Memory effect in the current-voltage characteristic of a low-band gap conjugated polymer

Abstract

Diodes formed by electrodeposition of the low-band gap polymer poly(4-dicyano methylene-4H-cyclopenta[2,1-b:3,4-b′]dithiophene), onto glass slides coated with indium tin oxide (ITO) and furnished with evaporated aluminum counterelectrodes exhibit a reversible bistability in their current-voltage (I-V) characteristics. Applying +5 V to the ITO electrode induces a "high" conductance state while applying -5 V induces a "low" conductance state. The effect is identical in most respects to recent observations in diodes formed from thin films of chromium-doped SrZrO3 sandwiched between SrRuO3 and gold electrodes. A number of mechanisms are discussed but the evidence points to the controlling influence of an interfacial depletion layer at the ITO-polymer interface. It is also shown that the high capacitances associated with such layers can lead to higher than expected displacement currents being generated during the automated collection of I-V data. The presence of such currents distorts the I-V characteristics in the low-bias low-current regime. © 2001 American Institute of Physics.