Recombination profiles in poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] light-emitting electrochemical cells

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Abstract
We present a study on the optical and electronic properties of light-emitting electrochemical cells (LECs) based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with the goal of understanding emission profiles and characterizing salt and electrode dependence. Direct imaging of photoluminescence and electroluminescence profiles of planar LECs and simulations of optical interference effects were performed in order to gain insight into emission profiles in vertical structure LECs. While our results are consistent with oxidative doping, they imply a lack of reductive doping in LECs under normal operating conditions. We observe that trends in emission profiles are independent of thickness, salt, and electrode type. In addition, device current-voltage (I-V) and radiance characteristics were measured as a function of salt and electrode type. Variations in the I-V characteristics, turn-on voltage, and rectification are observed for devices with Al versus. Au contacts and for salts with varied cation type. Finally, we discuss the implications of our findings on the operating mechanism of LECs.