KR101265511B1 - Low band gap polymers, the synthesis of the polymers, and the organic photovoltaic cell comprising the polymers - Google Patents

Abstract

(P1) (P2)The present invention relates to a polymer having a low bandgap including repeating units represented by the following formula (P1) or (P2), a method for preparing the same, and a high efficiency organic solar cell using the same.

(P1) (P2)

Description

Low band gap polymers, a method for manufacturing the same, and an organic solar cell including the same

The present invention relates to a novel polymer and a method for manufacturing the same, and more particularly, to a polymer having a low bandgap, a method for manufacturing the same, and a high efficiency organic solar cell using the same.

Recently, the finiteness of fossil raw materials, which are representative energy sources, and carbon dioxide emissions from fossil raw material combustion, cause environmental problems such as greenhouse effect, and emphasize the necessity of developing environmentally friendly alternative energy. As part of efforts to overcome these problems, various energy sources such as hydropower and wind power have been studied, and solar light, which can be used indefinitely, is also being studied as an energy source of renewable energy. Solar cells using solar light can be classified into solar cells using inorganic materials such as silicon and solar cells using organic materials. Especially, organic thin film solar cells using polymers have lower production cost and freedom than inorganic solar cells using silicon. A lot of research is being conducted due to the advantage of the large area of the flexible element that can be bent by material. Polyhexylthiophene (poly (3-hexylthiophene), P3HT) is a typical material used for the photoconversion active layer of organic thin film solar cells, and it is 4-5% when the device is manufactured with C60 fullerene derivative having high electron affinity. It is reported to yield about efficiency. However, P3HT has a disadvantage that the light absorption region is limited to about 650 nm (G. Li, V. Shrotriya, JS Huang, Y. Yao, T. Moriarty, K. Emery and Y. Yang, Nat . Mater ., 2005, 4, 864-868, WL Ma, CY Yang, X. Gong,. K. Lee and AJ Heeger, Adv. Funct. Mater, 2005, 15, 1617-1622). Therefore, in order to overcome these shortcomings and to make a high efficiency organic solar cell, there is a need to develop a new polymer having a low band gap with a wide light absorption region, excellent hole mobility, and an appropriate molecular level.

The present invention provides a polymer having a low bandgap that can be used in an organic solar cell, and a method of manufacturing the same. The present invention also provides a high efficiency organic solar cell including a polymer having a low band gap.

The present invention provides a polymer comprising a repeating unit of formula (P1) or (P2).

(P1)

(P1)

(P2)

(P2)

In the above formula, R ₁ and R ₂ are each independently C ₁ -C ₂₀ linear or branched saturated or unsaturated alkyl group, n is an integer of 1 to 100,000, and molecular weight is 500 to 10,000,000.

According to one embodiment of the invention, the repeating unit is preferably selected from the following formula (P1-1) or (P2-1).

(P1-1)

(P1-1)

(P2-1)

(P2-1)

In another aspect, the present invention provides a method for producing a polymer comprising a repeating unit of formula (P1-1) or (P2-1) according to the following scheme (1) or (2).

<Reaction Scheme 1>

<Reaction Scheme 2>

In another aspect, the present invention provides a high efficiency organic solar cell comprising the polymer. At this time, the polymer is included in the photoconversion active layer of the organic solar cell device, it is preferable to further include a fullerene derivative.

Since the polymer according to the present invention has a low band gap, it can be applied to a high efficiency organic solar cell. In the present invention, by introducing a thiophene monomer into the polymer structure, it is possible to provide a conductive polymer material having high photon absorption ability and improved hole mobility. In addition, by introducing a diketopyrrolopyrrole monomer that attracts electrons together, the polymer can be moved to a long wavelength region to obtain a polymer material having a low band gap. Through these features, polymers containing thiophene and diketopyrrolopyrrole monomer can be used as organic electronic materials such as organic thin film transistor (OTFT) and organic light emitting diode (OLED), and C ₆₀ fullerene derivative which is n-type material. Alternatively, the bulk heterojunction type photoelectric conversion layer may be used together with the C ₇₀ fullerene derivative to be applied to an organic solar cell. Further efficiency can be achieved in the development of n-type materials with appropriate energy levels.

