KR101146832B1 - Method for manufacturing high conductive organic film by solvent treatment and method for manufacturing organic solar cell having the organic film - Google Patents

Abstract

The present invention relates to a highly conductive organic thin film using a liquid surface treatment and a method for manufacturing a high efficiency organic solar cell using the same. The organic solar cell includes a substrate, an indium tin oxide (ITO) transparent electrode, a PEDOT: PSS layer which is a conductive organic thin film, a P3HT: PCBM photoactive layer, and a LiF / Al electrode, wherein the PEDOT: PSS layer is formed of dimethylformamide ( N, N-dimethylformamide (DMF) to increase the electrical properties and efficiency of the device by including a liquid surface treatment step.

Description

Highly conductive organic thin film using liquid surface treatment and method for manufacturing organic solar cell using same {Method for manufacturing high conductive organic film by solvent treatment and method for manufacturing organic solar cell having the organic film}

The present invention relates to a method for manufacturing a highly conductive organic thin film using a liquid surface treatment and an organic solar cell using the same, and in particular, a method for producing a PEDOT: PSS conductive organic thin film having improved electrical characteristics and an electrical device of the device using the organic thin film. The present invention relates to a method of manufacturing an organic solar cell having improved characteristics. Compared to the conventional PEDOT: PSS organic thin film and the method for producing a mixed liquid phase PEDOT: PSS organic thin film, the present invention enables improved physical properties through simple surface treatment. In particular, the technique of the present invention is applied to the organic solar cell device to contribute to the performance improvement of the device.

In recent years, organic solar cells can be manufactured with environmentally friendly, low cost, and high efficiency devices compared to conventional silicon-based solar cells. However, while conventional silicon solar cells exhibit high light conversion efficiency of 20%, organic solar cells have difficulty in commercialization due to low light conversion efficiency of up to 5-6%. As a way to overcome this, there is a method of adjusting the series resistance and the shunt resistance of the device. Since the series resistance represents the electrical loss of the entire device and the shunt resistance is related to the leakage current, it is possible to implement a high performance organic solar cell device by controlling the resistance value described above in the conventional organic solar cell.

In addition, in the organic material system, holes formed by light have higher mobility than electrons and thus accumulate in the organic solar cell. In addition, the high specific resistance of the organic thin film and the high contact resistance between the organic thin film layers make it difficult to move holes to the electrode. This, in turn, leads to a decrease in the photocurrent, leading to a deterioration of the device performance.

In order to solve this problem, PEDOT: PSS thin film is formed by adding a liquid such as polyalcohols and ethylene glycol to a conductive organic solution, PEDOT: PSS, which is frequently used, Techniques for improving conductivity have been reported. However, in the case of the reported technology, since the phase change effect is different depending on various process variables such as the type and amount of the added liquid, there is a disadvantage that the selection and doping level of the liquid phase must be carefully controlled.

In addition, a technique for improving conductivity by immersing PEDOT: PSS polymer fibers synthesized using a previously reported wet spinning method in a dimethylformamide solution synthesizes a polymer in the form of fibers, and thus, unlike the present invention, a constant thickness on a substrate Since it is difficult to form an organic thin film and has a contact resistance in a layered device, there is a limitation in that it is difficult to apply to a layered organic solar cell device using a substrate of the present invention.

The present invention is proposed to solve the high specific resistance of organic thin films, high contact resistance between organic thin film layers, and high series resistance of devices.

According to the present invention, by forming an organic thin film having a uniform thickness that can be applied to the electronic device of the layer structure in a simple process, the conductivity stabilized from the reduction of the contact resistance and series resistance between adjacent layers through the improvement of the conductivity and further the surface roughness Production of organic thin films is possible.

In addition, the present invention can provide an organic solar cell device having improved electrical characteristics and light conversion efficiency.

Furthermore, the present invention provides various electronic devices having improved electrical characteristics and efficiency.

