Solar energy – do you really understand organic thin film solar cells?

Solar energy - do you really understand organic thin film solar cells?

Organic photovoltaics (OPV) have many advantages over most other solar cell technologies, including wide color range and tunability, good performance at low light levels and indirect light exposure, low raw material cost, and Consumption, high material utilization, light weight, ease of manufacture with high-throughput printing and coating processes, easy scale-up, etc., and low initial investment.

Not as high as conventional solar cells, but it’s considerably cheaper to build and can have many more uses. Made of organic materials, the new solar cells are ultra-thin, bendable, and can be applied over large areas. A large solar panel can be made by printing or spraying organic substances on a plastic sheet, and when using, just spread the roll of solar panels on the roof. In addition, the batteries can also be made in different colors, making them attractive building materials; or made transparent so that they can be attached directly to windows. The researchers are now planning to combine new materials and techniques to increase the photoelectric conversion efficiency to at least 5 percent, making the technology attractive for commercialization. With further commercialization research and development, the photoelectric conversion efficiency of organic material solar energy is expected to reach 5%~10%.

Japanese researchers can greatly improve the photoelectric conversion rate of solar cells by changing the molecular arrangement of organic thin-film solar cells. The Institute of Physics and Chemistry of Japan stated in late June 2008 that organic thin-film solar cells with low cost, small quality and easy extension of area are particularly concerned by researchers. Among the raw materials for such solar cells, the mixture of oligothiophene and fullerene derivatives is promising. It is said that improving the photoelectric conversion rate of solar cells involves two key factors, one is how to make the two types of molecules in the mixture, namely the electron donor and the acceptor, in a phase-separated state, and the other is how to expand the contact area between the two .

Demonstration of the power generation and thermal insulation effect of organic thin film solar cell sheets on site
Demonstration of the power generation and thermal insulation effect of organic thin film solar cell sheets on site

In order to meet the above two conditions, researchers from the Japan Science and Technology Agency simulated the molecular structure of biofilms, adding hydrophobic side chains to oligothiophenes, adding hydrophilic side chains to fullerenes, and then combining these two substances. stand up. The research team analyzed the arrangement structure of the above-mentioned synthetic molecules in detail. After treatment under suitable temperature conditions, it was found with the help of a large synchrotron radiation accelerator that the molecules of this composite spontaneously arranged to form a liquid crystal state, and the hydrophobic oligothiophene sites and the hydrophilic fullerene sites were separated from each other to form layers. structure. The photoelectric conversion rate of the new material can be increased to about 10 times that without the addition of these two side chains.

Santa Barbara, a professor of physics at the University of California, USA, and his research team have developed a “cascaded” organic solar cell technology with an efficiency of 6.5%, which is the highest efficiency for a solar cell made of organic materials. The research team brought the solar cells developed by this technology to the market in 2000. The technology employs low-cost printing and coating techniques to support active materials on lightweight flexible substrates. A multi-layer setup is equivalent to two batteries in series. Each layer of the deposit in the multilayer structure is processed by a solution method, so that such solar cells can be produced inexpensively. “Cascaded” solar cell system combines two different

Solar cells with light-absorbing properties are combined to take advantage of a wide range of the solar spectrum. The cells are separated and connected by a transparent titanium oxide material (Ti Ox), which is the key to the high efficiency of the multilayer system. Ti Ox can transfer electrons and is the collection layer of the first cell. In addition, it is used as a stable basis for the second battery assembly.

The Belgian IMEC research center announced in late October 2008 that its IMOMEC laboratory had developed a method to stabilize the nanostructures of organic solar cells, thereby increasing their lifetime by a factor of 10. Solar cells with stable technology have efficiencies comparable to modern organic solar cells. This breakthrough paves the way for the commercial production of organic solar cells with a working life of over 5 years and conversion efficiencies of over 10%. The efficiency and operating lifetime of organic solar cells strongly depend on the nanostructure of the active layer, i.e. stable dopants of organic compounds that capture and extract light energy and deliver it to electronic contacts. IMEC research center says , the efficiency of such P3HT:PCBM-based organic solar cells is close to 5%. But so far the lifespan of such batteries for commercial use has been too short.

