WO2018014163A1

WO2018014163A1 - Donor-acceptor polymer with 4-alkoxyl thiophene as conjugated side chain and composition having the same

Info

Publication number: WO2018014163A1
Application number: PCT/CN2016/090325
Authority: WO
Inventors: Yongye Liang; Tingbin YANG; Wei Huang; Fengyuan LIN; Zhi Zhang
Original assignee: South University Of Science And Technology Of China
Priority date: 2016-07-18
Filing date: 2016-07-18
Publication date: 2018-01-25
Also published as: CN109153770A

Abstract

The present invention is directed to the field of organic semiconductor material. The present invention relates to a donor-acceptor conjugated polymer containing 4-alkoxy thiophene (AOT) ring as a conjugated side chain, a composition including the same and a photovoltaic device containing the same.

Description

DONOR-ACCEPTOR POLYMER WITH 4-ALKOXYL THIOPHENE AS CONJUGATED SIDE CHAIN AND COMPOSITION HAVING THE SAME

FIELD

The present application is generally directed to the field of organic semiconductor material, in particular, to a donor-acceptor conjugated polymer containing 4-alkoxy thiophene (AOT) as conjugated side chain and a photovoltaic device containing the same.

BACKGROUND

Bulk-heterojunction (BHJ) polymer solar cells (PSCs) are an emerging photovoltaic technology, which possess the potential for a variety of novel applications, such as semi-transparent green houses, windows and flexible organic electronic deveices. The power conversion efficiency (PCE) of PSCs has exceeded 10％in recent years, which is comparable to amorphous silicon solar cells. With easily accessible organic active-layer materials and large scale solution-processing fabrication, PSCs might require lower cost than inorganic counterparts. Other advantages, such as flexibility, semi-transparency, and light weight, render PSCs with potentials for novel applications where inorganic materials are difficult to be applied.

Semiconducting polymer donors are important in the development of high performance BHJ PSCs, which often blend with fullerenes acceptors to form active layers. Among these high performance conjugated polymers, benzo [1, 2-b: 4, 5-b'] dithiophene (BDT) appears to be a versatile constructing unit. The fused ring structure of BDT unit can enable the resulting polymers with rigid backbones and good planarity, which are beneficial for charge delocalization and inter chain interactions so as to improve the mobility of polymers. Besides, polymers with suitable energy level, solubility and properly side chains patterns can be readily synthesized through easy chemical modifications on BDT unit. Many works have focused on the chemical modifications of BDT unit for high performance photovoltaic polymers, ranging from alkoxyl, alkyl and alkylthiol to 2D conjugated side chains, such as alkyl, alkoxyl or alkylthiol substituented thiophene, benzene and alkyl substituented thieno [3, 2-b] thiophene.

Material cost and fabrication method are another important factors to be considered for PSCs as a viable solar harvesting technology. However, some high efficiency donor polymers require complex synthetic procedures. It’s theoretically estimated that the cost of active layer materials increase linearly with the number of synthetic steps needed to obtain each organic photoactive compound so easily accessible donor polymers with high performance are preferred. In another hand, most donor polymers require halogenated solvents such as chloroform (CF) , chlorobenzene (CB) and o-dichlorobenzene (o-DCB) for processing while such solvents are hazardous and not suitable for large scale fabrication. Most of the high performance donor materials exhibit much inferior photovoltaic performance (PCE lower than 8％) when processing from non-halogenated solvents. PTB7-Th and PffBT4T-2OD have achieved a PCE of 8.5％and 9.5％from o-xylene with anisaldehyde as additive, respectively. Nevertheless, these high performance PSCs processed from non halogenated solvents suffer from either a complexity of high temperature spin coating procedures and strong demands for additives or both.

SUMMARY

Technical Problem

An objective of the present invention is to provide a feasible way to improve the photovoltaic performance of BDT based polymers by introducing 4-alkoxy group modified thiophene as the conjugated side chain.

Another objective of the present invention is to provide a process for enhancing the open-circuit voltage of a donor-acceptor polymer by adding a 4-alkoxy thiophene (AOT) to the backbone thereof as a side chain.

A further objective of the present invention is to provide a photovoltaic device comprising a photoactive layer including the organic conjugated polymer.

A further objective of the present invention is to provide a photovoltaic device comprising a photoactive layer processed from non-halogenated solvents.

Technical Solution

According to an embodiment of the present invention, a donor-acceptor conjugated polymer comprising a 4-alkoxy thiophene (AOT) of formula (I) connected to the backbone of the polymer as a side chain is provided,

wherein R₁ is selected from the group consisting of - (CH₂) _mH, -O (CH₂) _mH and -S (CH₂) _mH, in which m is an integer in a range from 1 to 20, and R₂ is - (CH₂) _nH, in which n is an integer in a range from 1 to 12.

According to a preferred embodiment, R₁ is selected from the group consisting of CH₃, C₂H₅, C₄H₉, C₆H₁₃, C₈H₁₇, C₁₂H₂₅, 2-ethylhexyl, 2-butyloctyl, 2-hexyldecyl, and 2-octyldodecyl.

According to a further embodiment of the present invention, a photoactive layer comprising a conjugated polymer blended with a fullerene derivative or non-fullerene molecule is provided, wherein the conjugated polymer has an MOT (R₂ ＝ CH3) functional unit of the above formula (I) in the side chain.

Specifically, the fullerene derivative according to an embodiment is selected from the group consisting of PC₆₁BM and PC₇₁BM. The non-fullerene molecule according to an embodiment is selected from the group consisting of IC-6IDT and ITIC.

According to an embodiment of the present invention, the 4-alkoxy thiophene (AOT) rings of formula (I) is connected to each donor moiety on the backbone of the polymer on one side or both sides, i.e., the molar ratio of MOT to donor moiety in the conjugated copolymer is 1: 1 or 2: 1.

According to an embodiment of the present invention, a photovoltaic device comprising a semiconducting conjugated polymer blended with a fullerene derivative or non-fullerene molecule as the photoactive layer is provided. The semiconducting conjugated polymer has an MOT functional unit of the above formula (I) in the side chain, which can effectively lower the highest occupied molecular orbital (HOMO) level, thus enhancing the open-circuit voltage. Importantly, the short-circuit current and fill factor of the device do not significantly change. As a result, enhanced power conversion efficiency is achieved.

