Determination of carrier mobility in MEH-PPV thin-films by stationary and transient current techniques

Charge transport and shelf-degradation of MEH-PPV thin-films were investigated through stationary (e.g. current versus voltage — JxV) and transient (e.g. Time-of-Flight — ToF, Dark-Injection Space-Charge-Limited Current — DI-SCLC, Charge Extraction by Linearly Increasing Voltage — CELIV) current techniques. Charge carrier mobility in nanometric films was best characterized through JxV and DI-SCLC. It approaches 10^? 6 cm²/Vs under a SCLC regime with deep traps for light-emitting diode applications. ToF measurements performed on micrometric layers (i.e. ~ 3 μm) confirmed studies in 100 nm-thick films as deposited in OLEDs. All results were comparable to a similar poly(para-phenylene vinylene) derivative, MDMO-PPV. Electrical properties extracted from thin-film transistors demonstrated mobility dependence on carrier concentration in the channel (~ 10^? 7–10^? 4 cm²/Vs). At low accumulated charge levels and reduced free carrier concentration, a perfect agreement to the previously cited techniques was observed. Degradation was verified through mobility reduction and changes in trap distribution of states.