In situ study on the reorientation of polymer chains in operating polymer diodes

A reflection-absorption Fourier-transform infrared spectroscopy experiment has been designed to in situ monitor $\mathrm{poly(2-methoxy-5-}{\text{(2}}^{\prime }-\mathrm{ethylhexyloxy)-1,4-phenylene\hspace{0.17em}vinylene})$ (MEH-PPV)-based polymer light-emitting diodes under stress test. This method enables the in situ study of the co-relation between device performance and the conformational transformation of a conjugated polymer. The experimental results indicate that the plane of the conjugated π-electron cloud in MEH-PPV tends to align parallel to the substrate. This rearrangement enhances the π–π electron coupling and lowers the device operating voltage under high current densities.