layer deposition process was omitted.

Table 1 summarizes the open circuit voltage (Voc), the short-circuit current density (Jsc), the fill factor (FF) and the photoelectric conversion efficiency (Eff) of the reverse structure organic solar cells prepared in Preparation Examples 1 to 5 and Comparative Examples will be.

3 is a graph showing current-voltage characteristics of the reverse structure organic solar cells prepared in Preparation Examples 1 to 5 and Comparative Examples.

division Voc Jsc FF Eff Production Example 1 0.61 10.19 0.56 3.50 Production Example 2 0.61 10.02 0.57 3.49 Production Example 3 0.59 10.21 0.50 3.02 Production Example 4 0.59 10.27 0.51 3.10 Production Example 5 0.59 10.16 0.51 3.01 Comparative example 0.59 9.89 0.47 2.72

Referring to Table 1 and FIG. 3, it can be seen that the case where the atomic layer deposition process is applied (preparation examples 1 to 5) shows superior photoelectric conversion efficiency than when the atomic layer deposition process is omitted.

As mentioned above, although the preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation and the said by those of ordinary skill in the art within the technical idea and the scope of the present invention. Changes are possible.

110 and 210: substrate 120 and 220: first electrode
130, 230: electron transport layer 140, 240: photoactive layer
150, 250: hole transport layer 160, 260: second electrode
232: first electron transport layer 234: second electron transport layer

Claims (10)

Preparing a substrate provided with a first electrode; And
Sequentially stacking an electron transport layer, an organic photoactive layer, a hole transport layer, and a second electrode on the first electrode,
The electron transport layer is an inverse structure organic solar cell manufacturing method of forming a metal oxide thin film using an atomic layer deposition method. The method of claim 1,
The metal oxide thin film is a titanium oxide thin film, zinc oxide thin film or tin oxide thin film inverse structure organic solar cell manufacturing method. The method of claim 1,
Formation of the metal oxide thin film using the atomic layer deposition method,
Placing a substrate with the first electrode in an atomic layer deposition reactor and introducing a metal oxide precursor into the reactor;
Purging the reactor into which the metal oxide precursor is introduced;
Introducing an oxidant into the purged reactor; And
Inverted structure organic solar cell manufacturing method comprising the step of purging the reactor in which the oxidant is introduced. The method of claim 3,
The metal oxide precursor is tetrakis dimethyl amido titanium, tetrakis diethyl amido titanium, tetrakis ethyl methyl amido titanium, diethyl zinc, tin chloride, tetrakis dimethyl amido tin, tetrakis diethyl amido tin and A method for producing an inverse structure organic solar cell selected from tetrakis ethylmethylamido tin. The method of claim 1,
Before forming the metal oxide thin film, forming the nanoparticle thin film on the first electrode. The method of claim 5,
The nanoparticle thin film is a reverse structure organic solar cell manufacturing method comprising a metal oxide nanoparticles. The method according to claim 6,
The metal oxide nanoparticles are titanium oxide, zinc oxide or tin oxide inverse structure organic solar cell manufacturing method. The method of claim 5,
The nanoparticle thin film is a reverse structure organic solar cell manufacturing method is formed by applying a dispersion solution of nanoparticles on the first electrode. A first electrode, an electron transport layer, a photoactive layer, a hole transport layer, and a second electrode sequentially stacked on the substrate;
The electron transport layer is a reverse structure organic solar cell is a metal oxide thin film formed by atomic layer deposition. 10. The method of claim 9,
An inverse structure organic solar cell further comprising a nanoparticle thin film positioned between the first electrode and the metal oxide thin film.

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