#passivation

Peering inside perovskite: 3D imaging reveals how passivation boosts solar cell efficiency

Perovskite solar cells have garnered widespread attention as a low-cost, high-efficiency alternative to conventional silicon photovoltaics. However, defects in perovskite films impede charge transport, resulting in energy loss and compromised operational stability. Passivation treatments and their challenges One solution to this problem is "passivation treatment"—a process that adds chemicals such as simple salts or organic molecules to the film. These small molecules or ions latch onto defects in the perovskite material, preventing the defects from interfering with electrical flow. Unfortunately, verifying the internal efficacy of various passivation treatments remains challenging since most characterization techniques only probe the surface or provide averaged macroscopic information.

Passivation is the removal of exogenous ferrous material from the surface of stainless steel parts, creating a hard chrome “passive” layer to provide protection to the stainless steel, leaving the surface ferrous metal free. Two different paths to proper passivation can be used with proven success in ACT's systems: nitric or citric passivation. Care should be taken to research your passivation requirements, and to understand the ramifications of using nitric acid in production facilities. For this reason, the bulk of ACT’s passivation equipment and systems are engineered around citric passivation. ACT has a strong business relationship with Stellar Solutions, www.citrisurf.com, the world leader in citric passivation formulary. ACT’s passivation equipment and systems and Citrisurf® chemistries are ideal pairings for safe and cost effective passivation of stainless steel parts in any environment.

Polycrystalline formamidinium lead iodide (FAPbI3), widely used for making perovskite-based solar cells due to its superior optoelectronic properties, suffers from defects in its crystalline structure. Researchers from the Gwangju Institute of Science and Technology (GIST) introduced hexagonal polytype perovskite (6H) into the cubic polytype (3C) FAPbI3 to reduce these defects, which led to improved power conversion efficiency and operational stability of perovskite solar cells, when compared with their existing counterparts. Solar energy is a promising way of reducing our dependence on fossil-fuel-based energy resources and opt for cleaner energy forms. Over the years, solar cells that can harness this renewable energy have undergone significant progress. Metal-halide perovskite has gained significant attention as a promising light-absorbing material for solar cells due to their exceptional optoelectronic properties which enable them to efficiently generate energy from sunlight.

When water vapor meets metal, the resulting corrosion can lead to mechanical problems that harm a machine's performance. Through a process called passivation, it also can form a thin inert layer that acts as a barrier against further deterioration. Either way, the exact chemical reaction is not well understood on an atomic level, but that is changing thanks to a technique called environmental transmission electron microscopy (TEM), which allows researchers to directly view molecules interacting on the tiniest possible scale. Professor Guangwen Zhou -- a faculty member at Binghamton University, State University of New York's Thomas J. Watson College of Engineering and Applied Science -- has been probing the secrets of atomic reactions since joining the Department of Mechanical Engineering in 2007. Along with collaborators from the University of Pittsburgh and the Brookhaven National Laboratory, he has studied the structural and functional properties of metals and the process of making "green" steel.

Electronic self-passivation of single vacancy in black phosphorus

NUS scientists discovered that a two-dimensional (2D) semiconducting material, known as black phosphorus (BP), exhibits an electronic self-passivation phenomenon by re-arranging its vacancy defects. This may potentially enhance the charge mobility of the material and its analogs.

2D semiconductors with high carrier mobility are essential for the development of ultra-thin, high-speed and energy-efficient electronics and optoelectronics devices. However, many of the existing materials synthesis and device fabrication processes used for 2D semiconductors inevitably introduce surface defects, particularly vacancies with dangling bonds. These defects often act as undesirable sinks for charge carriers and nonradiative recombination centers of photoexcited electron-hole pairs, limiting device performance. Therefore, effective passivation of these surface vacancies in high-mobility 2D semiconductor materials is vital to maintain their high-performance device characteristics. BP is a type of high-mobility 2D material with numerous uses in optoelectronic and photovoltaic applications. As it comprises a single element, it displays unique defect passivation behaviors which are different from other 2D semiconductors made of two or more elements (for example, metal chalcogenides).

Constructive molecular configurations for surface-defect passivation of perovskite photovoltaics

Materials scientists aim to enable surface-trap-mediated nonradiative charge recombination to engineer highly efficient metal-halide perovskite photovoltaics (solar cells). Since unproductive charge recombination at surface defects can limit the efficiency of hybrid perovskite solar cells, scientists can passivate the defects (induce an acid-base chemical treatment) using small molecular binding. The ionic character of perovskite lattice can allow molecular defect passivation through interactions between functional groups and surface defects. However, there exists a lack of in-depth understanding on how molecular configurations can influence passivation effectiveness to facilitate rational molecular design.

In a new report on Science, Rui Wang and an interdisciplinary research team in the departments of Physics, Materials Science & Engineering, Nanoengineering, Chemistry & Biochemistry and the Institute of Functional Nano & Soft Materials in the U.S. and China, investigated the chemical environment of a functional group activated for defect passivation. They conducted experiments to achieve enhanced power conversion efficiencies for perovskite photovoltaics using theophylline, caffeine and theobromine compounds bearing carbonyl (C=O) and amino groups (N-H). In theophylline treated experiments, hydrogen bonding of the amino hydrogen to surface iodide optimized the carbonyl interaction with a lead (Pb) antisite defect to improve the efficiency of a perovskite cell from 21 to 22.6 percent.