Patent Application
20230397481
The present invention relates to a conjugated polymer compound for a donor contained in a photoactive layer of a polymer solar cell and to a polymer solar cell including the same.
Polymer solar cells (PSCs) are based on a bulk heterojunction (BHJ) structure formed by blending a conjugated electron donor and an electron acceptor and are fabricated through a solution process. Due to excellent properties, such as light weight, mechanical flexibility, and low-cost production in large-area, polymer solar cells have drawn great attention as electricity generation devices.
Typically, a p-type conjugated polymer donor contained in the photoactive layer formed of the bulk heterojunction structure includes an electron donor (D) and an electron acceptor (A), alternately, along a polymer backbone to reduce band gaps by promoting the creation of an intramolecular charge transfer (ICT) state.
Furthermore, incorporating a strong electron-withdrawing unit into a polymer structure with the formation of a D-A type architecture reduces the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) energy levels of a polymer to improve the open-circuit voltage (VOC) and PCE of a device. As a result, the incorporation is considered one of the potential methods of approach in terms of improving PSC photovoltaic perfoLmance.
In particular, with the characteristics, such as small size, high electron affinity, and low steric hindrance, fluorine (F) atoms can be preferentially considered electron-withdrawing units to be introduced into D-A type polymers. Accordingly, there were several remarkable early studies to implement high-performance PSCs based on polymers containing a fluorine atom.
However, PSC photovoltaic performance is required to be further improved by introducing strong electron-withdrawing functional groups, other than fluorine, into p-type conjugated polymers.
An object of the present invention is to provide a novel quinoxaline-based conjugated polymer compound for a polymer solar cell donor, into which a cyano group (—CN) is introduced as an electron-withdrawing unit, and a polymer solar cell including the same.
The present invention provides a conjugated polymer compound for a polymer solar cell donor, the polymer compound represented by Formula 1 below.
(In Formula 1,
n is an integer of 2 or more,
R is a substituted or unsubstituted alkyl having 2 to 10 carbon atoms, and
X is H or F.)
In addition, the conjugated polymer compound for the polymer solar cell donor represented by Formula 2 is provided:
In addition, the conjugated polymer compound for the polymer solar cell donor represented by Formula 3 is provided:
In addition, the conjugated polymer compound for the polymer solar cell donor represented by Formula 4 is provided:
In addition, in another aspect of the present invention, the present invention provides a polymer solar cell having a photoactive layer containing the conjugated polymer compound as a donor.
In this case, a stacking structure of the polymer solar cell and a material of each layer, according to the present invention, are not particularly limited.
For example, the polymer solar cell, according to the present invention, may be an inverted polymer solar cell (iPSC) including: a negative electrode positioned on a transparent substrate; a photoactive layer containing an electron acceptor and an electron donor made of the conjugated polymer compound; and a positive electrode.
The substrate may be made of a transparent material with high light transmittance. Examples of the substrate may include glass, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyamide, polyethersulfone, and the like.
In addition, the photoactive layer may be one in which a mixture including the electron acceptor and the electron donor, made of the conjugated polymer compound, is formed in a heterojunction structure. In this case, a fullerene derivative with high electron affinity, such as C60, C70, C76, C78, C82, C90, C94, C96, C720, C860, and the like may be used as the electron acceptor. Furthermore, non-fullerene-based acceptor, such as 2,2′-((2Z,2′Z)-((12,13-bis(2-butyloctyl)-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1- diylidene))dimalononitrile (Y6BO) and the like may be used as the electron acceptor.
Metal oxides, such as indium tin oxide (ITO), SnO2, In2O3—ZnO (IZO), aluminum-doped ZnO (AZO), and gallium-doped ZnO (GZO), aluminum (Al), transition metals, such as silver (Ag), gold (Au), and platinum (Pt), rare earth metals, and semimetals, such as selenium (Se), may be used as the positive electrode and the negative electrode. Preferably, the positive electrode and the negative electrode are formed in consideration of a work function.
Specific examples of the polymer solar cell, according to the present invention, may include a polymer solar cell in which an ITO substrate, the photoactive layer including the electron donor made of the conjugated polymer compound and the electron acceptor made of [6,6]-Phenyl C71 butyric acid methyl ester (PC71BM) or Y6BO, a metal oxide layer containing molybdenum oxide (MoO3), and a silver (Ag) electrode layer are sequentially stacked. In this case, a zinc oxide (ZnO) layer may be further included between the ITO substrate and the photoactive layer.
