Comments on "Unusual Thermoelectric Behavior Indicating a Hopping to   Bandlike Transport Transition in Pentacene"
  W. Chr. Germs, K. Guo, R. A. J. Janssen, and M. Kemerink [1] recently measured the temperature and concentration dependent seebeck coefficient in organic thin film transistor and found the seebeck coefficient increases with carrier concentration (corresponding to the gate voltage) in the low temperature regime. They further concluded that this unusual behavior is due to a transition from hopping transport in static localized states to bandlike transport, occurring at low temperatures. This is obviously in contrast to the previous theoretical prediction because it is widely accepted that hopping transport is more pronounced at low temperature. We will discuss the reason for this unusual behavior here and suggest that the density of states function plays an important role in concentration dependent seebeck coefficient. 
Ling Li, Nianduan Lu, and Ming Liu
cond-mat.dis-nn