1 is a graph of absorbance in solution and films of PQTDPP (Example 1) and PQTVTDPP (Example 2) synthesized according to the present invention.
2 is a graph of current density-voltage ( JV) curves of PQTDPP (Example 1) and PQTVTDPP (Example 2) synthesized according to the present invention.

The present invention will be described in more detail with reference to the following examples.

In the present invention, to obtain a high photoelectric conversion efficiency of the organic thin film solar cell, using a thiophene monomer and a dipyrrolopyrrole monomer reported as a material showing excellent hole mobility and high light absorption rate synthesized a new polymer having a low band gap did. The polymer according to the present invention is characterized by including a repeating unit of formula (P1) or (P2).

(P1)

(P1)

(P2)

(P2)

In the above formula, R ₁ and R ₂ are each independently C ₁ -C ₂₀ linear or branched saturated or unsaturated alkyl group, n is an integer of 1 to 100,000, and molecular weight is 500 to 10,000,000.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the Examples are presented by way of example in order to help understanding of the present invention and should not be construed as being limited thereto.

Synthetic example

Synthesis Example 1 3-dodecylthiophene (Formula 1)

3-bromothiophene (13.0 g, 0.080 mol) and Ni (dppp) Cl ₂ (2.16 g, 5 mol%) were dissolved in anhydrous THF (200 mL) and kept under nitrogen at −10 ° C. Dodecyl magnesium bromide (1 M in diethyl ether) (95.68 mL, 0.096 mol) was added slowly to the solution and the mixture was stirred at room temperature under nitrogen for 5 hours. When the reaction was completed, the reaction mixture was poured into water, extracted with chloroform and dried over anhydrous magnesium sulfate. After removing the solvent under vacuum, the product was purified by column chromatography using n-hexane.

Yield 84% (22.0 g) ¹ H NMR (CDCl _{3 ,} 400 MHz): δ7.24 (m, 1H), 6.95 (m, 2H), 2.63 (t, 2H), 1.67 (m, 2H), 1.26-1.38 (m, 18H), 0.88-0.91 (m, 3H)

Synthesis Example 2 2-Bromo 3-dodecylthiophene (Formula 2)

Compound 1 (8.0 g, 0.032 mol) was dissolved in chloroform (100 mL) and acetic acid (100 mL), and then N-bromosuccinimide (NBS; 5.92 g, 0.033 mol) was added. The solution was stirred at rt for 3 h. The mixture was poured into dilute aqueous sodium hydroxide solution and extracted with chloroform. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was evaporated in vacuo. The reaction product was purified by column chromatography using n-hexane.

Yield 96% (10.0 g) ¹ H NMR (CDCl _{3 ,} 400 MHz): δ 7.20 (d, 1H), 6.82 (d, 1H), 2.75 (t, 2H), 1.75 (m, 2H), 1.26-1.42 (m, 18H), 0.88-0.95 (m, 3H)

Synthesis Example 3: 2- (trimethylstannyl) -5- (5- (trimethylstannyl) thiophen-2-yl) thiophene (Formula 3)

To a 2,2'-bithiophene solution (1 g, 6.02 mmol) in anhydrous THF (80 mL) was slowly added t- BuLi (7.08 mL in pentane, 1.7 M) at -78 ° C. After stirring this solution at −78 ° C. for 1 h, trimethyltin chloride (13.23 mL in THF, 1.0 M) was added to the solution at −78 ° C. The reaction product was raised to room temperature, stirred overnight and the reaction was stopped with water and extracted with chloroform. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was evaporated in vacuo. The reaction product was recrystallized with methanol.