According to the present invention, a conjugated polymer for a polymer solar cell donor is provided in a D-A form in which an electron-donating unit (benzodithiophene, BDT) and an electron withdrawing-unit (quinoxaline, Qx) are combined, while a cyano (CN) substituent is introduced into the Qx unit instead of fluorine (F) to improve charge generation, charge transfer, and charge recombination properties of a polymer solar cell, regardless of types of acceptor contained in a photoactive layer. As a result, the polymer solar cell with greatly improved photoelectric conversion efficiency (PCE) can be implemented.
Furthermore, when the conjugated polymer for the donor containing the CN group in the Qx unit further includes two fluorine (F) atoms in a thiophene side chain of the BDT unit, photovoltaic performance is further improved. Therefore, the polymer solar cell exhibiting a significantly high photo-conversion efficiency of up to 14% can be implemented.
In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure unclear.
The embodiments according to the concept of the present invention can be variously modified and can take various forms, so that the embodiments are illustrated in the drawings and described in detail herein. It should be understood, however, that the embodiments according to the concepts of the present invention are not limited to the specific foinas disclosed, but include modifications, equivalents, or alternatives falling within the spirit and scope of the present invention.
The terms used herein are used for explaining a specific exemplary embodiment, not limiting the present inventive concept. Thus, the expression of singularity herein includes the expression of plurality unless clearly specified otherwise in context. The terms such as “include” or “comprise” used herein may be construed to denote a certain characteristic, number, step, operation, constituent element, or a combination thereof, but may not be construed to exclude the existence of or a possibility of addition of one or more other characteristics, numbers, steps, operations, constituent elements, or combinations thereof.
In addition, unless otherwise specified, the following terms and phrases used herein have the following meanings.
“Alkyl” is a hydrocarbon having normal, secondary, tertiary or cyclic carbon atoms. For example, an alkyl group may have 1 to 20 carbon atoms (i.e., C1-C20 alkyl), 1 to 10 carbon atoms (i.e., C1-C10 alkyl), or 1 to 6 carbon atoms (i.e., C1-C6 alkyl). Examples of suitable alkyl groups include methyl (Me, —CH3), ethyl (Et, —CH2CH3), 1-propyl (n-Pr, n-propyl, —CH2CH2CH3), 2-propyl (i-Pr, i-propyl, —CH(CH3)2), 1-butyl (n-Bu, n-butyl, —CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, —CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, —CH(CH3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, —C(CH3)3), 1-pentyl (n-pentyl, —CH2CH2CH2CH2CH3), 2-pentyl (—CH(CH3)CH2CH2CH3), 3-pentyl (—CH(CH2CH3)2), 2-methyl-2-butyl (—C (CH3)2CH2CH3), 3-methyl-2-butyl (—CH(CH3)CH(CH3)2), 3-methyl-1-butyl (—CH2CH2CH(CH3)2), 2-methyl-1-butyl (—CH2CH(CH3)CH2CH3), 1-hexyl (—CH2CH2CH2CH2CH2CH3), 2-hexyl (—CH(CH3)CH2CH2CH2CH3), 3-hexyl (—CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl (—C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl (—CH(CH3)CH(CH3)CH2CH3), 4-methyl-2-pentyl (—CH(CH3)CH2CH(CH3)2), 3-methyl-3-pentyl (—C (CH3) (CH2CH3)2), 2-methyl-3-pentyl (—CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (—C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (—CH(CH3)C(CH3)3, and octyl (—(CH2)7CH3). Examples of the alkyl group are not limited thereto.
The term “substituted” regarding alkyl and the like, for example, “substituted alkyl” and the like, means alkyl and the like in which one or more hydrogen atoms are each independently substituted with a non-hydrogen substituent. Typical substituents include —X, —R, —O−, ═O, —OR, —SR, —S−, —NR2, —N+R3, ═NR, —CX3, —CN, —OCN, —SCN, —N═C═O, —NCS, —NO, —NO2, ═N2, —N3, —NHC(═O)R, —C(═O)R, —C(═O)NRR, —S(═O)2O−, —S(═o)2OH, —S(═O)2R, —OS(═O)2OR, —S(═O)2NR, —S(═O)R, —OP(═O)(OR)2, —N(═O)(OR)2, —N(═O)(O−2, —N(═O)(OH)2, —N(O)(OR)(O−), —C(═O)R, —C(═O)X, —C(S)R, —C(O)OR, —O(O)O−, —O(O)O−, C(O)SR, —C(S)SR, —C(O)NRR, —C(S)NRR, and —C(═NR)NRR (where X is each independently a halogen: F, Cl, Br, or I, and R is each independently H, alkyl, aryl, arylalkyl, heterocycle, a protecting group, or a prodrug moiety). Examples of the substituent are not limited thereto.
