Sneyd Alexander J, Fukui Tomoya, Paleček David, Prodhan Suryoday, Wagner Isabella, Zhang Yifan, Sung Jooyoung, Collins Sean M, Slater Thomas J A, Andaji-Garmaroudi Zahra, MacFarlane Liam R, Garcia-Hernandez J Diego, Wang Linjun, Whittell George R, Hodgkiss Justin M, Chen Kai, Beljonne David, Manners Ian, Friend Richard H, Rao Akshay
Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
Department of Chemistry, University of Victoria, Victoria, BC V8P 5C2, Canada.
Sci Adv. 2021 Aug 4;7(32). doi: 10.1126/sciadv.abh4232. Print 2021 Aug.
Efficient energy transport is desirable in organic semiconductor (OSC) devices. However, photogenerated excitons in OSC films mostly occupy highly localized states, limiting exciton diffusion coefficients to below ~10 cm/s and diffusion lengths below ~50 nm. We use ultrafast optical microscopy and nonadiabatic molecular dynamics simulations to study well-ordered poly(3-hexylthiophene) nanofiber films prepared using living crystallization-driven self-assembly, and reveal a highly efficient energy transport regime: transient exciton delocalization, where energy exchange with vibrational modes allows excitons to temporarily re-access spatially extended states under equilibrium conditions. We show that this enables exciton diffusion constants up to 1.1 ± 0.1 cm/s and diffusion lengths of 300 ± 50 nm. Our results reveal the dynamic interplay between localized and delocalized exciton configurations at equilibrium conditions, calling for a re-evaluation of exciton dynamics and suggesting design rules to engineer efficient energy transport in OSC device architectures not based on restrictive bulk heterojunctions.
在有机半导体（OSC）器件中，高效的能量传输是理想的。然而，OSC薄膜中的光生激子大多占据高度局域化的状态，这将激子扩散系数限制在约10 cm/s以下，扩散长度限制在约50 nm以下。我们使用超快光学显微镜和非绝热分子动力学模拟来研究通过活性结晶驱动自组装制备的有序聚（3-己基噻吩）纳米纤维薄膜，并揭示了一种高效的能量传输机制：瞬态激子离域，即与振动模式的能量交换使激子在平衡条件下能够暂时重新进入空间扩展状态。我们表明，这使得激子扩散常数高达1.1±0.1 cm/s，扩散长度为300±50 nm。我们的结果揭示了平衡条件下局域化和离域化激子构型之间的动态相互作用，呼吁重新评估激子动力学，并提出设计规则，以在不基于限制性体异质结的OSC器件架构中设计高效的能量传输。