Yield 78% (2.30 g) ¹ H NMR (CDCl _{3 ,} 400 MHz): δ 7.28 (d, 2H), 7.09 (d, 2H), 0.32-0.46 (m, 18H)

Synthesis Example 4 2- (3-dodecylthiophen-2-yl) -5- (5- (3-dodecylthiophen-2-yl) thiophen-2-yl) thiophene (Formula 4)

Compound 3 (1.5 g, 3.05 mmol), compound 2 (2.53 g, 7.62 mmol) and Pd (PPh ₃ ) ₄ (0.18 g, 5 mol%) argon were treated and dissolved in 10 mL of degassed THF. The reaction product was heated to 80 ° C. under argon atmosphere. After the solution was stirred overnight, water was added to the reaction product to stop the reaction and extracted with chloroform. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was evaporated in vacuo. The reaction product was purified by column chromatography using hexane: ethyl acetate = 10: 1.

Yield 64%. (1.3 g) ¹ H NMR (CDCl _{3 ,} 400 MHz): δ 7.18 (d, 2H), 7.12 (d, 2H), 7.01 (d, 2H), 6.94 (d, 2H) 2.79 (t, 4H), 1.68 (m, 4H), 1.26-1.38 ( m, 36H), 0.83-0.88 (m, 6H)

Synthesis Example 5: 3-dodecyl-2- (5- (5- (3-dodecyl-5- (trimethylstannyl) thiophen-2-yl) thiophen-2-yl) -5- (trimethyls Tanyl) thiophene (Formula 5)

To a solution of compound 4 (0.6 g, 0.90 mmol) in dry THF (20 mL) was slowly added t- BuLi (1.22 mL in pentane, 1.7 M) at -78 ° C. After stirring this solution at -78 ° C for 1 hour, trimethylethyl tin chloride (2.70 mL in THF, 1.0 M) was added to the solution at -78 ° C. The reaction product was raised to room temperature, stirred overnight and the reaction was stopped with water and extracted with chloroform. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was evaporated in vacuo. The reaction product was recrystallized with methanol.

Yield 97% (0.87 g). ¹ H NMR (CDCl _{3 ,} 400 MHz): δ 7.14 (d, 2H), 7.03 (d, 4H), 2.83 (t, 4H), 1.70 (m, 4H), 1.28-1.42 (m, 36H), 0.88-0.92 (m, 6H) , 0.34-0.48 (m, 18H)

Synthesis Example 6 2- (trimethylstannyl) -5-((E) -2- (5- (trimethylstannyl) thiophen-2-yl) vinyl) thiophene (Formula 6)

2-((E) -2- (thiophen-2-yl) vinyl) thiophene (1.0 g, 5.20 mmol) was added to dry THF (30 mL) and degassed hexane (15 mL) under argon at -78 ° C. Dissolved. Then, TMEDA (1.79 mL, 12 mmol) was injected into the mixed solution, and n-BuLi (5.20 mL in hexane, 2.5M) was slowly added at -78 ° C for 20 minutes. After addition of n-BuLi, the solution was heated at 70 ° C. for 1 hour, then the temperature was cooled to −78 ° C. and then trimethyltin chloride (13.0 mL in THF, 1.0 M) was added to the solution to raise to room temperature. The reaction mixture was stirred overnight and then extracted with chloroform and water. The product was dried over anhydrous magnesium sulfate and then the solvent was evaporated in vacuo. The reaction product was recrystallized with methanol.

Yield 61% (1.65 g). ¹ H NMR (CDCl _{3 ,} 400 MHz): δ 7.11 (d, 2H), 7.08 (s, 2H), 7.06 (d, 2H), 0.36-0.48 (m, 18H)

Synthesis Example 7: 3-dodecyl-2- (5-((E) -2- (5- (3-dodecylthiophen-2-yl) thiophen-2-yl) vinyl) thiophen-2- Thiophene (Formula 7)

Compound 2 (2.21 g, 6.66 mmol) and Pd (PPh ₃ ) ₄ (0.167 g, 5) dissolved in degassed toluene (18 mL) and DMF (3 mL) of mixed compound 6 (1.5 g, 2.90 mmol) filled with argon. mol%) solution was added. The reaction product was heated to 100 ° C. under argon atmosphere. The reaction product was stirred overnight and then washed with water and chloroform. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was evaporated in vacuo. The reaction product was purified by column chromatography using hexane: chloroform = 10: 1.