Advantageous Effects

According to the embodiments of the present invention, the introduction of MOT or the derivative thereof significantly lowers the HOMO level of the conjugated polymer about 0.05-0.1 eV per MOT and 0.1～0.2 eV for two MOTs in BDT unit. The resulting open-circuit voltage is increased correspondently compared to the control device made of polymer without MOT side chain. More importantly, the short-circuit current and fill factor of the MOT-device do not significantly change, leading to enhanced power conversion efficiency. Further, photovoltaic devices with the MOT polymers processed from non-halogenated solvents (e.g., o-xylene) also show excellent performance. This process can be applied to a variety of donor-acceptor type semiconducting polymers.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form as a part of the specification, illustrate embodiments of the present invention.

Figure 1 shows the device structure of polymer-fullerene solar cells according to an embodiment of the present application.

Figure 2 shows the absorption spectra of the polymers in solutions (a) and solid films (b) according to an embodiment of the present application.

Figure 3 shows temperature dependent absorptions of the polymers, (a) PMOT2, (b) PBQ-3, (c) PMOT5, (d) PBDTBDD in dilute o-dichlorobenzene solutions at a temperature interval of 10℃ according to an embodiment of the present application.

Figure 4 shows the energy levels of the electron donor polymers and electron acceptor PC₇₁BM measured by cyclic voltammetry method according to an embodiment of the present application.

Figure 5 shows the J-V measurement results of the device according to an embodiment of the present application, (a) The J-V characteristics of polymer solar cells fabricated with halogenated solvents, (b) the corresponding EQEs, (c) the J-V characteristics of polymer solar cells fabricated non-halogenated solvents, (d) EQE spectra of the corresponding devices of PMOT5 and PMOT2 fabricated from o-xylene, respectively.

Figure 6 shows the TEM images of the blending films (a) PMOT5: PC₇₁BM with 1％DIO, (b) PBDTBDD: PC₇₁BM with 1％DIO, (c) PMOT5: PC₇₁BM without DIO, (d) PBDTBDD: PC₇₁BM without DIO blend films processed from o-DCB with and PMOT5: PC₇₁BM blend films processing from o-xylene (e) with 1％DIO and (f) without additive, respectively, according to an embodiment of the present application.

Figure 7 shows the device structure of non-fullerene polymer solar cells in (a) , and the J-V characteristics of non-fullerene solar cells under AM 1.5G with a light intensity of 100 mW cm^-2 in (b) .

DETAILED DESCRIPTION

The following description is of preferred embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect.

The present application provides a donor-acceptor conjugated polymer comprising a 4-alkoxy thiophene (AOT) unit of following formula (I) connected to the donor moiety of the backbone,

wherein R₁ is selected from the group consisting of - (CH₂) _mH, -O (CH₂) _mH and -S (CH₂) _mH, in which m is an integer in a range from 1 to 20, and R₂ is - (CH₂) _nH, in which n is an integer in a range from 1 to 12. Preferably, R₁ is selected from the group consisting of CH₃, C₂H₅, C₄H₉, C₆H₁₃, C₈H₁₇, C₁₂H₂₅, 2-ethylhexyl, 2-butyloctyl, 2-hexyldecyl, and 2-octyldodecyl. More preferably, R₁ is a 2-ethylhexyl group.

According to an embodiment of the present application, there may be one or two MOT units connected to each donor moiety on the backbone of the polymer. Preferably, there are two MOT units connected to both sides of each donor moiety on the backbone of the polymer.

According to an embodiment of the present application, the conjugated copolymer has a backbone of donor-acceptor structure, wherein the molar ratio of donor moiety to acceptor moiety (D/A ratio) in the backbone is 1: 1, as shown as follows.

According to an embodiment of the present application, the number of the repeated donor-acceptor moieties in the backbone is 10 to 100.

The donor moiety in the conjugated polymer according to an embodiment of the present application may be the one commonly used in the field of organic photoelectric material. Preferably, the donor moiety may be selected from the group consisting of benzo [3, 4-b] dithiophene, thiophene, benzene and the derivatives thereof.

According to a preferable embodiment of the present application, the donor moiety of the conjugated copolymer can be any one of the following structures,

wherein R₁ is the same group as described in formula (I) . More preferably, the donor moiety of the copolymer is benzo [3, 4-b] dithiophene or the derivatives thereof.

According to an embodiment of the present application, the acceptor moiety on the backbone of the copolymer may be any one of the rings represented by the following structures,

In particular, the acceptor moiety on the backbone of the copolymer may be selected from the group consisting of benzo [c] [1, 2, 5] thiadiazole, benzo [c] [1, 2, 5] oxadiazole, isoindoline-1, 3-dione, quinoxaline, benzo [d] [1, 2, 3] triazole, thieno [3, 4-c] [1, 2, 5] thiadiazole, thieno [3, 4-b] pyrazine, thieno [3, 4-b] thiophene, benzo [1, 2-c: 4, 5-c'] bis ( [1, 2, 5] thiadiazole) , [1, 2, 5] thiadiazolo [3, 4-g] quinoxaline, pyrazino [2, 3-g] quinoxaline, [3, 3'-biindolinylidene] -2, 2'-dione, benzo [1, 2-c: 4, 5-c] dithiophene-4, 8-dione, quinoxaline, thieno [3, 4-c] pyrrole-4, 6 (5H) -dione, 2, 5-dihydropyrrolo [3, 4-c] pyrrole-1, 4-dione, and the derivatives with unsubstituted or alkyl substituted thiophene or unsubstituted or alkyl substituted thieno [2, 3-b] thiophene on two sides as bridging groups thereof, represented by the following structures,

where R is selected from the group consisting of H, CH₃, C₂H₅, C₄H₉, C₆H₁₃, C₈H₁₇, C₁₂H₂₅, 2-ethylhexyl, 2-butyloctyl, 2-hexyldecyl, and 2-octyldodecyl.

R₂ is selected from the group consisting of H, CH₃, C₂H₅, C₄H₉, C₆H₁₃, C₈H₁₇, C₁₂H₂₅, 2-ethylhexyl, 2-butyloctyl, 2-hexyldecyl, and 2-octyldodecyl.

According to a preferable embodiment of the present application, thiophene modified 1, 3-bis (thiophen-2-yl) -5, 7-bis (2-ethylhexyl) benzo- [1, 2-c: 4, 5-c] dithiophene-4, 8-dione (BDD-T) , thiophene modified 2, 3-diphenyl-5, 8-di (thiophen-2-yl) quinoxaline (DTQx-2F-T) , thieno [3, 4-b] thiophene (TT) and thieno [2, 3-b] thiophene modified thieno [3, 4-c] pyrrole-4, 6 (5H) -dione (TPD-TT) are employed as acceptor moieties as they can endow the obtained copolymers with good photovoltaic performance.

