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

该方案将开发高效率的薄膜金属卤化物钙钛矿型发光二极管(LED)。标准的无机LED，如蓝铟-氮化镓，依赖于p掺杂和n掺杂空穴和电子注入层的能力，并构建多量子阱结构，其中电子/空穴被限制并发光，所有这些都在异质外延结构中。这使得红色和蓝色可以接近热力学效率运行，但绿色(氮化物显示出大量损失)还不能。相比之下，有机发光二极管(OLED)被组装成不同分子材料的堆栈，选择带边位置以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进行的“掺杂”被用来辅助电极注射，但在整体上是不可能的。尽管OLED已商业化用于显示，但它需要漂移场来克服注入势垒，表现出非常低的载流子迁移率，并在远高于发射带隙的电压下工作。正如我们在上面的“记录”中所概述的，该团队成功地将OLED架构应用于金属卤化物钙钛矿制成的薄膜LED。这项工作中的关键部件将被开发：(A)限制e-h对的2D/3D超晶格，但具有可调的“井深”，以最小化驱动电压要求，将用于实现良好的电荷捕获；(B)钙钛矿型隔离层，使载流子远离传输层，以避免猝灭；(C)和(D)空穴和电子传输层，通过化学调谐和掺杂(确保与掺杂相关的陷阱/猝灭状态与发射钙钛矿区域足够远)在钙钛矿界面上进行欧姆注入，并在两个电极上进行欧姆接触。这需要在先进的表征技术的支持下，在一系列材料化学、材料加工和半导体工程任务上取得进展。发光二极管(LED)是当今许多显示器中使用的设备，如电视和手机中使用的那些，也可以越来越多地用于照明。对于这些应用，需要红光、绿光和蓝光LED。然而，节能和稳定的绿色发光LED的开发尤其具有挑战性。这项提议的重点是开发基于一种被称为金属卤化物钙钛矿的材料的高效绿色发射设备。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，解决为此类设备提供便利的工程问题。这项工作可能会产生新的商业上可行的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：为美国博士后研究员提供有机和金属有机合成方面的经验和一系列物理表征方法，并有机会参与密切的国际研究所间合作；帮助支持女性和未被充分代表的少数族裔学生的教育和培训。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.