Department of Physics, Imperial College London, London, UK, SW7 2BW.
Dalton Trans. 2009 Dec 7(45):10000-5. doi: 10.1039/b910675h. Epub 2009 Oct 6.
Transient and steady state optical spectroscopies were used to study thin films made from a series of polyfluorene polymers blended with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) in order to determine the influence of polymer ionisation potential on photoinduced charge separation. We find that the energy of the charge separated state DeltaE(CS), given by the energy difference between the ionisation potential of the polymer and the electron affinity of the fullerene, must be smaller than a threshold value of about 1.6 eV for charge separation to occur. When DeltaE(CS) is greater than this threshold, PCBM triplet formation is observed in preference to charge pair generation. If DeltaE(CS) is similar to the threshold value, both PCBM triplet formation and charge separation occur in the blend film, with a tendency for charge separation to dominate over PCBM triplet formation as PCBM concentration increases. The mechanism of triplet formation is believed to be energy transfer to the PCBM singlet state followed by intersystem crossing. The threshold value of DeltaE(CS) is found to be similar to the PCBM singlet energy.
采用瞬态和稳态光学光谱法研究了一系列聚芴聚合物与[6,6]-苯基 C61 丁酸甲酯（PCBM）共混制成的薄膜，以确定聚合物电离势对光致电荷分离的影响。我们发现，电荷分离态DeltaE(CS)的能量（由聚合物的电离势与富勒烯的电子亲和力之间的能量差给出）必须小于约 1.6 eV 的阈值，才能发生电荷分离。当DeltaE(CS)大于此阈值时，观察到 PCBM 三重态形成而不是电荷对生成。如果 DeltaE(CS)与阈值值相似，则在共混膜中既发生 PCBM 三重态形成又发生电荷分离，随着 PCBM 浓度的增加，电荷分离倾向于占主导地位而不是 PCBM 三重态形成。三重态形成的机制被认为是能量转移到 PCBM 单线态，然后是系间窜跃。发现 DeltaE(CS)的阈值与 PCBM 单线态能量相似。
