A Memory Effect in the Current-Voltage Characteristic of a Low-Bandgap Conjugated Polymer

Summary Diodes formed by electrodeposition of the low-bandgap polymer poly(4-dicyano methylene-4H-cyclopenta[2,1-b:3,4-b’]dithiophene), PCDM, onto glass slides coated with indium tin oxide (ITO) and furnished with evaporated aluminium counterelectrodes exhibit a reversible bistability in their current-voltage 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 SrZrO 3 sandwiched between SrRuO 3 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 distort the I-V characteristics in the low-bias, low-current regime.