ECCS-EPSRC: Superlattice Architectures for Efficient and Stable Perovskite LEDs

该提案将开发具有高效率的薄膜金属卤化物钙钛矿发光二极管（LED）。标准无机LED（例如蓝色铟镓氮化物）依赖于p掺杂和n掺杂空穴和电子注入层的能力，以及构建多量子阱结构的能力，在所述多量子阱结构内电子/空穴被限制并发光，所有这些都在异质外延结构中。这允许红色和蓝色接近热力学效率操作，但还不能用于绿色（其中氮化物显示出显著的损失）。相比之下，有机LED（OLED）被组装为不同分子材料的堆叠，其中带边缘位置被选择为允许电子或空穴传输到复合区。通过与氧化还原活性添加剂的电荷转移反应的“掺杂”用于辅助从电极的注入，但在本体中是不可能的。尽管OLED已商业化用于显示器，但OLED需要漂移场来克服注入势垒，显示出非常低的载流子迁移率，并且在远高于发射带隙的电压下工作。正如我们在上面的“跟踪记录”中所概述的，该团队成功地将OLED架构用于由金属卤化物钙钛矿制成的薄膜LED。在这项工作中的关键组成部分将开发：（a）2D/3D超晶格，限制e-h对，但具有可调的“阱深度”，以最小化驱动电压的要求，将在这些中使用，以实现良好的电荷捕获，（B）钙钛矿的间隔层，保持电荷载流子远离传输层，以避免淬火;（c）和（d）空穴传输层和电子传输层，其被设计为通过化学调节和掺杂（确保与掺杂相关的陷阱/猝灭状态离发射性钙钛矿区足够远）在钙钛矿界面处提供欧姆注入，并被设计为在两个电极处提供欧姆接触。这需要在一系列材料化学，材料加工和半导体工程任务方面取得进展，并以先进的表征技术为基础。 发光二极管（LED）是用于当今许多显示器的设备，例如用于电视和手机的显示器，并且还可以越来越多地用于照明。对于这些应用，需要红色、绿色和蓝色发光LED。然而，节能且稳定的绿色发光LED的开发尤其具有挑战性。该提案的重点是开发基于一类称为金属卤化物钙钛矿的材料的高效绿色发光器件。特别是，剑桥大学（英国）、牛津大学（英国）和科罗拉多大学（美国）的团队将相互合作，解决促进此类设备的工程问题。这项工作可能会导致新的商业上可行的LED技术，以及金属卤化物钙钛矿的其他新应用。除了对英国和美国新兴的半导体行业产生潜在影响外，该项目还将：为美国博士后研究人员提供有机和金属有机合成经验以及一系列物理表征方法，并有机会参与密切的国际机构间合作;该奖项反映了NSF的法定使命，并通过使用基金会的知识产权进行评估，被认为值得支持。优点和更广泛的影响审查标准。

This proposal will develop thin-film metal-halide perovskite light-emitting diodes (LEDs) with high efficiencies. Standard inorganic LEDs, such as blue indium-gallium nitride, rely on the ability to p-dope and n-dope the hole- and electron-injecting layers, and to construct multi-quantum-well structures within which electrons/holes are confined and emit light, all in a heteroepitaxial structure. This allows close to thermodynamic efficiency operation for red and blue, but not yet for green (where nitrides show substantial losses). In contrast, organic LEDs (OLEDs) are assembled as stacks of different molecular materials, with band-edge positions selected to allow electron or hole transport to the recombination zone. ‘Doping’ through charge-transfer reactions with redox-active additives is used to assist injection from electrodes, but is not possible in the bulk. Though commercialized for displays, OLEDs require drift fields to overcome injection barriers, show very low carrier mobilities, and operate at voltages well above the emission bandgap. As outlined in our ‘track-record’ above, the team successfully adopted the OLED architecture for thin-film LEDs made with metal-halide perovskites. The critical components in this work will be developing: (a) a 2D/3D superlattice that confines e-h pairs, but with a tuneable “well depth” in order to minimize drive voltage requirements will be used in these to achieve good charge trapping, (b) spacer layers of perovskite that keep charge carriers away from the transport layers to avoid quenching; (c) and (d) hole- and electron-transport layers engineered to give ohmic injection at the perovskite interfaces, through chemical tuning and doping (ensuring that trap/quenching states associated with doping are far enough away from the emissive perovskite zone) and designed to give ohmic contacts at the two electrodes. This requires advances across a range of materials chemistry, materials processing, and semiconductor engineering tasks, underpinned by advanced characterization techniques. Light-emitting diodes (LEDs) are devices that are used in many of today’s displays, such as those used in televisions and cell phones, and can also increasingly in lighting. For these applications red-, green-, and blue-emitting LEDs are needed. However, green-emitting LEDs that are energy efficient and that are stable are particularly challenging to develop. This proposal is focused on developing efficient green-emitting devices based on a class of materials known as metal-halide perovskites. In particular, teams at the Universities of Cambridge (UK), Oxford (UK), and Colorado (USA) will collaborate with one another to solve engineering problems facilitating such devices. This work may result in new commercially viable LED technologies, as well as other new applications for metal-halide perovskites. As well as having potential impacts on the emerging semiconductor industry in the UK and USA, this project will: provide a US postdoctoral researcher with experience in organic and metal-organic synthesis and a range of physical characterization methods, and with the opportunity to participate in a close international inter-institute collaboration; and help support the education and training of women and underrepresented minority students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.