On the electrical degradation and green band formation in oc- and (3-phase poly(9,9-dioctyfluorene) polymer light-emitting diodes

摘要

In this work we report a detailed comparison of optical and electrical degradation between ex- and p-phase poly(9,9-dioctyftuorene) (PFO) based diodes. Analysis of the EL spectra along continuous operation time in ex- and p-PFO based diodes reveals that the unwanted green emission traditionally associated to fluorenone is more likely to occur in cx-phase PFO. The relative spectral areas arising from excitonic and vibronic transitions as well as fluorenone defects have been quantified by means of Gaussian deconvolu-tion along the operation time. The relative spectral area associated to the formation of the fluorenone increases 13% for the p-PFO diode and up to 21% for the α-PFO diode only after 35 min of continuous operation. Analysis of the/-V curve before and after electrical stressing has lead to hole mobilities in pristine diodes of 1.4×10~(-4)cm~2/Vsand 1.6 x 10~(-5) cm~2/Vs for p-PFO and a-PFO respectively. Both p-PFO and ot-PFO degraded samples show a reduction in the hole mobility, as well as an increase in the width of the Caussian density of states.