ption ▁and ▁phot ol um ines c ence ▁spect ra ▁using ▁commercial ▁instrument ation . ▁However , ▁in ▁order ▁to ▁find ▁out ▁if ▁a ▁material ▁acts ▁as ▁an ▁electron ▁don or ▁or ▁accept or ▁one ▁has ▁to ▁determine ▁the ▁energy ▁levels ▁for ▁hole ▁and ▁electron ▁transport . ▁The ▁easiest ▁way ▁of ▁doing ▁this , ▁is ▁to ▁employ ▁cy clic ▁volt am met ry . ▁However , ▁one ▁has ▁to ▁take ▁into ▁account ▁that ▁using ▁this ▁technique ▁the ▁experiment ally ▁determined ▁ox id ation ▁and ▁reduction ▁potential ▁are ▁lower ▁bounds ▁because ▁in ▁volt am met ry ▁the ▁radical ▁c ations ▁and ▁an ions ▁are ▁in ▁a ▁polar ▁fluid ▁solution ▁and ▁are , ▁thus , ▁sol v ated . ▁Such ▁a ▁sol v ation ▁effect ▁is ▁absent ▁in ▁a ▁solid ▁spec imen . ▁The ▁relevant ▁technique ▁to ▁ener get ically ▁locate ▁the ▁hole ▁transport ing ▁states ▁in ▁a ▁solid ▁sample ▁is ▁U V - photo em ission ▁spect ro sc opy . ▁The ▁equivalent ▁technique ▁for ▁electron ▁states ▁is ▁inverse ▁photo em ission . ▁ ▁There ▁are ▁several ▁techniques ▁to ▁measure ▁the ▁mob ility ▁of ▁charge ▁carri ers . ▁The ▁traditional ▁technique ▁is ▁the ▁so - called ▁time ▁of ▁flight ▁( TO F ) ▁method . ▁Since ▁this ▁technique ▁requires ▁relatively ▁thick ▁samples ▁it ▁is ▁not ▁applicable ▁to ▁thin ▁films . ▁Alternatively , ▁one ▁can ▁extract ▁the ▁charge ▁car rier ▁mob ility ▁from ▁the ▁current ▁flow ing ▁in ▁a ▁field ▁effect ▁trans istor ▁as ▁a ▁function ▁of ▁both ▁the ▁source - d rain ▁and ▁the