KR102009245B1 - Polymer solar cell having cathode buffer layer including novel small molecular electrolytes - Google Patents

Abstract

(단, 상기 화학식에서 n은 3 내지 8임).The present invention relates to a polymer solar cell having a buffer layer (cathode) and an active layer (buffer layer) comprising a compound represented by the following formula, the polymer solar cell according to the present invention, Cathode buffer layer consisting of quaternary ammonium bromide with hydroxyl group (OH-) exhibits greatly improved efficiency by forming an interfacial dipole which reduces the electron collection barrier, thereby improving the short circuit current (J _sc ), In addition, the new buffer layer material not only improves the performance of the organic solar cell, but also enables mass production by one step synthesis and the purification process is very simple, thereby enabling to realize a high performance organic solar cell economically:

(Wherein n is 3 to 8).

Description

Polymer solar cell having cathode buffer layer including novel small molecular electrolytes

The present invention relates to a polymer solar cell including an anode buffer layer interposed between a photoactive layer and a cathode and including a novel low molecular electrolyte.

Recently, bulk-heterojunction (BHJ) polymer solar cells (PSCs) have attracted attention because of their high applicability as a clean energy source that is lightweight, flexible, and capable of producing large areas.

Through the synthesis of new conjugated polymers / oligomers and interface engineering, the power conversion efficiency (PCE) of PSCs has increased rapidly to over 10%.

Charge transport and collection characteristics at both electrode interfaces are important factors in improving the efficiency of the PSC. Important studies such as alcohol soluble / water soluble conjugated polyelectrolyte (CPE), nonconjugated polymer, alcohol soluble / water soluble conjugated or non-conjugated low molecular weight (SM), and polar solvent treatment to improve interfacial properties Was performed.

These materials enable the fabrication of multilayer devices without disrupting the pre-coated organic semiconductor layer by orthogonal solubility in the processing solvent, and a thin film made of these materials as an interlayer (IL) at the cathode interface. PSCs with R-C show significantly improved performance over devices lacking such interlayers.

In connection with such PSC performance improvement, the conjugated polymer is known to induce the formation of an interface dipole in which an ionic functional group at the side chain end of the skeleton is desirable, thereby reducing the work function of the negative electrode. Alternatively, SM can also reduce the work function of the cathode due to the formation of the interface dipole.

Furthermore, SM has the advantage of easy synthesis and purification compared to polymer materials, and unlike polymer materials, SM does not have a batch-to-batch problem or a wide molecular weight distribution in which solubility in solvents is different.

Korean Patent Publication No. 10-2006-0090002 (Published Date 2006.08.10) Korean Laid-Open Patent No. 10-2015-0089689 (Published Date 2015.08.05) United States Patent Application Publication US2006 / 0209382 (published September 21, 2006)

It is an object of the present invention to provide a polymer solar cell having a negative electrode buffer layer including a novel low molecular electrolyte that can be prepared by a simple manufacturing process without requiring a complicated synthesis process.

The present invention provides a polymer solar cell having a buffer layer including a compound represented by the following formula between a cathode and an active layer.

(Wherein n is 3 to 8).

In addition, the compound represented by the above formula is N, N, N, N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,4-diamine bromide (N, N, N , N, N, N-hexakis (2-hydroxyethyl) butane-1,4-diaminium bromide, C4) and N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,6- Diamine bromide (N, N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,6-diaminium bromide, C6) It is characterized in that at least one selected from.

In addition, the N, N, N, N, N, N, N, N- hexakis (2-hydroxyethyl) hexane-1, 4- dimethyl bromide (N, N, N, N, N, N- hexakis (2-hydroxyethyl) butane-1,4-diaminium bromide) or N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,6-dium bromide (N, N, N , N, N, N-hexakis (2-hydroxyethyl) hexane-1,6-diaminium bromide) is prepared by mixing 1,4-dibromobutane and triethanolamine in acetonitrile.

In addition, the buffer layer is characterized in that the thickness of 2 to 10 nm.

On the other hand, the polymer solar cell according to the present invention is not particularly limited as long as it includes the buffer layer between the cathode and the photoactive layer and the material of each layer.

In one example, a cathode formed on a transparent substrate; A buffer layer comprising a compound represented by the above formula; A photoactive layer having an electron acceptor and an electron donor; And an inverted type polymer solar cell (iPSC) including an anode.

In more detail, the substrate may be formed of a transparent material having high light transmittance, and may include glass, polycarbonate, polymethylmethacrylate, polyethyleneterephthalate, and poly Amides such as amide (polyamide), polysulfone (polyehtersulfone) and the like.

