New environmentally friendly polyazomethines with thiophene rings for polymer solar cells Agnieszka Iwan a,⇑ , Bartosz Boharewicz a , Igor Tazbir a , Marek Malinowski a , Michal Filapek b , Tomasz Kła˛b c , Beata Luszczynska c , Ireneusz Glowacki c , Krzysztof P. Korona d , Maria Kaminska d , Jacek Wojtkiewicz f , Malgorzata Lewandowska e , Agnieszka Hreniak a a Electrotechnical Institute, Division of Electrotechnology and Materials Science, M. Sklodowskiej-Curie 55/61 Street, 50-369 Wroclaw, Poland b Institute of Chemistry, University of Silesia, 9 Szkolna Str., 40-006 Katowice, Poland c Department of Molecular Physics, Faculty of Chemistry, Technical University of Lodz, ul. Zeromskiego 116, 90-924 Lodz, Poland d Faculty of Physics, University of Warsaw, ul. Hoza 69, 00-681 Warsaw, Poland e Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland f Department for Mathematical Methods in Physics, Faculty of Physics, Warsaw University, ul. Hoza 74, 00-682 Warsaw, Poland Received 18 August 2014; received in revised form 27 March 2015; accepted 30 March 2015 Available online 19 May 2015 Communicated by: Associate Editor Hari Mohan Upadhyaya Abstract We synthesized two new, air-stable and environmentally friendly polyazomethines and characterized their photovoltaic and electro- chemical impedance spectroscopic properties. Two polyazomethines with one (25Th-DMB) or three (2252Th-DMB) thiophene rings were synthesized and tested as donors in the active layer in solar cells. The investigated polymer solar cells contained different amounts of PCBM and PC 71 BM. The bulk heterojunction polymer solar cells were fabricated and studied, considering the architecture of the devices (i.e., LiF, TiO 2 , and TiO 2 :Ag) and the fabrication conditions (i.e., air, inert gas, and annealing). The highest power conversion efficiency, which was equal to 0.52% under simulated 100 mW/cm 2 AM 1.5G irradiation, was determined for the device using polyazome- thine with three thiophene rings and PC 71 BM created in air with the ITO/PEDOT:PSS (100 cP)/2252Th-DMB:PC 71 BM (1:2)/Al archi- tecture. In addition, the power conversion efficiency was strongly dependent on the viscosity of the PEDOT:PSS used. Ó 2015 Elsevier Ltd. All rights reserved. Keywords: Polyazomethines; Thiophene rings; Polymeric photovoltaics; Bulk heterojunction solar cells 1. Introduction Polyazomethines (PAZs), which is the condensation product of diamine and dialdehyde, are interesting for application as organic photovoltaics because they are inex- pensive and require facile purification because water is the only co-product of the reaction (Iwan and Sek, 2008, 2011). Therefore, PAZ is environmentally friendly and can be applied to generate green energy. Much effort has been focused on the synthesis of new polymers and small molecule chemical compounds for application in organic solar cells e.g., (Bundgaard and Krebs, 2007; Gu¨nes et al., 2007; Zhan and Zhu, 2010; Jayawardena et al., 2013; Cai et al., 2010; Li, 2012; Kesters et al., 2014; Chen et al., 2009; Venkataraman http://dx.doi.org/10.1016/j.solener.2015.03.051 0038-092X/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: a.iwan@iel.wroc.pl (A. Iwan). www.elsevier.com/locate/solener Available online at www.sciencedirect.com ScienceDirect Solar Energy 117 (2015) 246–259