Optimized polymer wrapping for high-purity semiconducting carbon nanotubes in field-effect transistors

Single-walled carbon nanotubes (SWNTs) are promising materials for next-generation electronics, but their application is limited by the coexistence of semiconducting (s-SWNTs) and metallic (m-SWNTs) species produced during synthesis. Here, we systematically optimized the separation of s-SWNTs using the conjugated polymer poly (9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFDD) by varying polymer concentration and decoupling the effects of sonication time and temperature: we evaluated temperature dependence at fixed sonication times (1, 2, and 3 h) and time dependence at fixed temperatures (25 °C, 35 °C, and 45 °C). Increasing PFDD concentration enhanced yield but reduced purity due to non-selective interactions with m-SWNTs. Excessive sonication (e.g. 45 °C for 3 h) further degraded selectivity, while extending sonication beyond 1 h offered little additional yield and shortened nanotube length. The optimal conditions-PFDD 1 mg ml^-1and sonication at 45 °C for 1 h-balanced yield, purity, and length. Field-effect transistors fabricated with s-SWNTs separated under these conditions showed a low off-current (∼10^-11A), a high ON/OFF ratio of 10⁶, and a mobility of 2.2 cm²V^-1s^-1, confirming the effectiveness of this systematic optimization for high-performance electronic devices.