Over the long term, all solar cells based on compounding of organic semiconductor materials will suffer from poor performance due to the compound’s segregation, which tends to separate into different phases. , and then reduce the efficiency of converting light into electricity. The IMEC research center pointed out that this phase segregation is related to the mobility of organic polymers, and the immobilization of polymer nanostructures can prolong the working life.

IMEC/IMOMEC have now cited new methods and new paired polymers that can be used to stabilize the nanostructure of the active layer far from phase segregation over long operating times. Experiments on organic solar cells based on different combinations of this new material have shown that the efficiency does not deteriorate after more than 100 hours of use, while the reference cells have deteriorated after a few hours of use. This shows that the battery life is increased by at least 10 times. Future research aims to further improve this approach by optimizing the chemical structure of the paired polymers.

New Energy Technology announced in early June 2009 that it has developed transparent glass Solar Windows by coating the world’s smallest organic solar cell on the surface of glass, and can generate electricity. New energy technology company Tycorun technology uses organic solar cell arrays, which achieve transparency through the use of conductive polymers, which have electrical properties like the semiconductor silicon that is widely used in the world, and can be well absorbed from light. Absorbing photons and emitting electricity, the company’s ultra-small solar cells, smaller than 1/4 the size of a grain of grain, assembled from environmentally friendly hydrogen-carbon-based materials, can successfully generate electricity.

Unlike other solar technologies, New Energy Technologies’ ultra-small solar cells generate electricity not only from the visible spectrum of sunlight, but also from artificial light, such as visible light from fluorescent lighting typically set up in offices and commercial buildings. While the majority of solar cells commercialized today can only use direct sunlight, New Energy Technologies’ ultra-small solar cells can be set up anywhere, using direct sunlight or artificial lighting New Energy Technologies’ Solar Windows technology, Using ultra-small solar cells, it is possible to arrange solar arrays on a wide range of matrix materials such as glass, plastic, and even paper. The fabricated natural polymers are soluble in liquids for easy application, and these ultra-small solar cells do not require the expensive and complex high-temperature or high-vacuum production techniques commonly used in other solar coatings.

The excellent optical absorption properties of New Energy Technologies’ ultra-small solar cells have enabled the development of ultra-thin-film cells that are only 1/1000 the thickness of a hair, or 1/10 μm. In photovoltaic applications such as glazing where transparency is important, today’s thin film solar cells cannot be used to form transparent solar glazing in homes, offices and commercial buildings. There are nearly 5 million commercial buildings and more than 80 million households in the United States, so ultra-small solar cells from new energy technology companies have application potential.

Mitsubishi Corporation, Japan’s Advanced Institute of Industrial Science and Technology (AIST) and Tokki Corporation announced on June 22, 2009 that they have developed new highly integrated organic photovoltaic modules. Like silicone PVs, organic photovoltaics use PN diode connections as the active layer. The biggest challenge of research and development in the past 30 years is to improve the low yield of PV. In January 2005, the Japan Advanced Industrial Science and Technology Research Institute used a large number of heterojunctions (i-layers) to make the photoelectric conversion efficiency reach 4.0%, which became the highest at that time. efficiency.

In the new highly integrated organic photovoltaic module, C60 from Frontier Carbon Corporation (FCC), a subsidiary of Mitsubishi Corporation and the world’s largest C60 producer, is used as a semiconductor (acceptor) N-type, Ganpu ligand (Cu P c ) as a semiconductor (donor) P-type. The new module uses a laser inscription technique on a glass substrate on which the organic semiconductor material is deposited and then laser divided into several cells, a technique that avoids the complicated precipitation methods used in conventional methods. The new module is highly integrated and can improve the photoelectric conversion efficiency of sunlight.

Organic photovoltaics are the well-known third-generation type of photovoltaics that use organic materials to manufacture thin, color-film PV modules. Organic photovoltaics are expected to be used in windows, walls, clothing, textiles, outdoor equipment and toys. These applications are quite difficult for the silicon-based PV modules in use today, and the use of OPV is expected to achieve high efficiency. To date, however, OPVs have been a problem with the efficiency of converting sunlight. Mitsubishi Corporation, Japan Advanced Institute of Industrial Science and Technology and Tokki Corporation believe that this problem can be solved by cooperating to develop a successful highly integrated technology.

