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History and Evolution of Perovskites

The discovery of perovskite crystals in the Ural Mountains in the 19th century was followed by the discovery of metal halide perovskites some 50 years later. Over a century passed before the remarkable electronic and light emitting characteristics of the material were realised. More recently perovskites have spurred an avalanche of research in the field of solar cell research. Here they show great potential as efficient and cost-effective materials with implications for a key role in the fight against climate change.

Besides solar cell research, the versatility of perovskites sees their use in myriad applications such as superconductors and catalytic converters. In the future we will witness an increasing role for perovskites in computing. Here we review the original discovery of perovskites as a backdrop to the later scientific innovation that occurred in the 20th and 21st centuries.

The Discovery of Perovskites in the Russian Mountains

The perovskite story is a mysterious one. The hitherto unknown naturally occurring mineral of calcium titanate was found in the Russian Ural Mountains. What remains uncertain is who exactly first found the crystal. What is known is that after the discovery was made, the mysterious mineral was sent to Chief Mines Inspector August Alexander Kämmerer (1789 - 1858), a Russian mineralogist, in 1839, who then passed it to Gastavus Rose at the University of Berlin for physicochemical analysis. Gustavus “Gustav” Rose (1798 - 1873) was born in Berlin and studied at the University of Berlin where he later became Associate Professor of Mineralogy in 1826.

In 1829 Rose joined a scientific expedition through Imperial Russia, taking in the Altai and Ural Mountains - as well as the Caspian Sea - with the German naturalists Alexander von Humboldt (1769 - 1859) and Christian Gottfried Ehrenberg (1795 - 1876). Both were distinguished men of science and now renowned in the history of science. Humboldt was a German polymath, geographer, explorer and naturalist who founded the field of biogeography. Ehrenberg was likewise a naturalist and also zoologist, comparative anatomist, geologist, and microscopist credited with founding the field of micropaleontology (the study of fossil microorganisms). Rose himself identified many minerals that were novel to science and made important contributions to the fields of crystallography and petrology (a branch of geology).

During the nine-month expedition, Rose was tasked with mineralogical investigation and henceforth he developed an excellent reputation in the field. This explains why Rose was given the crystal upon its original discovery. Rose published a paper giving the results of the expedition in Poggendorffs Annalen der Physik und Chemie volume XXXXVIII in 1839. It was upon Kämmerer's suggestion that the rock be named 'Perovskite' after the Russian politician Count Lev Aleksevich Perovskite (1792 - 1856). Perovskite was not himself a scientist, but he was a collector and fine connoisseur of minerals.

Perovskite chemical formula Perovskite mineral
Perovskite, Chlorite. Chemical formula (left) and pictured (right) a sample of Russia Perovskite crystal with an edge length of 7 mm from the Achmatovsk Mine, Achmatovsk, Slatoust, Ural Mountains (reproduced with permission of Antje Dittmann, Museum für Naturkunde Berlin).

Calcium titanate (Perovskite) is a colourless mineral with a naturally crystalline structure (designated a type of orthorhombic crystal in the scientific field of crystallography). Half a century after its discovery, in 1892, Horace L. Wells at the Sheffield Scientific School, Yale University, discovered the first synthetic halide (a binary compound made up of halogen and one other element of any kind) perovskite based on caesium and lead.

Nowadays the structure we call perovskite can be readily made using chemical and industrial processes. Thus, a diversity of minerals sharing the crystal lattice (akin to the original) also bear the perovskite name (namely inorganic compounds with the structure ABX3). Meanwhile, the naturally occurring crystalline form is actually quite rare. According to the Museum für Naturkunde (Museum of Natural Science) in Berlin “Type samples of minerals are generally very valuable in terms of science and the history of science because the number of known minerals is relatively low - approximately 5,000.” Perovskites are thus valuable as a titanium ore and occur in a range of geographical locations such as Switzerland, Italy, Arkansas, and the Urals.

