KR20140124435A - Low band gap polymers, the organic photovoltaic cell comprising the same, and the synthesis thereof - Google Patents

Abstract

The present invention relates to a novel polymer compound with a low band gap, a manufacturing method thereof and a highly efficient organic photovoltaic cell using the same. The conductive polymer as an electron donor with a low ban gap according to the present invention can be used for the development of not only a material for organic photoelectronic devices, which can be applied to various fields such as an organic photodetector (OPD), an organic thin-film transistor (OTFT), an organic light-emitting diode (OLED) and an organic photovoltaic cell, but also an n-type material as the conductive polymer has high photon absorbing capacity and excellent hole mobility.

Description

TECHNICAL FIELD [0001] The present invention relates to a polymer compound having a low band gap, an organic solar cell including the same, and a method for manufacturing the same,

More particularly, the present invention relates to a novel low bandgap electron donor conductive polymer compound having high photon absorption capacity and improved hole mobility, a process for preparing the same, and an organic solar cell comprising the same will be.

Solar cells using solar light can be roughly classified into solar cells using inorganic materials such as silicon and solar cells using organic materials. Particularly, organic thin film solar cells using polymers have a problem in that they are easy to process, Compared with batteries, it is easy to fabricate devices and is expected to be used in a wide range of applications such as power sources for low-cost or next-generation flexible electronic devices. The efficiency of the organic thin film solar cell has been remarkably improved in the last 3-4 years. However, in order to obtain an energy conversion efficiency of 10% or more, a donor material having a low band gap having an improved charge transfer speed, an acceptor having a band gap optimized for the donor material, Development of new types of devices using new concepts such as development of new materials such as materials, application of surface plasmon resonance phenomenon, improvement of light utilization efficiency through up-conversion or down-conversion, and so on.

In particular, a method for increasing J _SC and V _OC , which is a condition to be considered in the development of a low energy gap organic semiconductor for achieving high efficiency, has recently been reported. First, in order to improve J _SC , the polymer should be designed to have a low energy gap and a high extinction coefficient, absorb light in the near-infrared region as well as light in the visible region, and absorb more light at the same thickness Should be designed. These low-energy-gap polymers can be synthesized by forming a polymer chain in which electron-rich structures (Donor) and insufficient structures (Acceptor) are alternately combined. However, when the polymer is synthesized in such a manner, the HOMO energy level of the polymer increases in many cases, resulting in a decrease in V _OC . In order to increase V _OC , the HOMO energy level of the low energy gap polymer should be lowered. This can be obtained by introducing a substituent which attracts electrons to the polymer chain.

In addition, a number of studies have been reported to improve not only J _SC but also V _OC by synthesizing low energy gap polymers by mixing the two methods mentioned above. For example, a substitute such as a fluorine group or an ester group is introduced into a donor acceptor alternating polymer to realize an organic solar cell with a high efficiency of 7% or more. However, in spite of high efficiency improvement of the low energy gap polymer solar cell, It is difficult to uniformly control the factors such as the molecular weight, polydispersity and stereoregularity of the polymer directly affecting the performance of the battery, and the synthesis and purification processes are complicated and the charge mobility is low have.

On the other hand, poly (3-hexylthiophene) and P3HT are typical materials used for the photo-conversion active layer of the organic thin film solar cell, and P3H and the electron acceptor substance PCBM act as electron carriers and electron acceptors, respectively. And exhibits a relatively high light conversion efficiency of about 4-5%. However, P3HT having an energy gap of about 2.0 eV is limited to a light absorption region up to about 650 nm (G. Li, V. Shrotriya, JS Huang, Y. Yao, T. Moriarty, K. Emery and Y. Yang 2005, 4, 864-868, WL Ma, CY Yang, X. Gong, K. Lee and AJ Heeger, Adv. Funct. Mater., 2005, 15, 1617-1622) There is a problem in that it is difficult to expect the improvement of the photocurrent. Therefore, since the light conversion efficiency is required to be 10% or more for the practical use of the organic solar cell, a new organic semiconductor material which can replace P3HT has been developed.

In 2008, TQ Nguyen group reported the efficiency of 4.4% by mixing DPP (TBFu) ₂ and PC ₇₀ BM, which are small molecules of diketopyrrole family using dye molecular structure. Recently, AJ Heeger group (PTTh ₂ ) ₂ and PC ₇₀ BM in a solution prepared by using DIO as an additive. [Organic solar cell research trends and practical application strategies, Lee Jung Yong, Physics and Advanced Technology JANUARY / FEBRUARY 2012].