The German OPEG (Organic Photovoltaic Energy Supply) research project achieved a major breakthrough in early August 2009, increasing the conversion efficiency of organic solar cells to 5.9%, 0.5 percentage points higher than the world record of 5.4%. This new achievement provides the possibility for the future production of lightweight, efficient, and low-cost organic solar cells, plastic solar cells. The result was jointly developed by BASF and the Institute for Applied Photophysics of the University of Dresden. Project research work will continue until June 2011.

The preparation method of a polymer solar cell invented by the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences was authorized by the State Intellectual Property Office in early November 2009. In order to solve the problem of low efficiency of polymer solar cell devices, post-thermal annealing or solvent annealing is traditionally used. However, if the annealing conditions are not properly controlled, the device efficiency will drop sharply. Therefore, how to improve the performance of polymer solar cells under mild conditions has become a difficult problem. The invention realizes the preparation of high-performance annealing-free solar cell device in one step under mild conditions, greatly simplifies the processing technology of the polymer solar cell, and can greatly reduce the production cost. The conversion efficiency of the device prepared by this method is close to 4%, which realizes the high efficiency of polymer solar cell device without annealing. IMEC Corporation of the United States announced on November 30, 2009 that it has developed a better organic solar cell, this proven all-solution process organic solar cell has a sprayed active layer and a metal sprayed contact surface on top, Its photoelectric conversion efficiency (>3%) is comparable to cells fabricated with spin-coated organic layers and vacuum-evaporated top metal contacts. For metal top contacts, IMEC’s ​​spray solution contains silver nanoparticles, which are compatible with flexible substrate processing at 150°C. The advantage is that this process does not dissolve the underlying layer and is not detrimental to the temperature required to sinter the silver nanoparticles.

It is said that this structure has no technical limit to breaking the world record (6.7%) for organic photovoltaic conversion efficiency. The company’s research shows that spraying is a suitable deposition technique and can be used to deposit all layers, including metal top contacts. Spraying is a high-rate, large-area deposition technique that ensures a wide variety of morphologies and topographies on different surfaces.

US Solar me energy company announced on December 2, 2009 that plastic solar cells with a conversion efficiency of 7.9% were certified by the National Renewable Energy Laboratory of the US Department of Energy. The company has been developing plastic solar panels since 2006 for the growing organic photovoltaic industry. In the production of medium-sized production lines, this milestone in photoelectric conversion efficiency will make its plastic solar cells practical in 2010. The company uses low-cost plastics as active materials that convert light energy into electricity. The active plastic layer is extremely thin, less than 1/1000 that of a silicon cell, and the company uses low-cost printing technology to make plastic solar cells. The combination of the above technologies can make the cost of generating corresponding electric energy lower, which is 10%-20% lower than that of crystalline silicon technology.

In addition, at the beginning of January 2010, the material research of the German Institute of Microsystem Technology (IMTEK) and the University of Freiburg reached 2%, and the relevant research results were published in the “Applied Physics Letters”. Organic solar cells are solar cells whose core parts are composed of organic materials. They belong to the so-called third-generation solar cells and are still in the research stage. Compared with ordinary silicon solar cells, organic solar cells are thin, flexible, inexpensive, and can be produced quickly. Although its light conversion efficiency is not high and its service life is relatively short, it has broad application prospects in application integration and providing self-sufficient energy for time-limited systems. Both components of the photoactive layer of a pure organic solar cell consist of organic substances. In hybrid solar cells, the photoactive layer is composed of a mixture of inorganic nanoparticles and (organic) polymers. Using so-called cadmium selenide quantum dots, researchers at the German Institute for Microsystem Technology and the Center for Materials Research at the University of Freiburg have succeeded in developing a nanoparticle surface treatment method that can significantly improve the efficiency of organic solar cells, reaching 2% higher efficiency. The measurements were confirmed by the Fraunhofer Institute for Solar Energy Systems (ISE) working group “Dye and Organic Solar Cells”.

Previously, this efficiency value was only 1% to 1.8%. The method developed so far, which is in principle applicable to a wide variety of nanoparticles, opens up broad prospects for further improving the efficiency of this type of solar cell.
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