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

在无机半导体中，例如硅，电子激发与晶格振动的相互作用是不期望的扰动;它限制电荷载流子迁移率并介导非辐射复合。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种扰动，它移动到中心阶段：一些振动模式非常柔和，并且具有强烈的非谐性，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）通过晶格变形的“云”而局部化，这导致电荷迁移率和激子扩散长度不合需要地小，从而限制了光电器件的性能。我们最近发现的系统中，这种传统的范式不成立，但其中的结构动力学是非常有益的，并介导令人惊讶的快速，长距离的激发运输。这完全违背了为硅等传统半导体开发的模型，因为声子限制了电子传输。该机制涉及振动模式耦合带边缘附近的局域态到带内的高度离域态，然后可以在前所未有的长尺度上传输电荷和能量。这种独特的瞬态离域机制，其中激发能够有效地“冲浪”的结构晶格扭曲，是没有发现在硅中，并首次发现在OSC。我们的目标是在具有软结构动力学的其他功能材料中探索类似的物理，例如杂化有机-无机钙钛矿（HOIP）半导体，2D共轭共价/金属有机框架（COFs/MOFs）和无机陶瓷及离子导体。愿景与抱负：在拟议的计划中，我们的目标是追求这种振动增强运输（VET）制度作为一个通用的范例，实现快速和长期的，范围电子电荷，离子和能量传输在一个广泛的有机和无机，功能材料与软结构动力学。我们将（i）开发新的实验/理论方法，以实现对振动增强传输的基础机制的深刻基本理解，包括识别和介导它的最有效振动模式的分子工程，（ii）设计新的自组装功能材料，其中可以实现超过微米的传输长度尺度，以及（iii）利用这种长的长度尺度，以在广泛的（生物）电子、光电、能量存储和光催化应用中实现新的器件结构和转换器件性能改进。

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.