In addition, the photoactive layer may be formed of a bilayer or a heterojunction structure in which a mixture including an electron donor and an electron acceptor having a high electron affinity, which may easily make excitons due to excellent photoreaction.

The electron donor may be a conjugated polymer such as polythiophene, carbazole, benzothiadiazole, cyclopentadithiophene, diketopyrrolopyrrole, or the like. .

In addition, as the electron acceptor, fullerene derivatives such as C60, C70, C76, C78, C82, C90, C94, C96, C720, and C860 having high electron affinity may be used, and PC ₆₁ BM, PC ₇₁ BM, and C84- PCBM, bis-PCBM, etc. are typical examples.

The anode and cathode are metal oxides such as indium tin oxide (ITO), SnO ₂ , IZO (In ₂ O ₃ -ZnO), aluminum doped ZnO (AZO), gallium doped ZnO (GZO), aluminum (Al); Transition metals such as silver (Ag), gold (Au), platinum (Pt), semimetals such as rare earth metals, selenium (Se) may be used, and are preferably formed in consideration of the work function.

Specific examples of the inverted polymer solar cell according to the present invention, ITO substrate; A buffer layer comprising a compound represented by the above formula; Poly [[4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,5-b '] dithiophene-2,6-diyl] [3-fluoro-2- [ (2-ethylhexyl) carbonyl] thieno [3,4-b] thiophendiyl [Poly [[4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,5- b '] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b] thiophenediyl]], PTB7] and [6,6] -phenyl-C71 An active layer comprising -butyl acid methyl ester ([6,6] -Phenyl C71 butyric acid methyl ester, PC ₇₁ BM); A metal oxide layer including molybdenum oxide (MoO ₃ ); And a silver (Ag) electrode layer; and a polymer solar cell sequentially stacked, and may further include a zinc oxide layer (ZnO layer) between the ITO substrate and the buffer layer.

In the polymer solar cell according to the present invention, a cathode buffer layer made of quaternary ammonium bromide to which a plurality of hydroxyl groups (OH-) is added forms an interfacial dipole which reduces the electron collection barrier and thus a short circuit current (J _sc). ) Shows a greatly improved efficiency.

In addition, the new buffer layer material not only improves the performance of the organic solar cell, but also enables mass production by a single step synthesis and the purification process is very simple, thereby enabling to implement a high performance organic solar cell economically.

1 is a chemical structural formula of compounds (C4 and C6) constituting the cathode buffer layer in the present embodiment.
2 is a scheme for the synthesis of C4 and C6.
3 is the ¹ H and ¹³ C NMR spectra of C4.
4 is the ¹ H and ¹³ C NMR spectra of C6.
FIG. 5 shows (a) ITO / ZnO and ITO / C4 or C6 based device structures, (b) energy levels of the materials used in the present invention, and (c) under AM 1.5 G simulated illumination with an intensity of 100 mW / cm ² . Current density-voltage curve of iPSC (insertion: dark state; rectangle: ITO / ZnO-containing device, circle: ITO / C4-containing device, triangle: ITO / C6-containing device).
6 shows the structure of an iPSC under (a) ZnO and ZnO / C4 or C6 based device structures, (b) energy levels of materials used in the present invention, and (c) AM 1.5 G simulated illumination with an intensity of 100 mW / cm ² . Current-voltage curve (insertion: dark state; rectangle: device with ITO / ZnO / MeOH, circle: device with ITO / ZnO / C4, triangle: device with ITO / ZnO / C6).
7 is an IPCE spectrum of a device based on ZnO / MeOH, ZnO / C4 and ZnO / C6.

In describing the present invention, when it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Embodiments according to the concept of the present invention can be variously modified and can have various forms, and specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiments in accordance with the concept of the present invention to a particular disclosed form, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof that is described, and that one or more other features or numbers are present. It should be understood that it does not exclude in advance the possibility of the presence or addition of steps, actions, components, parts or combinations thereof.

Hereinafter, the present invention will be described in detail with reference to Examples.

<Example>

In this embodiment, after synthesis of C4 and C6 represented by the chemical structural formula shown in Figure 1 as a quaternary ammonium bromide containing a plurality of hydroxyl groups, using this as a negative electrode buffer layer material to prepare a polymer solar cell The battery characteristics were examined.

For reference, to examine the effect of hydrophobicity on the interfacial properties, C4 and C6 are designed to have alkyl chains of different lengths.

