KR20160141541A

KR20160141541A - Hole transfer material, method for preparation thereof, and solar cell comprising the same

Info

Publication number: KR20160141541A
Application number: KR1020150077365A
Authority: KR
Inventors: 서경창; 전성호; 홍성길; 이태섭; 김용미
Original assignee: 주식회사 엘지화학
Priority date: 2015-06-01
Filing date: 2015-06-01
Publication date: 2016-12-09

Abstract

The present invention relates to a hole transport material represented by chemical formula 1, a method for preparing the same, and a solar cell comprising the same. The hole transport material according to the present invention has a high lowest unoccupied molecular orbital (LUMO) energy level due to the steric effect of the ortho-substituted methoxy. Thus, the hole transport material can improve the performance index of a solar cell significantly, when it is used for a hole transport layer for a solar cell. In chemical formula 1, R_1 and R_2 are the same as defined in the specification.

Description

TECHNICAL FIELD The present invention relates to a hole transport material, a method of manufacturing the same, and a solar cell including the same,

The present invention relates to a hole transport material, a method of manufacturing the same, and a solar cell including the same.

Researches on renewable and clean alternative energy sources such as solar energy, wind power, and hydro power are actively being conducted to solve the global environmental problems caused by the depletion of fossil energy and its use.

Of these, there is a great interest in solar cells that change electrical energy directly from sunlight. The term "solar cell" as used herein refers to a cell that generates a current-voltage by utilizing a photovoltaic effect that absorbs light energy from sunlight to generate electrons and holes.

Currently, np diode-type silicon (Si) single crystal based solar cells with a light energy conversion efficiency of more than 20% can be manufactured and used for actual solar power generation. Compound semiconductors such as gallium arsenide (GaAs) There is also solar cell using. However, since such an inorganic semiconductor-based solar cell requires a highly refined material for high efficiency, a large amount of energy is consumed for refining the raw material, and expensive process equipment is required in the process of making single crystal or thin film using raw material And the manufacturing cost of the solar cell can not be reduced.

Accordingly, in order to manufacture a solar cell at a low cost, it is necessary to drastically reduce the cost of the core material or the manufacturing process of the solar cell. As an alternative to the inorganic semiconductor-based solar cell, a dye- Solar cells are being actively studied.

Dye-sensitized solar cell (DSSC) was first developed by Professor Michael Gratzel of the Lausanne University of Technology in Switzerland (1991) and introduced to Nature magazine (Vol. 353, p. 737) .

In the early dye-sensitized solar cell structure, a dye that absorbs light is adsorbed on a porous photo-electrode on a transparent electrode film through which light and electricity pass, and then another conductive glass substrate is placed on top and a simple structure . The working principle of a dye-sensitized solar cell is as follows. When dye molecules chemically adsorbed on the surface of a porous photocathode absorb solar light, dye molecules generate electron-hole pairs, and electrons are converted into conduction tines of semiconductor oxide used as a porous photocathode Injected and transferred to the transparent conductive film to generate a current. The holes remaining in the dye molecules are transferred to the photocathode by the hole conduction or hole conductive polymer by the oxidation-reduction reaction of the liquid or solid electrolyte, and form a complete solar cell circuit, .

In this dye-sensitized solar cell structure, the transparent conductive film is mainly composed of fluorine doped tin oxide (FTO) or indium doped tin oxide (ITO), and a nanotube having a wide band gap is used as the porous photo cathode. The dyestuff is particularly well absorbed and has a lowest unoccupied molecular orbital (LUMO) energy level of the dye than the energy level of the condiction band of the photocathode material, which facilitates the separation of the exciton produced by the light, Various materials are chemically synthesized and used. The highest efficiency of liquid dye-sensitized solar cells reported so far is 11-12% for about 20 years. Although the efficiency of the liquid dye-sensitized solar cell is relatively high, it is likely to be commercialized. However, there is a problem in terms of stability with time due to volatile liquid electrolyte and low cost due to use of expensive ruthenium (Ru) dye.

In order to solve this problem, a nonvolatile electrolyte using an ionic solvent, a polymer gel electrolyte, and a pure organic dyestuff have been studied in place of a volatile liquid electrolyte, but a dye sensitized with a volatile liquid electrolyte and a ruthenium dye There is a problem that the efficiency is lower than that of the solar cell.

