Injection of current densities over kA/cm2 in organic thin films and investigation of charge-carrier transport mechanisms in current density region between nA/cm2 and kA/cm2

Abstract

We investigate current density-voltage (J-V) characteristics of copper phthalocyanine thin-film devices, with active areas ranging from S = 1,000,000 to 7.9 μm2, and analyze their charge-carrier transport mechanisms under current densities between nA/cm2 and kA/cm2. We demonstrate injection of 128 kA/cm2 in the smallest device having S = 7.9 μm2. Furthermore, we find that J-V characteristics are divided into three regions between nA/cm2 and kA/cm2: ohm current, shallow-trap space-charge-limited current (SCLC), and trap-free SCLC. In a shallow-trap SCLC region, we observe a large shift in J-V characteristics depending upon the active areas. From analyses of carrier traps with a thermally stimulated current (TSC) measurement, we see that TSC signal intensities of these films decrease as the active area is reduced. Hence, we conclude that a large shift in J-V characteristics is attributable to the change of carrier trap concentrations in these films.