Crossover from capacitive to pseudoinductive charge-relaxation in organic/polymeric light-emitting diodes

In this work we propose a phenomenological microscopic approach to deal with pseudoinductive charge-relaxation processes (named also as negative capacitance phenomena) in organic molecules (tris-8-hydroxyquinoline-aluminum) and polymeric [poly(2-metoxy-5-(2'-etil-hexiloxy)-1,4-phenylene vinylene)] light-emitting diodes (OLEDs and PLEDs, respectively). The approach is based mainly on the fact that the recombination rate is higher than the slower carrier transit time to reach the recombination zone. The approach is supported by the fact that in both PLEDs and OLEDs, the strong pseudoinductive relaxation process was mainly observed when electron-hole recombination takes place, suggesting this is a recombination dependent phenomenon. Besides, the negative branch, in the real part of the complex capacitance representation as a function of the frequency, was not observed in PLED homopolar devices