Simultaneous Sign Change of Magneto-Electroluminescence and Magneto-Conductance in Polymer/Colloidal Quantum Dot Nanocomposites

Nanocomposites of conjugated polymer and colloidal quantum dots (QDs) have attracted considerable attention for optoelectronic and photovoltaic applications. Here the effects of magnetic field on the electroluminescence and current in poly[2-(4-(3',7'-dimethyloctyloxyphenyl)-1,4-phenylenevinylene] (P-PPV)/CdSe-CdS-ZnS QDs composites are studied. Our results show that by increasing the concentration of CdSe-CdS-ZnS QDs in the hybrid nanocomposites from 0 to 25 wt %, the polarities of magneto-electroluminescence (MEL) and magneto-conductance (MC) are simultaneously changed from positive to negative. In addition, the amplitudes of negative MEL and MC are enhanced as the temperature decreases, showing an abnormal temperature dependence. We attribute these magnetic field effects to CdSe-CdS-ZnS QDs-induced direction reverse in spin-mixing of loosely bound polaron pairs in P-PPV matrix prior to energy transfer to QDs. With this study we show that incorporating QDs in polymer matrix can strongly influence spin-selective interactions in the hybrid nanocomposites, which may pave the way for spin-related applications of these fascinating hybrid nanocomposites.