1.Synthesis of quaternary ammonium bromide with hydroxyl group (OH-) for cathode buffer layer

(1) Synthesis of N, N, N, N, N-hexakis (2-hydroxyethyl) butane-1,4-diamine bromide (C4)

As shown in FIG. 2, a mixture of 1,4-dibromobutane (0.432 g, 2.00 mmol) and triethanolamine (0.627 g, 4.20 mmol) in acetonitrile was refluxed for 12 hours. After cooling to room temperature, the white precipitate was filtered off and washed with plenty of acetonitrile and diethyl ether.

The yield of white solid was 74.8% (0.769 g). Melting point: 110 ° C.

¹ H-NMR (400 MHz, CD ₃ OD, ppm): δ 4.04-3.96 (m, 12H), 3.87 (br, 6H), 3.73-3.66 (m, 12H), 3.67-3.60 (m, 4H), 1.94-1.86 (m, 4H). ¹³ C NMR (100 MHz, CD ₃ OD, ppm): δ 62.86, 61.5, 56.65, 20.45. Anal. Calcd. For C ₁₆ H ₃₈ Br ₂ N ₂ O ₆ : C, 37.37; H, 7. 45; N, 5.45. Found: C, 37.47; H, 7. 35; N, 5.39. (See FIG. 3)

(2) Synthesis of N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,6-dium bromide (C6)

As shown in FIG. 2, a mixture of 1,4-dibromobutane (0.488 g, 2.00 mmol) and triethanolamine (0.627 g, 4.10 mmol) in acetonitrile was refluxed for 12 hours. After cooling to room temperature, the white precipitate was filtered off and washed with plenty of acetonitrile and ether.

The yield of white solid was 65.8% (0.713 g). Melting point: 119 ° C.

¹ H-NMR (400 MHz, CD ₃ OD, ppm): δ 4.04-3.96 (m, 12H), 3.87 (br, 6H), 3.71-3.64 (m, 12H), 3.60-3.50 (m, 4H), 1.90-1.81 (m, 4H), 1.49-1.41 (m, 4H). ¹³ C NMR (100 MHz CD ₃ OD, ppm): δ 62.71, 62.32, 56.67 25.56, 22.88. Anal. Calcd. For C ₁₈ H ₄₂ Br ₂ N ₂ O ₆ : C, 39.86; H, 7.81; N, 5.17. Found: C, 39.79; H, 7.87; N, 5.29. (See FIG. 4)

2. Polymer solar cell (PSC) manufacturing

Two inverted polymer solar cells with or without IL were prepared between the ZnO layer and the active layer.

Specifically, an inverse polymer stacked in the order of ITO / ZnO (40 nm) / IL (~ 5 nm) / active layer (PTB7: PC ₇₁ BM) (100 nm) / MoO ₃ (10 nm) / Ag (100 nm) A solar cell was produced.

First, a ZnO layer was deposited using sol-gel process on ITO. The sol-gel solution was prepared with ethanolamine (0.05 ml) dissolved in zinc acetate dehydrate (0.164 g) and methoxyethanol (1 ml). The mixture was stirred overnight at 60 ° C. before thin film deposition was performed. The thin film of ZnO precursor was cured at 200 ° C. for 10 minutes to partially crystallize the ZnO film. IL was prepared by spin coating the corresponding solution in MeOH (1 mg / mL) on ITO or ZnO at 5000 rpm for 60 seconds. Typical thickness of the cathode buffer layer was less than 5 nm at room temperature. Then, in 1 mL of chlorobenzene containing 3% (volume ratio) of 1,8-diiodooctane (DIO), dissolve 10 mg of PTB7 and 15 mg of PC ₇₁ BM for 120 seconds at 1800 rpm. The resulting blend solution of PTB7 and PC ₇₁ BM was spin-cast to form an active layer. Prior to spin coating, the active solution was filtered through a 0.2 μm membrane filter. MoO ₃ and Ag layers were successively thermally deposited through a shadow mask having a device area of 0.13 cm ² at 2 × 10 ⁻⁶ Torr.

3. Fabrication of electron-only device

Two single electron-only devices with or without IL were fabricated between the ZnO layer and the PC ₇₁ BM layer.

Specifically, a single electronic device laminated in the order of ITO / ZnO (40 nm) / IL (~ 5 nm) or without / PC ₇₁ BM (80 nm) / Al (100 nm) was prepared.

First, a PC ₇₁ BM layer was formed through spin-casting from a PC ₇₁ BM solution containing chloroform as a solvent on an ITO / ZnO substrate with or without IL. The PC ₇₁ BM solution was filtered through a 0.20 μm membrane filter before spin coating. The Al layer was deposited through a shadow mask having a device area of 0.13 cm ² . Current density vs. field curves were recorded using a Keitley Model 2400 source-measure unit.