The following examples illustrate the present application in detail without limiting the scope thereof. In the following examples, only the copolymers containing BDT (benzo [1, 2-b: 4, 5-b'] dithiophene) as a donor moiety and BDD, DTQx-2F or TT as an acceptor moiety are illustrated, however, the copolymers containing other donor moieties and acceptor moieties listed above can be prepared in similar processes to those of Examples 1-3.

Some examples of MOT (EH) added to a D-A copolymer as a side chain are described below, however, those skilled in the art should appreciate that other derivatives of MOT represented by formula (I) are all suitable for connecting to the donor moiety on the backbone of the copolymer.

Example 1

Synthesis of PMOT5

Into a 25 mL pre-dried flask was charged with Sn2-BDT-MOT (169.2 mg, 0.1754 mmol) , BDD-Br2 (134.48 mg, 0.1754 mmol) and Pd (PPh3) 4 (8.8 mg, 0.00778 mmol) . The flask was successively evacuated and refilled with argon for 3 cycles. Then toluene (4.2 mL) and was added. The mixture was reacted at 120 ℃ for 12 hours. The crude product was collected by precipitating from MeOH. The solid was then rinsed in a Soxhlet extractor with MeOH, acetone, hexane and chloroform successively. The solution in chloroform was concentrated, and then precipitated in MeOH. After drying at a reduced pressure, 205 mg of the copolymer was obtained. Yield: 93.80％. Mn: 45.9 kDa； PDI: 2.45.

Comparative Example 1

Synthesis of PBDTBDD

The PBDTBDD was reported by Hou et al. previously (D. Qian, L. Ye, M. Zhang, Y. Liang, L. Li, Y. Huang, X. Guo, S. Zhang, Z. a. Tan, J. Hou, Macromolecules 2012, 45, 9611. ) Here, the copolymer was obtained through the same procedure as PMOT5, yield: 76.90％. Mn: 30 kDa； PDI: 2.52.

Example 2

Synthesis of PMOT2

The copolymer was obtained through the same procedure as PMOT5, by using Sn2-BDT-MOT and 2, 3-diphenyl-5, 8-di (thiophen-2-yl) quinoxaline (DTQx-2F) as monomers. yield: 93.59％. Mn: 27 kDa； PDI: 1.95.

Comparative Example 2

Synthesis of PBQ-3

The PBQ-3 was reported previously by Hou et al. . (D. Liu, W. Zhao, S. Zhang, L. Ye, Z. Zheng, Y. Cui, Y. Chen, J. Hou, Macromolecules 2015, 48, 5172. ) Here, the copolymer was obtained through the same procedure as PMOT5, yield: 90.97％. Mn: 23.5 kDa； PDI: 2.04.

Example 3

Synthesis of PMOT1

To further confirm the universality of the functionality of the MOT unit, a low bandgap polymer containing an MOT unit in the side chain was also synthesized and used for the fabrication of polymer photovoltaics according to the present application. The molecular structure of the low bandgap polymer PMOT1 is represented as following.

1. Preparation of Sn₂-BDT-MOT as donor moiety

The synthesis of Sn₂-BDT-MOT was carried out in accordance with the following procedure.

A 3-methoxythiophene was firstly functionalized with a 2-ethylhexyl chain to give 2- (2-ethylhexyl) -3-methoxythiophene (3MOT) . Then such 3MOT was reacted with benzo [1, 2-b: 4, 5-b'] dithiophene-4, 8-dione to afford a 3MOT substituted benzo [1, 2-b: 4, 5-b'] dithiophene (BDT-MOT) . The resulted BDT-MOT was further functionalized through lithiation with lithium diisopropylamide (LDA) and subsequent stannylation with Me₃SnCl to give the title compound.

Synthesis of 2- (2-ethylhexyl) -3-methoxythiophene (3MOT) : To a pre-dried 500 mL flask was charged with 3-methoxythiophene (14.95 g, 130.95 mmol) and anhydrous THF (125 mL) , and the solution was cooled to -78 ℃ at which a n-BuLi solution (2.4 M in hexane, 57.3 mL) was added dropwise under the protection of argon. The mixture was stirred at ambient temperature for 1.5 hours, and then cooled down again to -78 ℃, followed by a slow addition of 2-ethylhexyl bromide (50.6 g, 262 mmol) . The flask was kept at ambient temperature for 0.5 hour, heated at 50 ℃ for 2 hours, and stirred overnight at ambient temperature. The reaction was quenched with H₂O. Then the organic layer was extracted with EtOAc, washed with H₂O for 3 times, dried with MgSO₄, and concentrated at reduced pressure. The target compound was obtained by distillation (0.1 MPa, 70-80 ℃) . 12.65 g, yield: 42.67％.

¹H NMR (500 MHz, CDCl₃, δ) : 6.98 (d, 1H) , 6.79 (d, 1H) , 3.80 (s, 3H) , 2.63 (m, 2H) , 1.53 (m, 1H) , 1.37-1.21 (m, 8H) , 0.89 (m, 6H) .

Synthesis of BDT-MOT: Into a pre-dried 250 mL flask was charged with 3MOT (6.0 g, 26.5 mmol) and anhydrous THF (106 mL) , and the solution was cooled to 0 ℃ at which a n-BuLi solution (1.6 M in hexane, 18.2 mL) was added dropwise under the protection of argon. The mixture was kept at 0 ℃ for 1.5 hour, and then warmed to room temperature. After that, benzo [1, 2-b: 4, 5-b'] dithiophene-4, 8-dione (2.43 g, 11.03 mmol) was added in one portion. The reaction was conducted at 80 ℃ for 1.5 hour. After cooling to 0 ℃, SnCl₂·2H₂O (14.9 g, 66.03 mmol) in 10 ％HCl (60 mL) was introduced, and the mixture was stirred for another 2 hours at 80 ℃. The mixture was poured into ice water after cooling to ambient temperature. The organic layer was extracted with EtOAc, and washed several times with H₂O. Further purification was performed by column chromatography with CH₂Cl₂/hexane (v/v: 1/9) as the eluent to yield a yellow oil. 4.27 g, yield: 60.58％.

