Efficient photoluminescence and electroluminescence from environmentally stable polymer/clay nanocomposites

Abstract

The potential use of polymer light-emitting devices is ultimately limited by their low quantum efficiency as well as by their poor stability against oxygen and moisture. To simultaneously solve these drawbacks, light-emitting devices using the polymer/layered silicate nanocomposite with good gas-barrier properties were fabricated by blending poly-[2-methoxy-5-(2 ' -ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with organoclay. The 2-dimensional nanocomposite film shows higher photoluminescence (PL) output and better photostability when compared with the pure MEH-PPV film of the same thickness. Electroluminescence (EL) efficiency is also enhanced. This 2-dimensional lamellar type nanocomposite structure efficiently confines not only both electrons and holes to enhance the recombination rate but also excitons to improve singlet radiative decay. By analyzing transient EL behavior, it was found that the charge carrier mobility of the nanocomposite device was reduced, which suggests that effective charge blocking improves the bipolar recombination rates. Additionally, the isolation of polymer chains within a confined geometry by intercalation prevents excitons from finding low-energy trap sites. Therefore, PL and EL quantum yield is improved.