Charge trapping and electroluminescence at quantum dots embedded in a polymer matrix

Abstract

We unambiguously demonstrate that mechanisms of photoluminescence (PL) and electroluminescence (EL) are different for CdSe/ZnS quantum dots (QDs) embedded in a polymer host. With increase in concentration of QDs, EL intensity increases exponentially when the impressed current is kept the same. In contrast, PL intensity shows only a linear dependence on the concentration of quantum dots. In the case of EL, the QDs of 3.2nm diameter act as giant centers with a nearly temperature independent capture cross-section in the temperature range of 10–300K. A phenomenological model of carrier capture is proposed in which the hole capture cross-section is exponentially distributed due to non-uniform distribution of QD particles in the host. We also show that EL yield and effective carrier mobility (μeff) share identical non-Arrhenius temperature dependence for each concentration of embedded QDs. Possible origin of hole capture mechanisms are discussed in the light of these experimental observations.