Carbon Nanotube-based Solar Cells

Author: LePing Yu

Yu, LePing, 2018 Carbon Nanotube-based Solar Cells, Flinders University, School of Chemical and Physical Sciences

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Due to the excellent optoelectronic properties of carbon nanotubes, they are considered one of the most promising materials for transparent conducting electrodes for application in future photovoltaics. In the majority of this Thesis, p-type CNT-based transparent conducting films are used to form a heterojunction solar cell with n-type Si.

Several strategies are used to enhance the performance of such devices. Firstly, it is shown that a hybrid film made of CNTs and the conducting polymer, polyaniline, can improve the properties of the heterojunction by separating electron-hole pairs more efficiently. Secondly, a grid design of front metal electrode dramatically reduces the internal series resitance of the CNT based transparent films and thus improves the efficiency of the devices. Thirdly, the application of an organic interlayer, spiro-OMeTAD, can improve the exciton separation efficiency by suppressing the recombination of separated holes and electrons, and thus decreasing the reverse saturation current caused from the electrons tunnelling from Si to CNT based films. Fourthly, different approaches, including the incorporation of AgNWs with CNT based network and p-type doping of the transparent films, are used to improve the optoelectronic properties and/or the charge carrier density, which reveals that the hybridisation of CNT based transparent conducting film with AgNWs is the best way to improve the optoelectronic properties while the increase in the charge carrier density by p-type dopants is more important in improving the performance of heterojunction solar cells. Fifthly, a textured Si surface is applied instead of a planar Si substrate, in which the surface reflection is reduced and the intimate contact area between CNT based electrodes and Si surface is improved and both effects contribute to a higher output of photocurrent.

Though the best performing solar cell in this Thesis is above 13 %, which is one of the highest values in the literature, the non-ideal long-term stability of the devices is an issue (the oxidation of the silicon always ruins the performance of the solar cells over the course of a few days) to be addressed before commercialisation. One potential way to solve this problem is to create a different solar cell structure which contains two layers of SWCNTs of different chiral species as the light absorbing active layers (without Si layer). Thus, at the end of this Thesis, more than 15 single chiral species have been separated by two different methods, gel chromatography and aqueous two phase extraction, for future fabrication of a new type of solar cell.

Keywords: Solar cells, Carbon nanotubes

Subject: Nanotechnology thesis

Thesis type: Doctor of Philosophy
Completed: 2018
School: School of Chemical and Physical Sciences
Supervisor: Joe Shapter