Perovskites are materials that share a crystal structure similar to the mineral called perovskite, which consists of calcium titanium oxide (CaTiO3).
Depending on which atoms/molecules are used in the structure, perovskites can possess an impressive array of interesting properties including superconductivity, ferroelectricity, charge ordering, spin dependent transport and much more. Perovskites therefore hold exciting opportunities for physicists, chemists and material scientists.
Lead-based perovskites have become key materials in photovoltaics research thanks to their facile solution processability and impressive performance. However, despite their great potential, a persistent threat on future use and commercialization is the issue of toxicity and lead-content.
Lead (and its oxide form) is highly hazardous to animals and humans. Hence, succeeding to develop lead-free perovskites that could be used instead of the lead-based ones is a much desired accomplishment. While producing lead-free perovskite materials is not very hard to do, and various candidates exist (Sn-based perovskites, for example) these tend to perform poorly compared to lead-based perovskite materials, and exhibit limited optoelectronic performance and stability. However, vigorous research is taking place and hopefully it will yield lead-free perovskites that can serve as a viable replacement to lead-based ones.
The latest Perovskite toxicity news:
Tin (Sn)-based metal halide perovskites (MHPs) could be an environmentally benign alternative to lead-based ones, which are toxic. However, some critical issues need to be resolved before Sn-based MHPs can be leveraged in planar semiconductor devices. When arranged into a 2D structure (or quasi-2D structure with a few layers), defects in the crystal structure of Sn-based MHPs called “grain boundaries” hamper the mobility of charge carriers throughout the material. If used in a TFT, this phenomenon results in a large series resistance that ultimately degrades performance. In addition, a TFT made using an Sn-based MHP arranged into a 3D structure faces a problem of extremely high carrier density of the 3D material, that causes the transistor to be permanently ON unless very high voltages are applied.
Scientists from Tokyo Tech, National Institute for Materials Science and Silvaco Japan have proposed a novel concept based on a hybrid structure for Sn-based metal halide perovskites (MHPs), called the “2D/3D core–shell structure.” In this structure, 3D MHP cores are fully isolated from one another and connected only through short 2D MHP strips (or “shells”). This alternating arrangement manages to address both these issues, according to the team.
Scientists at the National Renewable Energy Laboratory (NREL) and Northern Illinois University (NIU) have developed a way to prevent lead from escaping damaged perovskite solar cells. This could go a long way in addressing concerns about potential lead toxicity.
The light-absorbing layer in perovskite solar cells contains a small amount of lead. Simply encapsulating solar cells does not stop lead from leaking if the device is damaged. Instead, chemical absorption may hold the key. The researchers report being able to capture more than 99.9% of the leakage.
University of Cambridge and Cornell University Researchers have done ‘cradle-to-grave’ life cycle assessments of a variety of perovskite solar cell architectures, and found that substrates with conducting oxides and energy-intensive heating processes are the largest contributors to primary energy consumption, global warming potential and other types of impact.
The team therefore focus on these materials and processes when expanding to ‘cradle-to-cradle’ analyses with recycling as the end-of-life scenario. Their results revealed that recycling strategies can lead to a decrease of up to 72.6% in energy payback time and a reduction of 71.2% in greenhouse gas emission factor.
Researchers from EPFL, Universität Tübingen and University of Fribourg, led by Professor Michael Grätzel at EPFL’s School of Basic Sciences, used a novel method with multimodal host-guest complexation to significantly improve the stability of perovskite solar cells while also reducing the release of lead into the environment. The strategy involves using a member of the crown ethers, a family of cyclic compounds whose ring-like atomic structure resembles a crown.
The researchers used the dibenzo-21-crown-7 in the fabrication of formamidinium lead iodide perovskite solar cells. They demonstrated the efficiency of this synergistic approach with cesium metal ions, for which the crown ether shows a strong affinity. Acting as a vehicle, the crown ether assembles at the perovskite film’s interface and delivers the cesium ions into its interior.
Semiconductors that can exploit the omnipresent visible spectrum of light for different technological applications are highly sought after, but such semiconductors are often dexpensive and toxic. A group of scientists from Tokyo Institute of Technology and Kyushu University have collaborated to develop a low-cost and non-toxic narrow-gap semiconductor material with potential 'light-based' or photofunctional applications.
Tin-containing oxide semiconductors are cheaper than most semiconductor materials, but their photofunctional applications are constrained by a wide optical band gap. The team of scientists, led by Dr. Kazuhiko Maeda, Associate Professor at the Department of Chemistry, Tokyo Institute of Technology, developed a perovskite-based semiconductor material that is free of toxic lead and can absorb a wide range of visible light.