Institute for Solar and Sustainable Energies (RISE), Gwangju Institute of Science and Technology (GIST) , 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61002, Republic of Korea.
Department of Chemistry and Centre for Plastic Electronics, Imperial College London , Exhibition Rd., London, SW7 2AZ, U.K.
ACS Appl Mater Interfaces. 2017 Jul 19;9(28):24011-24019. doi: 10.1021/acsami.7b04214. Epub 2017 Jul 10.
Fluorine (F) substitution on conjugated polymers in polymer solar cells (PSCs) has a diverse effect on molecular properties and device performance. We present a series of three D-A type conjugated polymers (PBT, PFBT, and PDFBT) based on dithienothiophene and benzothiadiazole units with different numbers of F atoms to explain the influence of F substitution by comparing the molecular interactions of the polymers and the recombination kinetics in PSCs. The preaggregation behavior of PFBT and PDFBT in o-DCB at the UV-vis absorption spectra proves that both polymers have strong intermolecular interactions. Besides, more closely packed structures and change into face-on orientation of fluorinated polymers are observed in polymer:PCBM blends by GIXD which is beneficial for charge transport and, ultimately, for current density in PSCs (4.3, 13.0, and 14.5 mA cm for PBT, PFBT, and PDFBT, respectively). Also, the introduction of F atoms on conjugated backbones affects the recombination kinetics by suppressing bimolecular recombination, thereby improving the fill factor (0.41, 0.68, and 0.69 for PBT, PFBT, and PDFBT, respectively). Consequently, the PCE of PSCs reached 7.3% without any additional treatment (annealing, solvent additive, etc.) in the polymer containing difluorinated BT (PDFBT) that is much higher than nonfluorinated BT (PBT ∼ 1%) and monofluorinated BT (PFBT ∼ 6%).
在聚合物太阳能电池（PSCs）中，共轭聚合物上的氟（F）取代对分子性质和器件性能有多种影响。我们提出了一系列基于二噻吩并噻吩和苯并噻二唑单元的 D-A 型共轭聚合物（PBT、PFBT 和 PDFBT），它们具有不同数量的 F 原子，通过比较聚合物的分子相互作用和 PSCs 中的复合动力学，解释 F 取代的影响。PFBT 和 PDFBT 在 o-DCB 中的预聚集行为在紫外-可见吸收光谱中证明了两种聚合物都具有很强的分子间相互作用。此外，通过 GIXD 观察到氟化聚合物的结构更加紧密堆积并转变为面取向，这有利于电荷传输，最终提高 PSCs 的电流密度（PBT、PFBT 和 PDFBT 分别为 4.3、13.0 和 14.5 mA cm）。此外，共轭主链上 F 原子的引入通过抑制双分子复合来影响复合动力学，从而提高填充因子（PBT、PFBT 和 PDFBT 分别为 0.41、0.68 和 0.69）。因此，在含有二氟化 BT（PDFBT）的聚合物中，无需进行任何额外处理（退火、溶剂添加剂等），PSC 的 PCE 就达到了 7.3%，远高于非氟化 BT（PBT∼1%）和单氟化 BT（PFBT∼6%）。
