Donley Carrie L, Zaumseil Jana, Andreasen Jens W, Nielsen Martin M, Sirringhaus Henning, Friend Richard H, Kim Ji-Seon
Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, England.
J Am Chem Soc. 2005 Sep 21;127(37):12890-9. doi: 10.1021/ja051891j.
Spin-coated poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) films of different molecular weights (Mn= 9-255 kg/mol), both in the pristine and annealed state, were studied in an effort to elucidate changes in the polymer packing structure and the effects this structure has on the optoelectronic and charge transport properties of these films. A model based on quantum chemical calculations, wide-angle X-ray scattering, atomic force microscopy, Raman spectroscopy, photoluminescence, and electron mobility measurements was developed to describe the restructuring of the polymer film as a function of polymer chain length and annealing. In pristine high molecular weight films, the polymer chains exhibit a significant torsion angle between the F8 and BT units, and the BT units in neighboring chains are close to one another. Annealing films to sufficiently high transition temperatures allows the polymers to adopt a lower energy configuration in which the BT units in one polymer chain are adjacent to F8 units in a neighboring chain ("alternating structure"), and the torsion angle between F8 and BT units is reduced. This restructuring, dictated by the strong dipole on the BT unit, subsequently affects the efficiencies of interchain electron transfer and exciton migration. Films exhibiting the alternating structure show significantly lower electron mobilities than those of the pristine high molecular weight films, due to a decrease in the efficiency of interchain electron transport in this structure. In addition, interchain exciton migration to low energy weakly emissive states is also reduced for these alternating structure films, as observed in their photoluminescence spectra and efficiencies.
研究了不同分子量（Mn = 9 - 255 kg/mol）的旋涂聚（9,9 - 二正辛基芴 - -alt - 苯并噻二唑）（F8BT）薄膜，包括原始状态和退火状态，以阐明聚合物堆积结构的变化以及该结构对这些薄膜的光电和电荷传输性质的影响。基于量子化学计算、广角X射线散射、原子力显微镜、拉曼光谱、光致发光和电子迁移率测量建立了一个模型，以描述聚合物薄膜作为聚合物链长度和退火的函数的结构重组。在原始的高分子量薄膜中，聚合物链在F8和BT单元之间表现出显著的扭转角，相邻链中的BT单元彼此靠近。将薄膜退火到足够高的转变温度，使聚合物能够采用较低能量的构型，其中一个聚合物链中的BT单元与相邻链中的F8单元相邻（“交替结构”），并且F8和BT单元之间的扭转角减小。这种由BT单元上的强偶极决定的结构重组，随后影响链间电子转移和激子迁移的效率。具有交替结构的薄膜显示出比原始高分子量薄膜显著更低的电子迁移率，这是由于该结构中链间电子传输效率的降低。此外，如在它们的光致发光光谱和效率中观察到的，对于这些交替结构薄膜，链间激子向低能量弱发射态的迁移也减少了。
