Optimized Polymer Wrapping for High-Purity Semiconducting Carbon Nanotubes in Field-Effect Transistors

Single-walled carbon nanotubes (SWNTs) exhibit outstanding electronic and mechanical characteristics. Nevertheless, the simultaneous presence of both semiconducting (s-SWNTs) and metallic SWNTs poses a significant challenge in semiconductor applications. In this study, we systematically optimized the separation process of s-SWNTs using the conjugated polymer Poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFDD) by adjusting the polymer concentration, sonication temperature, and sonication time. As the PFDD concentration increases, the s-SWNT yield improves; however, stronger interactions with metallic SWNTs result in a decrease in purity. Sonication times exceeding 1 hour did not significantly contribute to the improvement of s-SWNT yield but instead resulted in a reduction in s-SWNT length. The yield of s-SWNTs showed no significant variation at sonication temperatures ranging from 25°C to 45°C. This indicates that sufficient PFDD side-chain mobility for effective SWNT wrapping is present within this range. Using the optimized s-SWNT solution, the fabricated field-effect transistors exhibited an off current of ~10¹¹ A, a high ON/OFF ratio of ~10⁶, and a field-effect mobility of 2.2 cm² V⁻¹ s⁻¹, confirming the effectiveness of the separation technique.