Engineering interfacial gates for enhanced functionality in organic optoelectronic devices

有机半导体是一类新型的电子材料，目前正受到人们的关注，用于下一代信息显示、高效固态照明和低成本太阳能转换应用。这些材料因其高性能以及与最终可实现低成本器件和系统制造的高吞吐量、卷对卷加工技术的兼容性而备受关注。在所有这些应用中，增强器件设计和整体高性能的关键组件是设计在电激发(如发光器件，LED)或光激发(如太阳能电池)下产生的分子激发态的限制和运动的能力。与更常见的载流子(电子或空穴)的情况不同，到目前为止，它被证明很难通过施加外部电压来影响电荷中性分子激发态的运动。这项拟议的工作将开发新的、特别设计的接口，能够充当门，允许将分子激发态输送到设备中的特定位置。在LED中，这可以提高发光效率，而在太阳能电池中，这可以使用简单的设备架构将分子激发态更有效地转换为可用电流。技术：包括光伏电池(OPV)和发光器件(OLED)在内的许多有机光电子器件的设计都受到这些材料激子特性的严重影响。有机半导体的激发导致形成紧密结合的激子，这些激子通过热和电两种方式抵抗解离。在OPV中，激子必须解离到它的组成部分载流子中，才能产生光电流。解离通常是在电子给体-受体界面上实现的，这需要从光生成点到解离点的有效激子扩散。在OLED中也存在类似的激子管理挑战，关键是将激子限制在器件发射层，并避免激子和极化子密度之间的空间重叠，以减少非辐射猝灭过程。在最先进的设备中，与激子管理相关的问题通常通过影响设备体系结构的大规模更改来处理，这虽然有效，但避免了解决负责传输的实际过程。例如，在OPV中，激子收集通过使用被称为体异质结的混合施主-受主结构来最大化。在OLED中，限制通常是通过使用宽能隙阻挡层来实现的。这一提议形成了一种替代的、更直接的方法来应对激子管理的挑战。工作的中心是使用直接影响负责扩散的激子能量转移速率的体系结构。初步结果表明，构建单向激子门是可能的，它克服了正常扩散的限制，允许激子直接传输。这种方法的新奇之处在于使用了直接解决激子迁移缺陷的器件设计概念。在解决器件操作中固有的激子挑战方面，直接激子传输的能力对OPV和OLED的设计具有广泛的影响。

Organic semiconductors are a novel class of electronic materials currently receiving attention for next generation information display, highly efficient solid-state lighting, and low-cost solar energy conversion applications. These materials are of interest for their high performance and also for their compatibility with high throughput, roll-to-roll processing techniques that could ultimately enable low-cost device and system fabrication. In all of these applications, a critical component to enhanced device design and overall high performance is the ability to engineer the confinement and motion of molecular excited states created under electrical (as in a light-emitting device, LED) or optical excitation (as in a solar cell). Unlike the more familiar case of charge carriers (electrons or holes), it has to date proved difficult to affect the motion of charge-neutral molecular excited states through the application of an external voltage. The proposed work will develop novel, specially designed interfaces capable of acting as gates, permitting the funneling of molecular excited states to specific locations in a device. In an LED, this could permit an enhanced efficiency of luminescence, while in a solar cell this could permit a more efficient conversion of molecular excited states into useable electric current using simple device architectures. Overall, the proposed work will lead to the design of advanced optoelectronic devices for light-emission and photoconversion, among others.Technical:The design of many organic optoelectronic devices including photovoltaic cells (OPVs) and light-emitting devices (OLEDs) is heavily impacted by the excitonic character of these materials. Excitation of an organic semiconductor leads to the formation of tightly bound excitons that resist dissociation by both thermal and electric means. In OPVs, the exciton must be dissociated into its component charge carriers in order to generate a photocurrent. Dissociation is typically realized at an electron donor-acceptor interface, necessitating efficient exciton diffusion from the point of photogeneration to the point of dissociation. A similar challenge in exciton management exists in OLEDs, where it is critical to confine excitons to the device emissive-layer, and avoid spatial overlap between the exciton and polaron densities to reduce non-radiative quenching processes. In state-of-the-art devices, problems related to exciton management are often dealt with by affecting large-scale changes in device architecture, which while effective, avoid addressing the actual processes responsible for transport. For instance, in OPVs, exciton harvesting is maximized through the use of blended donor-acceptor structures known as a bulk heterojunctions. In OLEDs, confinement is often realized through the use of wide-energy gap blocking layers. This proposal forges an alternate and more direct approach to the challenge of exciton management. Work is centered on the use of architectures that directly impact the rates of excitonic energy transfer responsible for diffusion. Preliminary results suggest that it is possible to construct one-way excitonic gates, which overcome the limitations of normal diffusion and permit direct exciton transport. The novelty in this approach is in the use of device design concepts that directly address deficiencies in exciton migration. The ability to direct exciton transport has broad implications for the design of OPVs and OLEDs in terms of addressing the fundamental excitonic challenges inherent in device operation.