Fine-Tuning the Backbone Coplanarity and Energy Level of Diketopyrrolopyrrole-Based Conjugated Polymers for Single-Walled Carbon Nanotube Sorting and Field-Effect Transistor Applications

Abstract

Sorting single-walled carbon nanotubes (SWCNTs) with conjugated polymers enables the production of high-purity semiconducting SWCNTs (s-SWCNTs). When the bandgaps and energy levels of polymers better match those of s-SWCNT, field-effect transistors show improved performance. Notably, ambipolar conjugated polymers have narrow bandgaps, enabling better energy-level matching and potentially promoting charge transport of s-SWCNTs, which has never been investigated. With this regard, this study examines the effect of donor–acceptor conjugated polymer bandgap on device performance by polymerizing diketopyrrolopyrrole with different comonomers—bithiophene (2T), benzothiadiazole (BT), and thienylene-vinylene-thienylene (TVT). UV–Vis–NIR absorption spectra indicate higher sorting yields for 2T and BT. Although TVT is the second-most coplanar, its excessive rigidity and poor solubility result in an extremely low sorting yield. Raman spectra show a lower defect density in 2T and a lower metallic SWCNT (m-SWCNT) fraction in BT. Photoluminescence excitation spectra show higher chirality selectivity for the BT. Simulation results show that 2T has better coplanarity and stronger wrapping ability. The 2T/s-SWCNT shows higher yield and fewer defects, leading to higher mobility and lower hysteresis. Although BT has a narrower bandgap and a higher on/off current ratio due to favorable energy-level alignment with s-SWCNT and a lower m-SWCNT fraction, its overall device performance is inferior to that of 2T. Higher coplanarity (2T) increases the sorting yield, whereas lower coplanarity (BT) reduces yield but improves selectivity to larger chirality s-SWCNTs. In summary, this study provides a rigorous sieving of the energy levels and backbone coplanarity of conjugated polymers for sorting s-SWCNTs.