Organic photovoltaics (OPVs), which have been studied extensively since mid-1990, have been used to study organic materials with electron donor (D or often called hole acceptor) characteristics and electron acceptor (A) . When a solar cell made of organic molecules absorbs light, electrons and holes are formed. This is called an exiton. The exciton moves to the DA interface to separate the charge, the electrons move to the electron acceptor, and the hole moves to the electron donor, generating a photocurrent.

Since the distance that the exciton generated from the electron donor can travel normally is very short, about 10 nm, the photoconductivity can not be accumulated thickly, and the efficiency of the photoconductivity is low due to low light absorption. In recent years, however, efficiency has greatly increased with the introduction of the so-called bulk heterojunction (BHJ) concept of increasing the surface area at the interface and the development of donor organic materials having a small band gap that is easy to absorb a wide range of solar light, Organic solar cells with efficiency over 8% have been reported (Advanced Materials, 23 (2011) 4636).

Organic solar cells are easier to fabricate than existing solar cells because of their easy processability and diversity of organic materials and low unit cost. Therefore, it is possible to realize low cost manufacturing cost compared to existing solar cells. However, in the organic solar cell, the structure of the BHJ is deteriorated by moisture or oxygen in the air and the efficiency thereof is rapidly lowered, that is, there is a serious problem in the stability of the solar cell. As a method to solve this problem, it is possible to increase the stability by introducing the full sealing technology, but there is a problem that the price is increased.

As a method for solving the problems of the dye-sensitized solar cell by the liquid electrolyte, Prof. Mikael Gratzel of the Department of Chemistry, Lausanne University of Technology, Switzerland, inventor of the dye-sensitized solar cell, proposed a solid-type hole conductive organic material Spiro-OMeTAD (N, N-di-p-methoxyphenylamine) -9,9'-spirobifluorine) was used as a dye-sensitized solar cell with an efficiency of 0.74%.

Thereafter, research on increasing the power generation efficiency of the solar cell by modifying the chemical structure of the Spiro-OMeTAD has been progressing. Recently, as a part of the methoxy group of Spiro-OMeTAD, ortho- (J. Am. Chem. Soc., 2014, 136 (22), pp. 7837-7840). Nevertheless, a method for increasing the efficiency of the solar cell is still required.

Accordingly, the inventors of the present invention studied compounds capable of enhancing the efficiency of solar cells as compared with Spiro-OMeTAD, and thus the compounds described below can remarkably increase the efficiency of solar cells compared with Spiro-OMeTAD derivatives reported so far To complete the present invention.

The present invention is to provide Spiro-OMeTAD derivatives of novel structure and a process for their preparation.

The present invention also provides a composition for hole transport comprising the compound. The present invention also provides a solar cell comprising the above compound.

In order to solve the above problems, the present invention provides a compound represented by the following formula (1): < EMI ID =

[Chemical Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently C ₁ _-4 alkoxy.

The compound represented by the above formula (1), eight C ₁ _-4 alkoxy (methoxy), unlike the structure of the Spiro-OMeTAD release conventionally used has a characteristic that is substituted at the ortho (ortho) of the phenyl. The C ₁ _-4 alkoxy (methoxy) substituted in the orthosus induces distortion of the overall chemical structure of Formula 1 due to the steric effect, thereby lowering the resonance stabilization of Formula 1 to obtain LUMO The energy level can be increased.

Therefore, when the compound of Formula 1 is used as a hole transporting layer of a solar cell, the electron blocking effect is enhanced by the increased LUMO energy level, so that the series resistance of the solar cell is decreased and the parallel resistance is increased, It is possible to remarkably improve the performance index and the power generation efficiency.

Preferably, R ₁ and R ₂ are the same as each other.

Also preferably, R ₁ and R ₂ are methoxy.

The present invention also relates to a process for preparing a compound represented by the general formula (1), which comprises reacting a compound represented by the following general formula (2) and a compound represented by the following general formula (3) A method for producing the compound is provided.

[Reaction Scheme 1]

In the above Reaction Scheme 1, R ₁ and R ₂ are as defined above.

The molar ratio of the compound represented by Formula 2 and the compound represented by Formula 3 is preferably 1: 4 to 6. The molar ratio is preferably 1: 4 or more, and when the molar ratio is more than 1: 6, the reaction efficiency does not substantially increase.

Also, for the efficiency of the reaction, 1) sodium tert-butoxide or potassium tert-butoxide; 2) tris (dibenzylideneacetone) dipalladium (0) or palladium acetate (Pd (OAc) ₂ ); And 3) tri-tert-butylphosphine. The amount of the substance to be used is preferably 6 to 10 mol, 0.05 to 0.2 mol, and 0.1 to 0.4 mol, respectively, based on 1 mol of the compound represented by the formula (2).