The present invention provides a method of manufacturing a conductive organic thin film comprising forming a conductive organic thin film on a substrate and surface treating the surface of the conductive organic thin film. In particular, a method of preparing a conductive organic thin film and a poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate) (PEEDOT: PSS) conductive organic thin film having improved electrical properties Provided is a method of manufacturing an organic solar cell having improved electrical characteristics of the device.

In order to manufacture the conductive organic thin film, the surface of the PEDOT: PSS layer formed on the substrate is subjected to a surface treatment using a dimethylformamide (N, N-dimethylformamide, DMF) liquid phase.

In addition, the present invention comprises the steps of forming a PEDOT: PSS layer on the substrate, liquid phase surface treatment using dimethylformamide on the PEDOT: PSS layer and a photoactive layer and an electrode on the liquid surface treated PEDOT: PSS layer It provides a method for manufacturing an electronic device comprising the step of forming a.

The present invention also provides an electronic device comprising a PEDOT: PSS layer having a liquid surface surface-treated with dimethylformamide as a conductive organic thin film, and an organic solar cell including the conductive organic thin film between an electrode and a photoactive layer. to provide.

In the step of forming a PEDOT: PSS layer on the substrate, a PEDOT: PSS solution is deposited on a glass substrate using a spin-coating method, followed by heat treatment at 150 ° C using a hot plate to form an organic thin film. To form. At this time, it is possible to control the organic thin film by adjusting the spin coating speed and the heat treatment temperature and time. In the case of the PEDOT: PSS organic thin film, the conductivity was measured to have a value of about 1.26 S / cm through the Hall measurement system. Therefore, the organic solar cell using the same is difficult to move holes due to low conductivity, the light current value is low, and eventually has a limit on the light conversion efficiency value.

In order to solve this problem, in the present invention, liquid surface treatment is performed by using a method such as spin coating or drop coating a dimethylformamide liquid phase, which is a polar material having a dipole moment of 3.86 D, on a preformed PEDOT: PSS organic thin film. After that, heat treatment using hot plate. At this time, it is possible to control the organic thin film by adjusting the spin coating and the heat treatment speed and time. Through the liquid surface treatment, the interchain interaction between the dimethylformamide, which is a polar material, and the PEDOT: PSS organic material, which is formed, occurs, thereby inducing phase separation in the PEDOT: PSS organic thin film to form a highly conductive PEDOT-rich domain. To contribute to improved conductivity.

Compared to the conventional PEDOT: PSS organic thin film, the present invention enables the production of a highly conductive and stabilized PEDOT: PSS organic thin film through a simple process called liquid surface treatment. In particular, the present invention can be fabricated by improving the light conversion efficiency according to the low series resistance and contact resistance by incorporating this into the production of organic solar cells. Furthermore, the electrical characteristics are improved by applying the organic thin film to various electronic devices such as organic thin film transistors and OLEDs as well as organic solar cells.

1 is a cross-sectional view of a PEDOT: PSS thin film manufacturing method and a manufactured thin film according to an embodiment of the present invention.
2 is a cross-sectional view of a method for producing a PEDOT: PSS thin film and liquid film surface-treated with dimethylformamide according to an embodiment of the present invention.
3 is a cross-sectional view of a process sequence and a completed device of an organic solar cell device having a PEDOT: PSS thin film according to an embodiment of the present invention.
4 is a polymer mixture constituting the photoactive layer of the present invention.
5 is a view for explaining the mechanism of movement of electron-holes generated when light is applied to the organic solar cell device fabricated according to the embodiment of the present invention.
6 is an atomic microscope image of a PEDOT: PSS thin film (a) without liquid surface treatment and a PEDOT: PSS thin film (b) with liquid surface treatment according to an embodiment of the present invention.
7 is a UV-Vis absorbance spectrum, in which a P3HT: PCBM photoactive layer is formed on a PEDOT: PSS thin film without liquid surface treatment (a) and a P3HT: PCBM photoactive layer on a PEDOT: PSS thin film with liquid surface treatment Is a diagram showing the absorbance according to the photon energy of (b).
8 is an organic solar cell having an AC impedance plot (a) of an organic solar cell device having a PEDOT: PSS thin film without a liquid surface treatment and a PEDOT: PSS thin film with a liquid surface treatment according to an embodiment of the present invention. It is a figure which shows AC impedance plot (b) of an element.
9 is an organic solar cell device having a JV characteristic (a) of an organic solar cell device having a PEDOT: PSS thin film without a liquid surface treatment and a PEDOT: PSS thin film having a liquid surface treatment according to an embodiment of the present invention. It is a figure which shows the JV characteristic (b).

