Schematic diagram of a new composite flexible transparent electrode
Because organic materials have the advantages of good flexibility, light weight, wide source of materials, and low cost, organic solar cells are of great significance for the large-scale use of solar energy and the provision of cheap electrical energy.
Among the various technologies for human use of solar energy, solar cells that directly convert solar energy into electrical energy are one of the most promising technologies. Among them, organic solar cells are a newly emerging research direction. Because organic materials have the advantages of good flexibility, light weight, wide source of materials, and low cost, organic solar cells are of great significance for the large-scale use of solar energy and the provision of cheap electrical energy.
Recently, Professor Li Yaowen of the Academician Li Yongfang of the Department of Materials and Chemistry and Chemical Engineering of Suzhou University and others published an article in "Science China Chemistry". They used silver nanowires to dope transparent conductive polymers with nano-imprinted grids. The silver flexible substrate is compounded to produce a new type of flexible transparent composite electrode with low surface resistance and high visible light transmittance. The efficiency of flexible organic solar cells based on this electrode exceeds 12%.
"Plastic" can also conduct electricity
At present, commercial solar cells are mainly prepared with inorganic semiconductor materials such as crystalline silicon as the active layer. However, such solar cell production has the disadvantages of complicated process, high cost, high energy consumption in raw material production process, and heavy pollution. At the same time, due to the rigid structure of the inorganic semiconductor itself, it is difficult to prepare flexible devices for such solar cells. Therefore, the preparation of new organic solar cells with low cost, high efficiency, strong flexibility, and environmental friendliness is becoming the goal of scientists from various countries.
In the impression of people, plastic is not conductive. However, the winner of the 2000 Nobel Prize in Chemistry broke this common sense. In the 1970s, American scientists Alan J. Heeger, Alan G. Mac Diarmid and Japanese scientist Hideki Shirakawa discovered that after oxidation or reduction doping, a class of conjugated polymers can become conductors or semiconductors.
Plastic is a polymer. For a polymer to be able to conduct electricity, its main chain carbon atoms must have a conjugated structure that is alternately bonded with single bonds and double bonds, and it must also be doped: through oxidation or reduction reactions, its main chain loses or gains electrons So as to be conductive. Alan J. Heeger et al. Found through research that iodine doping of the conjugated polymer polyacetylene, polyacetylene can exhibit metal-like conductivity.
"Alan J. Heeger and others have pioneered the field of conductive polymers. The electrode material of transparent conductive polymers is an important application field of conductive polymers. Organic solar cells use organic semiconductor materials such as conjugated polymers or conjugated organic molecules. Succeeded. "Li Yaowen told the China Science News.
Compared with inorganic semiconductor materials represented by silicon, organic semiconductors have many advantages such as low cost, material diversity, adjustable functions, and flexible printing preparation. Therefore, the research interest in organic solar cells is rising. Especially in recent years, the research on organic solar cells has achieved rapid development, and its photoelectric conversion efficiency has been constantly refreshed. Organic solar cells have reached the "eve of dawn" of commercialization.
Photoelectric conversion efficiency breaks through 12%
The organic solar cell active layer material has excellent flexibility, which makes it show great application potential in the field of flexible solar cells.
Li Yaowen said that high-performance flexible transparent electrodes, efficient and low-cost organic semiconductor photovoltaic materials, preparation technology of large-area flexible organic solar cells, and device packaging and stability research are the keys to the current commercial application of flexible organic solar cells.
Li Yaowen told reporters that commercialized indium tin oxide flexible transparent electrodes, due to their brittleness, poor bending resistance, high surface resistance, and low light transmittance, have limited their applications in flexible organic solar cells. Therefore, it is particularly important to develop new flexible transparent electrodes with excellent mechanical flexibility, low surface resistance, and high light transmittance.
According to reports, the conductive film based on silver nanowires not only has excellent mechanical properties, but also has excellent optical and electrical properties, and has become a flexible transparent electrode material with great application prospects. However, the shortcomings of large roughness, weak adhesion and unstable morphology still limit its application in high-performance flexible organic solar cells.
