  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.