Perovskites in the 20th Century

During the 1950s advances in technology enabled the synthetic structure, first described by Wells and the team at Yale, to be elucidated at the molecular level of detail. The structure was determined by C.K. Møller at the Royal Veterinary and Agricultural College in Copenhagen, Denmark. This vastly improved our knowledge and opened up new avenues for modifying the structure of this remarkable compound. Perovskites demonstrate ion oxide mobility through crystal lattices (hence they are very versatile, and researchers can tweak and 'finetune' their characteristics) and in 1947 Philips (Eindhoven) and in 1955 Western Electric (New York) scientists used oxide perovskites in condensers and electrochemical transducers.

Perovskites are not only electrical conductors, but they display good thermal and chemical stability. They are supermagnetic, photocatalytic and thermoelectric and dielectric (electrical insulators that can otherwise be polarised with the application of an electric field). This means they can be utilized in the fabrication of a wide variety of products including catalysts, superconducting devices, fuel cells, heating elements, multilayer capacitors and glass ceramic articles.

Later on, in the late 1970s Dieter Weber at the University of Stuttgart, Germany discovered the first hybrid organic-inorganic halide perovskite. Weber replaced trimethyl ammonium ion in the caesium lead halide (first synthesised by Wells) to form a class of compounds called Hybrid Organic Inorganic Perovskites (HOIP). The commercial implications were realised some twenty years later when scientists at IBM, based at the T.J. Watson Research Center, New York, developed light-emitting devices based on luminescent organic-inorganic halide perovskites. Then, just before the turn of the new millennium Japanese scientists at the National Institute of Advanced Industrial Science and Technology, Tokyo, created an optical absorption layer for a solar cell using a rare earth oxide with a perovskite crystal structure.

Perovskites in the 21st Century: Focus on Solar Cell Research

The Perovskite story really heats up in the 21st century. In recent years interest in the structure has grown rapidly. In solar cell research, perovskites have been brought in through the back door, so to speak, at least on the commercial front. Here silicon is already the mainstay material. It's a reliable and trusted component of the solar cell. Any material has to be efficient in converting solar energy to electrical energy and be robust enough to guarantee at least 25 years sustainability as a product. Silicon fits the bill, but it is very expensive to produce en masse. This is not least in part due to the fact it is required to demonstrate high levels of uniformity. An advantage of perovskite is its ability to remain functional despite some structural defectiveness. The material can still perform well in the presence of imperfections. This reduces the costs involved in fabricating products with perovskite.

Although perovskites show great promise, they do not yet play a starring role in solar energy generation. Their role in terms of energy efficiency is not yet recognized as being on a par with that of silicon, a long recognized and trusted material. But hope is on the horizon for perovskites as researchers have demonstrated improved conversion rates of solar to electrical power with respect to this material. In 2009 the figure was in the region of 3% (Kojima et al., 2009) - still an exciting finding at the time in question, when scientists were fascinated that prospect perovskites could be used to produce electrical energy from solar light. In 2013 perovskites solar cells based on hybrid organic-inorganic metal halides as the light absorbing material, emerged in the field of photovoltaics and spurred an avalanche of research. Since that time, researchers have demonstrated the efficiencies middling 20% for Perovskite Solar Cells (PSCs) and this figure is expected to rise in the coming years.

What are perovskite solar cells?

At present researchers are experimenting with a dual system of energy production that utilizes both silicon and perovskite as core material components of the solar cell. The silicon combined with perovskite tandem approach allows the introduction of perovskites onto the market while limiting the risks, until such a day comes when efficiency and reliability has improved to the extent that perovskites may outright replace silicon.

Want to make your own perovskite solar cells? See the ultimate guide to making perovskite solar cells

A Bright Outlook for Perovskites in Computing

The perovskite structure lends itself to many opportunities for optimising its composition and physical properties and this chemical versatility means the materials can be utilized in a broad range of applications. At present there is growing excitement amongst scientists about optical approaches tied to the utilization of perovskites for innovations in next generation computing and the internet of things (IoT). By using light to transfer data rather than electricity, we will see vastly faster internet speeds. Scientists anticipate breakthrough technology like terahertz data transfer will become a possibility in the near future. This ground-breaking application utilizes the terahertz region of the electromagnetic spectrum (situated between infrared and microwave) to send data at speeds 1000 times faster than those currently known.

Electromagnetic spectrum showing THz region
Electromagnetic spectrum showing THz region.

References

Contributing Authors

Written by

Dr. Nicola Williams

Professional Science Writer

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