Research Article Study of Electrical Transport Properties of Thin Films Used as HTL and as Active Layer in Organic Solar Cells, through Impedance Spectroscopy Measurements Camilo A. Otalora, 1 Andres F. Loaiza, 2 and Gerardo Gordillo 3 1 Chemistry Department, Universidad Nacional de Colombia, Bogot´ a 111321, Colombia 2 Research Department, Fundaci´ on Universidad de Am´ erica, Bogot´ a 111711, Colombia 3 Physics Department, Universidad Nacional de Colombia, Bogot´ a 111321, Colombia Correspondence should be addressed to Camilo A. Otalora; caotalorab@unal.edu.co Received 14 December 2015; Revised 31 May 2016; Accepted 12 June 2016 Academic Editor: Jamal Berakdar Copyright © 2016 Camilo A. Otalora et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Impedance spectroscopy (IS) is used for studying the electrical transport properties of thin flms used in organic solar cells with structure ITO/HTL/active layer/cathode, where PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid) and CuPC (tetrasulfonated copper-phthalocyanine) were investigated as HTL (hole transport layer) and P3HT:PCBM (poly-3- hexylthiophene:phenyl-C61-butyric acid methyl ester) blends prepared from mesitylene and chlorobenzene based solutions were studied as active layer and Ag and Al were used as cathode. Te study allowed determining the infuence of the type of solvent used for the preparation of the active layer as well as the speed at which the solvents are removed on the carriers mobility. Te efect of exposing the layer of P3HT to the air on its mobility was also studied. It was established that samples of P3HT and P3HT:PCBM prepared using mesitylene as a solvent have mobility values signifcantly higher than those prepared from chlorobenzene which is the solvent most frequently used. It was also determined that the mobility of carriers in P3HT flms strongly decreases when this sample is exposed to air. In addition, it was found that the electrical properties of P3HT:PCBM thin flms can be improved by removing the solvent slowly which is achieved by increasing the pressure inside the system of spin-coating during the flm growth. 1. Introduction Currently, silicon and inorganic thin flms solar cells tech- nologies dominate the photovoltaic (PV) market [1]. How- ever, partially due to the high production cost and related environmental issues, conventional PV technology must be replaced by emerging technologies such as organic-based PV (OPV) or hybrid solar cells. Organic semiconductors show great promise owing to their synthetic variability, low- temperature processing, and the possibility of producing lightweight, fexible, easily manufactured, and inexpensive solar cells [2–4]. Great progress has been made in increasing the power conversion efciency (PCE) of solution processed devices during the last ten years. In OPV, in 2001, Shaheen et al. [5] reported a record efciency of 2.5% and about 10 years later PCE > 10% has been demonstrated for lab devices [6]. On the other hand, perovskite solar cells emerged around 2012 with efciencies of 9% [7] and nowadays those PCE have been increased to more than 20% [6]. However, those efciencies are too low for practical uses at present, so that the device efciency must be increased by improving processing condi- tions [8], postfabrication treatments [9], or the use of new advanced materials with new device designs [10, 11]. P3HT is a widely studied material for OPV manufacture mixed with PCBM (phenyl-C61-butyric acid methyl ester) [12] and a promising hole transport material in emerging perovskite based solar cells devices [13]. Chlorobenzene is the most used solvent to date for deposition by spin-coating of P3HT and P3HT:PCBM flms used in organic solar cells [14]. However, using new solvents is a recognized approach to improve the properties of the solution processing-deposited materials. Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2016, Article ID 7267634, 7 pages http://dx.doi.org/10.1155/2016/7267634