¹H NMR (500 MHz, CDCl₃, δ) : 7.69 (d, 2H) , 7.46 (d, 2H) , 7.23 (s, 2H) , 3.89 (s, 6H) , 2.76 (d, 4H) , 1.66 (m, 2H) , 1.49-1.25 (m, 16H) , 0.98-0.88 (m, 12H) .

Synthesis of Sn₂-BDT-MOT: BDT-MOT (0.50 g, 0.78 mmol) was dissolved in anhydrous THF (12 mL) in a 100 mL argon-purged flask, and then n-BuLi solution (1.6 M in hexane, 1.47 mL) was added at -78 ℃. The reaction mixture was then stirred for 1.5 hours at this temperature. Subsequently, trimethylstannyl chloride (1.0 M in THF, 2.58 mL) was added and the mixture was stirred overnight at ambient temperature. The organic layer was extracted by diethyl ether, washed several times by water, and concentrated to obtain the crude product. The target compound was attained through recrystallization from isopropanol. 0.51 g, yield: 67.57％.

¹H NMR (500 MHz, CDCl₃, δ) : 7.73 (s, 2H) , 7.25 (s, 2H) , 3.91 (s, 6H) , 2.77 (d, 4H) , 1.67 (m, 2H) , 1.49-1.25 (m, 16H) , 0.98-0.88 (m, 12H) , 0.41 (s, 18H) .

2. Preparation of Br₂-TT as acceptor moiety

2-ethylhexyl 4, 6-dibromo-3-fluorothieno [3, 4-b] thiophene-2-carboxylate (Br₂-TT) was synthesized according to the processes reported.

3. Preparation of donor-acceptor copolymer

The donor-acceptor copolymer was prepared by Stille poly-condensation reaction between the bis-stannylated BDT-based donor moieties and dibrominated acceptor moieties, with Pd (PPh₃) ₄ as a catalyst and toluene/DMF mixture as the reaction solvent.

The preparation process of PMOT1 was summarized as follows.

Into a 25 mL pre-dried flask was charged with Sn₂-BDT-T (2EH3MO) (210 mg, 0.218 mmol) , Br₂-TT (103 mg, 0.218 mmol) and Pd (PPh₃) ₄ (10.1 mg, 0.009 mmol) . The flask was successively evacuated and refilled with argon for 3 cycles. Then toluene (4.4 mL) and DMF (0.88 mL) was added. The mixture was kept at 120 ℃ for 24 hours. The crude product was filtrated through celite, and collected by precipitating from acetone. The solid was then rinsed in a Soxhlet extractor with MeOH, acetone, hexane and chloroform successively. The solution in chloroform was concentrated, and then precipitated in hexane. After drying at a reduced pressure, the copolymer was obtained. 182 mg, yield: 88.1％.

Example 4

Synthesis of BDT-T/MOT-TT

1. Preparation of Sn₂-BDT-T/MOT as donor moiety

The synthesis of Sn₂-BDT-T/MOT was carried out in accordance with the following procedure.

2- (2-ethylhexyl) thiophene and 3MOT were firstly lithiated with a butyl lithium reagent, and the resultants were reacted with benzo [1, 2-b: 4, 5-b'] dithiophene-4, 8-dione successively to afford a 3MOT substituted benzo [1, 2-b: 4, 5-b'] dithiophene (BDT-T/MOT) . The resulted BDT-MOT was further functionalized through lithiation with lithium diisopropylamide (LDA) and subsequent stannylation with Me₃SnCl to give the title compound.

Synthesis of BDT-T/MOT: Into a pre-dried 250 mL flask was charged with 2- (2-ethylhexyl) thiophene (2.744 g, 14.0 mmol) and anhydrous THF (28 mL) , and the solution was cooled to 0 ℃ at which a n-BuLi solution (2.4 M in hexane, 5.82 mL) was added dropwise under the protection of argon. The mixture was kept at room temperature for 1.5 hour. After that, the reaction mixture was transferred into a flask where benzo [1, 2-b: 4, 5-b'] dithiophene-4, 8-dione (3.42 g, 15.5 mmol) was dissolved in anhydrous THF (31 mL) . The reaction was conducted at 60 ℃ for 2.5 hours, during which a reaction of 3MOT (7.2 g, 31.8 mmol) in anhydrous THF (60 mL) with n-BuLi solution (2.4 M in hexane, 5.82 mL) was performed at 0 ℃ for 1.5 hour. After cooling to room temperature, the lithiated 3MOT solution was introduced, and the reaction was continued for another 1.5 hour at 80 ℃. SnCl₂·2H₂O (24.53 g, 108.7 mmol) in 10 ％HCl (98.5 mL) was introduced at 0 ℃, and the mixture was stirred for another 2 hours at 80 ℃. The mixture was poured into ice water after cooling to ambient temperature. The organic layer was extracted with EtOAc, and washed several times with H₂O. Further purification was performed by column chromatography with CH₂Cl₂/hexane (v/v: 1/9) as the eluent to yield a yellow oil. 3.15 g, yield: 33.2％.

¹H NMR (400 MHz, CDCl₃, δ) : 7.70 (d, 1H) , 7.65 (d, 1H) , 7.47 (dd, 2H) , 7.30 (d, 1H) , 7.24 (s, 1H) , 6.90 (d, 1H) , 3.90 (s, 3H) , 2.87 (d, 2H) , 2.77 (d, 2H) , 1.68 (m, 2H) , 1.49-1.27 (m, 16H) , 0.98-0.88 (m, 12H) .

Synthesis of Sn₂-BDT-T/MOT: BDT-T/MOT (0.78 g, 1.28 mmol) was dissolved in anhydrous THF (20 mL) in a 100 mL argon-purged flask, and then LDA solution (2.0 M in THF, 2.57 mL) was added at -78 ℃. The reaction mixture was then stirred for 2.0 hours at this temperature. Subsequently, trimethylstannyl chloride (1.0 M in THF, 5.65 mL) was added and the mixture was stirred overnight at ambient temperature. The organic layer was extracted by diethyl ether, washed several times by water, and concentrated to obtain the crude product. The target compound was attained through recrystallization from isopropanol. 0.31 g, yield: 51.8％.

¹H NMR (400 MHz, CDCl₃, δ) : 7.71 (d, 2H) , 7.31 (d, 1H) , 7.24 (s, 1H) , 6.90 (d, 1H) , 3.90 (s, 3H) , 2.87 (dd, 2H) , 2.76 (dd, 2H) , 1.68 (m, 2H) , 1.49-1.25 (m, 16H) , 0.98-0.88 (m, 12H) , 0.40 (s, 18H) .

