Wide energy-window view on the density of states and hole mobility of   poly(p-phenylene vinylene)
  Using an electrochemically gated transistor, we achieved controlled and reversible doping of poly(p-phenylene vinylene) in a large concentration range. Our data open a wide energy-window view on the density of states (DOS) and show, for the first time, that the core of the DOS function is Gaussian, while the low-energy tail has a more complex structure. The hole mobility increases by more than four orders of magnitude when the electrochemical potential is scanned through the DOS. 
I. N. Hulea, H. B. Brom, A. J. Houtepen, D. Vanmaekelbergh, J. J.   Kelly, and E. A. Meulenkamp