Carrier injection and transport characteristics of copper phthalocyanine thin films under low to extremely high current densities

We investigated current density-voltage (J-V) characteristics of copper phthalocyanine (CuPc) thin films depending on active device areas. We prepared CuPc thin-film devices with active areas smaller than S=625μm2 using a photolithography technique. The maximum breakdown current density (JMAX) and voltage (VMAX) of the devices markedly increased as the active area was decreased from S=625 to 7.9μm2. In the smallest device, with S=7.9μm2, we obtained not only an extremely high current density of JMAX=128kA∕cm2 at VMAX=9.2V, but also unique J-V characteristics, indicating that the carrier conduction process shifted from the Fowler-Nordheim tunneling injection mechanism to shallow-trap and trap-free space-charge-limited current mechanisms.