Hereinafter, the present invention will be described in detail with Example.
In Example, three quinoxaline (Qx)-based conjugated polymers (PTB-FQx, PTB-CNQx, and PTBF-CNQx) with a typical D-A arrangement were synthesized (see
1. Synthesis of Quinoxaline-Based Conjugated Polymers (PTB-FQx, PTB-CNQx, PTBF-CNQx, and PTB-CNQx-mH)
(1) Synthesis of PTB-FQx, PTB-CNQx, and PTBF-CNQx
As shown in
Then, an existing fluorine atom in (1) was substituted with a CN group to synthesize 4,7-bis(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole-5-carbonitrile (2).
An F substituent-containing dibrominated Qx monomer (3) and a CN substituent-containing dibrominated Qx monomer (4) were synthesized through reactions of 1,2-bis(4-((2-ethylhexyl)oxy)phenyl)ethane-1,2-dione with benzothiadiazole derivatives of (1) and (2), respectively, under successive Zn-involved reduction and condensation reaction conditions.
A BDT monomer (4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (5) underwent Stille polymerization with the F substituent-containing dibrominated Qx monomer (3) and the CN substituent-containing dibrominated Qx monomer (4) to obtain D-A type polymers, PTB-FQx and PTB-CNQx, respectively.
Lastly, under the same conditions, PTBF-CNQx was synthesized through polymerization between a fluorinated BDT monomer (4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo-[1,2-b:4,5-by]dithiophene-2,6-diyl)bis(trimethylstannane) (6) and the Qx monomer (4).
1) Synthesis of 4,7-bis(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole-5-carbonitrile (Compound 2)
4,7-bis(5-bromothiophen-2-yl)-5-fluorobenzo[c][1,2,5]thiadiazole (Compound 1, 0.66 mmol), KCN (0.85 mmol), and 18-crown-6 (0.085 mmol) were added to a round-bottom flask and dissolved in a mixed solvent of anhydrous THF (20 mL) and DMF (5 mL). Then, the resulting solution was bubbled with nitrogen, and the mixed solution was refluxed at a temperature of 65° C. for 48 hours under an N2 atmosphere. THF was evaporated under reduced pressure, and the residue was dissolved in dichloromethane (MC) and washed with water three times. An ammonia solution was added to a water phase to eliminate the remaining cyanides, and an organic phase was dried with magnesium sulfate (MgSO4) and then filtered. The solvent in the solution was removed using a rotary vacuum evaporator. A crude product was further purified via recrystallization using methanol and chloroform.
Yield: 78% (red powder). 1H NMR (600 MHz, CDCl3): δ (ppm)=7.98 (d, 1H, J =4.02 Hz), 7.96 (s, 1H), 7.83 (d, 1H, J=4.02 Hz), 7.25 (d, 1H, J=4.02 Hz), 7.20 (d, 1H, J=4.02 Hz). 13C NMR (150 MHz, CDCl3): δ (ppm)=152.6, 152.5, 138.4, 135.9, 131.3, 131.0, 130.5, 129.7, 128.5, 126.9, 126.1, 119.5, 118.5, 116.8, 108.5. MALDT-TOF MS: m/z calcd, 482.799; found, 482.942 [M+]
2) Synthesis of 5,8-bis(5-bromothiophen-2-yl)-2,3-bis(4-((2-ethylhexyl)oxy)phenyl)-6-fluoroquinoxaline (Compound 3)
4,7-bis(5-bromothiophen-2-yl)-5-fluorobenzo[c][1,2,5]thiadiazole (Compound 1, 1 mmol) and Zn powder (20 mmol) were added to a 30 mL of acetic acid solution, and then stirred for 6 hours until the color changed to white. The mixed solution was directly filtered after reactions were completed to remove the zinc powder. Then, 1,2-bis(4-((2-ethylhexyl)oxy)phenyl)ethane-1,2-dione (1 mmol) was rapidly added to the filtrate and stirred overnight at a reflux temperature. Next, the mixed solution was cooled to room temperature, poured into water, and extracted with ethyl acetate. An organic phase was separated and dried with magnesium sulfate (MgSO4). A rotary vacuum evaporator was used to remove the solvent, and a crude product was then purified by column chromatography using a solution of dichloromethane and hexane (1:7 (v/v)) as an eluent.
