Forward/Reverse dc bias or ac electroluminescence in poly(p-phenylene vinylene) prepared via sulfonium-salt and xanthate routes

In light-emitting diodes (LEDs) of standard configuration — Indium-Tin-Oxide (ITO)/polymer/metal, we observed light emission under ac or forward/reverse dc bias, using poly(p-phenylene vinylenes) prepared via the sulfonium salt (S-PPV) or xanthate (X-PPV) routes as active electroluminescent layers. S-PPV devices exhibited approximately symmetrical current-voltage characteristics under forward and reverse dc bias with the same onset voltage. The electroluminescence (EL) spectra either under a dc forward/reverse bias or ac were identical. X-PPV showed EL under reverse bias at higher voltage than in forward bias. Symmetrical current-voltage characteristics in SPPV devices is attributed to ionic impurities present in the polymer.