Harnessing vibration-induced enhancement of transport in functional materials with soft structural dynamics

在无机半导体中，如硅，电子激发与晶格振动的相互作用是一种不受欢迎的微扰；它限制了载流子的迁移率，并促成了非辐射复合。在具有非共价键的低维功能材料中，结构动力学不仅仅是一个扰动，它移动到中心阶段：一些振动模式非常软并且强烈的非谐，因此电子过程发生在强烈波动的结构景观中。传统观点认为，由此产生的强电子-振动耦合也是有害的：例如，在有机半导体(OSC)中，电子电荷和中性电子-空穴对(激子)被晶格变形的“云”局域化，这导致电荷迁移率和激子扩散长度过小，从而限制了光电子器件的性能。我们最近发现了一些系统，在这些系统中，这种传统的范式并不成立，但结构动力学是非常有益的，它调节着令人惊讶的快速、远距离的激发传输。这完全与为硅等传统半导体开发的模型背道而驰，因为声子限制了电子的传输。这一机制涉及振动模式，将带边缘附近的局域态耦合到带内的高度离域状态，然后这些状态可以在前所未有的长尺度上传输电荷和能量。这种独特的瞬时离域机制，在这种机制中，激发能够有效地在结构晶格扭曲的波上冲浪，这在硅中没有发现，并首次在OSC中发现。我们的目标是探索其他具有软结构动力学的功能材料中的类似物理，例如杂化有机-无机钙钛矿(HOIP)半导体、2D共轭共价/金属有机骨架(COFS/MOF)以及无机陶瓷和离子导体。愿景和抱负：在拟议的计划中，我们的目标是将这种振动增强传输(VET)机制作为一种通用范例，在一大类具有软结构动力学的有机和无机功能材料中实现快速和远程的电子电荷、离子和能量传输。我们将(I)开发新的实验/理论方法来深入了解振动增强传输的基础机制，包括识别和分子工程中最有效的振动模式，(Ii)设计新的自组装功能材料，其中传输长度超过微米的尺度是可以实现的，以及(Iii)利用这种长尺度来在(生物)电子、光电、能量存储和光催化的广泛应用中实现新的器件结构和转换性器件性能的改进。

In inorganic semiconductors, such as silicon, the interaction of electronic excitations with lattice vibrations is an undesirable perturbation; it limits charge carrier mobilities and mediates non-radiative recombination. In low-dimensional functional materials with non-covalent bonding the structural dynamics is not a mere perturbation, it moves centre-stage: Some vibrational modes are very soft and strongly anharmonic so that electronic processes occur in a strongly fluctuating structural landscape. The traditional view is that the resulting strong electron-vibrational coupling is also detrimental: In organic semiconductors (OSCs), for example, electronic charges and neutral electron-hole pairs (excitons) are localized by a 'cloud' of lattice deformations, which causes charge mobilities and exciton diffusion lengths to be undesirably small, thus limiting performance of optoelectronic devices. We have recently discovered systems in which this traditional paradigm does not hold, but in which the structural dynamics is highly beneficial and mediates surprisingly fast, long-range excitation transport. This runs completely against models developed for traditional semiconductors such as silicon, for which phonons limit electronic transport. The mechanism involves vibrational modes coupling localized states near the band edges to highly delocalised states within the bands that can then transport charges and energy over unprecedentedly long length scales. This unique transient delocalization regime, in which excitations are effectively able to "surf on the waves" of structural lattice distortions, is not found in silicon and was first discovered in OSCs. Our goal is to explore similar physics in other functional materials with soft structural dynamics, such as hybrid organic-inorganic perovskite (HOIP) semiconductors, 2D conjugated covalent/metal organic frameworks (COFs/MOFs) and inorganic ceramics and ion conductors.VISION AND AMBITION: In the proposed programme we aim to pursue this vibration-enhanced transport (VET) regime as a general paradigm for achieving fast and long-range electronic charge, ion and energy transport in a broad class of organic and inorganic, functional materials with soft structural dynamics. We will (i) develop new experimental/theoretical methodologies to achieve a deep fundamental understanding of the underpinning mechanisms for the vibration-enhanced transport, including identification and molecular engineering of the most effective vibrational modes mediating it, (ii) design new self-assembled functional materials in which transport length scales exceeding micrometers are achievable and (iii) exploit such long length scales to enable new device architectures and transformational device performance improvements in a broad range of (bio)electronic, optoelectronic, energy storage and photocatalytic applications.