Exciton Dissociation and Mobility in Conducting Polymers and Oligomers

Abstract

A survey of the literature shows that reverse bias current IL of an illuminated conducting polymer Schottky diode increases with voltage. We suggest that this increase in IL with applied reverse bias is due to a combination of two factors: (1) increase of mobility, and (2) dissociation of excitons. The experimental results agree with the values of IL calculated using either of the two mechanisms. Therefore it is difficult to determine the relative importance of the two mechanisms. The relative importance can be determined only if reliable values of material parameters are available. We have fabricated Schottky diodes and FETs using 5-ring n-octyloxy-substituted oligo[p-phenylene vinylene](Ooct-OPV5) and C60. The mobility of the oligomer derived from the measured characteristics of the diode is 3.29×10−7cm2/Vs and from the FET data, 3.24 × 10−4 cm2/Vs. These results show that the mobility (and other material parameters) depend strongly on the structure of the device. Therefore for interpreting the IL data it is important to measure the material parameters on the same structure on which IL measurements are made.