Yield 64% (1.3 g) ¹ H NMR (CDCl _{3 ,} 400 MHz): δ 7.18 (d, 2H), 7.01 (d, 2H), 6.99 (s, 2H), 6.98 (d, 2H), 6.94 (d, 2H), 2.81 (t, 4H), 1.70 (m , 4H), 1.27-1.39 (m, 36H), 0.87-0.90 (m, 6H)

Synthesis Example 8: 3-dodecyl-2- (5-((E) -2- (5- (3-dodecyl-5- (trimethylstannyl) thiophen-2-yl) thiophen-2-yl ) Vinyl) thiophen-2-yl) -5- (trimethylstannyl) thiophene (Formula 8)

To a solution of compound 7 (1.0 g, 1.40 mmol) in anhydrous THF (20 mL) was slowly added t- BuLi (1.87 mL in pentane, 1.7 M) at -78 ° C. The solution was stirred for 1 h at -78 ° C, then trimethyltin chloride (3.6 mL, 1.0 M in THF) was added to the -78 ° C solution. The reaction mixture was raised to room temperature, stirred overnight, and then extracted with chloroform and water. The product was dried over anhydrous magnesium sulfate and then the solvent was evaporated in vacuo. The reaction product was recrystallized with methanol.

Yield 54% (0.79 g). ¹ H NMR (CDCl _{3 ,} 400 MHz): δ99 (d, 2H), 6.97 (s, 2H), 6.96 (d, 2H), 6.95 (s, 2H), 2.81 (d, 4H), 1.66 (m, 4H), 1.29-1.34 (m , 36H), 0.85-0.88 (m, 6H), 0.30-0.44 (m, 18H)

Synthesis Example 9 Compounds of Formulas 9, 10, and 11

Compounds 9, 10 and 11 are described in G.-Y Chen et. al . J. Polym . Sci . Part A: Poly. Chem. 2010, 48 , 1669-1675].

Synthesis Example 10 Poly [3- (5- (4-dodecyl-5- (5- (5- (3-dodecylthiophen-2-yl) thiophen-2-yl) thiophen-2-yl ) Thiophen-2-yl) thiophen-2-yl) -2,5-bis (2-ethylhexyl) -6- (thiophen-2-yl) pyrrolo [3,4-c] pyrrole-1 , 4 (2H, 5H) -dione] (Formula P1-1: PQTDPP)

Compound 5 (0.4 g, 0.40 mmol) and Compound 11 (0.28 g, 0.40 mmol) were dissolved in 4 mL of anhydrous toluene. Pd (PPh ₃ ) ₄ (9.3 mg, 0.008 mmol) was added to this solution and heated to 80 ° C. under argon atmosphere. After stirring for 72 hours, 2-bromo-5-methylthiophene (0.005 mL, 7.14 mmol) was added to stop the reaction and the mixture was stirred for another 12 hours.

The reaction mixture was poured into a methanol / hydrochloric acid solution, and the resulting polymer was reprecipitated with methanol. The precipitated material was purified by Soxhlet extraction using methanol, hexane and acetone. The remaining polymer was then dissolved in chloroform and dried in vacuo. Polymer yield 88% (417 mg)

Synthesis Example 11: Poly [3- (5- (4-dodecyl-5- (5-((E) -2- (5- (3-dodecylthiophen-2-yl) thiophen-2-yl) thiophen-2-yl ) Vinyl) thiophen-2-yl) thiophen-2-yl) thiophen-2-yl) -2,5-bis (2-ethylhexyl) -6- (thiophen-2-yl) pyrrolo [ 3,4-c] pyrrole-1,4 (2H, 5H) -dione] (Formula P2-1 PQTVTDPP)

Using Compound 8 (0.3 g, 0.29 mmol) and Compound 11 (0.2 g, 0.29 mmol) in the same manner as in Synthesis Example 10. Yield 0.30 g (51%).

