Improving power factor of multiwalled carbon nanotube films through dual doping and sequential energy filtering of charge carriers

Free-standing multiwalled carbon nanotubes (MWCNTs) sheet exhibits low thermoelectric power factor due to poor inter-junctions’ connectivity. The present work demonstrates a simultaneous improvement of two anti-correlated thermoelectric parameters-Seebeck coefficient and electrical conductivity of free-standing MWCNTs sheet through dual doping with PEDOT: PSS and SnTe. The sequential energy dependent scattering of charge carriers at MWCNT/PEDOT-SnTe interfaces leads to a significant improvement of Seebeck coefficient. The enhanced carrier concentration along with the facile transport of the high energy charge carriers through PEDOT-SnTe composites due to improved connectivity between MWCNTs renders improvement of electrical conductivity. Such a synergetic combination of improved Seebeck coefficient and electrical conductivity resulted in a 7-fold enhancement in power factor of MWCNT/PEDOT: PSS-SnTe composite films. Simultaneous improvement of Seebeck coefficient and electrical conductivity is observed in ternary composite MWCNT sheet. Sequential energy filtering of charge carriers at MWCNT/PEDOT-SnTe interfaces is responsible for improvement of Seebeck coefficient. SnTe crystallites in the PEDOT matrix acts like charge reservoirs that help in improving the MWCNTs inter-junction connectivity.