2. Preparation of Br₂-DPP (BO) as acceptor moiety

Br₂-TT was prepared with the same process as Example 1.

3. Preparation of donor-acceptor copolymer

The Synthesis of BDT-T/MOT-TT from the Sn₂-BDT-T/MOT and Br₂-TT was carried out through the same procedure as that of BDT-MOT-TT in Example 1.

Synthesis of PMOT16

Into a 10 mL pre-dried flask was charged with BDT-MOT-Sn₂ (169.3 mg, 0.1755 mmol) , TPD based monomer (172.0 mg, 0.1755 mmol) and Pd (PPh₃) ₄ (5 mg, 0.0043 mmol) . The flask was successively evacuated and refilled with argon for 3 cycles. Then toluene (3.6 mL) and anhydrous DMF (0.36ml) was added. The mixture was refluxing for 12 hours. The crude product was collected by precipitating from MeOH. The solid was then rinsed in a Soxhlet extractor with MeOH, acetone, hexane and chloroform successively. The solution in chloroform was concentrated, and then precipitated in MeOH. After drying at a reduced pressure, 252 mg of the copolymer was obtained.

Comparative Example 5

Synthesis of PTh22

The PTh22 was reported previously. (J. -H. Kim, J. B. Park, I. H. Jung, A. C. Grimsdale, S. C. Yoon, H. Yang, D. -H. Hwang, Energy Environ. Sci. 2015, 8, 2352. ) Here, PTh22 was synthesized with the similar procedures to PMOT16 with the monomers BDT-T-Sn₂ and BDT-MOT/T-Sn₂, respectively.

Example 6

Synthesis of PMOT27

PMOT27 was synthesized with the similar procedures to PMOT16 with the monomers BDT-T-Sn₂ and BDT-MOT/T-Sn₂, respectively.

Example 7

Manufacture and test of photovoltaic device containing PMOT5

An photovoltaic device having the structure of ITO/PEDOT: PSS/active layer/PDINO/Al as shown in Figure 1 was made, wherein the indium tin oxide (ITO) was the bottom layer. The device includes a transparent metal oxide electrode, i.e. ITO and a layer of poly (3, 4-ethylenedioxythiophene) : poly (styrenesulfonate) (PEDOT: PSS) as an anode, a buffer layer perylene diimides functionalized with amino N-oxide poly [ (9, 9-bis (3’ - (N, N-dimethylamino) propyl) -2, 7-fluorene) -alt-2, 7- (9, 9-dioctylfluorene) ] (PDINO) modified Al as a cathode, and the photoactive layer made from MOT polymer and PCBM is sandwiched between the two electrodes. In this Example, the MOT polymer is PMOT5, the PCBM is [6, 6] -phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) , and in the comparative Example, the polymer is PBDTBDD, the PCBM is the same as this Example.

The process for fabricating the optoelectronic device is summarized as follows. An ITO substrate was ultrasonically washed in detergent, deionized water, acetone, and isopropanol sequentially. Then the ITO substrate was dried in an oven and treated in an ultraviolet-ozone chamber for 4 min. A PEDOT: PSS aqueous solution was filtered through a 0.22 μm filter membrane and spin-coated at 2500 rpm for 30 s on the ITO electrode, then baked at 150℃ for 10 min in air. The PEDOT: PSS layer has the thickness of about 40 nm. Subsequently, the substrate consisting of ITO layer and PEDOT: PSS layer was transferred to the nitrogen-filled glove-box. The PMOT5 prepared in Example 1 was mixed with PC₇₁BM (1: 1.2, w/w) (PC₇₁BM: [6, 6] -phenyl C₇₁-butyric acid methyl ester) and the mixture was dissolved in 1, 2-dichlorobenzene/1, 8-diiodoctance (99: 1, v/v) . The molecular structure of PC₇₁BM can be represented by formula (II) .

The obtained solution was spin-coated on the PEDOT: PSS layer in the glove-box to form an active layer (PMOT5 film) with the thickness of about 110 nm. A PDINO layer was covered onto the active layer before Al electrode deposition. Finally, this obtained structure was transferred to a vacuum chamber and a 100 nm of Al was thermally deposited on the PDINO layer under a base pressure of 3×10^-6 mbar. The photoactive layer area of the obtained device was 4.5 mm².

The current density versus voltage (J-V) measurement of the obtained device under AM1.5G solar simulator illumination (100 mW cm^-2) was performed on a computer-controlled Keithley 2400 Source Measure Unit in air. The external quantum efficiency (EQE) was measured under ambient atmosphere at room temperature using a quantum efficiency system (QE-R) . A bromine tungsten lamp was used as the light source in this test.

Comparative Example 3

Manufacture and test of photovoltaic device containing PBDTBDD

In this Example, the manufacture method of the control device was the same as that of Example 5 except that the MOT contained in the active layer was replaced by thiophene. The PBDTBDD made in comparative Example 1 was mixed with PC₇₁BM (1: 1.2, w/w) and the mixture was dissolved in 1, 2-dichlorobenzene/1, 8-diiodoctance (99: 1, v/v) . The obtained solution was coated on the substrate consisting of ITO layer and PEDOT: PSS layer in the glove-box to form an active layer with the thickness of about 110 nm.

Example 8

Manufacture and test of photovoltaic device containing PMOT2

A photovoltaic device having the structure of ITO/PEDOT: PSS/active layer/PDINO/Al as shown in Figure 1 was made, wherein the ITO was the bottom layer. An indium tin oxide (ITO) substrate was obtained and ultrasonic washed in detergent, deionized water, acetone, and isopropanol sequentially. Then the ITO substrate was dried in an oven and treated in an ultraviolet-ozone chamber for 4 min. A PEDOT: PSS aqueous solution filtered through a 0.22 μm filter membrane was spin-coated at 2500 rpm for 30 s on the ITO substrate, then baked at 150℃ for 10 min in air. The obtained PEDOT: PSS layer has the thickness of about 40 nm. Subsequently, the structure consisting of ITO layer and PEDOT: PSS layer was transferred to the nitrogen-filled glove-box. The PMOT2 made in Example 2 was mixed with PC₇₁BM (1: 1.5, w/w) (PC₇₁BM: [6, 6] -phenyl C₇₁-butyric acid methyl ester) and the mixture was dissolved in chloroform/1, 8-diiodooctance (97: 3, v/v) . The molecular structure of PC₆₁BM can be represented by formula (III) .

