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Perovskite in Photovoltaic Systems

Just in the last couple of days, there have been some news about perovskite and how to use it in photovoltaic systems.

Scientists at the Tokyo Institute of Technology announced they made a breakthrough in material science. The discovery of a new kind of perovskite that incorporates unusually high oxide-ion conductivity could mark a milestone in the development of oxide-ion conductors.

In addition to that, a consortium for the advanced production of perovskites has formed in the United States.

But what exactly is perovskite and what makes it so versatile?

What is Perovskite?

Perovskite is a mineral that consists of calcium titanate and has the formula CaTiO3. It was first discovered in Russia in 1839 and named after the mineralogist Lev Perovski who found it. When perovskite is mentioned in the context of electronics or material science, it’s not the mineral, that’s meant. Perovskite also refers to a class of material, that has the same cubic structure, as calcium titanate, also commonly referred to as perovskite structure. Perovskite structures can be formed by different elements, such as bridgmanite (MgSiO3) or calcium silicate (CaSiO3). Many of these are oxides, but not all of them.

The physical and chemical properties of perovskites are quite remarkable. These include for example superconductivity, which describes a sudden decrease in electrical resistance to nearly zero after passing a critical temperature. Furthermore, the resistance value of perovskites also changes if a magnetic field is applied. Which is called magnetoresistance. Just like graphite, perovskite is able to be layered, which increases the stability of the resulting material. The perovskite family is also one of the very few known high-oxide ion conductors. Usually, conductors refer to the movement of electrons. But there is also the possibility of moving whole atoms or even molecules in the same way. Due to its dielectric characteristics, it is used in the electronics industry already, for example in a solar capacitor.

There are some other interesting characteristics to perovskite, but for the usage in electronics, and especially photovoltaics, these are the main ones.

Perovskite mineral
Rob Lavinsky iRocks.com
Perovskite molecular vizualization
Edumol Molecular Vizualization, flickr

Perovskite in photovoltaic cells

A photovoltaic or solar cell is a device that converts light directly into electrical energy. It does so by utilizing the photovoltaic effect. This describes the ability of a material to change current, voltage, and resistance value when exposed to sunlight. Not just solar cells use this effect. This is also the basis of photo detective or infrared electronic components.

The traditional material used in photovoltaic cells is crystalline silicon. Second generation of solar cells uses thin-film technology. This means pairing active layers of silicone between layers of glass, much like a sandwich. A few layers of thin-film silicone combined are called multijunction cells.

The theoretical efficiency limit of undoped crystalline silicon photovoltaic cells is at 29.43%, also called the Auger-limit. This means that a square meter of crystalline silicon solar panel will produce 294.3 kWh per year. Efficiency values of mass-produced solar panels are much lower, at about 14 to 19%.

To overcome the limits of pure silicon photovoltaics, the development of perovskite silicon tandem solar cells could be an option, among others. They include a material with a perovskite structure, as an active layer. So far, these are mostly lead or tin-based. Perovskite solar cells can use the high-energy blue and green light much more efficiently than silicon solar cells. However, the silicon solar cells use the red and infrared light, which the perovskite solar cells are not able to do. By combining these efficient individual cells, it is possible to achieve efficiencies beyond the limit of 29.43%. The use of silicon for the lower solar cell is attractive because it allows building on an established and low-cost production technology and enables increased efficiency with a perovskite solar cell that can potentially be produced cheaply.

Perovskite chips
UC San Diego Jacobs School of Engineering, Flickr

The future for Perovskite in photovoltaic systems

The use of materials with a perovskite structure in solar cells promises great results. However, there is still a long way to go, until commercially produced solar panels based on perovskite will be available on the market. Another interesting development has been made by scientists at the University of Tokyo, who have created a clear semiconductor based on tin-oxide, which could also be of great use in the development of more efficient solar cells.

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