Wan Yan, Wiederrecht Gary P, Schaller Richard D, Johnson Justin C, Huang Libai
College of Chemistry , Beijing Normal University , Beijing 100875 , China.
Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , United States.
J Phys Chem Lett. 2018 Dec 6;9(23):6731-6738. doi: 10.1021/acs.jpclett.8b02944. Epub 2018 Nov 12.
Singlet fission provides a promising route for overcoming the Shockley-Queisser limit in solar cells using organic materials. Despite singlet fission dynamics having been extensively investigated, the transport of the various intermediates in relation to the singlet and triplet states is largely unknown. Here we employ temperature-dependent ultrafast transient absorption microscopy to image the transport of singlet fission intermediates in single crystals of tetracene. These measurements suggest a mobile singlet fission intermediate state at low temperatures, with a diffusion constant of 36 cms at 5 K, approaching that for the free singlet excitons, which we attribute to the spin-entangled correlated triplet pair state [TT]. These results indicate that [TT] could transport with a similar mechanism as the bright singlet excitons, which has important implications in designing materials for singlet fission and spintronic applications.
单线态裂变提供了一条很有前景的途径，可用于克服使用有机材料的太阳能电池中的肖克利-奎塞尔极限。尽管单线态裂变动力学已得到广泛研究，但与单重态和三重态相关的各种中间体的传输情况在很大程度上仍不清楚。在这里，我们采用温度依赖的超快瞬态吸收显微镜来成像并四苯单晶中单线态裂变中间体的传输。这些测量结果表明，在低温下存在一个可移动的单线态裂变中间态，在5 K时扩散常数为36 cm²/s，接近自由单线态激子的扩散常数，我们将其归因于自旋纠缠的相关三重态对态[TT]。这些结果表明，[TT]可以通过与明亮单线态激子类似的机制进行传输，这对于设计用于单线态裂变和自旋电子应用的材料具有重要意义。