In this regard, Li Yaowen and others used alcohol-soluble silver nanowires with high conductivity and high regularity to dope the transparent conductive polymer, and effectively adjust the transmittance and conductivity of the conductive polymer film by adjusting the doping ratio. Compounded with nano-imprinted grid silver flexible substrate, a new type of composite flexible transparent electrode was constructed.
They further studied and found that the incorporation of silver nanowires provides an additional charge transport channel for conductive polymer films and can achieve higher electrical conductivity. The test results show that the average transmittance of the new composite flexible transparent electrode in the visible light range has been significantly improved, with the highest transmittance reaching 86%. At the same time, the surface resistance is reduced, and the conductive film and the substrate also exhibit good adhesion and thermal stability.
"These features help to prepare high-performance flexible organic solar cells in the next step." Li Yaowen said.
Next, the researchers found that the efficiency of the flexible organic solar cell prepared based on this new composite electrode reached 12.07%, showing a comparable efficiency (12.94%) to the organic solar cell prepared based on the glass substrate. This is also the highest efficiency reported for non-indium tin oxide flexible organic solar cells.
Industrialization is just around the corner
The "Thirteenth Five-Year Plan" strategic emerging industry development plan and the recently released "Energy Technology Revolution Innovation Action Plan (2016-2030)" of the National Development and Reform Commission Energy Bureau clearly pointed out that it will focus on the development of solar energy based on organic, perovskite semiconductor materials battery.
Li Yaowen said that although the energy conversion efficiency of organic solar cells still has a large gap with the efficiency of silicon-based and perovskite solar cells, its unique advantages in flexible and translucent devices provide a wide range for its industrialization. Space helps to complement silicon-based solar cells and fill the gaps in the photovoltaic market in terms of flexible and translucent devices.
First, the organic / polymer materials used in the photoactive layer of organic solar cells have inherent advantages in the preparation of flexible organic solar cells.
In addition, the photoactive layer of the organic solar cell usually not only has a thin thickness (100 ~ 300nm), but also its optical band gap can be effectively controlled by chemical tailoring of the active material, thereby expanding the translucency and color of the organic solar cell Applications in the field of batteries.
"Organic solar cells are uniquely light-weight, translucent, colorful, flexible, and roll-to-roll mass-produced. They will be used in future wearable energy equipment, building photovoltaic integration, photovoltaic tents, and photovoltaic greenhouses. It will shine in applications. "Li Yaowen said," Therefore, research on flexible, translucent organic solar cells will become a hot spot. At present, there are many research groups in China that have been engaged in research on related content. In the next few years, China will There should be greater breakthroughs in this field, and there will be many scientific research results. "
It is understood that Li Yongfang, an academician of the Chinese Academy of Sciences, a researcher of the Institute of Chemistry of the Chinese Academy of Sciences, and a professor of Suzhou University, has embarked on the relevant industrialization layout and established a photovoltaic center at the Organic Optoelectronic Technology Research Institute of Jiangsu Industrial Technology Research Institute. The photovoltaic center has been equipped with relevant R & D personnel and equipment, mainly to carry out amplified synthesis of organic solar cell photovoltaic materials, and large-scale preparation and stability research of flexible organic solar cells.
Speaking of the industrialization of flexible organic solar cells, Li Yongfang told the China Science Journal: "The industrialization of flexible organic solar cells needs to be advanced step by step." He said that the first is the development of high-efficiency and low-cost organic photovoltaic materials and Scale-up synthesis, and development and large-area preparation of high-performance flexible transparent electrodes; secondly, research on large-area preparation technology, device stability, packaging materials and processes of flexible devices is needed; finally, cooperation with the company is required to prepare flexible organic solar cell modules And establish a flexible organic solar cell production line to achieve large-scale application of flexible organic solar cells.
"Organic solar cells are a research field led by the Chinese. We must take the lead in realizing the industrialization of flexible organic solar cells in China." Li Yongfang said.
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