History of Perovskites and Perovskite Solar Cells
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 perovskite materials 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.
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.
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 technological advances in solid state physics, such as X-ray crystallography (i.e. using X-rays to look at crystal structures), revolutionised solid state physics. For example, it allowed researchers to better understand the molecular properties of crystals such as perovskites.
This opened up new avenues for modifying and manipulating 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. In 1947 Philips (Eindhoven) and in 1955 Western Electric (New York) scientists used oxide perovskites in condensers and electrochemical transducers.
Perovskites can have a wide range of properties based on the materials they are made from. For example, they can be highly conductive with relatively good levels of chemical and thermal stability. 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.
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: Perovskite Solar Cells
In recent years, interest in perovskite materials has grown rapidly, particularly in regards to perovskite solar cells. In terms of solar cell materials, silicon is the standard and has dominated the market since the early 70s. Any competing PV material has to compete. In other words, any competing material must be efficient in converting solar energy to electrical energy and be robust enough to guarantee at least 25 years sustainability as a product.
Perovskite solar cells were first reported in 2009. These had an efficiency of roughly 3% (Kojima et al., 2009) - which was an exciting finding at the time. Scientists were fascinated that prospect perovskites could be used to produce electrical energy from solar light.
In 2012, perovskites solar cells were made using only hybrid organic-inorganic metal halides (i.e. perovskites) as the light absorbing material. This spurred an avalanche of research. Since that time, researchers have demonstrated perovskite Solar Cells (PSCs) with efficiencies of over 25%. This figure is expected to rise in the coming years.
At present researchers are experimenting with tandem solar cells which use both silicon and perovskite in the solar cell. Here, a wide bandgap perovskite material is placed on top of a silicon wafer. The perovskite-silicon tandem approach allows perovskites to build onto the current solar panel landscape.
Although perovskites show great promise, they do not yet play a starring role in solar energy generation. 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.
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.
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History of Solar Cells
The history of solar cells involves scientific discovery, invention, and rivalry. We often consider solar power to be a new technology, but it dates back to ancient times. Humans have been using solar energy for light and heat for hundreds of years. Chinese, Greek, and Roman inventors built structures that tracked the sun to capture light and warmth. Later, concentrated light was applied to ignite fires using curved metallic objects known as 'burning mirrors'. By the 18th century, natural philosophers were trapping solar heat with glass.
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Introduction to MAPbI3 : Methylammonium Lead Iodide, CH3NH3PbI3
Solar panels are typically made of thin silicon wafers encapsulated in multiple protective layers. While their structure may look complex, manufacturers are able to produce them with relative ease. Producing the silicon wafers needed for solar panels requires 5 stages: heating, purification, doping, shaping and polishing. This produces the high quality silicon you need for use in solar panels.
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- American Chemical Society (2021) Molecule of the Week Archive - Perovskites. March 2021. Online: https://www.acs.org/molecule-of-the-week/archive/p/perovskite.html
- BCC Research Editorial (2018) A History of Perovskite Solar Cells. Online: https://blog.bccresearch.com/a-history-of-perovskite-solar-cells
- Chanana, A., et al. (2017) Colour selective control of terahertz radiation using two-dimensional hybrid organic inorganic lead-trihalide perovskites. Nat Commun 8, 1328 Doi: 10.1038/s41467-017-01517-0