The obtained solution was spin-coated on the PEDOT: PSS layer to form an active layer with the thickness of about 100 nm. A PDINO layer was covered on the active layer. Finally, this obtained structure was transferred to a vacuum chamber and a 100 nm of Al was thermally deposited on the PFN layer under a base pressure of 3×10^-6 mbar. The photoactive layer area of the obtained device was 4.5 mm².

The J-V measurement of the obtained device was performed with the same process as that of Example 5.

Comparative Example 4

Manufacture and test of photovoltaic device containing PBQ-3

The structure and preparation method of the device in this Example were the same as that of Example 6 except that the PMOT2 contained in the active layer was replaced with PBQ-3. The preparation method of this device can be summarized as: an ITO substrate was ultrasonic washed in detergent, deionized water, acetone, and isopropanol sequentially. Then it was dried in an oven and treated in an ultraviolet-ozone chamber for 4 min. A PEDOT: PSS layer of 40 nm was coated on the ITO substrate. The PBQ-3 made in comparative Example 2 was mixed with PC₇₁BM (1: 1.5, w/w) and they were dissolved in chlorobenzene/diphenylethylenediamine (97: 3, v/v) . This solution was coated on the PEDOT: PSS layer to form an active layer of 100 nm. A PDINO layer was covered on the active layer, and then an Al layer of 100 nm was deposited on the PDINO layer to give the title device. The photoactive layer area of the device was 4.5 mm².

Example 9

Manufacture and test of photovoltaic device containing PMOT16

A photovoltaic device having the structure of ITO/ZnO/active layer/MoO₃/Ag, wherein the ITO was the bottom layer and the active layer comprises the PMOT16 made in Example 5. The ITO substrate was treated using the procedures made in Example 7. The ZnO thin film was obtained from the procedures made in Example 9. Subsequently, the substrates were transferred to a N₂-filled glove box. The active layers were prepared from PMOT16: IC-6IDT-IC (1: 1 weight ratio) in chloroform: DIO (99.5: 0.5 volume ratio) with a total concentration of 24 mg mL^-1. Then, a MoO₃ (～10 nm) hole transport layer and Ag (～100 nm) anode were thermally evaporated on the top of the active layer at a pressure of 2× 10^-6 mbar. The device area was 4.5 mm^-2. The IC-6IDT-IC was reported previously by Zhan et al. (Y. Lin, Q. He, F. Zhao, L. Huo, J. Mai, X. Lu, C. -J. Su, T. Li, J. Wang, J. Zhu, Y. Sun, C. Wang, X. Zhan, J. Am. Chem. Soc. 2016, 138, 2973. ) The molecular structure of IC-6IDT-IC can be represented as following.

Comparative Example 5

Manufacture and test of photovoltaic device containing PTh22

A photovoltaic device having the structure of ITO/ZnO/active layer/MoO₃/Ag, wherein the ITO was the bottom layer and the active layer comprises the PMOT16 made in Example 5. The ITO substrate was treated using the procedures made in Example 7. The ZnO thin film was obtained from the procedures made in Example 9. Subsequently, the substrates were transferred to a N₂-filled glove box. The active layers were prepared from PTh22: IC-6IDT-IC (or ITIC) (1: 1 weight ratio) in chloroform: DIO (99.5: 0.5 volume ratio) with a total concentration of 24 mg mL^-1. Then, a MoO₃ (～10 nm) hole transport layer and Ag (～100 nm) anode were thermally evaporated on the top of the active layer at a pressure of 2× 10^-6 mbar. The device area was 4.5 mm^-2. The ITIC was reported previously by Zhan et al. (Y. Lin, J. Wang, Z. -G. Zhang, H. Bai, Y. Li, D. Zhu, X. Zhan, Adv. Mater. 2015, 27, 1170. ) The molecule structure of ITIC can be represented by following.

Example 10

Manufacture and test of photovoltaic device containing PMOT27

A photovoltaic device having the structure of ITO/ZnO/active layer/MoO₃/Ag, wherein the ITO was the bottom layer and the active layer comprises the PMOT27 made in Example 5. The ITO substrate was treated using the procedures made in Example 7. The ZnO thin film was obtained from the procedures made in Example 9. The active layers were prepared from PMOT27: ITIC (1: 1 weight ratio) in chloroform: DIO (99.5: 0.5 volume ratio) with a total concentration of 24 mg mL^-1. Then, a MoO₃ (～10 nm) hole transport layer and Ag (～100 nm) anode were thermally evaporated on the top of the active layer at a pressure of 2× 10^-6 mbar. The device area was 4.5 mm^-2.

Results

Figure 1 shows the conventional device structure in the study, where the ITO coated with a PEDOT: PSS layer is used as the anode, and PDINO/Al is used as the cathode. The normalized absorption spectra of the polymers in CB solution and in film are shown in Figure 2. It was found that the BDT-MOT based polymers showed slight blue shifts of absorption edge in both solution and solid state compared with the control thiophene polymers. PMOT2 and PMOT5 exhibited different absorption pattern at the π-π*band region from 300 to 500 nm when comparing with PBQ-3 and PBDTBDD, respectively, suggesting different charge distributions on BDT backbone with the introduction of 4-alkoxy group. All polymers exhibited a noticeable absorption shoulder peak at longer wavelength in solution (Figure 2) . It was attributed to the aggregation of polymers in solutions at ambient temperature, which was further confirmed by temperature dependent absorptions in o-DCB (Figure 3) . As solution temperature increases, all polymers show decreasing intensity of vibronic shoulder peaks. At 85℃, the vibronic shoulder peaks in MOT polymers (PMOT5 and PMOT2) almost disappeared while the thiophene polymers (PBDTBDD and PBQ-3) still retained a distinct vibronic shoulder peak. We reasoned that the pendant methoxy groups on MOT could help the dissolution of PMOT5 and PMOT2 in solution at high temperature. When casted in film, the absorption peaks and onsets of band edge of four polymers exhibited red shifts of about 10 to 20 nm compared to those in solution. PMOT2 showed a more intense vibronic shoulder peak than that of PBQ-3, which was probably because the 4-alkoxy thiophene could enhance the interchain interactions by non-convalent bonds. Interestingly, both PMOT5 and PMOT2 exhibited higher extinction coefficients on the peak absorption when comparing with the thiophene polymer counterparts in both solution and film, which is possibly owing to the enhancement of interchain interactions. All the photophysical properties are summarized in Table 1.

