This study focuses on a liquid type light-emitting device with simple structure, an organic electrochemiluminescence (ECL) device. To realize long luminescence, polymer ECL devices using π-conjugated polymers, poly(2,5-dioctylphenylene-1,4-ethynylene) (PPE) and poly(3-octylthiophene-2,5-diyl) (P3OT), were fabricated. The luminescence properties of each device were investigated. Both polymer ECL devices exhibit luminescence from an excited-state polymer which is formed by redox and annihilation reaction. In particular, a low threshold voltage of about 2.4 V and long luminescence for about 6000 s were obtained from the P3OT ECL device. This is a longer luminescence than from a typical low molecular ECL device using a ruthenium complex. Moreover, the concentration of emitting material and the frequency applied were important parameters in order to obtain the long luminescence. Applying high frequency AC voltage (5.0 V at 1000 Hz) to the emitting solution with moderate P3OT concentration of 3.0 wt% emitted light for a long period. On the other hand, the PPE ECL device suggested the instability of the radical cation and its luminescence conditions were stringent. Its luminescence was short (about 180 s).
