Photocurrent generation under forward bias with interfacial tunneling of carrier at pentacene/F16CuPc heterojunction photodetector

Abstract

Fabrication of a bilayer organic photodetector (OPD) based on pentacene and copper–hexadecafluoro-phthalocyanine (F16CuPc) has been done employing thermal evaporation method. The photo-response characteristics of OPD have been investigated under illumination of light having different wavelengths. Absorption from 300 nm to 900 nm has been observed for this series of OPD, obtained after annealing at different temperatures. Experimental results on this series of OPD reveal quite symmetric current density – voltage (J-V) characteristics both at forward and reverse bias condition. We have attributed such symmetric J-V response to efficient electron tunneling between highest occupied molecular orbital of pentacene to lowest unoccupied molecular orbital of F16CuPc. This is being confirmed further using Fowler-Nordheim tunneling model. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) images indicate degradation of device responsivity with increase in annealing temperature. The relatively higher responsivity (0.0029 A/W) with respect to available reports indicate that the pentacene/F16CuPc heterojunction will be one of the promising materials for optoelectronics mixer and photodetector applications below 850 nm.