Table 1. Optical and physical properties of the polymers involved in this work.

The optical band gap of four polymers was determined from the absorption edge in solid state and it was 1.83 eV, 1.78 eV for PMOT5, PMOT2 and 1.82 eV, 1.73 eV for PBDTBDD, PBQ-3, respectively. Clearly, BDT-MOT based polymers exhibited slightly larger bandgaps than that of BDT-T based polymers, which were similar to BDT-F based polymers.

Cyclic voltammetry (CV) was used to evaluate the HOMO and LUMO levels of the polymers by using ferrocene as internal standard. The energy level diagram was depicted in Figure 4. The HOMO/LUMO energy levels are -5.22 eV/-3.21 eV and -5.10 eV/-3.15 eV for PMOT2 and PBQ-3, -5.28 eV/-3.22 eV and -5.16 eV/-3.11 eV for PMOT5 and PBDTBDD, respectively. Both PMOT5 and PMOT2 showed lower HOMO level (ca 0.1 eV) than the thiophene counterparts. For all the polymers, the energy offset of the LUMO energy levels between polymers and PC₇₁BM are larger than 0.3 eV, which indicates that charge transfer between the polymer donor and the fullerene acceptor can be efficient.

In order to investigate the photovoltaic properties of the polymers, conventional structure devices were fabricated with the architecture of indium tin oxide (ITO) /poly (3, 4-ethylenedioxythiophene) : poly (styrenesulfonate) (PEDOT: PSS) /donor polymer: PC₇₁BM/perylene diimides functionalized with amino oxide (PDINO) /Al (Figure 1) . Typical current density–voltage (J–V) curves of PSCs are shown in Figure 5 and the corresponding device parameters are summarized in Table 2.

Table 2. Summary of device parameters of the polymer-fullerene solar cells processed from chlorinated or non-chlorinated solvents under AM1.5G solar radiation (100 mW cm^-2) .

For PMOT5, when processing from o-DCB with 1％DIO as additive, the device showed a V_oc of 0.96 V, a J_sc of 13.45 mA cm^-2, and a FF of 71.4％, leading to a PCE of 9.25％with the D/A ratio of 1: 1.2. In contrast, the thiophene counterpart PBDTBDD exhibited an inferior performance, with a V_oc of 0.84 V, a J_sc of 12.45 mA cm^-2, a FF of 64.6％and PCE of 6.77％ (Table 2) . PMOT2 also showed a higher performance than PBQ-3, with V_oc of 0.88 V vs 0.81 V and PCE of 7.73％vs 6.48％, respectively (Figure 6 and Table 2) . The superior performance of PMOT5 and PMOT2 resulted from larger V_oc and slightly higher FF, which could be attributed to lower HOMO levels and enhanced interchain interactions in PMOT5 and PMOT2. It should be pointed out that the controls PBDTBDD and PBQ-3 showed comparable performance to that reported in literature. The corresponding external quantum efficiency (EQE) spectra of respective champion devices were measured and depicted in Figure 5. It is clear that the polymers were very efficient to convert the photons into electrons in 400-700 nm range. The integrated J_sc from the EQE spectra correlated well with the respective J_sc measured from J-V curve within 5％mismatch (Table 2) .

Most of the high performance donor materials could yield inferior performance when processed from non-halogenated solvents. It is possibly due to the lower solubility in non-halogenated solvents, which affords nonoptimal BHJ morphology. Longer or branching alkyl chains could improve the solubility of the polymers, but hinder the interchain interactions and make the photovoltaic performance improvement in non-halogenated solvents difficult. It is intriguing to find that BDT-MOT based polymers exhibited enhanced inter-chain interactions in solid state while better dissolution ability than the thiophene counterparts at elevating temperatures. We also fabricated PSC devices by employing o-xylene as processing solvent. For PMOT5, when processed from o-xylene with 1％DIO, a V_oc of 0.95 V, J_sc of 13.36 mA cm^-2, FF of 68.9％and PCE up to 8.77％was obtained in the champion device (Figure 5 and Table 2) . Similarly, PMOT2 can also achieve a PCE exceeding 8％with o-xylene and 3％DPE as the processing solvents (Figure 5 and Table 2) . The thiophene based polymers also exhibited inferior performance compared to MOT based polymers from o-xylene (Table 2) . Comparing with the devices processed from o-DCB, the devices from o-xylene just showed a slight decrease on FF. Even without any additives, the PSC of PMOT5 still exhibited a PCE exceeding 8％when processed from o-xylene (Figure 5 and Table 2) . To the best of our knowledge, PMOT5 is one of the few examples that could be processed from o-xylene without any additives with over 8％efficiency at room temperature, which may be suitable for printing electronics fabrication. The EQE spectra of corresponding devices are included in Figure 5d.

The bulk and surface morphology of active layers were investigated by transmission electron microscopy (TEM) (Figure 6) . When processed from o-DCB with DIO additive, both PMOT5: PC₇₁BM and PBDTBDD: PC₇₁BM blends exhibited fine structures with nanofiber morphology, while PMOT5 demonstrated more prominent nanofibrous networks than that of PBDTBDD. It was reported that the interpenetrating nanowires in BHJ solar cells were advantageous for high performance of PSCs. When the processing solvent changed from o-DCB to o-xylene with DIO as additive, PMOT5: PC₇₁BM blend exhibited less obvious nanofiber networks. And the nanofiber network morphology disappeared in PMOT5: PC₇₁BM blend processed from o-xylene without DIO. Such morphology changes might account for the decrease of FF in devices processed from o-xylene.

