Making solar cells with chlorophyll

At present, the world consumes at least 13 megawatts (1 megawatt = 1 trillion watts) of energy each year. The non-renewability of fossil fuels such as oil determines that people must look for alternatives.

The sun, which has a power of 120,000 watts, has entered the sight of the people. In theory, as long as the collection of solar energy for one hour, it can meet the human energy needs throughout the year.

In order to effectively collect solar energy, people have tried various methods, such as the development of large-area, high-efficiency, low-cost solar cells. There are currently industrialized crystalline silicon (monocrystalline, polycrystalline silicon) solar cells, and some of the thin-film batteries (amorphous/microcrystalline silicon-based thin films, cadmium telluride, and copper indium gallium selenide) that have been put into production, as well as those that are mainly under research. Dye-sensitized batteries, organic thin-film batteries, etc.

A chlorophyll solar cell has attracted much attention because it mimics photosynthesis in the natural world as much as possible.

Fire from Yangshuo to solar cells

In other words, the history of human use of solar energy has existed for a long time. In the 9th century BC, the Chinese began to collect light with “Yangshuo” (concave mirror). In the 7th century AD, it began to use solar energy to collect solar energy.

In modern times, the use of solar energy has become widespread. In the 1950s, two major technological breakthroughs were made in the field of solar energy utilization. First, the Bell Labs in the United States developed 6% of practical monocrystalline silicon cells in 1954. Second, in Israel, Tabor proposed selective absorption of surface concepts and theories in 1955 and developed successfully. Selective solar absorbing coating. These two breakthroughs laid the technical foundation for the universal application of solar energy.

Since the 1970s, given the limited supply of conventional energy and the increase in environmental pressure, many countries have set off an upsurge in the development and utilization of solar energy.

For decades, solar energy utilization technology has made great progress in research and development, commercial production, and market development, and has become one of the world's fastest and more stable emerging industries. For example, crystalline silicon (monocrystalline silicon, polysilicon) solar cells have been widely used in industrialization, and some thin-film batteries have also been put into production.

At present, in order to promote solar energy technology on a large scale, light energy conversion efficiency and effective energy storage are two major problems that cannot be solved.

The photoelectric conversion efficiency of crystalline silicon cells is theoretically up to 32%, and the current industrialization level is between 14% and 18%. However, the high manufacturing cost has greatly limited the scope of its use. At present, the theoretical service life of crystalline silicon cells is 20 years (the actual operation also takes into account the cleanliness of the cell surface and accidental damage caused by inclement weather), and the power generation price during the entire period of use is about the same as the traditional price of electricity over the same period. 2 times.

Some newly developed high-efficiency solar panels cost more. For example, a composite photocell with a conversion efficiency of up to 41% can cost thousands of dollars in 10 cm square, and the voltage is only 0.5 volts. Even Ike Weber, director of the German Wolfberry Solar Energy Research Institute who invented the battery, believes: "If you have such a high price, you must buy it and you will be hesitant."

In addition, how to store energy is also one of the challenges.

Natural light capture system

Is there a way to effectively avoid the above problems?

In fact, nature has always had a solar capture system. Since the birth of the first green life, this system has been operating for 2.7 billion years. This is photosynthesis.

At present, German scientists have discovered that a membrane protein called LHC-II is most abundant in green plants and is considered as a light-harvesting complex. This is a hollow sphere with typical icosahedral symmetry characteristics, which is filled with pigment molecules to absorb light energy and transmit it.

These pigment molecules include Chlorophylla, Chlorophyll b, Carotenoids, and the like. It is known that during the long course of evolution, plants only selected chlorophyll a that absorbs red light and chlorophyll b that absorbs blue-violet light.

Recent studies have found that in response to low light conditions, some plants have also derived pigments that absorb long-wave light. In 2010, researchers accidentally extracted this chlorophyll from a phage colony in Shark Bay, Western Australia, and named it chlorophyll f. It is capable of absorbing red and infrared light in the wavelength range of 0.7 μm to 0.8 μm (infrared wavelengths of 0.77 μm to 1000 μm, divided into near-infrared and mid-infrared).