Thus, in order to overcome the above-mentioned problems and to make a high-efficiency organic solar cell, it is urgently required to develop a new polymer having a wide absorption region, a low band gap, an excellent hole mobility and an appropriate molecular level .

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a novel conductive polymer having a wide absorption band, a low band gap, a high hole mobility and a suitable molecular level, and a method for producing the same.

Another object of the present invention is to provide a high-efficiency organic solar cell comprising the novel conductive polymer.

In order to solve the above problems, the present invention provides a conductive polymer represented by the following formula (1).

In the above formula (1)

,

,

, ,

,

,

,

,

,

,

,

,

,

,

및

로 이루어지는 군으로부터 선택되는 1종이고,The Ar

,

,

, ,

,

,

,

,

,

,

,

,

,

,

And

And one species selected from the group consisting of

Each of R ¹ and R ² is independently a straight chain or branched C ₁ -C ₂₀ alkyl group, a straight chain or branched C ₁ -C ₂₀ alkoxy group or a C ₆ -C ₂₀ aryl group;

And n is an integer of 5 to 100,000.

In addition, the present invention provides a method for producing the conductive polymer as shown in Reaction Scheme 1 below.

[Reaction Scheme 1]

The definitions of Ar and n in the above-mentioned Reaction Scheme 1 are the same as those in the above Chemical Formula (1).

Further, the present invention provides a high efficiency organic solar cell comprising the conductive polymer represented by the above formula (1).

The conductive polymer as a low bandgap electron donor according to the present invention has high photon absorption ability and excellent hole mobility and thus can be used as an organic light sensor (OPD), an organic thin film transistor (OTFT), an organic light emitting diode (OLED) The present invention can be used not only for materials for organic optoelectronic devices that can be applied to various fields such as light emitting devices, but also for developing n-type materials.

1 is a graph showing the results of measurement of absorbance of a conductive polymer compound according to Example 1 of the present invention.
2 is a graph of current density-voltage curves of an organic solar cell including a conductive polymer according to Example 1 of the present invention.

Hereinafter, the present invention will be described in more detail.

One aspect of the present invention relates to a conductive polymer compound represented by the following formula (1).

[Chemical Formula 1]

In the above formula (1)

,

,

,

,

,

,

,

,

,

,

,

,

,

,

및

로 이루어지는 군으로부터 선택되는 1종이고,The Ar

,

,

,

,

,

,

,

,

,

,

,

,

,

,

And

And one species selected from the group consisting of

R ¹ and R ² are each independently a linear or branched C ₁ -C ₇ alkyl group, a linear or branched C ₈ -C ₂₀ alkyl group, a linear or branched C ₁ -C ₇ alkoxy group, a linear or branched C ₈ -C ₂₀ alkoxy group Or a C ₆ -C ₂₀ aryl group,

and n is an integer of 5 to 100,000.

According to a preferred embodiment of the present invention, R ¹ and R ² are each independently selected from the group consisting of ethylhexyl, butyloctyl, hexyldecyl, and octyldodecyl, and n is an integer of 100 to 50,000 , With a molecular weight of 500 to 5,000,000.

The conductive polymer according to the present invention can be used as an organic photovoltaic device, an organic light emitting diode (OLED), or the like using such a photoelectric conversion property as measured in a band gap of 1.6 eV, , An organic thin film transistor (OTFT), and an organic solar cell.

Another aspect of the present invention relates to a method for producing a polymer represented by the above formula (1), as shown in Reaction Scheme 1 below, wherein a compound represented by the formula (2) and a compound represented by the formula Dissolving the compound in a reaction solvent, adding a palladium catalyst and reacting, and then adding 2-bromothiophene to the reaction mixture to increase the viscosity, thereby obtaining a polymer represented by Formula 1 .

[Reaction Scheme 1]

In the above Reaction Scheme 1,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

및

로 이루어지는 군으로부터 선택되는 1종이고,The Ar

,

,

,

,

,

,

,

,

,

,

,

,

,

,

And

And one species selected from the group consisting of

R ¹ and R ² are each independently a linear or branched C ₁ -C ₇ alkyl group, a linear or branched C ₈ -C ₂₀ alkyl group, a linear or branched C ₁ -C ₇ alkoxy group, a linear or branched C ₈ -C ₂₀ alkoxy group Or a C ₆ -C ₂₀ aryl group,

and n is an integer of 5 to 100,000.