Yield=43% (yellow-orange solid). 1H NMR (600 MHz, CDCl3): δ (ppm)=7.88 (d, 1H, J=13.56 Hz), 7.77 (d, 1H, J=3.54 Hz), 7.68 (dd, 4H, J=11.10, 8.58 Hz), 7.55 (d, 1H, J=4.02 Hz), 7.16 (d, 1H, J=4.02 Hz), 7.14 (d, 1H, J=4.02 Hz), 6.94 (dd, 4H, J=8.58, 3.00 Hz), 3.93-3.89 (m, 4H), 1.78-1.74 (m, 2H), 1.53-1.39 (m, 8H), 1.35-1.33 (m, 8H), 0.97-0.91 (m, 12H). 13C NMR (150 MHz, CDCl3): δ (ppm)=160.3, 160.2, 159.1, 157.4, 151.7, 150.4, 137.9, 137.2, 137.1, 133.5, 133.1, 132.0, 131.8, 130.4, 130.3, 130.1, 130.0, 129.9, 129.8, 128.8, 128.7, 125.5, 118.1, 117.5, 115.6, 115.5, 114.6, 114.4, 114.1, 70.5, 39.4, 30.4, 29.1, 23.8, 23.1, 14.1, 11.2. MALDI-TOF MS: m/z calcd, 878.793; found, 879.308 [M+].
3) Synthesis of 5,8-bis(5-bromothiophen-2-yl)-2,3-bis(4-((2-ethylhexyl)oxy)phenyl)quinoxaline-6-carbonitrile (Compound 4)
Compound 4 was synthesized through a synthetic procedure similar to that of Compound 3 above. 4,7-bis(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole-5-carbonitrile (2, 0.42 mmol) and 1,2-bis(4-((2-ethylhexyl)oxy)phenyl)ethane-1,2-dione (0.42 mmol) were used as reactants, and a ratio of dichloromethane to hexane contained in an eluent for column chromatography was 1:7 (v/v).
Yield=73% (orange solid). 1H NMR (600 MHz, CDCl3): δ (ppm) 8.22 (s, 1H), 7.87 (d, 1H, J=4.02 Hz), 7.72 (d, 2H, J=8.58 Hz), 7.66 (d, 2H, J=8.58 Hz), 7.58 (d, 1H, J=4.02 Hz), 7.21 (d, 1H, J=4.02 Hz), 7.17 (d, 1H, J=4.08 Hz), 6.96-6.92 (m, 4H), 3.92-3.89 (m, 4H), 1.78-1.73 (m, 2H), 1.52-1.40 (m, 8H), 1.35-1.33 (m, 8H), 0.97-0.91 (m, 12H). 13C NMR (150 MHz, CDCl3): 161.0, 160.8, 153.3, 152.8, 137.3, 137.2, 136.4, 135.3, 133.7, 132.0, 131.9, 130.7, 130.2, 129.6, 129.5, 129.2, 129.1, 127.8, 126.1, 120.0, 119.2, 118.5, 114.4, 114.3, 108.5, 70.6, 70.5, 39.3, 30.5, 29.1, 23.8, 23.0, 14.1, 11.1. MALDI-TOF MS: m/z calcd 885.818; found, 886.189 [M+].
4) Synthesis of D-A type Polymer by Stille Coupling Reaction
In a Schlenk flask, a BDT monomer (Compound 5 or 6), a dibrominated DPQ monomer (Compound 3 or 4), and Pd(PPh3)4 (3% mol) were mixed in degassed toluene. The mixed solution was bubbled with nitrogen for 15 minutes and stirred at a temperature of 90° C. for 48 days under an N2 atmosphere. Polymerization was completed by adding two end-capping agents (2-trimethylstannylthiophene and 2-bromothiophene) at 2-hour intervals. Thereafter, the polymer solution was precipitated in methanol, and the solid polymer was collected by filtration. Soxhlet extraction using methanol, acetone, hexane and chloroform was continuously performed to purify the polymer. A chloroform fraction was concentrated, and the polymer was then precipitated again in methanol. Lastly, the solid polymer was dried in vacuo at a temperature of 50° C.
i) PTB-FQx
4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (Compound 5, mmol) and a dibrominated DPQ monomer (Compound 3, 0.2 mmol) were used as reactants.
