†Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States.
‡Department of Chemistry and the James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States.
J Am Chem Soc. 2015 May 6;137(17):5759-69. doi: 10.1021/ja513002h. Epub 2015 Apr 21.
Four new low-bandgap electron-accepting polymers-poly(4,10-bis(2-butyloctyl)-2-(2-(2-ethylhexyl)-1,1-dioxido-3-oxo-2,3-dihydrothieno[3,4-d]isothiazol-4-yl)thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H-dione) (PNSW); poly(4,10-bis(2-butyloctyl)-2-(5-(2-ethylhexyl)-4,6-dioxo-5,6-dihydro-4H-thieno[3,4-c]pyrrol-1-yl)thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione) (PNTPD); poly(5-(4,10-bis(2-butyloctyl)-5,11-dioxo-4,5,10,11-tetrahydrothieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinolin-2-yl)-2,9-bis(2-decyldodecyl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone) (PNPDI); and poly(9,9-bis(2-butyloctyl)-9H-fluorene-bis((1,10:5,6)2-(5,6-dihydro-4H-cyclopenta[b]thiophene-4-ylidene)malonitrile)-2-(2,3-dihydrothieno[3,4-b][1,4]dioxine)) (PECN)-containing thieno[2',3':5',6']pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione and fluorenedicyclopentathiophene dimalononitrile, were investigated to probe their structure-function relationships for solar cell applications. PTB7 was also investigated for comparison with the new low-bandgap polymers. The steady-state, ultrafast dynamics and nonlinear optical properties of all the organic polymers were probed. All the polymers showed broad absorption in the visible region, with the absorption of PNPDI and PECN extending into the near-IR region. The polymers had HOMO levels ranging from -5.73 to -5.15 eV and low bandgaps of 1.47-2.45 eV. Fluorescence upconversion studies on the polymers showed long lifetimes of 1.6 and 2.4 ns for PNSW and PNTPD, respectively, while PNPDI and PECN showed very fast decays within 353 and 110 fs. PECN exhibited a very high two-photon absorption cross section. The electronic structure calculations of the repeating units of the polymers indicated the localization of the molecular orbitals in different co-monomers. As the difference between the electron affinities of the co-monomers in the repeating units decreases, the highest occupied and lowest unoccupied molecular orbitals become more distributed. All the measurements suggest that a large difference in the electron affinities of the co-monomers of the polymers contributes to the improvement of the photophysical properties necessary for highly efficient solar cell performance. PECN exhibited excellent photophysical properties, which makes it to be a good candidate for solar cell device applications.
四种新型低带隙电子受体聚合物——聚（4,10-双（2-丁基辛基）-2-（2-（2-乙基己基）-1,1-二氧代-3-氧代-2,3-二氢噻吩[3,4-d]异噻唑-4-基）噻吩[2',3':5,6]吡啶并[3,4-g]噻吩[3,2-c]异喹啉-5,11(4H,10H-二酮）（PNSW）；聚（4,10-双（2-丁基辛基）-2-（5-（2-乙基己基）-4,6-二氧代-5,6-二氢-4H-噻吩[3,4-c]吡咯-1-基）噻吩[2',3':5,6]吡啶并[3,4-g]噻吩[3,2-c]异喹啉-5,11(4H,10H）-二酮）（PNTPD）；聚（5-（4,10-双（2-丁基辛基）-5,11-二氧代-4,5,10,11-四氢噻吩[2',3':5,6]吡啶并[3,4-g]噻吩[3,2-c]异喹啉-2-基）-2,9-双（2-癸基十二烷基）蒽[2,1,9-def:6,5,10-d'e'f']二异喹啉-1,3,8,10(2H,9H）-四酮）（PNPDI）和聚（9,9-双（2-丁基辛基）-9H-芴-双（（1,10:5,6）2-（5,6-二氢-4H-环戊[b]噻吩-4-亚基）丙二腈）-2-（2,3-二氢噻吩[3,4-b][1,4]二恶烷））（PECN）-含噻吩[2',3':5',6']吡啶并[3,4-g]噻吩[3,2-c]异喹啉-5,11(4H,10H）-二酮和芴二环戊噻吩二丙二腈，用于探究它们在太阳能电池应用中的结构-功能关系。还研究了 PTB7 以与新型低带隙聚合物进行比较。所有有机聚合物的稳态、超快动力学和非线性光学性质都进行了探测。所有聚合物在可见光区域都表现出宽吸收，其中 PNPDI 和 PECN 的吸收延伸到近红外区域。聚合物的 HOMO 能级范围为-5.73 至-5.15 eV，带隙为 1.47-2.45 eV。聚合物的荧光上转换研究表明，PNSW 和 PNTPD 的寿命分别为 1.6 和 2.4 ns，而 PNPDI 和 PECN 的寿命则在 353 和 110 fs 内非常快地衰减。PECN 表现出非常高的双光子吸收截面。聚合物重复单元的电子结构计算表明，分子轨道在不同共聚单体中发生了定位。随着重复单元中共聚单体的电子亲和力差异的减小，最高占据和最低未占据分子轨道变得更加分布。所有的测量结果表明，聚合物中共聚单体的电子亲和力差异较大有助于提高高效太阳能电池性能所需的光物理性质。PECN 表现出优异的光物理性质，使其成为太阳能电池器件应用的良好候选材料。
