Conjugated wrapping polymer influences on photoexcitation of single-walled carbon nanotube-based thin film transistors

Abstract

The fabrication of high-purity semiconducting single-walled carbon nanotubes (sc-SWNTs) often utilizes conjugated polymers to isolate the semiconducting from the metallic species. These polymers preferentially sort and disperse certain sc-SWNT chiralities and often remain wrapped around sc-SWNTs during device integration. In this study, we expose three different SWNT based thin film transistors (TFT), each with a different dispersion polymer Poly(carbazole-co-fluorene) (PCF), poly(fluorene-co-dimethoxybenzene) (PFMB), or poly(fluorene-co-bipyridine) (PFO-BPy), to three different laser wavelengths. The wavelengths were selected to overlap both the optical transitions of the polymer-wrapped sc-SWNTs and the polymer absorption maxima. We report fundamental TFT metrics to monitor changes after light exposure, such as the current profile, the threshold voltage, and the mobility. We show that two phases emerge. An initial soak, where the devices change after an initial exposure which permanently increases the mobility. The second phase, the photo cycling, produces repeatable device performance between exposures “On Cycling” and post exposures “Off Cycling”, such as consistent threshold voltage shifts with an overall average shift of 3.6 ± 0.6 V, highly dependant on the wavelength and polymer, thus providing greater motivation for tunable SWNT-based TFT photodetectors. Although the general behaviour is shared among most TFT types and wavelengths, discrepancies in intensity emerge, especially when exciting the polymer. Hence, we show the importance of polymer choice when considering desirable parameters, in addition to their selected SWNT chirality.