In the production method according to the present invention, the reaction solvent is at least one selected from the group consisting of water, toluene, acetone, methanol, ethanol, tetrahydrofuran (THF), chlorobenzene and dimethylformamide (DMF) , Preferably toluene and water.

In addition, the palladium catalysts include _{PdCl 2, Pd (OAc) 2} , Pd (CH 3 CN) 2 Cl 2, Pd (PhCN) from _{2 Cl 2, Pd 2 dba 3} CHCl 3 , and the group consisting of Pd (PPh _{3) 4} One species is selected.

More specifically, the compound represented by the general formula (2) and the compound represented by the general formula (3) are mixed in the same molar amount, the remaining solvent is removed by a vacuum pump, and then dissolved in a mixed solvent of toluene and water in a ratio of 10: After the completion of the reaction, the reaction mixture was mixed with methanol and water at a ratio of 4: 1. After the completion of the reaction, 2-bromothiophene was added to the reaction mixture, It can be added to a solvent to obtain a polymer.

Another aspect of the present invention relates to an organic solar cell comprising a polymer compound represented by the following formula (1).

[Chemical Formula 1]

In the above formula (1)

,

,

,

,

,

,

,

,

,

,

,

, ,

,

및

로 이루어지는 군으로부터 선택되는 1종이고,The Ar

,

,

,

,

,

,

,

,

,

,

,

, ,

,

And

And one species selected from the group consisting of

R ¹ and R ² are each independently a straight chain or branched C ₁ -C ₂₀ alkyl group, a straight chain or branched C ₁ -C ₂₀ alkoxy group or a C ₆ -C ₂₀ aryl group,

and n is an integer of 5 to 100,000.

Organic solar cells must meet high energy conversion efficiency. In order to obtain high energy conversion efficiency, a large amount of photons must be absorbed in the light absorbing layer, and excited excited excitons migrate to the interface between donor and acceptor, , And many researchers have tried to move the separated holes and electrons losslessly to the anode and the cathode. Thus, the conventional organic solar cell showed high energy conversion efficiency, but it has a direct effect on the performance of the solar cell It is difficult to uniformly control the factors such as the molecular weight, polydispersity and stereoregularity of the polymer, and the synthesis and purification processes are complicated and the charge mobility is low.

However, since the conductive polymer as the low bandgap electron donor for organic solar cells of the present invention has high photon absorption capacity and hole mobility (see Experimental Examples 1 and 2), the synthesis and purification process is simple (see Example 1) The present invention can be effectively applied to materials for organic optoelectronic devices that can be applied to fields such as organic light emitting diodes (OLEDs), organic light sensors (OPD), organic thin film transistors (OTFT), organic light emitting diodes (OLED) in accordance moved in the long wavelength area with the polymer by introducing the diketopyrrolopyrrole monomer to pull electrons to the conductive polymer and to obtain a polymer material having a lower band gap, according to this aspect, the n- type material C ₆₀ in combination with the fullerene derivative or a C ₇₀ fullerene derivative constituting the photoelectric conversion layer, a bulk hetero junction type (bulk heterojunction type) in an organic solar cell enemy Can.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It will be clear to those who have knowledge.

PREPARATION EXAMPLE 1 Synthesis of 2,5-bis (trimethylstannyl) thieno [2,3- b ] Thiophene

[Reaction Scheme 1]

A 250 mL round bottom flask was flame dried three or more times and then thieno [2,3- b ] thiophene (0.950 g, 6.775 mmol) dissolved in tetrahydrofuran (60 mL) (1.0849 g, 16.936 mmol) was slowly added dropwise to the solution, followed by the addition of TMEDA (1.9680 g, 16.936 mmol) to a solution of . After stirring at room temperature for 30 minutes or longer, the temperature is lowered to -78 ° C or lower using dry ice. Trimethyltin chloride (3.3071 g, 16.936 mmol) is slowly added dropwise, followed by stirring at room temperature for 2 hours or longer, and the reaction is terminated. The mixture was extracted with water and chloroform solution using a separatory funnel. The solvent of the chloroform layer was evaporated and the residue was redissolved in methanol to obtain 1.37 g (43.5%) of the target compound.

