Determination of trap states in ladder type polymers

Electrically active defects have a profound impact on the semiconducting properties of conjugated polymer systems. Defect-induced thermally stimulated current (TSC), technique is used to probe the trap levels in these polymers. Detailed TSC investigations in oriented and as cast films of poly(benzimadazobenzophenanthroline) BBL, a ladder-type, high-temperature conjugated polymer are carried out. We estimate the energetics and the density of the trap states in BBL using this technique. Results obtained from complimentary experiments such as long-lived photocurrent studies are correlated with that obtained from TSC. We also demonstrate the applicability of this approach to characterise trap states in other conjugated polymer systems such as poly-3-octylthiophene, P3OT and poly(2-methoxy-5-(2′-ethyl-hexoxy)-1,4-para-phenylenevinylene) (MEHPPV).