Investigation of electronic trap states in organic photovoltaic   materials by current-based deep level transient spectroscopy
  Current-based deep level transient spectroscopy was used to study trap states in poly(3- hexylthiophene-2,5-diyl) (P3HT), [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and P3HT:PCBM blend. The obtained spectra showed traps of 87 meV activation energy in pure P3HT and 21 meV for PCBM. The blend shows a complex emission rate spectrum consisting of several different emission rate bands in the range of (0.1-30) s^-1, yielding activation energies between about 30 meV and 160 meV. 
Stefan Neugebauer, Julia Rauh, Carsten Deibel, Vladimir Dyakonov
cond-mat.mtrl-sci