The energy problem is a serious problem facing mankind. The inexhaustible and inexhaustible solar energy is the darling of the clean energy era.

Solar cells are important devices that convert solar energy into electrical energy, and their photoelectric conversion efficiency and stability have become the focus of attention in the industry. A few days ago, Professor Wang Lianzhou’s research group from the University of Queensland in Australia published an article titled “Flexible Solar Energy” on “Energy Storage Materials” based on new explorations in the field of solar cells, fast-charging energy storage batteries and integrated solar rechargeable batteries in recent years. Overview of “Charging System”.

In China, Li Yongfang, an academician of the Chinese Academy of Sciences, has been engaged in the research of transferring conjugated polymers into organic polymer solar cells since 2000. He told China Science News: “Compared with traditional silicon-based solar cells, organic polymer solar cells have the biggest feature that they can be made flexible and translucent, and the overall energy consumption is much lower.”

Looking for battery device materials

In the 1950s, solar cells began to rise and develop so far. Nowadays, silicon-based solar cells are more commonly used. In addition, there are inorganic semiconductor thin film solar cells, dye-sensitized solar cells, perovskite solar cells, organic polymer solar cells and so on.

Different solar cells have different structures. For example, the organic photosensitive band of organic polymer solar cells is composed of a donor composed of P-type organic semiconductors (easy to give electrons) and an acceptor composed of N-type semiconductors (easy to receive electrons). The flexible active layer generates photocurrent when the external circuit is turned on. Perovskite solar cells are similar to organic polymer solar cells and have a sandwich structure. The main difference lies in the photosensitive layer, which is a perovskite structure composed of an organic-inorganic hybrid.

Li Yongfang used silicon-based solar cells as an example to introduce that silicon-based solar cells consume a lot of energy during the production process, especially when raw materials are dominated, and silicon must be purified to 99.9999%. This purification process also requires energy.

He said: “It takes 6 to 7 years for silicon-based solar cells to recover the energy consumption in the production process, while the energy consumption of organic polymer solar cells can be recovered in about a year, but there are stability problems that lead to The service life is not long. In contrast, the service life of silicon-based solar cells can reach 20 years.

In 2017, 15 corporate research institutions in 7 countries including the United Kingdom, Italy, and Spain formed the European Powerweave R&D team to carry out in-situ integration based on the organic combination of dye-sensitized fiber material solar photovoltaic cell technology and electric energy storage fiber material thin film battery technology Technical research.

Ge Ziyi’s team, a researcher from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, found that most current research results on organic solar cells are based on rigid tin oxide (ITO) glass substrates. However, ITO has problems such as poor conductivity and mechanical brittleness on plastic substrates. In addition, ITO is usually processed by vacuum sputtering at high temperatures, which makes it expensive and not conducive to large-area printing and roll-to-roll preparation.

To this end, Ge Ziyi’s team developed a low-temperature acid-treated PEDOT/PSS electrode to replace the expensive ITO electrode that requires high-temperature sputtering. The team said that this kind of all-solution-processed flexible organic solar cells meets the technical requirements of large-area manufacturing processes such as roll-to-roll printing and blade coating, and provides an important reference for the low-cost flexible preparation of organic solar cells.

Improve photoelectric conversion efficiency

The reporter was informed that Ge Ziyi’s team used full-solution processing technology and used PBDB-T and IT-M non-fullerene active layers to prepare a fully wet-processed non-ITO single-junction flexible organic solar cell. The energy conversion efficiency of the battery reached 10.12%. .

The research of organic polymer solar cells began in the 1960s, when the conversion efficiency was very low. When Li Yongfang first started his research on organic polymer solar cells, the efficiency was not high due to poor conditions. Around 2004, Li Yongfang’s team began to think about how to improve the photoelectric conversion efficiency of materials.

“The conversion of solar energy into electric energy requires photovoltaic materials to have broad and strong absorption of light. In addition, donor materials must have high hole mobility, and acceptor materials must have high electron mobility.” Li Yongfang recalled, ” We chose the fullerene derivative acceptor, which has a high electron mobility, and then our focus shifted to the donor material.”

“At that time, we thought of the concept of conjugated side chains.” Li Yongfang explained, “Because the main chain of the conjugate peak is transmitted quickly, having conjugated side chains is like building a bridge, so that the charge is The transport on the yoke side chain is also faster, which improves hole mobility, thereby improving photovoltaic performance.”

In recent years, improving the photoelectric conversion efficiency of materials has become the mainstream research direction of solar cells. Professor Chen Yongsheng of the School of Chemistry of Nankai University discovered in the field of flexible transparent electrodes and flexible organic solar cells that obtaining high-performance flexible transparent electrodes is a prerequisite for the development of high-efficiency flexible organic optoelectronic devices, and it is also a core problem in this field. “Therefore, how to obtain a green, flexible transparent electrode with high conductivity, high light transmission, low surface roughness, and simple preparation method is a huge challenge.”

In November 2019, Chen Yongsheng’s team published an article in Nature-Electronics, introducing the team’s preparation of silver nanowire flexible transparent electrodes with high conductivity, high light transmission, and low surface roughness, which were used to construct flexible organic The performance of solar cells is equivalent to that of devices using commercial indium tin oxide glass electrodes. The photoelectric conversion efficiency can reach 16.5%, breaking the highest record of the photoelectric conversion efficiency of flexible organic/polymer solar cells reported in the literature at that time.

Potential applications in multiple fields

In the review article, Wang Lianzhou’s team pointed out that due to the instability and intermittent nature of sunlight, researchers in this field are encouraged to further explore the integrated system of photovoltaic energy generation and storage, and promote the development of solar charging energy storage systems.

Chen Yonghua, a professor at the Advanced Materials Research Institute of Nanjing University of Technology, told the China Science News: “Solar charging energy storage systems are more suitable for applications in the Internet of Things and human-computer interaction, provided that the efficiency of photoelectric conversion and storage needs to be improved.” Previously, the team of Chen Yonghua Looking for and designing organic amine molecules that can stabilize the perovskite structure, the photoelectric conversion efficiency of the prepared layered perovskite solar cell has been significantly improved.

Nowadays, solar charging energy storage systems have been widely studied and applied to smart grids, house energy supply, commuter electric vehicles, home electronics, and portable wearable electronic devices. When designing a new generation of wearable portable energy devices, especially solar charging energy storage systems, the Wang Lianzhou team realized that flexibility and portability are two key indicators that must be considered.

Wang Lianzhou’s team said that compared to traditional rigid devices, flexible thin-film solar cells have greatly reduced costs due to low-temperature preparation and easy-to-implement panel mounting technology. In addition, the combination of a flexible thin-film photovoltaic system and an energy storage system can not only realize wireless charging of portable wearable devices, but also greatly increase the working time of the battery and realize more extensive and sophisticated applications.

Yuan Guo Feng, an associate researcher of the Institute of Electrical Engineering, Chinese Academy of Sciences, introduced to the China Science Daily that the flexible solar photovoltaic power generation and storage integration technology has obvious advantages such as strong surface structure adaptability, flexibility, light weight, and no additional installation costs. , Can be flexibly applied to clothing, outdoor equipment, buildings, transportation tools, electronic equipment and other objects that require shading and complex structures, and can also be used as an integrated photovoltaic power generation and storage system.

Yuan Guo Feng also pointed out: “The integration of flexible solar photovoltaic power generation and storage technology still faces many issues such as material preparation and stability, material life under complex conditions, photoelectric conversion efficiency, charge and discharge efficiency, safety and cost.”