Effect of doping on the electrical and optical properties of organic semiconductors

Addition of small quantities of dyes modifies the optoelectronic properties of organic semiconductors. This type of doping enhances the photo as well as electro luminescence properties of the semiconductor by transferring their exciton energy to the dye molecules. Phosphorescent dyes are routinely used to harvest triplet excitons in organic light emitting diodes to enhance their internal efficiency to almost 100%. In most cases, energy from the host molecules is transferred to dye molecules through Forster or Dexter type energy transfer processes. In some cases, dye molecules traps charge carriers from the matrices and recombines with opposite charges (trap assisted recombination) to form excitons resulting in very efficient light emission. It is usually assumed that the addition of dyes do not modify the electrical properties of the matrices. We have made detailed optical and electrical studies on a zinc complex, zinc hydroxyphenyl benzoxozolate(Zn(hpb)₂) doped with DCM dye and found that the dye doping has seriously affected the transport properties of Zn(hpb)₂.