Collaborative Research: Predictive theory, synthesis and characterization of a new type of transparent conductor without doping

非技术描述：光伏太阳能电池、智能窗户、发光二极管、触摸屏传感器、电子纸和平板显示器等技术需要一个既是电导体又是光学透明的关键部件，即所谓的透明导体。这些化合物是独一无二的，因为透明度和导电性通常是化合物的互斥性质。事实上，光学透明度(如窗户玻璃)通常与电绝缘有关，而导电性(如铜或金)通常与光学不透明的金属有关。已知的透明导体，如掺锡的氧化铟，是通过在透明绝缘体中注入电导而制成的。该研究小组的目标是通过设计金属的透明度来开发一种新型的透明导体--金属陶瓷。这为设计有别于电子性质的光学性质提供了一种新的方法。这一方法具有令人兴奋的智力影响，因为它建议了一种通用的逆向设计方法--从用作计算材料选择的“过滤器”的基于科学的设计原则开始，然后识别出代表性的例子，然后进行实验室验证。科罗拉多州立大学博尔德分校和西北大学的研究生和博士后有机会参与这项尖端研究工作。技术说明：透明导电氧化物是构成现代技术基础的矛盾材料，如触摸屏、平板显示器、太阳能电池板等。目前发现新透明导体的方法依赖于重掺杂透明绝缘体，直到它们成为导体。不幸的是，由于所谓的“掺杂瓶颈”的存在，宽禁带材料本质上对电荷的掺杂具有抵抗力。也就是说，在绝缘体中引入高浓度的自由载流子通常会导致自发形成具有极性的结构缺陷，以补偿有意掺杂的结构缺陷。因此，在寻找和优化这种技术关键的透明导电氧化物材料方面的进展一直令人沮丧地缓慢。研究小组提出了一种相反的、可能更有成效的设计金属透明度的替代方案，即寻找符合一套具有特定能带结构的“设计原则”的化合物。这种本征透明导体的设计规则是：(I)识别具有金属能带结构的化合物；(Ii)它具有较低的等离子体频率和(Iii)跨费米能级的低带间光吸收，以及(Iv)将合成和表征应用于‘类中最好的’化合物，这里是Ba-Nb-O。金属透明导体最明显的优点是，它们的导电性来自于其高的本征载流子浓度。提案中复杂的理论-实验方法能够实现更有效的进展，作为以前使用的试错法的替代方法。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。

Non-technical description: Technologies such as photovoltaic solar cells, smart windows, light emitting diodes, touch-screen sensors, electronic papers, and flat panel displays require for their operation a critical component that is both an electrical conductor and optically transparent, the so-called transparent conductors. These compounds are unique, as transparency and conductivity are generally mutually exclusive properties of compounds. Indeed, optical transparency (as in window glass) is generally associated with electrical insulation, whereas electrical conductivity (such as in copper or gold) is generally associated with optically opaque metals. Known transparent conductors such as indium oxide doped with Sn are made by instilling conductivity in transparent insulators. The research team aims to develop a novel family of transparent conductors - metallic ceramics - by designing transparency in metals. This presents a new method to design optical properties as distinct from electronic properties. The approach has an exciting intellectual impact as it suggests a general approach for inverse design - starting from science-based design principles used as 'filters' for computational material selection, followed by identification of representative examples and then laboratory validation. The graduate students and postdocs of CU Boulder and Northwestern Universities are given exciting opportunities to participate in this cutting edge research effort.Technical description: Transparent conducting oxides are paradoxical materials that form the basis of modern day technologies, such as touch screens, flat panel displays, solar panels, etc. The current method of choice for discovering new transparent conductors have relied on heavily doping transparent insulators until they become conducting. Unfortunately, wide band gap materials are intrinsically resistant to doping of charges because of the existence of so-called 'doping bottlenecks'. Namely, the introduction of a high concentration of free carriers into insulators generally leads to the spontaneous formation of structural defects with polarity that compensate that of the intentional doping. Consequently, the progress in finding and optimizing such technologically critical transparent conducting oxide materials has been frustratingly slow. The research team proposes an opposite, and likely more fruitful alternative of designing transparency in metals by looking for compounds that obey a set of 'design principles' with specific band structures. The design rules for such intrinsic transparent conductors are: (i) identify a compound with metallic band structure; such that (ii) it has low plasma frequency and (iii) low inter-band optical absorption across the Fermi level, and (iv) apply synthesis and characterization to the 'best of class' compounds, here Ba-Nb-O. The most visible advantage of metallic transparent conductors is that their conductivity comes from their high, indigenous carrier concentration. The complex theory-experimental approach in the proposal enables more efficient progress as alternative to the previously used trial-and-error method.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.