Optical properties of graphite

Optical constants of graphite for ordinary and extraordinary waves are modeled with a modified Lorentz-Drude model with frequency-dependent damping. The model enables the shape of the spectral line to vary over a range of broadening functions with similar kernels and different wings, the broadening type being its adjustable parameter. The model parameters are determined by the acceptance-probability-controlled simulated annealing algorithm. Good agreement with the experimental data is obtained in the entire investigated spectral range (0.12-40 eV for ordinary wave and 2.1-40 eV for extraordinary wave). The significant discrepancies between the experimental data obtained by the reflectance measurements and the electron-energy-loss spectroscopy data are analyzed in details. Inconsistency in terms of unsatisfied Kramers-Kronig relations is discovered in the index of refraction data derived from reflectance measurements, and a method for correcting the data is proposed. © 1999 American Institute of Physics.published_or_final_versio

Crystal structure prediction of (quasi-)two-dimensional lead halide perovskites

Two-dimensional lead halide perovskites are promising materials for optoelectronics due to the tunability of their properties with the number of lead halide layers and the choice of an organic spacer. Physical understanding for the rational design of materials primarily requires knowledge of crystal structure. 2D lead halide perovskites are usually prepared in the form of films complicating the experimental determination of structure. To enable theoretical studies of experimentally unresolvable structures as well as high-throughput virtual screening, we present an algorithm for crystal structure prediction of lead halide perovskites. Using automatically prepared classical potential we show that our algorithm enables fast access to a structure that can be used for further first-principles studies

A Novel Cryo-controlled Growth Technique for High Performance Organometal Halide Perovskite Solar Cells

The recent trend of the high-performance perovskite solar cell (PSC) is based on multi-component perovskite materials. The reproducible perovskite growth techniques are crucial for acquiring mixed halide perovskite films with precise stoichiometry, desirable morphology, and low defect density

Roadmap on commercialization of metal halide perovskite photovoltaics

Perovskite solar cells (PSCs) represent one of the most promising emerging photovoltaic technologies due to their high power conversion efficiency. However, despite the huge progress made not only in terms of the efficiency achieved, but also fundamental understanding of the relevant physics of the devices and issues which affect their efficiency and stability, there are still unresolved problems and obstacles on the path toward commercialization of this promising technology. In this roadmap, we aim to provide a concise and up to date summary of outstanding issues and challenges, and the progress made toward addressing these issues. While the format of this article is not meant to be a comprehensive review of the topic, it provides a collection of the viewpoints of the experts in the field, which covers a broad range of topics related to PSC commercialization, including those relevant for manufacturing (scaling up, different types of devices), operation and stability (various factors), and environmental issues (in particular the use of lead). We hope that the article will provide a useful resource for researchers in the field and that it will facilitate discussions and move forward toward addressing the outstanding challenges in this fast-developing field

Outdoor stability testing of perovskite solar cells: Necessary step toward real-life applications

Perovskite solar cells (PSCs) are among the most promising emerging photovoltaic technologies, due to their high efficiency, comparable to that of silicon solar cells. However, concerns about the stability of these devices remain, despite great progress achieved in recent years. To address these concerns, comprehensive investigations of their stability under realistic operating conditions are necessary. In this Perspective, we will discuss the outdoor testing of PSCs. We will first introduce degradation mechanisms relevant for intrinsic stability, as well as degradation mechanisms due to ambient exposure. Effective encapsulation of PSCs will then be discussed, followed by a summary of achieved progress and discussion of testing protocols and equipment to make outdoor testing more accessible. Finally, challenges and future outlook will be discussed