Abstract

Charge carriers photogeneration in organic semiconductors occurs when excitons break into positive and negative polarons; this process can be affected by an external electric field Field-induced (FI) charge generation was previously indirectly studied by transient photoluminescence quenching [1]. In this work we report on the direct observation of FI charge generation in conducting polymer LEDs with femtosecond time resolution. We have used methyl substituted ladder type poly(para-phenylene) (m-LPPP) because of its well-characterized photophysics [2]. The LEDs consist of 100 nm thick m-LPPP films sandwiched between aluminum and ITO electrodes. The pump beam is a frequency doubled Ti: Sapphire laser and the probe is obtained by continuum generation. Field-dependent changes (ΔT/T)_F in the spectrum are measured by subtracting field-on and field-off data at different pump-probe delays.

© 1998 IEEE