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent by reference to the embodiments described in detail below with reference to the accompanying drawings.

Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. The shape and the size of the elements in the drawings may be exaggerated for clarity and the same elements are denoted by the same reference numerals in the drawings.

1 to 3 are diagrams for explaining a PEDOT: PSS thin film and an organic solar cell device having the same according to an embodiment of the present invention.

First, as shown in FIG. 3, an ITO layer, which can be used as a transparent electrode layer, for example, is formed on a glass substrate. Thereafter, the ITO layer-coated glass substrate is patterned into a rectangular shape by photolithography and then wet etching. A PEDOT: PSS layer, which is a conductive organic thin film, is then formed on the glass substrate coated with the ITO layer. This organic thin film layer can be subjected to, for example, spin coating followed by baking to form a PEDOT: PSS layer as a cured layer. Multiple spin coating may be used to form the PEDOT: PSS layer. In the multiple spin coating method, an organic thin film layer having a required thickness can be formed by alternately repeating the spin coating step and the baking step two or more times.

Thereafter, as shown in FIG. 2, the cured PEDOT: PSS layer is subjected to spin coating and baking followed by surface treatment of dimethylformamide. Dimethylformamide proceeds in the same manner as the method for forming the PEDOT: PSS layer. The PEDOT: PSS layer, which is a manufactured organic thin film, can exhibit p-type conductivity as an example.

3, the P3HT: PCBM solution was then placed in an argon atmosphere to form a photoactive layer, P3HT: PCBM (shown in Figure 4), on the PEDOT: PSS layer surface-treated with dimethylformamide. The solution was mixed at a mass ratio of 1: 0.8 at and dissolved in a chlorobenzene solvent to prepare a solution at a concentration of 15 mg / ml. Thereafter, sterling for 1 hour in an argon atmosphere allows P3HT: PCBM to be uniformly soluble in chlorobenzene. The prepared P3HT: PCBM solution is spin coated on the surface-treated PEDOT: PSS layer in an argon atmosphere and then baked to form a photoactive layer.

Thereafter, a LiF layer and an Al layer are successively deposited using a thermal evaporator to form a LiF / Al electrode. At this time, the thickness of the LiF is formed thinner than 5nm. Thereby, the organic solar cell element provided with the surface-treated PEDOT: PSS organic thin film is obtained. As described later, the organic solar cell device can exhibit improved J-V characteristics, thereby improving light conversion efficiency of the organic solar cell device. This improvement in J-V properties is due to the liquid surface treated PEDOT: PSS layer, and as described below, the liquid surface treatment for PEDOT: PSS increases the conductivity of PEDOT: PSS used as the conductive organic thin film.

In addition, the liquid surface-treated PEDOT: PSS thin film may be used not only for the organic solar cell device described above, but also for pn junction devices, OLEDs, organic thin film transistors, and display panels that require organic thin films. In particular, since the liquid surface-treated PEDOT: PSS thin film has increased conductivity, it may be usefully used as a hole injection layer of an OLED.

