Free-Volume Trapping in Charge Generating Layers

Abstract

The concept of free-volume trapping was first reported for single-layer aggregate (SLA) photoconductors.More recently, we have studied this phenomenon in multi-active photoconductors with separate charge generation and charge transport layers, CGL and CTL, respectively. We have found that trapping occurs in the CGL at weakly absorbed wavelength. It was proposed that excess free-volume amplified trapping by a dopant at the surface of the charge generating material enhanced recombination of the geminate hole pair, resulting in lower photoregeneration efficiency.In this work, we have studied the free-volume trapping phenomenon in multi-active photoconductors doped with molecules of various oxidation potentials. These studies have made it possible to isolate free-volume from intrinsic trapping. We have reconfirmed the role of the charge generation layer and the importance of surface and bulk charge generation. Free-volume trapping is dominant at trap depth below 0.2 V. Above that, intrinsic trapping completely dominates at the trap concentration level of the experiment. Lower trap concentration will most likely delay the dominance of intrinsic trapping.