氟对含噻并[3,2-b]噻吩π桥的苯并三氮唑基共聚物的光伏性能影响
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摘要
以噻并[3,2-b]噻吩(TT)修饰的二维苯并[1,2-b:4,5-b′]二噻吩(BDT)作给电子单元、TT作共轭π桥、苯并[d][1,2,3]三氮唑(BTA)或5,6-二氟苯并[d][1,2,3]三氮唑(FBTA)作缺电子单元,在三(二亚苄基丙酮)二钯(Pd2(dba)3)、三(邻甲苯基)膦(P(o-tol)3)催化剂体系下通过Stille缩合聚合方法制备了宽带隙共聚物PTTBDT-BTA和PTTBDT-FBTA。用核磁共振氢谱(~1 H-NMR)和碳谱(~(13)C-NMR)、元素分析、凝胶渗透色谱(GPC)、热重分析、紫外-可见吸收光谱和循环伏安法等对其进行了表征。系统研究了氟取代对材料的热稳定性、成膜性、吸收光谱、溶液状态下的聚集行为、固态薄膜的光稳定性、能级和光伏性能的影响。研究表明:相比PTTBDT-BTA,氟代聚合物PTTBDT-FBTA失重5%的热分解温度提高了20℃、溶解性明显变差、薄膜态吸光范围稍微变窄、氯苯溶液状态下聚合物链间聚集作用显著增强、薄膜的光稳定性提高且最高分子占有轨道能级(EHOMO)下降了0.10V。光伏性能测试显示氟取代使PTTBDT-FBTA基器件的能量转换效率(PCE)提高了49.3%,这获益于开路电压(UOC)提高了16.9%、短路电流密度(JSC)提高了13.2%和填充因子(FF)提高了11.8%。
Two wide bandgap copolymers,PTTBDT-BTA and PTTBDT-FBTA,have been prepared by the Stille coupling polymerization method in the presence of tris(dibenzylideneacetone)dipalladium(Pd2(dba)3)and tri(o-toyl)phosphine(P(o-tol)3),based on the two dimensional 4,8-bis(5-(2-butyloctyl)thieno[3,2-b]thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene(BDT)as donor(D)moiety,thieno[3,2-b]thiophene(TT)as conjugatedπbridge and benzo[d][1,2,3]triazole(BTA)/5,6-difluorobenzo[d][1,2,3]-triazole(FBTA)as acceptor(A)unit,respectively.Both copolymers were characterized by a set of methods including ~1 H-NMR,~(13)C-NMR,elemental analysis,gel permeation chromatography(GPC),thermogravimetric(TG)analysis,UV-Vis absorption and cyclic voltammetry(CV),etc.And the effects of fluorine on thermal stability,film-forming property,absorption spectra,aggregation ability in chlorobenzene(CB)solution,energy level and photovoltaic performance were investigated.Compared with PTTBDT-BTA,PTTBDT-FBTA showed an increase for decomposition temperature(Td,5% mass-loss)of 20 ℃,decreased solubility,slightly narrowed absorption range,significantly enhanced aggregation in CB solution and a decrease for the highest occupied molecular orbital energy level(EHOMO)of 0.10 eV.The photovoltaic devices were fabricated with a structure of ITO/PEDOT:PSS/active layer/PFN/Al,using PTTBDT-BTA or PTTBDT-FBTA as donor and[6,6]phenyl-C_(61) butyric acid methyl ester(PC_(61) BM)as acceptor,and their photovoltaic properties were investigated under the AM 1.5,100 mW/cm~2.It was found that the optimal device based on fluorinated PTTBDT-FBTA exhibited a 49.3%increase in power conversion efficiency(PCE),which was originated from a 16.9% enhancement of open circuit voltage(UOC),a 13.2%improvement of short circuit current density(JSC)and a 11.8% rise of fill factor(FF)compared with PTTBDT-BTA-based devices.These results demonstrated that fluorination was an effective strategy for tuning the material structure and improving the photovoltaic property.
