A New High-sensitivity Organic Photoconductor for Electrophotography

A new organic photoconductor has been developed, consisting essentially of a 1:1 molar ratio of one molecule of 2, 4, 7-trinitro-9-fluorenone (TNF) to one monomer unit of poly-N-vinylcarbazole (PVCz). This photoconductor (1:1 TPC) is nearly panchromatic in the visible range of the spectrum and has a white-light sensitivity approximately equal to that of amorphous selenium when used for electrostatic imaging. The photosensitivity, which is due mainly to the TNF-PVCz complex, is greater for negative corona charging than for positive charging. Charge acceptance of the 1:1 TPC is high, ≈1200 volts for a 13 µm film, indicating good dielectric strength. Dark decay of the charge is affected by substrate materials and substrate surface conditions. In general dark decay is slower for negative charging than for positive charging. Quantum efficiency (Q.E.) is nominally about 0.15 in the range of 400 to 500 nm but decreases somewhat for shorter and longer wavelengths. The Q.E. increases rather markedly with field strength, but decreases somewhat at high light intensities. Field-controlled photogeneration of carriers is indicated, and thermal measurements show a field-dependent activation energy in the range of 0.06 to 0.20 eV. The absence of residual potentials in light decay curves and the lack of a thickness effect in photodischarge currents indicate that no deep traps are present in the 1:1 TPC layers.