High-work-function metal/carbon nanotube/low-work-function metal hybrid junction photovoltaic device

Abstract

Photovoltaic devices based on nanotechnology have attracted much attention because of their great potential for application in electronic and energy fields. Here, a photovoltaic device based on a high-work-function metal/single-walled carbon nanotube (SWNT)/low-work-function metal hybrid junction was investigated. In the device, asymmetric metal electrodes (palladium and aluminum) were fabricated on opposite ends of a single semiconducting SWNT, which was used as the photosensitive material. This structure allowed a strong built-in electric field to be generated in the SWNT to efficiently separate photogenerated electron-hole pairs and achieve good photovoltaic effect. In the dark, the device behaved as a gate-dependent Schottky diode and exhibited the electrical characteristics of a rectifier. The SWNT diameter (band gap) was found to have a significant effect on the device characteristics. For the device fabricated with a 1.4-nm-diameter SWNT, a high rectification ratio (I forward /I reverse ) of INTRODUCTIONPhotovoltaic devices have attracted much attention owing to their numerous applications in electronic and energy fields. The unique and excellent physical and mechanical properties of single-walled carbon nanotubes (SWNTs) make them good building blocks for photovoltaic devices. 1,2 SWNTs have a direct band gap that increases with decreasing diameter, and they exhibit strong photoabsorption in the spectral range from ultraviolet to infrared. They also have a separated electronic sub-band structure, which can prevent the rapid relaxation of hot carriers, allowing more photogenerated carriers to be collected by the electrodes. Moreover, ideal SWNTs have defect-free structures and can greatly inhibit the recombination of photogenerated electronhole pairs. In addition, they exhibit high carrier mobility and good mechanical strength. SWNTs have been used in some photovoltaic devices such as organic solar cells 3,4 and dye-sensitized solar cells 5,6 to improve the photoelectric conversion efficiency. However, in these devices, SWNTs only acted as the conductive material or as the transparent electrode that conducted or collected the photogenerated charge carriers. The power conversion efficiency of these cells was low (~0.11%) 3 or was only slightly enhanced compared with that of the traditional cells without SWNTs. 5,6 To fully exploit the properties of SWNTs and produce high-performance photovoltaic devices, it is desirable to use SWNTs as the photosensitive material in the device.To achieve a photovoltaic effect, a photovoltaic device must have a strong built-in electric field to separate photogenerated electron-hole

An Overview of the Recent Progress in the Synthesis and Applications of Carbon Nanotubes

“…Non-covalent doping can tune the doping type and degree of the SWNT without producing structure defects [195]. The diameter of SWCNT can be used to control its energy gap to produce the p-n junction diodes with different characteristics [196]. Furthermore, the characteristics of high intrinsic mobility (>100,000 cm 2 /Vs) and up to 109 A cm −2 current-carrying capacity make SWNTs promising for use in the high-performance diodes fabrication [197].…”

Carbon nanotube intramolecular p-i-n junction diodes with symmetric and asymmetric contacts

“…The work function of Pd was 5.1 eV, the Fermi level of Pd would be located at the top of the valence band of SWCNT at the Pd-SWCNT contact. The work function of Al was 4.1 eV, the Fermi level of Al would be close to the bottom of the conduction band of SWCNT at the Al-SWCNT contact 9 . The difference in the values of the work functions of the source and drain electrodes caused the bending of the energy band in the SWCNT and made the device showed the diode characteristics.…”

“…The doping type and degree of the SWCNT can be controlled by non-covalent or adsorption doping without introducing any defects in SWCNTs to keep the excellent material characteristics of the SWCNTs 8 . The energy gap (Eg) of the SWCNT can be tuned by its diameter 9 to fabricate the diodes with different built-in electric field. Besides, SWCNTs have extremely high intrinsic mobility 10 (>100 000 cm 2 /Vs) and large current-carrying capacity 11 as high as 10 9 A cm −2 .…”

Localized heat perturbation in harmonic 1D crystals: Solutions for the equation of anomalous heat conduction

“…Nowadays investigation of nonlinear thermomechanical processes in low-dimensional structures attracts high interest due to the rapid development of nanoelectronical devices based on materials with microstructure [1,2,3,4]. Achievements in nanotechnology allowed for an experimental proof of the wave nature and finite propagation velocity of thermal perturbations [5,6].…”