Enhancement of thermoelectric property of carbon nanotubes by p-type doping with judicious molecular design of spiro-bifluorene derivatives

Although thermoelectric composites of carbon nanotubes (CNTs) with organic polymers or small organic molecules have witnessed explosive achievements, judicious molecular design still remains a great challenge. Here, p-type doping using spiro-bifluorene derivatives is proposed to significantly improve single-walled CNT (SWCNT) thermoelectric performance. The composite shows an increase of ∼108% in room-temperature power factor relative to the pristine SWCNT (112.6 ± 4.3 μW m-1 K-2), with the maximum of 239.2 ± 4.2 μW m-1 K-2. The corresponding mechanism of effective p-type doping and strong interfacial interaction are elucidated by calculated energy levels, SWCNT surface coating and photophysical spectroscopic measurements. Finally, the thermoelectric device connected in series display an open-circuit voltage and an output power of 9.77 mV and 57.3 nW, respectively at a temperature gradient of 30 K. The results will benefit the exploitation of novel CNT-based TE composites and their applications.