As an important optoelectronic material, transparent conductive film (TCF) has a wide range of applications in the fields of electronic and optoelectronic devices such as touch screens, flat panel displays, photovoltaic cells, and organic light-emitting diodes. At present, indium tin oxide (ITO) is the most widely used transparent conductive film material in the industry. The commonly used ITO preparation process involves high temperature and high vacuum energy consumption and complex processes. In addition, ITO is a brittle metal oxide and indium resources are scarce, making it increasingly difficult to meet the needs of technological development, especially for the new generation of flexible electronic devices. Single-walled carbon nanotubes have excellent mechanical, electrical and optical properties, so they are considered as one of the most competitive flexible transparent conductive materials. The preparation methods of carbon nanotube transparent conductive film are mainly divided into wet method and dry method. Wet method refers to dispersing carbon nanotubes in a suitable solvent and depositing them on the corresponding substrate by methods such as suction filtration, dip coating, spray coating, or spin coating; dry method refers to directly growing carbon nanotubes by chemical vapor deposition (CVD) The tube film or the carbon nanotube array is drawn into a film.
Group A05, Advanced Materials and Structure Analysis Laboratory, Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics, has long been committed to basic research on the preparation, physical properties and applications of carbon nanostructures. Under the guidance of researcher Zhou Weiya and academician Xie Sishen, Dr. Zhang Qiang of the research group, together with senior engineers Wang Yanchun, graduate students Xia Xiaogang, Li Kewei, Dr. Zhang Nan, Dr. Xiao Zhuojian, Dr. Qingxia Fan and others, developed a new continuous direct preparation of large-scale The method of self-supporting transparent conductive carbon nanotube (CNT) film-inflation aerosol method (BACVD), and applied for invention patents (ZL 201310164499.5, ZL 201811117042.8, PCT patent US 10,144,647 B2). Based on BACVD, the output of CNT TCFs can reach hundreds of meters per hour and the carbon conversion rate (the rate of conversion from carbon source to CNT) can exceed 10%, which is higher than the corresponding index of traditional floating catalytic chemical vapor deposition (FCCVD) for preparing CNT TCFs 3 orders of magnitude higher.
BACVD was developed under the inspiration of blown film preparation process and floating catalytic chemical vapor technology. Its mechanism is to use a special CNT synthesis reactor to realize the process of "blowing" during the process of preparing CNTs by FCCVD. The specific preparation process includes two steps. First, the aerosol bubble of the CNT is stably inflated, and then the aerosol bubble is "cured" into an aerogel by increasing the length of the CNT during the CNT growth process. Finally, the CNT transparent conductive film is ejected from the end of the reactor along with the carrier gas.
The research team thoroughly studied the preparation process and gave a generalized phase diagram of the BACVD method. According to the specific preparation conditions, the phase diagram is divided into four regions, corresponding to different products. This phase diagram has guiding significance for further understanding of BACVD and film performance improvement. In addition, the method can realize the synthesis of thin films without hydrogen, which means that the preparation process is safe and efficient. The prepared thin film with a light transmittance of 90%, after simple doping, has a sheet resistance of about 40 ohm/sq, showing excellent photoelectric properties. For the ultra-thin CNT film prepared by BACVD, they designed a "roll" collection device to achieve continuous online collection of the film. Related research results were published on Advanced Materials (10.1002/adma.202004277). In the process of writing the thesis, Prof. Esko Kauppinen of Aalto University in Finland gave constructive opinions from the perspective of aerosol.
In addition to CNT TCFs, the research team also used this method to conduct research on highly conductive and high-strength fibers. The prepared cylindrical film can be directly converted into continuous CNT fibers through a liquid shrinking agent. Then, through acid treatment, the performance of the fiber has been greatly improved. Especially after chlorosulfonic acid treatment, the strength of the fiber reached 2 GPa, while the conductivity reached 4.3 MS/m. Related research was published in Chinese Physics B (Chinese Physics B 26.2 (2017): 28802-028802. The BACDV method, as a new method for preparing CNT thin films, is of great significance in basic research and industrial applications. This work proposes a A new CNT macro-body construction idea-first use airflow to assist in the construction of a specific form of short CNT aerosol, and then combine the synthesis of CNTs to use the continuous increase of the length of the carbon tube to achieve the solidification of the aerosol. In addition, ultra-high The yield and carbon conversion rate of CNTs are of great significance to the industrialization of CNTs, especially for CNTs as “engineering materials” such as transparent conductive films, electrodes and fibers.