Yield: 92% (deep blue solid). 1H NMR (600 MHz, CDCl3): δ (ppm)=8.04-7.45 (br, 7H), 7.45-7.35 (br, 2H), 7.22-7.01 (br, 4H), 7.01-6.60 (6H), 4.31-3.78 (br, 4H), 3.20-2.80 (br, 4H), 2.27-1.99 (br, 4H), 1.52-1.40 (br, 16H), 1.40-1.25 (br, 16H), 1.10-0.90 (br. 24H). Molecular weight by GPC: number-average molecular weight (Mn)=38.40 KDa, polydispersity index (PDI)=3.90. Elemental analysis: calcd (%) for C78H87FN2O2S6: C 72.29, H 6.77, N 2.16, S 14.85; found: C 71.83, H 6.61, N 2.07, S 13.14.
ii) PTB-CNQx
4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (Compound 5, 0.2 mmol) and a dibrominated DPQ monomer (Compound 3, 0.2 mmol) were used as reactants.
Yield=88% (deep green solid). 1H NMR (600 MHz, CDCl3): (ppm)=7.91-7.56 (br, 7H), 7.44-7.30 (br, 2H), 7.14-7.02 (br, 4H), 6.98-6.78 (br, 6H), 4.26-3.65 (br, 4H), 3.15-2.74 (br, 4H), 1.89-1.79 (br, 4H), 1.45-1.36 (br, 16H), 1.32-1.18 (br, 16H), 1.01-0.87 (br, 24H). Molecular weight by GPC: number-average molecular weight (Mn)=59.89 KDa, polydispersity index (PDI)=3.02. Elemental analysis: calcd (%) for C79H87N3O2S6: C 72.82, H 6.73, N 3.23, S 14.77; found: C 72.19, H 6.82, N 2.91, S 14.97.
iii) PTBF-CNQx
(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo-[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (Compound 6, 0.17 mol) and a dibrominated DPQ monomer (Compound 4, 0.17 mmol) were used as reactants. The synthesized polymer was dissolved in a chlorobenzene fraction.
Yield=84% (deep green solid). 1H NMR (600 MHz, CDCl3): (ppm)=7.90-7.83 (br, 3H), 7.81-7.71 (br, 3H), 7.47-7.35 (br, 6H), 6.98-6.88 (br, 5H), 4.03-3.82 (br, 4H), 3.00-2.78 (br, 4H), 1.51-1.45 (br, 9H), 1.45-1.35 (br, 19H), 1.09-0.91 (br, 32H). Molecular weight by GPC: numberaverage molecular weight (Mn)=26.07 KDa, polydispersity index (PDI)=3.20 Elemental analysis: calcd (%) for C79H85F2N3O2S6: C 70.76, H 6.54, N 3.13, S 14.35; found: C 69.64, H 6.66, N 3.09, S 15.61.
(2) Synthesis of PTB-CNQx-mH
As shown in
Yield=93.6% (deep green solid). 1H-NMR (400 MHz, CDCl 3) δ 7.50 (s, 2H), 7.39 (s, 2H), 7.35 (s, 1H), 7.31 (s, 1H), 7.28 (s, 2H), 7.20 (s, 4H), 7.10 (d, J=5.0 Hz, 3H), 6.98 (s, 3H), 6.87 (t, J=5.0 Hz, 1H), 3.43 (d, J=5.0 Hz, 4H), 2.69 (d, J=6.9 Hz, 4H), 2.14 (s, 4H), 1.68 (s, 2H), 1.57 (s, 8H), 1.49 (s, 6H), 1.27-1.23 (m, 22H), 0.90-0.84 (m, 10H). Molecular weight by GPC: number-average molecular weight (Mn)=18.22 KDa, polydispersity index (PDI)=3.43. Elemental analysis: calcd (%) for C75H77F2N3O2S6: C 70.11, H 6.20, N 3.27, S 14.97; found: C 69.58, H 6.21, N 3.16, S 16.86.
