Contents lists available at ScienceDirect Reactive and Functional Polymers journal homepage: www.elsevier.com/locate/react Synthesis of conjugated polymers with directly coupled 2- butyloctyloxybenzodithiophene and benzothiadazole units for application as active layers in organic solar cells Jose Jonathan Rubio Arias a, ⁎ , Laura Crociani b , Igor Tenório Soares a , Isabela Custodio Mota a , Bianca Pedroso Silva Santos a , Rogério Valaski c , Maria De Fátima Vieira Marques a a Universidade Federal do Rio de Janeiro, Instituto de Macromoléculas Eloisa Mano, IMA-UFRJ, Cidade Universitária, Av. Horácio Macedo, 2.030, Centro de Tecnologia, Bloco J, Rio de Janeiro, RJ, Brazil b Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE), Consiglio Nazionale delle Ricerche (CNR), C.so Stati Uniti 4, 35127 Padova, Italy c Instituto Nacional de Metrologia, qualidade e tecnologia INMETRO, Laboratório de dispositivos orgânicos, Avda. Nossa Senhora das Graças 50, Xerém, Duque de Caxias, Brazil ARTICLE INFO Keywords: Conjugated polymer Atomic Force Microscopy Polymer solar cell Benzodithiophene ABSTRACT One of the fastest growing areas in polymer science is the photovoltaic organic devices, which conjugated polymers are an important part of, since they constitute the core of bulk heterojunction active layer. In this work two ben- zodithiophene based polymers containing fluorinated and non-fluorinated benzothiadiazole units were successfully synthesized. It was observed that chain growth depends upon the nature of the electron deficient monomer, being fluorinated monomer able to produce higher chain size and distribution. Low band gap was obtained (1.71 and 1.72 eV for fluorinated and non-fluorinated polymers, respectively) as well as values of −3.78 and −3.66 eV for LUMO orbitals energy were estimated. The synthesized polymers presented degradation temperatures above 280 °C, which makes them able to be processed through roll-to-roll deposition techniques. Charge carriers mobilities are 4.6×10 −6 and 1.0 × 10 −5 cm 2 V −1 .s −1 for non-fluorinated and fluorinated polymers, respectively: this last higher charge carrier mobility was attributed to the interaction between the fluorine atoms and the adjacent aromatic sulfur, which according to other authors promotes planarity and consequently, it favors the charge carriers mobility. AFM images showed a higher roughness correlated with phase separation for fluorinated polymer; conduction paths with dimensions less than 25 nm were detected which is positive for future improvement of solar devices. 1. Introduction The design of conjugated polymers containing alternated π electron abundant and π electron deficient units (donor-acceptor-donor D-A-D) has become an important research field in the search for photovoltaic poly- mers with enhanced performance. Thanks to low energy payback time (EPBT), organic photovoltaics (OPVs) turn out to be a feasible option for energy market. It is expected that an increase in power conversion effi- ciencies (PCE) of active layers, will boost the EPBT and therefore, increase OPVs participation in energy market [2]. One of the ways in which such PCE increase is expected to occur is through the synthesis and application of D-A-D fashion conjugated polymers. Among them, benzodithiophene (π electron abundant unit) based polymers are worth to be highlighted. One of the problems observed for benzodithiophene based polymers alternated with π deficient units is their low solubility. The present work involved the synthesis of a benzodithiophene monomer containing the 2 butyl-octyl chains as side groups, since it has been previously reported [3,4] that the commercially available monomer containing 2-ethylhexyl chains gen- erates well performed polymers, however, with low solubility. Several approaches have been tried to produce D-A-D fashion poly- mers. Benzodithiophene, dithiophene and carbazole have been more often used as electron rich structural units, while benzothiadiazole, benzofur- andiazole and several of its derivatives have been explored as electron deficient units [5]. Most authors have preferred to approach the electron density difference of A-D consecutive units through the use of a thiophene bridge, which, according to their claims, increases the efficiency of poly- mers due to pi spacing [6]; nevertheless, some other known polymers possess direct coupling between high and low electron density units and perform outstandingly (PTB7 for example) [7], aiming to explore fur- thermore the aforementioned direct coupling, the present work proposes https://doi.org/10.1016/j.reactfunctpolym.2019.104355 Received 18 June 2019; Received in revised form 27 August 2019; Accepted 6 September 2019 ⁎ Corresponding author. E-mail addresses: jonathanrubio@ima.ufrj.br (J.J.R. Arias), laura.crociani@cnr.it (L. Crociani), bianca.pedroso3@ima.ufrj.br (B.P.S. Santos), rvalaski@inmetro.gov.br (R. Valaski), fmarques@ima.ufrj.br (M.D.F.V. Marques). Reactive and Functional Polymers 144 (2019) 104355 Available online 10 September 2019 1381-5148/ © 2019 Elsevier B.V. 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