退火温度对高分子薄膜中掺杂小分子的结晶和光谱学响应特性的影响

研究了小分子材料苝(EPPTC)在高分子材料聚芴衍生物(F8BT)薄膜中的结晶特性随温度的变化规律，以及由此引起的两种材料构成的异质结中激发复合体荧光发射特性的变化。实验结果表明，退火温度的升高会加强小分子与高分子材料在固体薄膜中的相分离。而小分子相在析出过程中，会在分子间作用力诱导下发生π—π团聚而结晶。晶体的尺度在达到小分子材料相变温度之前基本上随温度升高而增大。这一过程将破坏异质结结构，减小小分子与高分子间的接触面积，从而降低激发复合体的形成及其荧光发射强度。同时，由高分子向小分子发生的能量转移过程被显著减弱，而小分子晶相的荧光发射成分提高。这对于调控有机半导体异质结结构，进而改善光伏器件性能具有重要意义。

Effect of Annealing Temperature on the Crystallization and Spectroscopic Response of a Small-Molecule Semiconductor Doped in Polymer Film

The crystallization properties of the perylene (EPPTC) molecules doped in the solid film of the derivative of polyfluorene (F8BT) at different annealing temperatures, as well as the consequently induced spectroscopic response of the exciplex emission in the heterojunction structures, were studied in the present paper. Experimental results showed that the phase separation between the small and the polymer molecules in the blend film is enhanced with increasing the annealing temperature, which leads to the crystallization of the EPPTC molecules due to the strong π—π stacking. The size of the crystal phase increases with increasing the annealing temperature. However, this process weakens the mechanisms of the heterojunction configuration, thus, the total interfacial area between the small and the polymer molecules and the amount of exciplex are reduced significantly in the blend film. Meanwhile, the energy transfer from the polymer to the small molecules is also reduced. As a result, the emission from the exciplex becomes weaker with increasing the annealing temperature, whereas the stronger emission from the polymer molecules and from the crystal phase of the small molecules can be observed. These experimental results are very important for understanding and tailoring the organic heterojunction structures. Furthermore, this provides photophysics for improving the performance of photovoltaic or solar cell devices.