Two wide bandgap copolymers,PTTBDT-BTA and PTTBDT-FBTA,have been prepared by the Stille coupling polymerization method in the presence of tris(dibenzylideneacetone)dipalladium(Pd2(dba)3)and tri(o-toyl)phosphine(P(o-tol)3),based on the two dimensional 4,8-bis(5-(2-butyloctyl)thieno[3,2-b]thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene(BDT)as donor(D)moiety,thieno[3,2-b]thiophene(TT)as conjugatedπbridge and benzo[d][1,2,3]triazole(BTA)/5,6-difluorobenzo[d][1,2,3]-triazole(FBTA)as acceptor(A)unit,respectively.Both copolymers were characterized by a set of methods including ~1 H-NMR,~(13)C-NMR,elemental analysis,gel permeation chromatography(GPC),thermogravimetric(TG)analysis,UV-Vis absorption and cyclic voltammetry(CV),etc.And the effects of fluorine on thermal stability,film-forming property,absorption spectra,aggregation ability in chlorobenzene(CB)solution,energy level and photovoltaic performance were investigated.Compared with PTTBDT-BTA,PTTBDT-FBTA showed an increase for decomposition temperature(Td,5% mass-loss)of 20 ℃,decreased solubility,slightly narrowed absorption range,significantly enhanced aggregation in CB solution and a decrease for the highest occupied molecular orbital energy level(EHOMO)of 0.10 eV.The photovoltaic devices were fabricated with a structure of ITO/PEDOT:PSS/active layer/PFN/Al,using PTTBDT-BTA or PTTBDT-FBTA as donor and[6,6]phenyl-C_(61) butyric acid methyl ester(PC_(61) BM)as acceptor,and their photovoltaic properties were investigated under the AM 1.5,100 mW/cm~2.It was found that the optimal device based on fluorinated PTTBDT-FBTA exhibited a 49.3%increase in power conversion efficiency(PCE),which was originated from a 16.9% enhancement of open circuit voltage(UOC),a 13.2%improvement of short circuit current density(JSC)and a 11.8% rise of fill factor(FF)compared with PTTBDT-BTA-based devices.These results demonstrated that fluorination was an effective strategy for tuning the material structure and improving the photovoltaic property.
引文
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[22]ALBRECHT S,JANIETZ S,SCHINDLER W,et al.Fluorinated copolymer PCPDTBT with enhanced open-circuit voltage and reduced recombination for highly efficient polymer solar cells[J].J Am Chem Soc,2012,134(36):14932-14944.
[23]ZHANG Yong,ZOU Jingyu,CHEUH C C,et al.Significant improved performance of photovoltaic cells made from a partially fluorinated cyclopentadithiophene/benzothiadiazole conjugated polymer[J].Macromolecules,2012,45(13):5427-5435.
[24]XIAO Zeyun,SUBBIAH J,SUN Kuan,et al.Synthesis and photovoltaic properties of thieno[3,2-b]thiophenyl substituted benzo[1,2-b:4,5-b′]dithiophene copolymers[J].Polym Chem,2014,5(23):6710-6717.
[25]LI Zhengke,LIN Haoran,JIANG Kui,et al.Dramatic performance enhancement for large bandgap thick-film polymer solar cells introduced by a difluorinated donor unit[J].Nano Energy,2015,15:607-615.
[26]KAWASHIMA K,FUKUHARA T,SUDA Y,et al.Implication of fluorine atom on electronic properties,ordering structures,and photovoltaic performance in naphthobisthiadiazole-based semiconducting polymers[J].J Am Chem Soc.,2016,138(32):10265-10275.
[27]KIM J,PARK J B,LEE W H,et al.High-performance fluorine-containing BDT-based copolymer for organic solar cells with a high open circuit voltage[J].J Polym Sci:Part A.Polym Chem,2017,55(15):2506-2512.
[28]ZHANG Qianqian,YAN Liang,JIAO Xuechen,et al.Fluorinated thiophene units improve photovoltaic device performance of donor-acceptor copolymers[J].Chem Mater,2017,29(14):5990-6002.
[29]孙景彪,郭鹏智,同军锋.氟对噻并噻吩-苯并二噻吩基共聚物光伏性能的影响[J].广州化工,2017,45(6):96-101.
[30]HUO Zejuan,ZHANG Peng,LI Jianfeng,et al.Wide bandgap conjugated polymers based on bithiophene and benzotriazole for bulk heterojunction solar cells:Thiophene versus thieno[3,2-b]thiophene asπ-conjugated spacers[J].J Macromol Sci A,2017,54(9):565-574.
