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。”

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.