Defects in halide perovskites: The lattice as a boojum?
- PDF / 1,094,714 Bytes
- 7 Pages / 585 x 783 pts Page_size
- 92 Downloads / 227 Views
ntroduction Defects can make or break a material, as taught in most materials science courses. Controlling defects (also called imperfections) is often of decisive importance for the use of a given material, at least for a certain function. The relevant defect densities for a given material depend on the function that is affected or enabled by them (e.g., optical emission, mechanical strength, magnetic hardness of superconductors, electrical transport and conductance). For semiconductors especially, relevant densities are in the parts per million range or less, making their control a major chemical challenge. After great efforts, materials such as Ge and Si were cleaned up, and they could be doped to form desired defects in a controllable fashion. This has been the case for all semiconductors that we use hitherto, including organic and amorphous (statically disordered) ones. Halide perovskites present a surprise, in that they can result from solution-based near-room-temperature synthesis, with defect densities that, for single crystals, approach those that are thermodynamically dictated (at room temperature in the 109–1011 cm–3 parts per trillion, or ppt range).1,2 This feature is accompanied by the unusual, though not unique, difficulty of extrinsically doping them.3,4 If such doping shows any effects, it is with orders of magnitude lower doping efficiency than for Si or GaAs.
Alongside the developing realization of the special features of HaPs, extensive work has been done to describe their behavior with the help of the established model of static point defects, which, for all tetrahedrally bonded semiconductors, has not only helped describe experimental observations, but also has shown clear predictive power. The model is used for computations of electronic energy levels5,6 (the level at which the defect will donate or accept an electron) and to interpret experimental results. Rather than providing a review of all of the work that has been done on defects in HaPs, we refer to a number of recent reviews7–11 to bring the reader no more than two clicks away from such results. Here, we will first give a summary of basic information on defects, provide salient HaP-relevant data, and then move to the unusual behavior and properties of defects in HaPs.
What are defects? Defects are imperfections in the order of the lattice structure of a solid. Together with the bandgap and its electronic structure, the defects in a semiconducting material control its optoelectronic properties. Defects can promote charge transport by generating extra free charge carriers (doping defects) or can impede it by trapping (which can affect the optical absorption and emission from the material) or scattering the carriers.
Sujit Kumar, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Israel; [email protected] Gary Hodes, Department of Materials and Interfaces, Weizmann Institute of Science, Israel; [email protected] David Cahen, Weizmann Institute of Science, Israel, and Bar-Ilan University, Israel; dav
Data Loading...