[31]FULLER L S,IDDON B,SMITH K A.Thienothiophenes:Part 2.Synthesis,metallation and bromine→lithium exchange reactions of thieno[3,2-b]thiophene and its polybromo derivatives[J].J Chem Soc Perkin Trans 1,1997,29(13):3465-3470.
[32]HUANG Fei,WU Hongbin,WANG Deli,et al.Novel electroluminescent conjugated polyelectrolytes based on polyfluorene[J].Chem Mater,2004,16(4):708-716.
[33]TONG Junfeng,AN Lili,LI Jianfeng,et al.Large branched alkylthienyl bridged naphtho[1,2-c:5,6-c′]bis[1,2,5]-thiadiazole-containing low bandgap copolymers:Synthesis and photovoltaic application[J].J Macromol Sci A,2017,54(3):176-185.
[34]MIN Jie,ZHANG Zhiguo,ZHAGN Siyuan,et al.Conjugated side-chain-isolated donor-acceptor copolymers based on benzo[1,2-b:4,5-b′]dithiophene-alt-thipheneylbenzotriazole:Synthesis and photovoltaic properties[J].Chem Mater,2012,24(16):3247-3254.
[35]ZHU Dangqiang,BAO Xichang,ZHU Qianqian,et al.Thienothiophene-based copolymers for high-performance solar cells,employing different orientations of the thiazole group as aπbridge[J].Energy Environ Sci,2017,10(2):614-620.
[36]POMMEREHNE J,VESTWEBER H,GUSS W,et al.Efficient two layer leds on a polymer blend basis[J].Adv Mater,1995,7(6):551-554.
[37]QI Boyuan,WANG Jizheng.Open-circuit voltage in organic solar cells[J].J Mater Chem,2012,22(46):24315-24325.
[38]GUADAL N S,BERLINGHOF M,KASSAR T,et al.Controlling additive behavior to reveal an alternative morphology formation mechanism in polymer:Fullerene bulk-heterojunctions[J].J Mater Chem A,2016,4(11):16136-16147.
[39]李自东,赵晓礼,杨小牛.聚合物太阳能电池器件热稳定性的研究进展[J].应用化学,2016,33(1):1-17.
[40]GAO Peili,TONG Junfeng,GUO Pengzhi,et al.Medium band gap conjugated polymers from thienoacene derivatives and pentacyclic aromatic lactam as promising alternatives of poly(3-hexylthiophene)in photovoltaic application[J].J Polym Sci:Part A.Polym Chem,2018,56(1):85-95.
[41]LEE H S,SONG H G,JUNG H,et al.Effects of backbone planarity and tightly packed alkyl chains in the donoracceptor polymers for high photostability[J].Macromolecules,2016,49(20):7844-7856.
[2]李永舫.聚合物太阳能电池高效共轭聚合物给体和富勒烯受体光伏材料[J].高分子通报,2011(10):33-49.
[3]ZHAO Wenchao,LI Sunsun,YAO Huifeng,et al.Molecular optimization enables over 13%efficiency in organic solar cells[J].J Am Chem Soc,2017,139(21):7148-7151.
[4]TONG Junfeng,LI Jianfeng,ZHANG Peng,et al.Naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-based conjugated polymers consisting of oligothiophenes for efficient polymer solar cells[J].Polymer,2017,121(14):183-195.
[5]GUO Pengzhi,LUO Guoping,SU Qiang,et al.Boosting up performance of inverted photovoltaic cells from bis(alkylthien-2-yl)dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4′,5′-b′]dithiophene-based copolymers by advantageous vertical phase separation[J].ACS Appl Mater Interfaces,2017,9(12):10937-10945.
[6]HE Zhicai,ZHONG Chengmei,SU Shijian,et al.Enhanced power-conversion efficiency in polymer solar cells using an inverted device structure[J].Nat Photonics,2012,6(9):591-595.
[7]ZHANG Zhiguo,WANG Jizheng.Structures and properties of conjugated donor-acceptor copolymers for solar cell applications[J].J Mater Chem,2012,22(10):4178-4187.