Experimental Example

To examine the effect of the interlayer (IL) on photovoltaic properties, iPSCs with ITO / ZnO or IL / PTB7: PC ₇₁ BM / MoO ₃ / Ag structures were prepared (FIG. 5 (a)). The current density vs. voltage curves of iPSCs under AM 1.5 G simulated illumination of intensity 100 mW / cm ² and in the dark are shown in FIG. 5 (c). The measured device performance is summarized in Table 1 below. V _oc and FF of ITO / C4 and ITO / C6 based devices were smaller than ITO / ZnO based devices, while J _sc of ITO / C4 and ITO / C6 based devices was 14.95 at 14.65 mA / cm ² . And 15.33 mA / cm ² . Thus, the PCE of ITO / C4 and ITO / C6 based devices was 6.03 and 6.65%, respectively, lower than that of ITO / ZnO based devices (7.35%).

The effective work functions of ITO and ITO / ZnO surfaces coated with C4 or C6 thin films as IL were investigated and Kelvin probe microscopy (KPM) measurements were performed to demonstrate the formation of interfacial dipoles on the substrate surface. The work function of C4 and C6 coated ITO with thin layers of C4 and C6 as IL decreased from 5.0 eV, the work function of ITO, to 4.76 and 4.86 eV, respectively. This value is greater than that of ITO / ZnO (4.4 eV). The energy barrier height between the work function of ITO coated with C4 or C6 thin film as IL and the LUMO level of PC ₇₁ BM is greater than the energy barrier height of ITO / ZnO (see FIG. 5 (b)). Thus, the performance of devices based on ITO coated with C4 thin film or C6 thin film as IL is lower than that of ITO / ZnO based devices. The KPM measurement work function data support the result that the performance of devices with C4 or C6 thin films as IL is lower than that of ITO / ZnO based devices. IIL as C4 or C6 thin films series resistance (R _s) values of the ITO-based devices that the coating is lower than the value of the series resistance (R _s) of the ITO / ZnO-based devices. Leakage current using ITO coated with C4 thin film or C6 thin film as IL (see also inset in FIG. 5 (c)) is significantly higher than that of ITO / ZnO based devices. This is because significantly lower than that of C4 C6 wafer, or shunt resistor of the thin film of the shunt resistance of the coated ITO-based devices (R _sh) The ITO / ZnO-based devices (R _sh) as IL. In addition, smaller R _sh values and larger leakage currents are possible reasons why ITO based devices coated with thin layers of C4 and C6 as IL exhibit lower PCE than ITO / ZnO based devices.

Highest PCE  Having a value ZnO Based on ITO / C4 and ITO / C6 iPSCs  Measurement results of various photovoltaic properties (average of photovoltaic variables for each device (average of 8 devices) is shown in parentheses) Buffer
Layer J _sc
(mA / cm ² )

)V _oc
(

) FF
(

) PCE
(

) R _s ^a
(Ωcm ² ) R _sh ^b
(kΩcm ² ) ZnO 14.48
(14.15) 0.76
(0.76) 66.8
(67.5) 7.35
(7.26) 10.4 0.38 ITO / C4 14.95
(14.98) 0.68
(0.68) 59.3
(58.6) 6.03
(5.94) 4.1 0.035 ITO / C6 15.33
(15.10) 0.71
(0.71) 61.1
(62.0) 6.65
(6.61) 3.5 0.045

a) and b) are measured from the device with the best PCE as series and parallel resistance, respectively

To improve device performance without sacrificing V _oc and FF, iPSCs were fabricated based on ITO / ZnO coated with C4 or C6 thin films as IL. The next layer of ITO / ZnO / under AM 1.5 G simulated illumination in the dark with an intensity of 100 mW / cm ² , with or without IL / PTB7: PC ₇₁ BM / MoO ₃ / Ag (FIG. 6 (a)) The current density-voltage relationship of the iPSC is shown in FIG. 6 (c). Device performance is summarized in Table 2. For conventional PSCs, polar solvent treatment at the cathode interface has been reported to have a positive effect on device performance. In order to eliminate possible synergistic effects of the intermediate layer treating solvent (methanol), the ZnO layer of the reference device was treated with methanol. The J _sc of the methanol treated device increased slightly from 14.48 mA / cm ² to 14.65 mA / cm ² , while V _oc and J _sc were almost identical. This means that methanol does not significantly affect the performance of iPSC in the present invention. However, methanol can reduce defects on the ZnO surface.