Example

In a preferred embodiment of the present invention, a PEDOT: PSS thin film purchased from Baytron (Baytron P AI 4083) was used. An example sample device (b) (organic solar cell having a liquid surface-treated PEDOT: PSS thin film) described below is a photolithography method for a glass substrate coated with an ITO layer, as shown in FIG. 3. After the etching process, a rectangular pattern is formed by wet etching, and a PEDOT: PSS thin film is formed on a glass substrate having a patterned ITO layer, and the surface of the PEDOT: PSS thin film having a p-type semiconductor property is dimethylformamide. After the treatment, a P3HT: PCBM thin film as a photoactive layer was formed to form a LiF / Al electrode. In addition, the organic solar cell element (a) which omitted the process of liquid-phase surface treatment using the dimethylformamide in the sample of the above-mentioned example is used as a comparative example sample for comparison with an Example.

Device substrate is 2 × 2 cm ² coated with ITO on the top It is a glass substrate of size and the ITO layer is about 100 nm thick. The ITO-coated glass substrate was wet-etched after the photolithography process to form a rectangular pattern, and then washed for 15 minutes using acetone, methanol, and deionized water in an ultrasonic bath. It was dried with a nitrogen gun.

Next, PEDOT: PSS was applied to the substrate with a thickness of about 30 nm by spin coating. After coating, the PEDOT: PSS layer was baked at 150 ^° C. in air for 10 minutes. In the experiment, two sets (first set and second set) of samples were prepared, each set consisting of six samples. In the first set of samples, the PEDOT: PSS thin film on the substrate was spin coated with dimethylformamide (dipole moment 3.4 D) and then baked at 150 ^° C. for surface treatment. In the second set of samples, a PEDOT: PSS thin film was produced without such liquid surface treatment. Thereafter, a P3HT: PCBM photoactive layer solution mixed at a mass ratio of 1:08 in a non-hygroscopic anoxic glove box was prepared at a concentration of 15 mg / ml, spin-coated to a thickness of about 200 nm, and baked at 120 ^° C. Thereafter, a LiF / Al electrode was deposited on the upper surface using a shadow mask, and further subjected to post-heat treatment at 120 ^° C. The active area of the fabricated device is about 0.04 cm ² . This device structure is shown in FIG. The fabricated device was measured using ABET Technology's Sun 2000 model solar simulator and measured its electrical characteristics (power conversion efficiency) using 100 mW / cm ² light intensity under AM 1.5 G. . The current density-voltage (JV) characteristics of the manufactured device are shown in FIG. 9. The series resistance value of the device fabricated using the measured current density-voltage characteristics was approximated at a voltage value of more than the open voltage (V _oc ). In addition, contact resistance was obtained by measuring the alternating current impedance spectra using the IVIUM Stats model of IVIUM Technologies under dark conditions. The work function of the PEDOT: PSS organic thin film was investigated using a Kelvin probe system, a KP-6500 model from McAllister Technical Services. And the absorption spectrum of the UV-visible light region of the thin film by which the P3HT: PCBM thin film was laminated | stacked on the PEDOT: PSS thin film was measured using the UV-2401PC model of SHIMADZU. The specific resistance and conductivity of the PEDOT: PSS thin film were measured using an Ecopia Hall measurement system. The roughness and surface state of the PEDOT: PSS thin film surface were measured in tapping mode using an AFM (atomic force microscope), a Veeco NanoScope IIIa model.

division V _oc
(V) J _sc
(mA / cm ² ) FF
(%) PCE
(%) R _s ^a
(Ωcm ² ) Conductivity ^b
(S / cm)
Work function ^c
(eV) (a) 0.57 7.8 55.3 2.50 15.6 1.27 5.08 (b) 0.57 17.5 51.1 5.14 8.7 152 5.06

^(a) PEDOT: PSS organic thin film without liquid surface treatment and an organic solar cell device comprising the same.

^(b) PEDOT: PSS organic thin film subjected to liquid surface treatment and organic solar cell device comprising the same

^a Calculated in the V> V _oc region of the current density-voltage (JV) curve.

^b Measured using Hall measurement system.

