As a bald doctor who studies the mantle, I have seen many reports about perovskite solar cells recently. Since June 2013, a new solar cell based on organic/inorganic composite perovskite materials has attracted great attention. The related work was rated as one of the top ten international scientific and technological advances in 2013 by Science magazine.
The top ten international scientific and technological developments in 2013 (Photo source: YouTube)
After thinking about it carefully, isn’t perovskite perovskite? How could that thing that lives deep underground come out to bask in the sun? Ever since, the editor searched for "perovskite" on Du Niang. It was found that except for unnecessary advertisements (the advertisements are also for solar cells), "Perovskite Solar Cells (Solar Cell Type Name) - Baidu Encyclopedia" followed closely, as well as various related scientific research reports.
So what’s the difference between perovskites and perovskite solar cells that live deep underground (in earth science)?
Perovskites in Earth Sciences
In the world of earth science, perovskite is a mineral that deserves its name. In 1839, German scientist Gustav Rose discovered the elemental composition CaTiO mineral in the Ural Mountains during a Russian expedition and named it "perovskite" in honor of the Russian mineralogist Lev Alekseyevich von Perovski of the same name (who proposed the creation of the Russian Geographical Society). However, the recognition of the existence of perovskite-structured silicates in the earth's mantle was not first proposed until 1962. In the late 1970s, scientists proposed that the seismic discontinuity at about 660 km in the earth's mantle represents a transition from a spinel structure to Phase transition of a mineral with an olivine composition (ringwoodite) to a perovskite with a forsterite composition. Perovskite-structured silicates are unstable on the Earth's surface and mainly exist in the lower 660km to 2900km of the Earth's mantle. But complete perovskite crystals may also be found in meteorite craters. The ultra-high pressure generated when meteorites impact the surface can cause surface minerals to phase into perovskite.
Lev Alekseyevich von Perovski (Image source: Wikipedia)
However, in 2014, perovskites deep in the earth had a new name: bridgmanite, in honor of physicist Percy Williams Bridgman, who won the Nobel Prize in Physics in 1946 for his contributions to the field of high-pressure physics. outstanding contributions).
Percy Williams Bridgman (Image source: Wikipedia)
Bridgmanite lives deep in the lower mantle. Its chemical formula is Mg1-xFexSiO3. It has a perovskite structure. It belongs to the orthorhombic crystal system and is the most important mineral in the lower mantle. Tschauner et al. discovered a natural sample of perovskite-structured silicate in meteorites in 2014, and named it Bridgmanite. Its content in the lower mantle accounts for about 80% (pyrolite composition model, One of the mantle models) or higher (piclogite composition model, one of the mantle models).
Mineral composition of the mantle (image source: Reference 2)
Another important mineral in the lower mantle is calcium-containing perovskite, which has a mass percentage of about 7%. It is the main form of calcium (Ca) in the lower mantle. At the high temperatures of the earth's mantle, it most likely exists in the cubic perovskite phase, like many well-known functional perovskite materials such as BaTiO, PbTiO and other ferroelectric materials.
Perovskite crystals on substrate (Image source: Wikipedia)
Perovskite Solar Cells
Perovskite solar cells are solar cells that use all-solid-state perovskite-type organic metal halide semiconductors as light-absorbing materials. They are third-generation solar cells, also known as new-concept solar cells. The preparation process of this material is simple and the cost is low. Taking CHNHPbI as an example, a uniform crystalline film can be obtained by mixing a solution containing PbI and CHNHI at room temperature and further spin coating. Simply put, a perovskite solar cell is a solar cell with a simple manufacturing process and low cost, using a perovskite structure as a light-absorbing material.
Schematic structural diagrams of two typical perovskite solar cells (picture source: Reference 3): (a) Mesoscopic structure perovskite solar cell; (b) Planar heterostructure perovskite solar cell.
The general structural formula of perovskite materials is ABX, where A is an organic cation, B is a metal ion, and X is a halogen group. In this structure, the metal B atom is located at the center of the cubic unit cell, the halogen X atom is located at the center of the cube's face, and the organic cation A is located at the vertex of the cube. Compared with structures connected by co-edges and co-planar structures, the perovskite structure is more stable and is conducive to the diffusion and migration of defects. See picture below:
Schematic diagram of perovskite ABX structure (picture source: Reference 3)
In summary, perovskite solar cells are perovskite-type materials. The structure of this material is similar to perovskite, and its general formula is ABX. This type of compound was first discovered in calcium titanate (CaTiO) in perovskite. , hence the name. Later, perovskite did not only refer to this perovskite composite oxide, but was used to refer to a series of compounds with the chemical formula ABX. Therefore, perovskite solar cells contain neither calcium nor titanium, nor are they an ore. They should be called perovskite solar cells.
A physical picture of a flexible perovskite solar cell device prepared by Kelly et al. in Canada (Picture source: Reference 4)
References
[1]Xu Hui, Zhu Jiandong. Bridgmanite—the most abundant mineral on earth[J]. Resources, Environment and Engineering, 2014(28):763.
[2] Wu Zhongqing, Wang Wenzhong. Research progress on first-principles calculations of mineral elasticity under high temperature and high pressure [J]. Science in China: Earth Sciences, 2016, 000(005): P.582-617.
[3] Bai Yubing, Wang Qiuying, Lu Ruitao, et al. Research progress of perovskite solar cells [J]. Science Bulletin, 2016, 61(Z1):489.
[4] Wei Jing, Zhao Qing, Li Heng, et al. Perovskite solar cells: new hope in the field of photovoltaics [J]. Chinese Science: Technical Sciences, 2014, 44(8):801-821.
Art Editor: ZYN
Proofreading: Zhang Tengfei
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Source: Institute of Geology and Geosciences, Chinese Academy of Sciences
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