Electrogenerated Chemiluminescence and Fluorescence Lifetime Spatial Heterogeneity of Poly (2-methoxy-5-(2-ethylhexyloxy
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Electrogenerated Chemiluminescence and Fluorescence Lifetime Spatial Heterogeneity of Poly (2-methoxy-5-(2-ethylhexyloxy)-1,4phenylenevinylene) in Presence of [6,6]-phenyl-C61-butyric Acid Methyl Ester Hongwei Geng1, Shanlin Pan1, Dehong Hu2 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487 USA 2 Fundamental and Computational Science Directorate, Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352 1
ABSTRACT We present electrogenerated chemiluminescence (ECL) and fluorescence lifetime mapping of MEH-PPV/PCBM thin films. The ECL results show that the oxidation peak of MEH-PPV near 0.7 V (vs. SCE) and ECL response of films shifted positively towards 1.2 V in the presence of PCBM. At the same time, the oxidation current density of MEH-PPV increases along with the decrease of ECL intensity in the presence of PCBM. The fluorescence lifetime images clearly show that the lifetime spatial heterogeneities are affected by different substrates and MEHPPV/PCBM ratios. Meanwhile, the lifetime of MEH-PPV decreases with the increasing of film thickness. The lifetimes of MEH-PPV films on TiO2 substrate are lower than films on glass. INTRODUCTION Conjugate polymers have been used for photovoltaic applications due to their potential to low cost, lightweight, tunable electronic properties and good compatibility with various printing techniques enabling flexible large solar cell fabrication.1-3 Particularly, a bulk heterojunction (BHJ) solar cell can be fabricated using interpenetrating network formed by a conjugate polymer and a fullerene derivative sandwiched between two electrodes with different work functions.4-6 Such interpenetrating network with a largely increased interfacial area for efficient charge separation and light absorption can be obtained by simple single step spin-coating method. Poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) has been considered as one of the most potential conducting polymers for BHJ solar cell fabrication. In this solar cell configuration, MEH-PPV acts as an electron donor (p-type semiconducting polymer) with a relatively low conductivity and [6, 6]-Phenyl-C61-Butyric Acid Methyl Ester (PCBM) is used as electron acceptor material for effective charge separation and exciton dissociation.7-9 The MEHPPV/PCBM has been extensively applied to understanding the interfacial charge transfer dynamics and solar energy conversion because of the interpenetrating networks formed by these two species.10-12 In order to successfully apply such BHJ solar cell based on conjugate polymers to real applications, not only the high power conversion efficiency but also the large area13, 14 and stability 15-17 are equally important in solar cell technologies. Fundamental research such as understanding the interfacial charge transfer dynamics and spatial distribution of the physical characteristics of conjugate polymer systems are critical to lay a solid foundation towards improving the efficiency and stability of an organic BHJ solar cell. Here we present t
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