From the chlorophyll-based light-harvesting system to the photoreaction center, plus the combined effect of 10 auxiliary factors (such as manganese, iron, magnesium, etc.), the complex and delicate system of photosynthesis transforms light into electricity. Converted to fixed-state chemical energy.

Using Photosynthesis to Build Batteries

In recent years, scientists have begun to try to use the principle of photosynthesis to develop batteries. For example, the chlorophyll in the plant is extracted and placed in an artificially prepared film, which produces electricity when light is applied. This is the chlorophyll battery.

In 2004, it was reported that American scientists have made use of the protein extracted from spinach to make chlorophyll cells. They separated proteins that could capture light from spinach and placed them between two layers of conductive material. When light strikes the micro device, a current is generated.

However, these protein molecules are very fragile and often cannot continue to work after they have been removed from the natural environment. So scientists mixed them in a soap-like molecule called a peptide surfactant. These protective molecules form a protective film around these energy-generating proteins, making them look like they are still in the plant environment.

The protein is placed on a thin sheet of gold with a layer of conductive metal and the top layer is a conductive organic material. When light shines on this "false sandwich," proteins release electrons and pass on to the next layer of metal to form an electric current.

Professor Lewis, who specializes in solar energy development at the California Institute of Technology, pointed out: "We want to design a process that is as similar as possible to the photosynthesis of green leaves." The implication is that the function of collecting sunlight should be realized, but its structure must be Try to simplify it.

In 2006, the team of Prof. Max Crosley of the University of Sydney, Australia, produced a synthetic chlorophyll molecule shaped like a soccer ball. It is a highly branched nanocluster synthesized from carbon, hydrogen, and nitrogen. Attached to it is a synthetic pigmentary porphyrin (an element that is essential for chlorophyll photosynthesis, located in the center of magnesium ions). Using synthetic chlorophyll, Crosley and his research team built a prototype of an organic solar cell. It is hoped that in the end it will be able to produce batteries that are more efficient than existing solar cells. Because green leaves can effectively convert 30%-40% of light energy into electrical energy.

Crusoe said: "We already have the main components that mimic photovoltaic equipment or solar cells. In the long run, we must manage to produce a thin layer of paint that can be applied to the roof. "Here," he said, the research team also hopes to create a storage device to replace metal-based batteries.

In fact, true chlorophyll solar cells are still in the research stage due to the difficulty of “green leaves”, but batteries that mimic the principle of photosynthesis have been manufactured. This is the dye-sensitized battery. Since the research team led by Prof. M. Gratzel (EPG) Professor Lausanne of Switzerland (EPFL) in 1991 achieved a breakthrough in this technology, developed countries such as Europe, the United States, and Japan have invested a lot of money in research and development.

Yang Weiguang, a researcher at the School of Materials Science at Shanghai University, told Shanghai State-owned Assets that the dye-sensitized batteries replaced chlorophyll in plants with sensitizer-based artificial dyes. At present, the British G24 Innovations Company has already possessed a production capacity of 30 megawatts, and it manufactures and sells battery module products with conversion efficiency of over 6%. In addition, companies such as Solarorix Switzerland and Israel 3Gsolar specialize in the production and sale of dye-sensitized solar cell materials such as dyes, pastes, electrolytes, and electrode materials. Yang Weiguang said that the highest efficiency of dye-sensitized battery modules is currently around 10%. This record was created by Japan Sharp Corporation. "But only at the R&D stage, there are no commercial products."

The development and industrialization of domestic dye-sensitized batteries also started. According to Yang Weiguang, apart from R&D of universities and research institutes, Rainbow Group Technology Center (Beijing) is currently the only enterprise R&D center for dye-sensitized batteries in China. In terms of industrialization, in 2009, China Shipbuilding Heavy Industry State-owned Hanguang Machinery Factory (与) cooperated with the Institute of Chemistry of the Chinese Academy of Sciences, with a total investment of 150 million yuan, to carry out the first “dye-sensitized solar cell” industrialization project in the country. Product for sale. According to another report, on November 19, 2011, China's first new dye-sensitized solar cell project was put into operation in the northern Jiaozhou Bay Park of Qingdao High-tech Zone.