Electron and hole transport in a green-emitting alternating block copolymer: space-charge-limited conduction with traps

The transport characteristics of electrons and holes in an alternating bloc k copolymer, poly(1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylen e-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-3,5-dimethoxy-1 ,4-phenylene), have been investigated by current-voltage measurements in me tal/polymer/metal sandwich structures. Strong evidence that the hole curren t is space-charge limited with a single discrete set of shallow traps and t he electron current is space-charge limited with an exponential distributio n of traps was obtained. A hole trap density of similar to 1 x 10(17) cm(-3 ) and a hole trap energy of similar to 0.1 eV relative to the highest occup ied molecular orbital level were determined. The characteristic energy of t he trap distribution, similar to 0.05 eV, and the trap density <3.7 x 10(17 ) cm(-3) for electrons were also estimated. It was found that the hole curr ent became trap-free, space-charge limited, when using Au, Pd or Ni (phi(Au ) approximate to phi(Pd) approximate to phi(Ni) approximate to 5.1 eV) inst ead of Cu as the anode, indicating that the hole trap energy must lie betwe en phi(Cu) (approximate to 4.65 eV) and phi(Au). A hole mobility of similar to 10(-6) cm(2) V-1 s(-1) in this copolymer was determined.