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7553984 
Journal Article 
Effect of blend layer thickness on the dielectric response of PCDTBT:PC71BM-based bulk heterojunction solar cells 
Dhibi, O; Ltaief, A; Bouazizi, A; , 
2014 
1 
Materials Science in Semiconductor Processing
ISSN: 1369-8001 
ELSEVIER SCI LTD 
OXFORD 
173-180 
WOS:000338820500024 
Bulk heterojunction solar cells based on a blend of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), were studied. The organic photoactive layers were spin coated onto a poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT-PSS) interfacial layer at speeds of 600 and 2000 rpm. The molecular structure of PCDTBT, PC71BM, and the PCDTBT:PC71BM blend was investigated using Fourier-transform IR (FTIR) spectroscopy, which confirmed the absence of interactions between the individual components of the composite. The dielectric properties of PCDTBT:PC71BM-based solar cells were studied under illumination by means of impedance analysis. The dielectric constant, impedance, and ac conductance were analyzed as a function of frequency at different bias voltages close to the open circuit voltage (V-OC). We found that the dielectric constant, dielectric loss, and conductance increased with increasing PCDTBT:PC71BM thickness. Impedance spectroscopy analysis revealed decreases in charge recombination and the resistance of the whole device with increasing spin coating speed for the active layer. Moreover, an increase in recombination resistance for the solar cells was observed close to V-OC. (C) 2013 Elsevier Ltd. All rights reserved.