Study on EL emission region of polymer thin film in PPV LED

In this paper, the intensity ratios I(lambda(1) = 515 nm)/I(lambda(2) = 550 nm) of both electroluminescence (EL) and photoluminescence (PL) spectra of poly( phenylene vinylene) (PPV) thin film in the same PPV light-emitting diode (LED) are measured in order to discuss the EL emission dominant region. In the EL spectrum, the ratio I-1(lambda(1))/I-1(lambda(2)) decreased from 1.35 to 1.25, when the bias voltage increased from 4 to 12 V. In the PL spectrum, the ratios I-1(lambda(1))/I-1(lambda(2)) and I-2(lambda(1))/I-2(lambda(2)) (here I-1 and I-2 denote the intensities emitting from the indium-tin oxide (ITO) glass side and the opposite side, respectively) approach 1.5 and 1.3, separately. Based on these results, it is deduced that the emission dominant region of EL of PPV thin film in a single-layer PPV LED is close to the top electrode and apart from that of PL. (C) 1997 Elsevier Science S.A.