^c Measured using a Kelvin probe system.

The conductivity of PEDOT: PSS thin film (b) with liquid surface treatment and PEDOT: PSS thin film (a) without liquid surface treatment was obtained from the Hall measurement system. The conductivity of the PEDOT: PSS thin film without the liquid surface treatment was 1.27 S / cm, whereas the conductivity of the PEDOT: PSS thin film with the liquid surface treatment increased by 2 order-magnitude to 152 S / cm. Increasing conductivity of PEDOT: PSS thin film with liquid surface treatment resulted in the change of thiophene structure due to the interchain interaction reaction between dimethylformamide and organic thin film with high dipole moment value or conductive pathways according to the changed organic arrangement. Results from formation. For comparison, when the liquid surface treatment was performed using the same method using chlorobenzene, there was no significant change in the conductivity before and after the surface treatment. This is because dimethylformamide has a dipole moment of 3.86 D, whereas chlorobenzene has a low value of 1.54 D, and thus does not cause a smooth reaction such as interchain interaction with organic molecules.

In addition, Kelvin probe system was used to observe the change of work function of PEDOT: PSS thin film with liquid surface treatment and PEDOT: PSS thin film without liquid surface treatment. The work function of the PEDOT: PSS thin film without the liquid surface treatment was 5.08 eV. The PEDOT: PSS thin film with the liquid surface treatment showed a 5.06 eV value. That is, since liquid surface treatment does not make a big difference in the work function change of the PEDOT: PSS thin film, the charge trapped loss due to the energy barrier does not create an energy barrier when holes are extracted from the photoactive layer of the organic solar cell to the PEDOT: PSS layer. Does not cause.

In addition, the absorbance was measured from the UV-Vis spectra to determine the optical properties of the PEDOT: PSS thin film with a liquid surface treatment and the PEDOT: PSS thin film without a liquid surface treatment. As a result, the optical properties of the PEDOT: PSS thin film with the liquid surface treatment and the PEDOT: PSS thin film without the liquid surface treatment were identical. This suggests that the liquid surface treatment of the PEDOT: PSS thin film in organic solar cells does not significantly affect the absorbance.

In order to observe the surface conformational change caused by the liquid surface treatment, AFM images of the PEDOT: PSS thin film with the liquid surface treatment and the PEDOT: PSS thin film without the liquid surface treatment were observed. From the AFM images of the two samples, it can be seen that the surface roughness was reduced from 1.512 nm to 1.258 nm and the PEDOT-rich domain was formed on the surface. This is because PEDOT-chain is transformed into extended-aggregated structure through inter-chain interaction between dimethylformamide and PEDOT-chain. This change improves conductivity by increasing hopping rate and ionic transport in polymeric materials.

Current density-voltage (JV) when a constant light is applied at an intensity of 100 mW / cm ² to an organic solar cell device fabricated using a liquid surface-treated PEDOT: PSS thin film and a liquid surface-treated PEDOT: PSS thin film. ) Characteristics are shown in FIG. 9. To ensure reproducibility, six cells were fabricated and the photovoltaic parameters of the photovoltaic devices were expressed as average values. For organic solar cell devices using PEDOT: PSS thin film without liquid surface treatment as buffer layer, V _oc = 0.57V, J _sc = 7.8mA / cm ² , FF = 55.3%, PCE = 2.50%, and the maximum PCE value is 2.61. Appeared in%. On the other hand, in the case of organic solar cell devices using a liquid surface-treated PEDOT: PSS thin film as a buffer layer, the maximum PCE was V _oc = 0.57 V, J _sc = 17.5 mA / cm ² , FF = 51.1%, and PCE = 5.14%. The value was 5.35%. For liquid surface treated devices, the most significant parameter is the current density (Jsc) value, which allows more efficient carrier transport than devices without liquid surface treatment.

