Department of Materials Science and Engineering and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Department of Chemistry and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
J Am Chem Soc. 2015 Oct 7;137(39):12565-79. doi: 10.1021/jacs.5b06462. Epub 2015 Sep 22.
As effective building blocks for high-mobility transistor polymers, oligothiophenes are receiving attention for polymer solar cells (PSCs) because the resulting polymers can effectively suppress charge recombination. Here we investigate two series of in-chain donor-acceptor copolymers, PTPDnT and PBTInT, based on thieno[3,4-c]pyrrole-4,6-dione (TPD) or bithiopheneimide (BTI) as electron acceptor units, respectively, and oligothiophenes (nTs) as donor counits, for high-performance PSCs. Intramolecular S···O interaction leads to more planar TPD polymer backbones, however backbone torsion yields greater open-circuit voltages for BTI polymers. Thiophene addition progressively raises polymer HOMOs but marginally affects their band gaps. FT-Raman spectra indicate that PTPDnT and PBTInT conjugation lengths scale with nT catenation up to n = 3 and then saturate for longer oligomer. Furthermore, the effects of oligothiophene alkylation position are explored, revealing that the alkylation pattern greatly affects film morphology and PSC performance. The 3T with "outward" alkylation in PTPD3T and PBTI3T affords optimal π-conjugation, close stacking, long-range order, and high hole mobilities (0.1 cm(2)/(V s)). These characteristics contribute to the exceptional ∼80% fill factors for PTPD3T-based PSCs with PCE = 7.7%. The results demonstrate that 3T is the optimal donor unit among nTs (n = 1-4) for photovoltaic polymers. Grazing incidence wide-angle X-ray scattering, transmission electron microscopy, and time-resolved microwave conductivity measurements reveal that the terthiophene-based PTPD3T blend maintains high crystallinity with appreciable local mobility and long charge carrier lifetime. These results provide fundamental materials structure-device performance correlations and suggest guidelines for designing oligothiophene-based polymers with optimal thiophene catenation and appropriate alkylation pattern to maximize PSC performance.
作为高性能晶体管聚合物的有效构建模块，齐聚噻吩因其能有效抑制电荷复合而受到聚合物太阳能电池（PSC）的关注。在此，我们基于噻吩[3,4-c]吡咯-4,6-二酮（TPD）或双噻吩亚胺（BTI）分别作为电子受体单元，研究了两个系列的链内给体-受体共聚物 PTPDnT 和 PBTInT，以及作为给体单元的齐聚噻吩（nTs），以获得高性能 PSC。分子内 S···O 相互作用导致 TPD 聚合物主链更加平面化，然而，主链扭转使 BTI 聚合物具有更大的开路电压。噻吩的加入逐渐提高聚合物 HOMO，但对其能带隙影响不大。傅里叶变换拉曼光谱（FT-Raman）表明，PTPDnT 和 PBTInT 的共轭长度与 nT 的连接长度成正比，当 n 达到 3 时增加，然后对于更长的寡聚物达到饱和。此外，还探索了齐聚噻吩烷基化位置的影响，表明烷基化模式极大地影响了薄膜形态和 PSC 性能。在 PTPD3T 和 PBTI3T 中具有“向外”烷基化的 3T 提供了最佳的π共轭、紧密堆积、长程有序和高空穴迁移率（0.1 cm²/（V s））。这些特性有助于 PTPD3T 基 PSC 获得高达 80%的填充因子，其光电转换效率（PCE）为 7.7%。结果表明，在 nTs（n=1-4）中，3T 是光伏聚合物的最佳给体单元。掠入射广角 X 射线散射、透射电子显微镜和时间分辨微波电导率测量表明，基于三噻吩的 PTPD3T 共混物保持高结晶度，具有可观的局部迁移率和长电荷载流子寿命。这些结果提供了基本的材料结构-器件性能相关性，并为设计具有最佳噻吩连接和适当烷基化模式的基于齐聚噻吩的聚合物提供了指导，以最大限度地提高 PSC 性能。