Also, the reaction is preferably carried out at 80 to 150 ° C.

After this reaction, purification steps commonly used in the art can be added.

Also, the present invention provides a composition for oral delivery comprising the compound represented by the above formula (1). The present invention also provides a solar cell comprising the compound represented by Formula 1.

As described above, the compound represented by Formula 1 has a high LUMO energy level, and thus can be usefully used as an electron transferring material. In addition, when used as a hole-transporting material for a solar cell, the performance index of the solar cell can be remarkably improved.

The solar cell according to the present invention may have a structure commonly used in the art, except that the compound represented by Formula 1 is used as a hole-transporting material.

According to one embodiment of the present invention, when the compound represented by Formula 1 according to the present invention is used as a hole transporting material instead of Spiro-OMeTAD, the efficiency of the solar cell is remarkably improved.

The compounds according to the present invention, has a higher LUMO energy level ortho by the steric effect of a C ₁ _-4 alkoxy which is substituted with a, so that if used as a major transfer layer of a solar cell to significantly increase the performance index of the solar cell Can be.

1 shows the ¹ H-NMR results of the compounds prepared in the examples of the present invention.
FIG. 2 shows the short-circuit current density-open-circuit voltage curve of a solar cell using the compound prepared in Examples and Comparative Examples of the present invention as a hole transport layer.

Best Mode for Carrying Out the Invention Hereinafter, preferred embodiments are shown to facilitate understanding of the present invention. However, the following examples are intended to illustrate the present invention without limiting it thereto.

Example

In a 50 mL flask, 2,2'-dimethoxydiphenylamine (2.00 g, 8.72 mmol), 2,2 ', 7,7'-tetrabromo-9,9'-spiro [9H-fluorene] Butoxide (1.12 g, 1.12 g, 11.6 mmol), tris (dibenzylideneacetone) dipalladium (0) (0.071 g, 0.078 mmol) and tri-tert- butylphosphine (0.025 g, 0.12 mmol) were mixed. 15 mL of anhydrous toluene was added to the flask under a nitrogen atmosphere. The reaction mixture was heated to 110 < 0 > C under reflux for 12 hours under a nitrogen atmosphere. The mixture was cooled to room temperature, extracted with ethyl acetate and brine, dried over anhydrous MgSO ₄ , hot filtered with ethanol, and washed with acetone to obtain 1.18 g of the title compound. ¹ H-NMR of the compound thus obtained is shown in Fig.

Comparative Example One

Compounds of the above structure were prepared according to the literature (J. Am. Chem. Soc., 2014, 136 (22), pp 7837-7840).

Comparative Example 2

Experimental Example One: HOMO / LUMO Calculation of

HOMO and LUMO of the compounds of the above Examples and Comparative Examples 1 and 2 were theoretically calculated. All calculations were performed with the Gaussian 09 program package (Gaussian 09, revision C.01, Gaussian, Inc., Wallingford CT, 2010). The structure optimization was performed using PBE function (Phys. Rev. Lett., 1997, 78, 1396) and TDDFT electronic excitation calculation using PBE0 functional (J. The calculated results are shown in Table 1 below.

HOMO LUMO Example -4.84 eV -1.58 eV Comparative Example 1 -4.92 eV -1.82 eV Comparative Example 2 -4.90 eV -1.62 eV

As shown in the above Table 1, the LUMO of the Examples is higher than that of Comparative Examples 1 and 2, which is due to the lower resonance stabilization because the 8 methoxy groups in the compounds of the Examples are substituted by ortho of phenyl do.

Experimental Example 2: Manufacturing and performance evaluation of solar cell

Step 1) Manufacture of solar cell

TiO ₂ (bl-TiO ₂ ), a 60 nm thick barrier layer, was blocked with 20 mM titanium diisopropoxide bis (acetylacetonate) at 450 ° C. to block direct contact between the FTO and the hole transport layer by spraying heat deposited _{F-doped SnO 2 (FTO,} Pilkington, TEC8) it is deposited onto a substrate. TiO ₂ particles having a diameter of about 40 nm were prepared by hydrothermally treating the amorphous TiO ₂ solution with colloidization from titanium isopropoxide (Aldrich, 98%) at 250 ° C. for 12 hours, and finally, TiO ₂ paste . The above paste was spin-coated on a bl-TiO ₂ / FTO substrate to form a 250 nm thick porous TiO ₂ (mp-TiO ₂ ) film. The film was sintered at 500 ° C. for 1 hour, Respectively.

