Quantum size effect on photoluminescence and electroluminescence properties in organic multiple quantum wells

We fabricated organic light emitting diodes (OLEDs) containing multiple quantum wells (MQW) structures in the active layer. MQWs consist of TPD (N,N'-bis(3-methilphenyl)-N.N-diphenyl benzidine) and DCM (4-(Dicyanomethilane)-2-methil-6-(p-dimethilamino-styryl)-4H-pyran). Electroluminescence (EL) measurements revealed that EL spectra of these samples presented double peaks. According to the numerical calculation of subband energies under the envelope function approximation, the double peaks in the observed EL spectra can be attributed to the radiative recombination from the ground and first excited states, respectively. The effective mass of the electrons is also estimated to be about 0.5 m(0).