U.S. Research Team Shows New Structure of Photovoltaic Cell Structure

As far as the function of solar panels is concerned, it is a general trend to convert as many photons as possible into energy. All along, researchers in the fields of chemistry, materials science, and electrical engineering have been tirelessly seeking to increase the efficiency of photovoltaic device energy absorption. However, current technologies are still subject to certain physical laws.

A few days ago, Penn University and Drexel University jointly announced the development of a new model for solar cells. This model not only promises to reduce the manufacturing costs of photovoltaic cells, making them easier to produce, but also increasing their conversion efficiency.

Photovoltaic cells currently work in the same mode: They absorb light and then excite electrons, causing them to flow in a specific direction. This flowing electrons become current. However, in order to achieve a consistent route or electrode, solar cells can not be made without two materials: light-absorbing materials and conductive materials. Once an excited electron crosses the former to the latter, it cannot be turned back.

Rappe said: "However, there is a small class of material in the world. Once it is illuminated by light, the electrons flow in a certain direction without going from one material to another."

“We call it the photovoltaic bulk effect, not the 'interface' effect that occurs in existing photovoltaic cells. This type of phenomenon was discovered as early as the 1970s, but we did not use this method to produce solar cells because ultimately It is confirmed that these effects can only convert ultraviolet light into energy, and most of the energy comes from the visible and infrared spectrum in the solar light."

Based on this, finding a material that exists in the photovoltaic bulk effect can greatly simplify the production process of photovoltaic cells. Moreover, the program can also avoid "Shockley-Queisser Limit", which means that some of the photon energy will be lost while the electronics are waiting in line for a jump.

Lape claims: "Imagine that the photons from the sun fall on you like rain. Different frequencies of light are like different types of currency: pennies, nickel coins, coins, etc. At this time, the material that absorbs light can be called Bandgap' - determines the 'denomination' you end up with."

What is "Shockley Quays Efficiency Limit"? In layman's terms, the face value that you end up with can only be the lowest value that the bandgap can hold. At present, there is no suitable material in the photovoltaic bulk effect. With professional material accumulation, the research team has developed a new model and has measured its properties.

As early as five years ago, the research team had started theoretical work and described the specific properties of this new compound. Each compound begins with a "mother" material that injects the final material into the polar aspect of the photovoltaic bulk effect. The so-called "mother" material is a material that can reduce the band gap of the compound.

Subsequently, both materials are ground and weighed, mixed together, and heated in a furnace until a chemical reaction occurs. The resulting crystals have the structure of a "mother" material, but the critical part has the elements from the final material so that it can absorb visible light.

Perovskite crystals produced in the laboratory

“The main challenge in design is to determine whether the material can retain visible light while still retaining polar properties.” Davis said, “According to theoretical calculations, the mutually exclusive property combinations in new materials can actually tend to stable."

This is a structure that is called a "perovskite crystal." The vast majority of light-absorbing materials have this symmetric type of crystal structure that allows atoms to repeatedly move up, down, left, and right within a fixed layout. This type of functionality can make the material non-polar, and from an electronic point of view, all directions look similar. Therefore, there is no ultimate direction for atoms.

The metal atoms of the perovskite crystals all have the same cubic lattice, each lattice contains an eight-sided oxygen atom, and each oxygen atom contains another type of metal atom. The relationship between the two metal elements can make them off-center, so that the entire structure has directional - rich polarity.

"All good polar or ferroelectric materials have this crystal structure." Lape said, "It looks very complicated. In fact, when you have a material that contains two kinds of metal elements and oxygen, this kind of Phenomenon will always appear in nature."

After several failed productions of specific perovskite crystals, the team succeeded in developing a band gap containing final product containing potassium niobate, parent materials, polar materials, and niobium niobate.

The team first used X-ray crystal technology and Raman scattering technology to produce symmetrical crystal structures. Subsequently, they investigated the switchable polarity and bandgap of the structure, making it clear that the structure could produce a photovoltaic body effect and increase the possibility of breaking the limits of Shockley Quays efficiency.

In addition, if the size of the final product band gap can be affected by the percentage of niobium niobate, then the advantages of this product are increased by one compared to interface solar cells.

Spanier pointed out: "The band gap of the 'mother' material is in the UV range. However, only 10% more Niobium niobate will move the band gap to the visible light range, making the conversion efficiency close to ideal. This is a feasible solution. As we add more niobium niobate, the band gap can still change in the visible range."

Another solution to the adverse effects of Shockley Queise's efficiency limit is the efficient and orderly accumulation of several solar cells with different band gaps.

These multi-junction photovoltaic cells have a high bandgap top layer that can capture the vast majority of valuable photons. The lower the band gap of the continuous layer, the greater the total energy of each photon. However, all this will increase the overall complexity and the production costs of photovoltaic cells.

“The entire family of materials runs through the entire solar spectrum.” Lapey explained, “Based on this, we can grow a material that slowly changes into a compound, making a single material behave like a multi-junction photovoltaic cell.”

"The material family is an extraordinary achievement." Spanier said, "Because it contains cheap, non-toxic and sufficient elements - this is by no means comparable to compound semiconductor materials used in thin-film photovoltaic cell technology."

The study was led by Andrew M. Rappe, a professor of chemistry at the Penn's School of Arts and Sciences, and Ilya Grinberg, a research professor, along with Peter K. Davies and Drexel, chairmen of the Engineering and Applied Sciences Department. Jointly completed by Jonathan E. Spanier, Professor of Materials Science and Engineering at the University. The paper report has been published in the journal Nature.

The study was jointly supported by the Ben Franklin Technology Partners' Energy Commercialization Agency, the US Department of Energy's Basic Science Office, the US Army Research Office, the Engineering Education Association and the Naval Research Office, and the National Science Foundation. In addition, Gaoyang Gou of the Department of Chemistry, D. Vincent West, David Stein, and Liyan Wu from the Department of Materials Science and Engineering, and Maria Torres, Andrew Akbashev, Guannan Chen, and Eric Gallo from Drexel University contributed to the study. . (Translator: Krystal)

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