Enhancement of thermoelectric figure-of-merit in a wide temperature range in In$_4$Se$_{3-x}$Cl$_y$ bulk crystals

Recently, we proposed that the charge density wave is a new pathway for high thermoelectric performance in bulk crystalline materials [1,2]. Through the quasi one-dimensional lattice distortion (Peierls distortion) in In$_4$Se$_{3-x}$ bulk single crystals, we have achieved a high thermoelectric figure-of-merit {\it ZT} of 1.48 at 705 K. From the Boltzman transport calculation, it was confirmed that the reported {\it ZT} could be further increased if we could increase the chemical potential of the In$_4$Se$_{3-x}$ crystals. Here we report the significant increase of {\it ZT} over a wide temperature range from 50 $^{\circ}$C to 425 $^{\circ}$C by chlorine doping in the In$_4$Se$_{3-x}$, which comes from the improvement of crystal quality and increase of chemical potential, resulting in the power factor enhancement and the thermal conductivity reduction. \\[4pt] [1] J.-S. Rhyee et al., J. Appl. Phys. {\bf 105}, 053712 (2009). \\[0pt] [2] Jong-Soo Rhyee et al., Nature (London) {\bf 459}, 965 (2009).