Characteristics of the photoelectric current in a surface functionalized single-wall carbon nanotube network

Abstract

Optoelectronic properties of carbon nanotube network have been the subject of interest recently due to their possible application as transparent photodetectors, large area optical switches, and bendable solar cells. Many reports have suggested several mechanisms by which photoelectric current arise in carbon nanotubes, such as, electron-hole pair generation within the nanotube, photodesorption of surface gases induced changes in surface doping characteristics, photon assisted Schottky barrier tunneling at the nanotube-metal contact interface. Here, we report on the characteristics of photoelectric current in surface functionalized low density single-wall carbon nanotube networks (NTN) prepared on a flexible and transparent silicone elastomer surface. The comparative responses of NTNs treated with difference surfactants may reveal which of the aforementioned effects will dominate in a low density NTN network with high optical transmittance. The NTN surfaces were functionalized using sodium dodecyl sulfide (SDS) and sodium dodecyl benzene sulfunate (NaDDBS). The NTN were formed by vacuum filtration and transferred to poly(dimethylsiloxane)(PDMS) by stamping the PDMS on the filtered membrane surface. The NTN on PDMS show nanotube density dependent optical transmittance characteristics around the 400 nm ~ 700 nm wavelength range with a 3 kΩ/sq. resistance NTN showing 70% transmittance. Upon exposure to white light, we observed an increase in NTN conductance, which was repeatable. Since the nanotubes within the network have a range of chirality and variation in diameter (1.5~2 nm) the electron-hole pair generation induced photocurrent has a statistical response to the wavelength of the applied radiation. The effect of nanotube density, surface functionality, partial pressure of gases known to change nanotube carrier concentration, laser intensity and light pulse frequency on the photoconductivity will be discussed.