2. Fabrication of Polymer Solar Cell (PSC) Containing PTB-FQx, PTB-CNQx, or PTBF-CNQx
To fabricate an inverted polymer solar cell in which ITO, ZnO, an active layer (conjugated polymer donor prepared in Example and PC71BM), MoO3, and Ag were sequentially stacked, a 25-nm-thick ZnO film was first deposited on an ITO surface using a sol-gel process. A ZnO film, which was partially crystalline, was prepared by heat curing of a pre-deposited ZnO precursor at a temperature of 200° C. for 10 minutes. The ZnO precursor solution was prepared by dissolving zinc acetate dehydrate (0.164 g) and ethanolamine (0.05 mL) in methoxyethanol (1 mL) and stirring the mixture for 30 minutes before film deposition. The active layer was prepared using a solution in which a polymer donor and chlorobenzene of the PC71BM acceptor (containing 3.0 vol. % of 1,8-diiodooctane as a process additive) were mixed by spin-coating. Before the spin-coating, the mixed solution was filtered through a 0.2-μm polytetrafluoroethylene membrane filter. Lastly, a 20-nm-thick MoO3 layer and a 100-nm-thick Ag layer were sequentially deposited by thermal evaporation at 2×10−6 Torr through a shadow mask with a device area of 0.09 cm2. The J-V characteristics of a device were analyzed using KEITHLEY Model 2400 source-measure unit under AM 1.5G illumination of 100 mW/cm2 from a 150 W Xe lamp. Conditions of solar simulation were calibrated before measurement using a Si reference cell with a KG5 filter certified by the National Institute of Advanced Industrial Science and Technology (AIST) in Japan.
The three polymers exhibited satisfactory solubility in chloroform, tetrahydrofuran (THF), and toluene. Gel peLmeation chromatography (GPC) using a THF eluent was performed to measure a number average molecular weight of each of the polymers. The number average molecular weight values of PTB-FQx, PTB-CNQx, and PTBF-CNQx were 38.40 KDa, 59.89 KDa, and 26.08 KDa, respectively. In addition, the polymers were confirmed to have high thermal stability through thermogravimetric analysis (TGA) at a heating rate of 10° C./min under a nitrogen atmosphere, and a decomposition onset temperature at 5% weight loss was above 430° C. (See
The optical properties of the polymers were examined using an UV-Vis absorption spectrum of the film. The results thereof are shown in
Such results may be related to an increase in band gaps of the polymers due to a decrease in a HOMO energy level. The absorption coefficients of the polymers contained in the films were 6.23×104 cm−, 6.73×104 cm−, and 7.32×104 cm−1 for PTB-FQx, PTB-CNQx, and PTBF-CNQx, respectively. The α value of the polymer was able to be increased stepwise by sequential chemical modification of the polymer, that is, CN group substitution for a fluorine atom in the electron-withdrawing Qx unit, followed by the addition of the two fluorine atoms to the electron-donating BDT unit. In addition, the optical band gaps of PTB-FQx, PTB-CNQx, and PTBF-CNQx measured using an absorption edge were 1.72 eV, 1.65 eV, and 1.67 eV, respectively. The tendency of the optical band gap values was well consistent with the change of the maximum ICT peaks of the polymers. To evaluate the HOMO energy level, the electrochemical oxidation behaviors of the polymers were examined through cyclic voltammetry measurements. As shown in
bEstimate from absorption edge,
cMaximum absorption wavelength of polymer film,
dAbsorption coefficient of polymer film,
eEstimate from oxidation onset level of CV curve,
fCalculated value from HOMO and optical band gap
To estimate frontier molecular orbitals and optimized geometries of the polymer, computational calculations based on density-functional theory (DFT) were performed on dimer model units at B3LYP/6-31** level of the Gaussian 09 program. The results are shown in
The photovoltaic properties of the polymers were studied using the inverted PSC composed of the ITO, ZnO, donor and acceptor, MoO3, and Ag. To optimize the performance of devices containing PC71BM acceptors, several devices were fabricated by varying critical parameters, such as mixing ratios of the donor and acceptor in the polymer, types and concentrations of processing additives, and thickness of the active layer, and then tested. The optimal mixing ratios of the polymer:PC71BM were determined to be 3:5 for PTB-FQx and PTB-CNQx, and 3:4 for PTBF-CNQx. In addition, the thickness of the active layer was adjusted to 75 nm, and 3.0 vol. % of 1,8-diiodooactane (DIO) was added as the processing additive under optimal conditions. The J-V curve of the devices based on PC71BM in the optimal condition under AM 1.5G illumination is shown in
aMass ratio of polymer to acceptor,
b3.0 vol. % of 1,8-diiodooctane added as process additive,