Example 1 Fabrication of Solar Cell Using PQTDPP

Using the polymer synthesized in Synthesis Example 10, a solar cell having an ITO / PEDOT: PSS / PQTDPP: PCBM (1: 0.8) / Al structure was prepared. The ITO substrate was washed with 10 minutes in isopropyl alcohol, 10 minutes in acetone, and finally for 10 minutes in isopropyl alcohol, and dried. The PEDOT: PSS solution was diluted 1: 1 in methanol on a dry ITO substrate and spin coated at a speed of 4000 rpm, which was then dried at 110 ° C. for 10 minutes. After spin-coating a solution prepared with a polymer PQTDPP (10 mg / 1 mL) and a PCBM in a ratio of 1: 0.8 in a chlorobenzene solution at a rate of 1000 rpm on the dried substrate, an aluminum electrode was deposited to a thickness of 100 nm.

Example 2: Fabrication of Solar Cell Using PQTVTDPP

Using the polymer synthesized in Synthesis Example 11, a solar cell having an ITO / PEDOT: PSS / PQTVTDPP: PCBM (1: 0.8) / Al structure was prepared. The ITO substrate was washed with 10 minutes in isopropyl alcohol, 10 minutes in acetone, and finally for 10 minutes in isopropyl alcohol, and dried. On a dry ITO substrate, the PEDOT: PSS solution was diluted 1: 1 in methanol and spin coated, and dried at 110 ° C. for 10 minutes. After spin-coating a solution prepared with a polymer PQTVTDPP (10 mg / 1 mL) and a PCBM in a ratio of 1: 0.8 in a chlorobenzene solution at a rate of 1000 rpm on the dried substrate, an aluminum electrode was deposited to a thickness of 100 nm.

Experimental Example 1 Evaluation of Characteristics of Polymer and Solar Cell Using the Same

1 is a graph of absorbance in solution and films of PQTDPP (Example 1) and PQTVTDPP (Example 2) synthesized according to the present invention. The absorbance peaks and optical bandgaps on the solutions and films determined from this data are listed in Table 1 below. In the absorbance graph of FIG. 1, it can be seen that the optical band gap is reduced through the packing of the polymer body in the film state of both PQTDPP and PQTVTDPP. From these values, it can be seen that these two polymers are suitable as materials with low bandgap for high efficiency.

Solution (λ _max ) Film (λ _max ) Optical bandgap (E _{g , opt} ) PQTDPP 647 nm 682 nm 1.36 eV PQTVTDPP 690 nm 700 nm 1.33 eV

In addition, the measurement results of the characteristics of the solar cells fabricated in Examples 1 and 2 are shown in Figure 2, the main index of the solar cell performance for this graph is described in [Table 2].

V _oc (V) J _{sc (} mA / cm ² ) FF PCE (%) PQTDPP 0.59 5.47 0.64 2.06 PQTVTDPP 0.50 7.60 0.51 1.97

Claims (7)

A polymer comprising a repeating unit of formula (P1):

(P1)
Wherein R ₁ and R ₂ are each independently a C ₁ -C ₂₀ straight or branched saturated or unsaturated alkyl group, n is an integer of 1 to 100,000, and a molecular weight is 500 to 10,000,000. The method of claim 1,
A polymer comprising a repeating unit of formula (P1-1):

(P1-1)
To prepare a polymer comprising a repeating unit of formula (P1-1) according to Scheme (1):
<Reaction Scheme 1>

delete An organic solar cell comprising a polymer comprising a repeating unit of formula (P1):

(P1)
Wherein R ₁ and R ₂ are each independently a C ₁ -C ₂₀ straight or branched saturated or unsaturated alkyl group, n is an integer of 1 to 100,000, and a molecular weight is 500 to 10,000,000. The method of claim 5,
The polymer is an organic solar cell, characterized in that contained in the photoconversion active layer. The method according to claim 6,
An organic solar cell, further comprising a fullerene derivative in the photoconversion active layer.

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