Charge injection into thin conjugated polymer films

We review several results on the charge injection into thin conjugated poly mer films and discuss tunnelling and space-charge limited current models. T he analysis of the currently available models reveals an apparent divergenc e in the literature which we try to eliminate via the consideration of both effects. tunnelling and space-charge formation, simultaneously. We analyse experimental results using a tunnelling model, which includes the contribu tion to the electronic potential originated by the space-charge effects due to the low mobility of charge carriers in conjugated polymers. As a conseq uence, the empty levels accessible for charge carriers in the polymer are s hifted and the potential barrier for charge injection at the electrode/poly mer interface is modified. This modification implies in a different tunnell ing current and consequently in different current versus voltage dependence s. We use our results to estimate the mobility of negative charge carriers in poly (p-phenylene vinylene) and to determine the trap centre concentrati on in the polymer layer of devices which present hysteresis in the current versus voltage curves.