¹ H-NMR (400 MHz, CDCl ₃ )? 7.24 (s, 2H), 0.41 (s, 18H)

Preparation Example 2 Synthesis of 3,6-bis (5-bromo-tetrahydrothiophen-2-yl) -octahydro-2,5-bis (2-octyldodecyl) pyrrolo [ Preparation of pilol-1,4-diol

[Reaction Scheme 2]

As shown in Reaction Scheme 2, the compound represented by Formula 4 is prepared by the method described in G.-Y Chen et al., J. Polym. Sci. 2010, 48 , 1669-1675.

Example 1 Preparation of pDPPT2TTi-OD

[Reaction Scheme 3]

(0.30 g, 0.6440 mmol) obtained in Preparation Example 1 and the compound represented by Chemical Formula 4 (0.6564 g, 0.6440 mmol) obtained in Preparation Example 2 were subjected to removal of the remaining solvent using a vacuum pump for 12 hours or longer then, the dissolved gas removal (degassing) of toluene (10 mL) and water (1 mL), tetrakis (triphenylphosphine) end of Pd _{(0) (Pd (PPh 3} ) 4) (0.0223 g, 0.0193 mmol), stirred at room temperature, and slowly heated to 60 < 0 > C to raise the temperature. After 2 hours, the mixture was slowly heated to 100 deg. C and the temperature was raised. After 1 hour, the temperature was elevated to 110 deg. C and the reaction was carried out with stirring for 20 hours or more. When the viscosity increased, 2-bromothiophene (0.1247 mL, 1.2880 mmol) was added and reacted for 3 hours or longer, and the reaction was terminated. After the reaction mixture was poured into a methanol: water (4: 1) solution, the resulting polymer was reprecipitated again with methanol, and the precipitated compound was purified by Soxhlet method using methanol, hexane and acetone . The remaining polymer was dissolved in chloroform and dried under vacuum to obtain 0.38 g (59.75%) of the target polymer compound.

¹ H-NMR (400 MHz, CDCl ₃ )? 9.32-8.69 (s, 2H), 7.63-6.48 (m, 4H), 4.37-3.22 (m, 4H), 2.28-0.59

Example 2 Preparation of Organic Solar Cell Using pDPPT2TTi-OD

A solar cell using the conductive polymer pDPPT2TTi-OD represented by the formula 1 obtained in Example 1 according to the present invention was prepared as follows.

At this time, the indium-tin-oxide (ITO) substrate was washed with isopropyl alcohol for 10 minutes, acetone for 10 minutes, isopropyl alcohol for 10 minutes, and dried.

First, a poly (3,4-ethylenedioxythiophene) poly (styrene sulfonate) (PEDOT: PSS) solution was diluted in methanol at a ratio of 1: 1 and spin-coated on the ITO substrate thus dried, Lt; 0 > C for 10 minutes. The polymer pDPPTTi-OD (8 mg) obtained in Example 1 according to the present invention was added to 1 ml of a 97: 3 mixed solution of chlorobenzene and 1,2-diiodobutane on a dried substrate, And a mixture of (6,6) -phenyl-C ₇₀ -butyric acid methyl ester (PC ₇₀ BM) (16 mg) in a ratio of 1: 1.5 was spin-coated at a rate of 1000 rpm. nm thick ITO / PEDOT: PSS / pDPPT2TTi-OD: PC ₇₀ BM (1: 2) / Al structure.

EXPERIMENTAL EXAMPLE 1 Measurement of Optical Bandgap of Conductive Polymer

The following experiment was conducted to measure the optical bandgap of the conductive polymer according to the present invention.

The absorbance was measured using a UV-vis spectrometer. The solution was dissolved in chloroform solution at 10 ^-5 M / cm (repeating unit basis) and absorbance was measured. The solid phase (ie, film) was dissolved in chloroform solution , And the absorbance was measured by spin coating on a glass substrate.

 division Solution (λ _max ) The film (? _Max ) The optical bandgap (E _{g, opt} ) Example 1
(pDPPT2TTi-OD) 706 nm 723 nm 1.6 eV

As shown in Table 1, the conductive polymer of Example 1 according to the present invention had an optical band gap of 1.6 eV, and the conductive polymer according to the present invention exhibited an optical band- It was confirmed that the gap was reduced (see FIG. 1).

Therefore, it can be used effectively as a material for any one optoelectronic device selected from an organic photovoltaic device, an organic light emitting diode (OLED), an organic thin film transistor (OTFT) have.