The J _sc values of devices with C4 or C6 thin films as IL are 17.22 and 16.78 mA / cm ² , respectively, which is a significant improvement over devices without intermediate layers (14.65 mA / cm ² ). The FF of devices based on C4 and C6 increased from 76.6% to 61.3%, respectively. Devices using C4 and C6 as cathode IL have the highest PCE values of 9.20% and 9.11%, respectively, indicating that the C4 and C6 layers induce good interface dipoles at the cathode interface of the device. The largest increase in PCE of devices with C4 or C6 thin films as IL is due to the improved J _sc . The effective work functions of the C4 and C6 coated ZnO surfaces calculated from KPM measurements are 3.98 and 3.99 eV, respectively, which decreased in the work function of methanol treated ZnO (4.4 eV). This is due to the formation of good interfacial dipoles by C4 or C6 thin films on the ZnO surface. J _sc results are closely related to work function data. To achieve high J _sc requires ohmic contact at the interface. However, the large Schottky barrier height prevents charge collection at the cathode interface. The J _sc improvement represents a typical transition from Schottky to ohmic contact, with PCE changes showing a good correlation with work function changes. Interestingly, V _oc of the device with C4 thin film or C6 thin film as IL is almost the same as the reference device. Even if the intermediate layer deforms the surface potential of the ZnO layer, it hardly affects the V _oc of the device.

R _sh of data elements with a C4 or C6 thin films as IL is lower than R _sh data of ITO / ZnO-based devices. This is related to devices with IL (insertion of Fig. 6 (c)) showing a larger leakage current under reverse bias. Devices with C4 or C6 thin films as IL are estimated to have smaller R _s values and larger FF values, indicating the formation of ohmic contacts at the cathode interface. Devices with C4 or C6 thin films as IL have higher leakage currents and smaller R _sh , but devices with PVA have better J _sc and FF than devices without C4 or C6 thin films as IL.

Highest PCE  Having a value ZnO Of MeOH , ZnO / C4 and ZnO / C6 Measurement results of various photovoltaic properties of iPSCs based on Buffer
Layer J _sc
(mA / cm ² )

)V _oc
(

) FF
(

) PCE
(

) R _s ^a
(Ωcm ² ) R _sh ^b
(kΩcm ² ) ZnO / MeOH 14.65
(14.25) 0.76
(0.75) 66.6
(66.2) 7.41
(7.08) 5.91 0.37 ZnO / C4 17.22
(16.97) 0.75
(0.75) 71.3
(71.0) 9.20
(9.10) 3.8 0.30 ZnO / C6 16.78
(15.67) 0.75
(0.75) 72.4
(71.7) 9.11
(9.06) 3.4 0.21

a) and b) are measured from the device with the best PCE as series and parallel resistance, respectively

On the other hand, the incident photocurrent efficiency (IPCE) curve of the device is very consistent with the change in the J _sc data of the device under 1.0 solar illumination (see FIG. 7). The device was then stored in a nitrogen filled glove box without passivation. Devices without IL maintained 79% of the initial PCE after 125 days. In contrast, PCE of devices with C4 and C6 showed better stability after 125 days, maintaining 86% and 90% of initial PCE values, respectively.

Claims (6)

N, N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,6-dium bromide represented by the following formula (N, N, N, N, N, N-hexakis ( A polymer solar cell having a buffer layer comprising 2-hydroxyethyl) hexane-1,6-diaminium bromide between a cathode and an active layer:

. delete The method of claim 1,
N, N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,6-diabromide (N, N, N, N, N, N-hexakis (2-hydroxyethyl) hexane-1,6-diaminium bromide),
A polymer solar cell, which is prepared by mixing 1,4-dibromobutane and triethanolamine in acetonitrile. The method of claim 1,
The buffer layer is a polymer solar cell, characterized in that the thickness of 2 to 10 nm. The method of claim 1,
ITO substrate;
A buffer layer comprising a compound represented by the above formula;
Poly [[4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,5-b '] dithiophene-2,6-diyl] [3-fluoro-2- [ (2-ethylhexyl) carbonyl] thieno [3,4-b] thiophendiyl [Poly [[4,8-bis [(2-ethylhexyl) oxy] benzo [1,2-b: 4,5- b '] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b] thiophenediyl]], PTB7] and [6,6] -phenyl-C71 An active layer comprising -butyl acid methyl ester ([6,6] -Phenyl C71 butyric acid methyl ester, PC ₇₁ BM);
A metal oxide layer including molybdenum oxide (MoO ₃ ); And
A silver (Ag) electrode layer; the polymer solar cell, characterized in that the inverted (inverted) structure sequentially stacked. The method of claim 5,
The polymer solar cell further comprises a zinc oxide layer (ZnO layer) formed between the ITO substrate and the buffer layer.

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