30 mL was reacted with hydroiodic acid (57% in water, Aldrich) with 27.86 mL of methylamine was stirred for 2 hours at 0 ℃ in (40% in methanol, Junsei Chemical Co., Ltd.) and 250 mL flask, CH ₃ NH ₃ < / RTI > The solvent was evaporated at 50 < 0 > C for 1 hour to recover the precipitate. The recovered precipitate was dissolved in ethanol, recrystallized with diethyl ether, and then dried in a vacuum oven at 60 DEG C for 24 hours. The synthesized CH ₃ NH ₃ I powder and PbI ₂ (Aldrich) were reacted in a solvent of gamma-butyrolactone: dimethyl sulfoxide (7: 3) at 60 ° C for 12 hours to give a solution of CH ₃ NH ₃ PBI ₃ wt%). The CH ₃ NH ₃ PBI ₃ solution was deposited on the mp-TiO ₂ / bl-TiO ₂ / FTO substrate by two steps of spin coating (1000 rpm / 90 sec and 5000 rpm / 30 sec) 1 mL was added dropwise onto the substrate. The substrate was dried on a hot plate at 100 DEG C for 10 minutes.

For the deposition of the hole transport layer, the compound prepared in the above Example or Comparative Example was dissolved in toluene to prepare a 10 mM solution. To this solution was added 10 μl Li-bis (trifluoromethanesulfonyl) imide (Li-TFSI) / acetonitrile (170 mg / 1 mL) and 5 μl TBP as an additive. The solution was spin-coated on CH ₃ NH ₃ PBI ₃ / mp-TiO ₂ / bl-TiO ₂ / FTO substrate at 3000 rpm for 30 seconds. Finally, a Au counter electrode was deposited by thermal evaporation. The active area of the electrode was fixed at 0.16 cm < 2 >.

2) Performance evaluation of solar cell

Short-circuit current density-Open-circuit voltage (JV curve) was measured using a solar simulator (Newport, Oriel Class A, 91195A) and a source meter (Keithley 2420) at 100 mA / NREL). The J-V curve was measured by masking the active area with a 0.096 cm2 metal mask. From this, the short circuit current density (Jsc), the open circuit voltage (Voc), the open circuit voltage, the FF factor and the power conversion efficiency (PCE) were measured. Table 2 and Fig.

Short circuit current density (mA / cm2) Open-circuit voltage (V) Performance Index (%) Power generation efficiency (%) Example 21.4 1.03 78.0 17.2 Comparative Example 1 20.9 1.00 70.7 14.8

As shown in Table 2 and FIG. 2, the solar cell using the compound according to the present invention as the hole transport layer has a higher performance index and power generation efficiency than the solar cell using the compound prepared in Comparative Example as the hole transport layer . Accordingly, it was confirmed that the performance index and the power generation efficiency of the solar cell can be remarkably improved by the increased LUMO energy level of the compound according to the present invention.

Claims

A compound represented by the following formula (1):
[Chemical Formula 1]

In Formula 1,
R ₁ and R ₂ are each independently C ₁ _-4 alkoxy.

The method according to claim 1,
Wherein R < ₁ > and R < ₂ >
compound.

The method according to claim 1,
Wherein R < ₁ > and R < ₂ > are methoxy.
compound.

Reacting a compound represented by the following formula (2) with a compound represented by the following formula (3) to prepare a compound represented by the following formula (1): < EMI ID =
[Chemical Formula 1]

(2)

(3)

In the above formulas (1) and (3)
R ₁ and R ₂ are each independently C ₁ _-4 alkoxy.

5. The method of claim 4,
Wherein the molar ratio of the compound represented by Formula 2 to the compound represented by Formula 3 is 1: 4 to 6,
Gt;

5. The method of claim 4,
The reaction is carried out in the presence of 1) sodium tert-butoxide or potassium tert-butoxide; 2) tris (dibenzylideneacetone) dipalladium (0) or palladium acetate (Pd (OAc) ₂ ); And 3) tri-tert-butylphosphine.
Gt;

5. The method of claim 4,
Characterized in that the reaction is carried out at from 80 to < RTI ID = 0.0 > 150 C. <
Gt;

A composition for hole transport comprising the compound of any one of claims 1 to 3.

A solar cell comprising a compound of any one of claims 1 to 3.