Surfaces and interfaces in sensors and photovoltaic devices

表面和界面控制着电子和光电子设备的大部分行为，但它们经常被忽视，或者在实验室设计和分析设备时使用最简单的模型来考虑。通常，Schottky-Mott和Anderson近似，分别假设在金属/半导体和半导体/半导体界面的真空水平对准，在文献中被假设。尽管它们被广泛使用，但自1947年以来，这些近似已经被认为是不正确的，当时John Bardeen注意到，由于两种材料之间的化学相互作用，以及固有的表面状态，由于配位减少，导致材料表面原子的键合几何形状的变化，与本体相比，界面排列将由半导体间隙内高密度的界面电子态控制。这些状态倾向于限制费米能级在半导体间隙内的运动，并且在界面附近产生的电荷形成“界面偶极子”，突然改变真空能级。表面的复杂性使沃尔夫冈·泡利（Wolfgang Pauli）调侃道：“上帝创造了体积；表面是魔鬼发明的。”“界面工程”是指表面与化学物质发生有意的反应，或者在电子设备的界面处包含薄的中间层（有时是一个分子厚），以便以有利的方式改变其性能。例如，具有定向偶极矩的物质层可以用来抵消两个半导体之间的能级，或者半导体和金属之间的能级，从而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沉积在另一种材料上的方式的变化。一个日常的例子是一辆刚打过蜡的汽车，在那里，沉积在油漆上的水不再散开并形成一层膜，而是“珠状”。蜡被用来“改造”油漆/水的界面。同样地，在一种材料（金属、电介质、衬底）上放置的层可以影响在其上生长的半导体膜的形态。在这个提议中，我们扩大了界面工程的典型定义，包括改变光从一种材料到另一种材料的传播和耦合的中间层。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)使用光学界面工程来实现一种新型传感器，可用于检测化学，生物和辐射威胁；2)研究和修改印刷电子传感器的界面；3)研究和修改无铅钙钛矿太阳能电池的界面，通过消除电荷提取障碍来提高其效率。

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.