Surfaces and interfaces in sensors and photovoltaic devices

表面和界面控制着电子和光电设备的大部分行为，但当在实验室设计和分析设备时，它们往往被忽略，或者被考虑到最简单的模型中。通常，文献中假定肖特基-莫特近似和安德森近似分别假定金属/半导体和半导体/半导体界面的真空能级排列。尽管它们被广泛使用，但自1947年以来，这些近似一直是已知的不正确的，当时约翰·巴丁指出，由于两种材料之间的化学作用(S)，界面排列将受到半导体禁带内高密度的界面电子态的控制，以及固有的表面态，因为与本体相比，材料表面的配位减少，导致原子的成键几何发生变化。这些态往往会限制费米能级在半导体(S)禁带(S)内的运动，由此产生的电荷在界面附近形成“界面偶极子”，导致真空能级的突然移动。表面的复杂性使沃尔夫冈·保利打趣说：“上帝创造了体积；表面是魔鬼发明的。”*“界面工程”是表面与化学物质的有意反应，或在电子设备的界面处包含薄的中间层，有时是一个分子厚的夹层，以便以有利的方式改变其性能。例如，具有定向偶极矩的物种层可以用来抵消两种半导体之间的能级，或者一种半导体和一种金属之间的能级，这种方式有助于电荷注入或提取。界面工程的另一个应用是影响一种材料在另一种材料上沉积方式的改变。这方面的一个日常例子是一辆刚上过蜡的汽车，沉积在油漆上的水不再扩散并形成一层膜，而是形成了珠子。蜡已被用来“设计”油漆/水界面。同样，放置在一种材料(金属、介质、衬底)上的层可以影响生长在顶部的半导体薄膜的形态。*在本提案中，我们扩大了界面工程的典型定义，以包括将光从一种材料的传播和耦合改变到另一种材料的中间层。*在这里，我们的目标是将我们在这些技术方面的经验应用于三个研究领域：1)使用光学接口工程来实现一种新型的传感器，该传感器可以用于检测暴露于化学、生物和辐射威胁中；2)研究和修改印刷电子传感器中的接口，3)研究和改进无铅钙钛矿太阳电池的界面，通过消除电荷提取势垒来提高电池的效率。

Surfaces and interfaces control much of the behaviour of electronic and optoelectronic devices, yet they are often ignored, or considered with the most simplistic models when devices are designed and analysed in the laboratory. Typically, the Schottky-Mott and Anderson approximations, which assume vacuum level alignment at metal/semiconductor and semiconductor/semiconductor interfaces, respectively, are assumed in the literature. Despite their wide use, these approximations have been known to be incorrect since 1947 when John Bardeen noted that interfacial alignment would be governed by high densities of interfacial electronic states within the semiconductor gap(s), due to chemical interactions between the two materials, as well as inherent surface states, due to reduced coordination and resulting changes in bonding geometries of atoms at the surface of a material, compared to those in the bulk. These states tend to restrict the movement of the Fermi level within the semiconductor(s) gap(s), and the resulting charges localized near the interface form “interface dipoles”, abruptly shifting the vacuum levels. The complexities of the surface caused Wolfgang Pauli to quip, “God made the bulk; surfaces were invented by the devil”.***“Interface Engineering” is the intentional reaction of a surface with chemical species, or the inclusion of thin interlayers sometimes one molecule thick at interfaces in electronic devices in order to modify their properties in advantageous ways. For instance, layers of species with oriented dipole moments can be used to offset the energy levels between two semiconductors, or a semiconductor and a metal, in a way that aids charge injection or extraction. Another application of interface engineering is to affect a change in the way one material deposits on another. An everyday example of this is a freshly-waxed car, where water deposited on the paint no longer spreads out and forms a film, rather, it “beads up”. Wax has been used to “engineer” the paint/water interface. Similarly, layers placed on one material (metal, dielectric, substrate), can affect the morphology of a semiconductor film grown on top.***In this proposal, we have broadened the typical definition of interface engineering to include interlayers that change the propagation and coupling of light from one material to another.***Here we aim to apply our experience with these techniques to three areas of research: 1) using optical interface engineering to enable a new type of sensor that can be use to detect exposure to chemical, biological and radiological threats, 2) studying and modifying the interfaces in printed electronic sensors, and 3) studying and modifying the interfaces in lead-free perovskite solar cells to improve their efficiency through the elimination of charge extraction barriers.**