Investigation of negative magneto-conductance properties of cobalt phthalocyanine thin films

The opto-electrical and magnetic field effects on cobalt phthalocyanine (CoPc) thin film single layer device were explored. The root mean square roughness of thin film was 5.8 nm. The mobility was estimated for space charge limited current region in the current–voltage characteristics. Magnetic field effect on injection current was studied in terms of organic magneto-conductance. The negative magneto-conductance (MC) was observed in CoPc thin film diode at different bias voltages. The negative values of MC were found to be 10.05, 8.29, 6.84, 4.98 and 3.13% for applied bias voltages 1, 2, 3, 4 and 5 V, respectively. The CoPc thin film absorbed the UV–visible wavelength range which were represented by two bands of CoPc molecule, B band and Q band. MC study of device under dark and light reveals the formation of trap assisted bipolarons and their quenching by the formation of photogenerated excitons. The device was checked for the resistive and capacitive behaviour by impedance spectroscopy. The contact resistance is approximately constant ~ 66 Ω at all applied bias voltages. The bulk and interface resistance vary from 1.8 to 0.6 kΩ and 50.06 to 1.43 kΩ, respectively. Similarly, the bulk and interface capacitance vary from 55.81 to 10.56 nF and 50.47 to 558.09 nF, respectively for applied bias voltages.