Preparation And Properties Of Single-wall Carbon Nanotube Film/Silicon Heterojunction Solar Cells

Single-wall carbon nanotubes(SWCNTs)have unique one-dimensional tubular structures and excellent optical and electrical properties.SWCNT films have characteristics of conductive,transparent,flexible,and highly stable.Therefore,they are expected to be used as transparent conductive materials and hole transport layers in various energy storage and conversion devices.Among them,heterojunction solar cells constructed with SWCNT film and crystalline silicon(Si)have attracted intense research interest brcause of their advantages of low-temperature fabrication,simple device structure and low cost.However,the power conversion efficiencies(PCEs)of the SWCNT/Si solar cells needs further improved.In this dissertation,we focuse on the preparation of high-performance SWCNT films,tuning the work function of SWCNTs,and optimizing the structure of SWCNT/Si heterojunction solar cells to enhance their performance and stability.The main results obtained are as follows:(1)Preparation and transfer of small-bundled SWCNT films.A pure and high-quality tansparent conductive film comprised of isolate/small-bundled large-dimater SWCNTs were synthesized by an injection FCCVD method.The isolate/small-bundled SWCNTs reduced the absorption of light.Large-dimater and high-quality SWCNTs enhanced carrier transport.The carbon-welding structure at X-junctions of SWCNT network decreased the contant resistance between nanotubes.As a result,the obtained SWCNT film showed excellent photoelectric performance,with a sheet resistance of 150 ?/sq at 90%transmittance,which was further decreased to 56 ?/sq after HNO3 doping.In addition,we developed an ethanol-assisted transfer method which enables efficient transfer of large-area,ultra-thin SWCNT films.(2)Construction and optimization of SWCNT/Si heterojunction solar cells.The high-quality SWCNT films prepared by the FCCVD method were used to fabricate SWCNT/Si solar cells.A PCE of 11.8%was achieved for the device employing SWCNT films with a transmittance of 90%,which was the highst value among previously reported SWCNT/Si solar cells without doping and coating antireflection layer used.The influences of window area,illumination intensity and time on the performance of the solar cells were studied.It was found that increasing the window area would lead to a decrease PCE due to the increase of series resistance.However,intensity and time of light illumination have little effect on the performance of the solar cells.The work function of the SWCNT fims was tuned by a slight fluorination at room temperature.The formation of ionic C-F bonds effectively improved the electronic conductivity and work function of the SWCNT films.In addition,the fluorination process increased the areal density of SWCNT films and decreased their surface roughness,leading to a better interface contact between SWCNTs and silicon.As a result,a high PCE of 13.6%and excellent stability were achieved for SWCNT/Si heterojunction solar cell constructed using the lightly fluorinated SWCNT film.(3)Construction of FeCl3-GO-SWCNT/Si heterojuncton solar cells.A simple drop-coating method was used to introduce GO and FeCl3 in the SWCNT/Si solar cell.It was found that the charge transfer doping of FeC13 effectively enhanced the conductivity and work function of the SWCNT film,which decreased the series resistance and increased the build-in potential of the constructed solar cells,leading to enhanced fill factor and open-circuit voltage.In addation,the GO coating serves as an antireflection layer that efficiently reduces incident light loss,and the photocurrent increased by a factor of?20%.As a result,the FeCl3-GO-SWCNT/Si heterojunction solar cell showed a record high conversion efficiency of 17.5%,-58%higher than the pristine SWCNT/Si solar cell.After an exposure of 15 days in air,the efficiency of the cells retained more than 90%of the initial value.