<Experimental Example 2> Evaluation of characteristics of organic solar cell including conductive polymer

The following experiment was conducted to examine the characteristics of the organic solar cell including the conductive polymer according to the present invention.

Of the electrochemical characteristics of the organic solar cell device prepared in Example 2, the fill factor and the energy conversion efficiency were calculated by the following equations (1) and (2). The results are shown in Table 2 and FIG.

[Equation 1]

V _mp is the voltage value at the maximum power point, I _mp is the current value at the maximum power point, V _oc is the optical open-circuit voltage, and I _sc is the optical short-circuit current.

&Quot; (2) &quot;

In the above, J _sc is the optical short-circuit current density and V _oc is the optical open-circuit voltage.

 division Open-circuit voltage (V _oc )
(V) The optical short-circuit current (J _sc )
(mA / cm ² ) Fill factor (FF) Energy conversion efficiency
(PCE) (%) Example 2 0.79 7.17 0.51 2.90

As shown in Table 2, the results of the current density-voltage measurement of the organic solar cell according to the present invention show that the short-circuit current and the fill factor are 7.17 mA / cm ² and 0.51 FF, respectively, and the energy conversion efficiency is 2.9% Respectively.

These results indicate that the conductive polymer of the present invention is suitable as a polymer for organic solar cells, and that not only the photon absorption capacity is improved but also the hole mobility is improved.

Accordingly, as described above, the conductive polymer according to the present invention can be effectively used as a low-bandgap electron donor for organic solar cells, and has improved photon absorption and hole mobility. Therefore, Can be used as a material for organic optoelectronic devices that can be applied to fields such as a transistor (OTFT), an organic light emitting diode (OLED), and an organic solar cell, and can be effectively used as an organic solar cell with improved energy conversion efficiency.

Claims (9)

A conductive polymer compound represented by the following Chemical Formula 1:
[Chemical Formula 1]

In the above formula (1)
The Ar

,

,

,

,

,

,

,

,

,

,

,

,

,

,

And

And one species selected from the group consisting of
R ¹ and R ² are each independently a linear or branched C ₁ -C ₇ alkyl group, a linear or branched C ₈ -C ₂₀ alkyl group, a linear or branched C ₁ -C ₇ alkoxy group, a linear or branched C ₈ -C ₂₀ alkoxy group Or a C ₆ -C ₂₀ aryl group;
And n is an integer of 5 to 100,000. The method according to claim 1,
Wherein R ₁ and R ₂ are each independently selected from the group consisting of ethylhexyl, butyloctyl, hexyldecyl, and octyldodecyl,
And n is an integer of 100 to 50,000. The method according to claim 1,
Wherein the conductive polymer compound is a low bandgap electron donor for an organic solar cell that satisfies a band gap of 1.4 to 2.0 eV. (1), which comprises reacting a compound represented by the following general formula (2) and a compound represented by the general formula (3) in a reaction solvent according to the following reaction scheme 1, Manufacturing method:
[Reaction Scheme 1]

In the above Reaction Scheme 1,
The Ar

,

,

,

,

,

,

,

,

,

,

,

,

,

,

And

And one species selected from the group consisting of
R ¹ and R ² are each independently a linear or branched C ₁ -C ₇ alkyl group, a linear or branched C ₈ -C ₂₀ alkyl group, a linear or branched C ₁ -C ₇ alkoxy group, a linear or branched C ₈ -C ₂₀ alkoxy group Or a C ₆ -C ₂₀ aryl group,
and n is an integer of 5 to 100,000. 5. The method of claim 4,
Wherein the reaction solvent is at least one selected from the group consisting of water, toluene, acetone, methanol, ethanol, tetrahydrofuran (THF), chlorobenzene, and dimethylformamide (DMF) &Lt; / RTI &gt; 5. The method of claim 4,
The palladium catalysts include _{PdCl 2, Pd (OAc) 2} , Pd (CH 3 CN) 2 Cl 2, Pd (PhCN) 2 Cl 2, Pd 2 dba 3 CHCl 3 and Pd (PPh ₃₎ selected from the group consisting of ₄ Lt; RTI ID = 0.0 &gt; 1. &Lt; / RTI &gt; An organic solar cell comprising a conductive polymer represented by formula (1) according to claim 1. 8. The method of claim 7,
Wherein the conductive polymer represented by Formula 1 is contained in the photo-conversion active layer. 9. The method of claim 8,
Wherein the photo-conversion active layer further comprises a fullerene derivative.

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