In this work PTB7:[70]PCBM (Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diy1] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b] thiophenediyl]]:[6,6]-Phenyl-C71-butyric acid methyl-ester ([70])) based solar cells with PEIE (Polyethylenimine, 80% Ethoxylated) as electron transport layer (ETL) have been characterized along two months using impedance spectroscopy (IS). The experimental data were fitted using an electrical circuit and the time evolution of circuital parameters was analyzed. At high voltages, the capacitance associated to the PEIE layer decreases within the first days of measurements while the resistance increases during the same period. The flat band voltage, V-fb, obtained from a Mott-Schottky analysis, decreases with measuring time around 0.1 V, suggesting a deterioration of PEIE interface that no longer improves the ITO work-function. Carrier mobility decreases from 2.2 x 10(-3) cm(2)/Vs to 2.4 x 10(-4) cm(2)/Vs within the first few days of measurements. (C) 2017 Elsevier Ltd. All rights reserved.