c0.5 vol. % of 1,8-diiodooctane added as process additive,
dcalculated from IPCE curve
In addition, similar inverted PSCs were fabricated using non-fullerene acceptors and tested. Y6BO, a well-known non-fullerene acceptor, enhances intermolecular interactions through polymer donors as well as complementary optical absorption in a long-wavelength region in a range of 600 nm to 900 nm, thereby improving photovoltaic performance of the PSCs. The photovoltaic properties of the PSCs were screened under various fabrication conditions. Then, the best device performance was realized at a polymer:Y6BO mixing ratio of 1:1 (w/w). In addition, an active layer thickness of the optimal device was controlled to be in a range of 85 nm to 90 nm using 0.5 vol. % of DIO. The J-V curve of the devices containing Y6BO in the optimal condition under AM 1.5G illumination is shown in
As a result, when synthesizing the donor polymer in Example of the present invention, it was confirmed that the D-A type Qx-based polymer obtained by the sequential synthesis strategy of replacing the fluorine atom with the CN group in the A unit of the reference polymer and adding fluorine atoms to the D unit was significantly useful in enhancing the PCE of the device regardless of the type of acceptor being used.
Charge transfer properties of the devices were examined by preparing a hole-only device formed of ITO, PEDOT and PSS, the polymer and the acceptor (PC71BM or Y6BO), and Au (50 nm) and an electron-only device formed of ITO, ZnO (25 nm), the polymer and the acceptor (PC71BM or Y6BO), and Al (50 nm). As expected, the hole-only device and the electron-only device containing the PC71BM or Y6BO acceptor exhibited the characteristics of space-charge-limited current behavior. The characteristics can be represented by using the famous Mott-Gurney law (
To obtain additional information on the photovoltaic properties of the polymers, the relation between photocurrent density (JPh) and effective voltage (Veff) of the devices containing the PC71BM acceptors was examined (where JPh=JL (current density under illumination)−JD (current density under dark condition) and Veff=V0 (voltage at JPh=0)−Va (applied voltage)). As shown in
The charge generation, charge extraction, and charge recombination properties of the device based on the Y6BO acceptor were also examined using the same device structure. As can be seen in
Molecular ordering and crystallinity of the active layer in the device are important in determining the overall photovoltaic performance of the PSC. Therefore, grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements were performed on the polymer films and the blend films containing the PC71BM or Y6BO acceptor. The resulting images and plots are shown in
Interestingly, the p-p stacking peaks along the IP and OOP directions and the scattering patterns in lamellas were reconstructed for the blend films containing each of the polymers and Y6BO (see
The morphologies of the blend films each independently based on the polymer and PC71BM and the polymer and Y6BO, with optimal processing conditions, were examined by transmission electron microscopy (see
The present invention is not limited to the above embodiments, but can be manufactured in a variety of different foLms. Those skilled in the art to which the present invention pertains will understand that other specific forms can be implemented without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the aforementioned embodiments are given by way of illustration only, and are not intended to be limiting in all aspects.
According to the present invention, a conjugated polymer for a polymer solar cell donor is provided a D-A form in which an electron-donating unit (benzodithiophene, BDT) and an electron-withdrawing unit (quinoxaline, Qx) are combined, while a cyano (CN) substituent is introduced into the Qx unit instead of fluorine (F) to improve charge generation, charge transfer, and charge recombination properties of the polymer solar cell, regardless of types of acceptor included in a photoactive layer. As a result, a polymer solar cell with greatly improved photoelectric conversion efficiency (PCE) can be implemented. In particular, when the conjugated polymer for the donor containlng the ON group in the Qx unit further contains two fluorine (F) atoms in a thiophene side chain of the EDT unit, photovoltaic performance is further improved. Therefore, the polymer solar cell exhibiting a significantly high photo-conversion efficiency of up to 14% can be implemented.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2020-0119947 | Sep 2020 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2021/001425 | 2/3/2021 | WO |