[8]CAI Ping,CHEN Zhenhui,ZHANG Lianjie,et al.An extendedπ-conjugated area of electron donating units in D-A structured polymers towards high-mobility field-effect transistors and highly efficient polymer solar cells[J].J Mater Chem C,2017,5(11):2786-2793.
[9]WANG Xiao,SUN Yeping,CHEN Song,et al.Effects ofπ-conjugated bridges on photovoltaic properties of donor-π-acceptor conjugated copolymers[J].Macromolecules,2012,45(6):1208-1216.
[10]KIM J H,PARK J B,XU Fei,et al.Effect ofπ-conjugated bridges of TPD-based medium bandgap conjugated copolymers for efficient tandem organic photovoltaic cells[J].Energy Environ Sci,2014,7(12):4118-4131.
[11]INTEMANN J J,YAO Kai,LI Yongxi,et al.Highly efficient inverted organic solar cells through material and interfacial engineering of indacenodithieno[3,2-b]thiophene-based polymers and devices[J].Adv Funct Mater,2014,24(10):1465-1473.
[12]PAN Xuexue,XIONG Wentao,LIU Tao,et al.Influence of 2,2-bithiophene and thieno[3,2-b]thiophene units on the photovoltaic performance of benzodithiophene-based wide-bandgap polymers[J].J Mater Chem C,2017,5(18):4471-4479.
[13]UNAY H,dos REIS BENATTO G A,BELIATIS M J,et al.High stability of benzotriazole and benzodithiophene containing medium band-gap polymer solar cell[J].Sol Energy Mater Sol Cells,2018,174:433-444.
[14]UY R L,YAN Liang,LI Wentao,et al.Tuning fluorinated benzotriazole polymers through alkylthio substitution and selenophene incorporation for bulk heterojunction solar cells[J].Macromolecules,2014,47(7):2289-2295.
[15]KIM B,YEOM H R,YUN M H,et al.A selenophene analogue of PCDTBT:Selective fine-tuning of LUMO to lower of the bandgap for efficient polymer solar cells[J].Macromolecules,2012,45(21):8658-8664.
[16]ZHANG Qianqian,KELLY M A,BAUER N,et al.The curious case of fluorination of conjugated polymers for solar cells[J].Acc Chem Res,2017,50(9):2401-2409.
[17]LECLERC N,CHAVEZ P,IBRAIKULOV O A,et al.Impact of backbone fluorination onπ-conjugated polymers in organic photovoltaic devices:A review[J].Polymers,2016,8(1):11.
[18]ZHOU Huaxing,YANG Liqiang,STUART A C,et al.Development of fluorinated benzothiadiazole as a structural unit for a polymer solar cell of 7%efficiency[J].Angew Chem,2011,50(13):3051-3054.
[19]IYER A,BJORGAARD J,ANDERSON T,et al.Quinoxaline-based semiconducting polymers:Effect of fluorination on the photophysical,thermal,and charge transport properties[J].Macromolecules,2012,45(16):6380-6389.
[20]PRICE S C,STUART A C,YANG Liqiang,et al.Fluorine substituted conjugated polymer of medium band gap yields7%efficiency in polymer-fullerene solar cells[J].J Am Chem Soc,2011,133(12):4625-4631.
[21]ZHAO Li,LU Jianping,TSE S C,et al.Synthesis and applications of difluorobenzothiadiazole based conjugated polymers for organic photovoltaics[J].J Mater Chem,2011,21(9):3226-3233.
[22]ALBRECHT S,JANIETZ S,SCHINDLER W,et al.Fluorinated copolymer PCPDTBT with enhanced open-circuit voltage and reduced recombination for highly efficient polymer solar cells[J].J Am Chem Soc,2012,134(36):14932-14944.
[23]ZHANG Yong,ZOU Jingyu,CHEUH C C,et al.Significant improved performance of photovoltaic cells made from a partially fluorinated cyclopentadithiophene/benzothiadiazole conjugated polymer[J].Macromolecules,2012,45(13):5427-5435.
[24]XIAO Zeyun,SUBBIAH J,SUN Kuan,et al.Synthesis and photovoltaic properties of thieno[3,2-b]thiophenyl substituted benzo[1,2-b:4,5-b′]dithiophene copolymers[J].Polym Chem,2014,5(23):6710-6717.
