| AVS 57th International Symposium & Exhibition | |
| Energy Frontiers Topical Conference | Monday Sessions |
| Session EN+PS-MoM |
| Session: | Plasmas for Photovoltaics & Energy Applications |
| Presenter: | T. Kaneko, Tohoku University, Japan |
| Authors: | T. Kaneko, Tohoku University, Japan S. Kodama, Tohoku University, Japan Y. Li, Tohoku University, Japan R. Hatakeyama, Tohoku University, Japan |
| Correspondent: | Click to Email |
Since the conventional silicon solar-cell conversion is limited to a certain window of solar cell photon energies over 1 eV, a full use of the solar spectrum is one of the crucial issues in order to greatly increase the solar cell efficiency. In this sense, carbon nanotubes (CNTs) are attracting much interest for photovoltaic energy conversion because of their broad absorption bands including the infrared range (0.2 ~ 1.3 eV) as well as other advantages such as large surface areas, high mobility of charge carrier, high mechanical strength, chemical stability, and so on. In this connection, we have developed a plasma-ion irradiation method, which enables pristine single-walled carbon nanotubes (SWNTs) to selectively encapsulate various kinds of atoms and molecules, such as metals and fullerenes, serving as electrons donors or acceptors inside their cavities. Then these enhanced p-type, n-type, and pn-junction housed semiconductor-SWNTs are applied toward the realization of high-efficient photovoltaic devices, which is composed of thin films of p- and n-types semiconductor SWNTs or an individual SWNT with p-n junction inside. Here, as a first step, electrical properties of p-n junctions fabricated using a combination of the thin films of pristine (empty) SWNT or C60-encapsulated SWNT (C60@SWNT), and n-doped Si (n-Si) are investigated.
The electrical properties of these SWNT film/n-Si devices show an obvious rectifying characteristic, and a short-circuit current ISC and an open-circuit voltage VOC through a downward shift of I-V curves are observed under illumination of light with wavelength of 1550 nm which corresponds to the photon energy of 0.8 eV. Moreover, it is found that the device fabricated with the C60@SWNT film has a larger VOC caused possibly by a large diffusion voltage in the interface of p-n junction compared with the device fabricated with the pristine SWNT film, due to the enhanced p-type behavior of SWNTs after C60 encapsulation. To investigate undesirable photovoltaic effects of n-Si, we fabricate a schottky barrier solar cell consisting of silver (Ag) and n-Si in the absence of SWNTs. It is confirmed that the Ag/n-Si schottky barrier solar cell generates photo currents in the visible range (1.5 ~ 3 eV), while there is almost no difference between with and without light in the infrared range (0.8 eV) because the light with photon energy less than 1 eV cannot be absorbed by Si.
Based on these results, high performance solar cells which work in the infrared region are for the first time demonstrated to be formed using SWNTs, especially p-type enhanced C60@SWNT.