To demonstrate the general characteristic of MOT moiety on the conjugated polymer solar cells, MOT-polymer: non-fullerene acceptor based photovoltaic devices were fabricated. The MOT polymers, PMOT16 and PMOT27, were used as the electron donor. The non-fullerene molecules, IC-6IDT-IC and ITIC were used as the electron acceptor. The device structure and J-V characteristics of fullerene-free polymer solar cells were shown in Figure 7. The device parameters of fullerene-free polymer solar cells illuminated under AM1.5 with a light intensity of 100 mW cm^-2 were summarized in Table 3. Polymer solar cells using PMOT16 as an electron donor, and IC-6IDT-IC as an electron acceptor, exhibited a V_oc of 0.925 V, a J_sc of 16.13 mA cm^-2, and a FF of 67.31％, resulting in a PCE of 10.04％. To comparison, polymer solar cells using the polymer without MOT side chain (PTh22) were fabricated. The device showed a V_oc of 0.822 V, a Jsc of 15.78 mA cm^-2, and a FF of 72.73％, leading to a PCE of 9.43％. It was found that PMOT16-based devices showed significant larger V_oc than that of PTh22-based devices. To confirm this regularity, another MOT polymer PMOT27, was also employed to fabricate polymer solar cells, in which the non-fullerene molecule was replaced by ITIC. The PMOT27 device showed a V_oc of 0.975 V, a J_sc of 16.85 mA cm^-2, and a FF of 65.4％, leading to a high PCE of 10.75％. To comparison, the PTh22: ITIC device was fabricated. The corresponding device exhibited a V_oc of 0.928 V, a J_sc of 15.31 mA cm^-2, and a FF of 65.59％, resulting in a PCE of 9.75％. It is obviously observed that the PMOT27 device has superior V_oc than the PTh22 device even the IC-6IDT-IC was replaced with ITIC. All these results demonstrate that the MOT-polymer based polymer photovoltaic devices have superior open circuit voltage and power conversion efficiency than the control devices, providing an effective way to fabricate efficient polymer based photovoltaic cells.

Table 3. Summary of device parameters of fullerene-free polymer solar cells measured under the illumination of AM1.5G, 100 mW cm^-2.

It should be appreciated that, the above description is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.

Reference throughout this specification to “an embodiment, ” “some embodiments, ” “one embodiment” , “another example, ” “an example, ” “aspecific example, ” or “some examples, ” means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the phrases such as “in some embodiments, ” “in one embodiment” , “in an embodiment” , “in another example, ” “in an example, ” “in a specific example, ” or “in some examples, ” in various places throughout this specification are not necessarily referring to the same embodiment or example of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that the above embodiments cannot be construed to limit the present disclosure, and changes, alternatives, and modifications can be made in the embodiments without departing from spirit, principles and scope of the present disclosure.

Claims

A donor-acceptor polymer comprising a 4-alkoxy thiophene (AOT) ring connected to the backbone thereof as a conjugated side chain.
The donor-acceptor polymer of claim 1, wherein the 4-alkoxy thiophene (AOT) ring is represented by a formula (I) ,

wherein R₁ is selected from the group consisting of - (CH₂) _mH, -O (CH₂) _mH and -S (CH₂) _mH, in which m is an integer in a range from 1 to 20, and R₂ is - (CH₂) _nH, in which n is an integer in a range from 1 to 12.
The donor-acceptor polymer of claim 1 or 2, wherein the 4-alkoxy thiophene (AOT) ring is connected to a donor moiety on the backbone of the polymer.
The donor-acceptor polymer of claim 3, wherein the molar ratio of 4-alkoxy thiophene (AOT) ring to the donor moiety on the backbone is 1: 1 or 2: 1.
The donor-acceptor polymer of claim 3, wherein the donor moiety on the backbone of the polymer is selected from the group consisting of benzo [3, 4-b] dithiophene, thiophene, benzene and the derivatives thereof.
The donor-acceptor polymer of claim 1 or 2, wherein the acceptor moiety on the backbone of the polymer is selected from the group consisting of benzo [c] [1, 2, 5] thiadiazole, benzo [c] [1, 2, 5] oxadiazole, isoindoline-1, 3-dione, quinoxaline, benzo [d] [1, 2, 3] triazole, thieno [3, 4-c] [1, 2, 5] thiadiazole, thieno [3, 4-b] pyrazine, thieno [3, 4-b] thiophene, benzo [1, 2-c: 4, 5-c'] bis ( [1, 2, 5] thiadiazole) , [1, 2, 5] thiadiazolo [3, 4-g] quinoxaline, pyrazino [2, 3-g] quinoxaline, [3, 3'-biindolinylidene] -2, 2'-dione, diketopyrrolopyrrole, thienopyrroledione, thienoisoindigo and derivatives with unsubstituted or alkyl substituted thiophene or unsubstituted or alkyl substituted thieno [2, 3-b] thiophene on two sides as bridging groups thereof.
The donor-acceptor polymer of claim 1 or 2, wherein the number of the donor-acceptor moieties on the backbone is 10 to 100.
A composition comprising the donor-acceptor polymer of any of claims 1 to 7 blended with a fullerene derivative or a non-fullerene derivative.
The composition of claim 8, wherein the fullerene derivative is selected from the group consisting of PC₆₁BM and PC₇₁BM, the non-fullerene derivative is selected from the group consisting of IC-6IDT-IC and ITIC:
A photovoltaic device comprising the composition of claim 8 or 9.
A method for improving the open-circuit voltage of a donor-acceptor polymer by connecting a 4-alkoxy thiophene (AOT) ring as a conjugated side chain to a donor moiety on the backbone of the polymer.
The method of claim 11, wherein the 4-alkoxy thiophene (AOT) ring is represented by a formula (I) ,

wherein R₁ is selected from the group consisting of - (CH₂) _mH, -O (CH₂) _mH and -S (CH₂) _mH, in which m is an integer in a range from 1 to 20, and R₂ is - (CH₂) _nH, in which n is an integer in a range from 1 to 12.
The method of claim 11 or 12, wherein the molar ratio of 4-alkoxy thiophene (AOT) ring to the donor moiety on the backbone is 1: 1 or 2: 1.
The method of claim 11 or 12, wherein the donor moiety on the backbone of the polymer is selected from the group consisting of benzo [3, 4-b] dithiophene, thiophene, benzene and the derivatives thereof.
The method of claim 11 or 12, wherein the acceptor moiety on the backbone of the polymer is selected from the group consisting of benzo [c] [1, 2, 5] thiadiazole, benzo [c] [1, 2, 5] oxadiazole, isoindoline-1, 3-dione, quinoxaline, benzo [d] [1, 2, 3] triazole, thieno [3, 4-c] [1, 2, 5] thiadiazole, thieno [3, 4-b] pyrazine, thieno [3, 4-b] thiophene, benzo [1, 2-c: 4, 5-c'] bis ( [1, 2, 5] thiadiazole) , [1, 2, 5] thiadiazolo [3, 4-g] quinoxaline, pyrazino [2, 3-g] quinoxaline, [3, 3'-biindolinylidene] -2, 2'-dione, diketopyrrolopyrrole, thienopyrroledione, thienoisoindigo and derivatives with unsubstituted or alkyl substituted thiophene or unsubstituted or alkyl substituted thieno [2, 3-b] thiophene on two sides as bridging groups thereof.