[25]LI Zhengke,LIN Haoran,JIANG Kui,et al.Dramatic performance enhancement for large bandgap thick-film polymer solar cells introduced by a difluorinated donor unit[J].Nano Energy,2015,15:607-615.
[26]KAWASHIMA K,FUKUHARA T,SUDA Y,et al.Implication of fluorine atom on electronic properties,ordering structures,and photovoltaic performance in naphthobisthiadiazole-based semiconducting polymers[J].J Am Chem Soc.,2016,138(32):10265-10275.
[27]KIM J,PARK J B,LEE W H,et al.High-performance fluorine-containing BDT-based copolymer for organic solar cells with a high open circuit voltage[J].J Polym Sci:Part A.Polym Chem,2017,55(15):2506-2512.
[28]ZHANG Qianqian,YAN Liang,JIAO Xuechen,et al.Fluorinated thiophene units improve photovoltaic device performance of donor-acceptor copolymers[J].Chem Mater,2017,29(14):5990-6002.
[29]孙景彪,郭鹏智,同军锋.氟对噻并噻吩-苯并二噻吩基共聚物光伏性能的影响[J].广州化工,2017,45(6):96-101.
[30]HUO Zejuan,ZHANG Peng,LI Jianfeng,et al.Wide bandgap conjugated polymers based on bithiophene and benzotriazole for bulk heterojunction solar cells:Thiophene versus thieno[3,2-b]thiophene asπ-conjugated spacers[J].J Macromol Sci A,2017,54(9):565-574.
[31]FULLER L S,IDDON B,SMITH K A.Thienothiophenes:Part 2.Synthesis,metallation and bromine→lithium exchange reactions of thieno[3,2-b]thiophene and its polybromo derivatives[J].J Chem Soc Perkin Trans 1,1997,29(13):3465-3470.
[32]HUANG Fei,WU Hongbin,WANG Deli,et al.Novel electroluminescent conjugated polyelectrolytes based on polyfluorene[J].Chem Mater,2004,16(4):708-716.
[33]TONG Junfeng,AN Lili,LI Jianfeng,et al.Large branched alkylthienyl bridged naphtho[1,2-c:5,6-c′]bis[1,2,5]-thiadiazole-containing low bandgap copolymers:Synthesis and photovoltaic application[J].J Macromol Sci A,2017,54(3):176-185.
[34]MIN Jie,ZHANG Zhiguo,ZHAGN Siyuan,et al.Conjugated side-chain-isolated donor-acceptor copolymers based on benzo[1,2-b:4,5-b′]dithiophene-alt-thipheneylbenzotriazole:Synthesis and photovoltaic properties[J].Chem Mater,2012,24(16):3247-3254.
[35]ZHU Dangqiang,BAO Xichang,ZHU Qianqian,et al.Thienothiophene-based copolymers for high-performance solar cells,employing different orientations of the thiazole group as aπbridge[J].Energy Environ Sci,2017,10(2):614-620.
[36]POMMEREHNE J,VESTWEBER H,GUSS W,et al.Efficient two layer leds on a polymer blend basis[J].Adv Mater,1995,7(6):551-554.
[37]QI Boyuan,WANG Jizheng.Open-circuit voltage in organic solar cells[J].J Mater Chem,2012,22(46):24315-24325.
[38]GUADAL N S,BERLINGHOF M,KASSAR T,et al.Controlling additive behavior to reveal an alternative morphology formation mechanism in polymer:Fullerene bulk-heterojunctions[J].J Mater Chem A,2016,4(11):16136-16147.
[39]李自东,赵晓礼,杨小牛.聚合物太阳能电池器件热稳定性的研究进展[J].应用化学,2016,33(1):1-17.
[40]GAO Peili,TONG Junfeng,GUO Pengzhi,et al.Medium band gap conjugated polymers from thienoacene derivatives and pentacyclic aromatic lactam as promising alternatives of poly(3-hexylthiophene)in photovoltaic application[J].J Polym Sci:Part A.Polym Chem,2018,56(1):85-95.
[41]LEE H S,SONG H G,JUNG H,et al.Effects of backbone planarity and tightly packed alkyl chains in the donoracceptor polymers for high photostability[J].Macromolecules,2016,49(20):7844-7856.