EFFECTS OF HUMIDITY ON THE DARK CONDUCTIVITY AND DIELECTRIC-PROPERTIES OF POLY(BENZIMIDAZOBENZOPHENANTHROLINE) THIN-FILMS

The dark conductivity and the dielectric constant of thin films of the conjugated ladder polymer poly(benzimidazobenzophenanthroline) (BBL) are found to exhibit large sensitivity to the relative humidity (RH). Although the dc part of the conductivity shows the largest sensitivity, increasing from 4 x 10(-14) to 5 x 10(-11) S/cm when the relative humidity changes from 0 % to 50 %, the ac part varies much less under similar changes in RH. At RH approaching 0 %, the dielectric constant was found to be frequency independent and close to 3 over the whole measured frequency range (10-10(6) Hz), whereas at 50 % RH the dielectric constant was about 5 at the highest frequency. Thermogravimetric analysis has also confirmed these findings by detecting about 2 % weight loss due to moisture removal from the films. The possible origins for these humidity effects on dark conductivity and dielectric properties are examined.