Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
J Am Chem Soc. 2010 Sep 15;132(36):12698-703. doi: 10.1021/ja1042462.
Organic photovoltaic devices are currently studied due to their potential suitability for flexible and large-area applications, though efficiencies are presently low. Here we study pentacene/C(60) bilayers using transient optical absorption spectroscopy; such structures exhibit anomalously high quantum efficiencies. We show that charge generation primarily occurs 2-10 ns after photoexcitation. This supports a model where charge is generated following the slow diffusion of triplet excitons to the heterojunction. These triplets are shown to be present from early times (<200 fs) and result from the fission of a spin-singlet exciton to form two spin-triplet excitons. These results elucidate exciton and charge generation dynamics in the pentacene/C(60) system and demonstrate that the tuning of the energetic levels of organic molecules to take advantages of singlet fission could lead to greatly enhanced photocurrent in future OPVs.
有机光伏器件因其在柔性和大面积应用方面的潜在适用性而受到研究，尽管目前效率较低。在这里，我们使用瞬态光学吸收光谱研究并五苯/C(60)双层结构；这种结构表现出异常高的量子效率。我们表明，电荷的产生主要发生在光激发后 2-10 纳秒。这支持了一种模型，即电荷的产生是在三重态激子缓慢扩散到异质结之后发生的。从早期(<200fs)就可以看出这些三重态的存在，并且是由单线态激子裂分形成两个自旋三重态激子而产生的。这些结果阐明了并五苯/C(60)体系中激子和电荷产生的动力学，并表明对有机分子能级的调整以利用单线态裂变，可能会导致未来有机光伏器件中光电流的大幅增强。