It is also related to the series resistance and shunt resistance of the device. The device with liquid surface treatment has a lower FF value than the device without liquid surface treatment, which results from the random leakage current formed in the buffer layer with liquid surface treatment, but the reduction is not as large as the device without liquid surface treatment. Therefore, in the fabricated device, the shunt resistance is high enough to ignore this leakage current. In the case of series resistance, it was 15.6 Ωcm ² in the device without the liquid surface treatment, but decreased to 8.7 Ωcm ² in the device with the liquid surface treatment. This is due to the reduced resistance of the PEDOT: PSS layer due to the liquid surface treatment, which results in improved charge collection, since lower series resistance values mean more effective internal electrical fields in the device.

In addition, AC impedence spectra was observed to investigate the effect of liquid surface treatment on the contact resistance of the PEDOT: PSS layer and the photoactive layer of the device. The observed frequency response resulted in the shape of a semicircle, and the device with liquid surface treatment showed lower contact resistance than the device without liquid surface treatment. Low contact resistance values affect not only the interfacial resistance between layers but also the reduction in series resistance. Therefore, it can be seen that the decrease in the resistance value increases the charge transport since it promotes carrier extraction and release accumulated holes.

The present invention is not limited by the above-described embodiment and the accompanying drawings. It is intended that the scope of the claims be defined by the appended claims, and that various forms of substitution, modification, and alteration are possible without departing from the spirit of the invention as set forth in the claims. Will be self-explanatory.

Claims (16)

delete Forming a conductive organic thin film on the substrate and surface treating the surface of the conductive organic thin film,
The conductive organic thin film is a PEDOT: PSS layer, and the surface of the PEDOT: PSS layer using a dimethylformamide solution surface treatment method for producing a conductive organic thin film.
The method of claim 2,
In the surface treatment step, a method of manufacturing a conductive organic thin film, characterized in that the PEDOT: PSS layer spin-coated dimethylformamide and then baking.
The method of claim 2,
In the surface treatment step, a method of producing a conductive organic thin film, characterized in that the PEDOT: PSS layer by coating the dimethylformamide drop coating.
The method of claim 2,
Forming a conductive organic thin film on the substrate,
After spin coating PEDOT: PSS on the substrate, baking the spin coated PEDOT: PSS.
6. The method of claim 5,
And forming a PEDOT: PSS layer using a multiple spin coating method in which the spin coating step and the baking step are alternately repeated two or more times.
Forming a PEDOT: PSS layer on the substrate;
Performing liquid surface treatment with dimethylformamide on the PEDOT: PSS layer; And
Forming a photoactive layer and an electrode on the liquid surface-treated PEDOT: PSS layer.
8. The method of claim 7,
Wherein said PEDOT: PSS layer is p-type and said photoactive layer is a mixture of polymeric materials forming electron-hole pairs by light.
The method of claim 8,
The polymer photoactive layer is a method of manufacturing an electronic device, characterized in that formed from a mixed solution of P3HT and PCBM.
8. The method of claim 7,
The electrode is a method of manufacturing an electronic device comprising the step of successively depositing LiF and Al using a thermal evaporator.
8. The method of claim 7,
A method of manufacturing an electronic device comprising the step of performing a post-heat treatment after forming the electrode.
8. The method of claim 7,
The substrate is a method of manufacturing an electronic device, characterized in that the transparent electrode layer is coated on the upper surface.
13. The method of claim 12,
Method of manufacturing an electronic device, characterized in that for patterning the transparent electrode layer coated on the substrate in a rectangular shape.
An electronic device comprising a PEDOT: PSS layer whose surface is liquid surface treated with dimethylformamide as a conductive organic thin film.
The method of claim 14,
The liquid surface-treated PEDOT: PSS layer is an electronic device, characterized in that used as any one of a hole injection layer, an electrode layer and a channel layer.
The method of claim 14,
The electronic device is an electronic device, characterized in that the organic solar cell comprising a liquid surface-treated PEDOT: PSS layer between the photoactive layer and the electrode.

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