Effects of bridging atom and p-bridge length on physical and photovoltaic properties of Aep-Dep-A oligomers for solution- processed organic solar cells Yuriy N. Luponosov a, *, 1 , Jie Min b, *, 1 , Artem V. Bakirov a, c , Petr V. Dmitryakov c , Sergei N. Chvalun a, c , Svetlana M. Peregudova d , Tayebeh Ameri b , Christoph J. Brabec b, e , Sergei A. Ponomarenko a, f a Enikolopov Institute of Synthetic Polymeric Materials of the Russian Academy of Sciences, Profsoyuznaya st. 70, Moscow 117393, Russia b Institute of Materials for Electronics and Energy Technology (I-MEET), Friedrich-Alexander-University Erlangen-Nuremberg, Martensstraße 7, 91058 Erlangen, Germany c National Research Centre “Kurchatov Institute”,1, Akademika Kurchatova pl., Moscow 123182, Russia d Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova St. 28, Moscow 119991, Russia e Bavarian Center for Applied Energy Research (ZAE Bayern), Haberstraße 2a, 91058 Erlangen, Germany f Chemistry Department, Moscow State University, Leninskie Gory 1-3, Moscow 119991, Russia article info Article history: Received 18 May 2015 Received in revised form 19 June 2015 Accepted 20 June 2015 Available online 2 July 2015 Keywords: Donoreacceptor oligomers Oligothiophenes Organic solar cells Alkyldicyanovinyl groups Dithienosilole Effect of heteroatom substitution abstract Synthesis of novel acceptoredonoreacceptor oligomers with electron-withdrawing alkyldicyanovinyl groups linked through an oligothiophene p-bridge with either dithienosilole or cyclopentadithiophene electron donor units is described. Changing the bridgehead atom from carbon to silicon in the central donor unit leads to a significant change in optical, thermal and structural properties of the oligomers. In addition, elongation of the oligothiophene p-bridge in the oligomers increases energies of HOMO and LUMO levels and leads to an unexpected hypsochromic shift of their absorption spectrum, because extension of the conjugation length cannot compensate a decrease of the intramolecular charge transfer between the dithienosilole and dicyanovinyl units. Although these minor changes in the chemical structures have a pronounced impact on the morphologies of their blends with PC 70 BM, the optimized solution-processed organic solar cells based on these small molecules demonstrate similar power con- version efficiencies. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Organic solar cells (OSCs) based on small molecules possess several potential advantages over the polymeric systems [1,2]. Compared to their polymeric counterparts, small molecules do not suffer from the effects of polydispersity, tend to have less batch-to- batch variation, and are easily functionalized and purified via standard techniques. The linear [3,4] or branched [5,6] derivatives of oligothiophenes are among the most investigated classes of materials for small molecules OSCs, since they may exhibit a combination of high-charge carrier mobility, good solubility in organic solvents, efficient light absorption as well as high stability. Nowadays the most successful design of oligothiophenes for OSCs was found to be when additional electron donor (D) and acceptor (A) units are introduced into the oligothiophene structure, which leads to the appearance of internal charge transfer (ICT) [7] be- tween the donor and the acceptor units and significantly reduces the bandgap of the compounds [3,8]. Along this theme, a large number of DeA molecules have been extensively investigated as donor materials for OSCs. Examples of DeA oligothiophenes have been reported that include the following acceptor and donor units: dicyanovinyl (DCV) [7], alkyl cyanoacetate [9], rhodanine [10], isoindigo [11], tetracyanobutadiene [12], arylamines [13,14], dithienosilole [15], benzodithiophene [16], and dithienopyrrole [17] etc. Although optimized OSCs based on small-molecule donor materials blended with fullerene acceptors achieved the effi- ciencies approaching 10% [18], development of the photoactive * Corresponding authors. E-mail addresses: luponosov@ispm.ru (Y.N. Luponosov), Min.Jie@ww.uni- erlangen.de (J. Min). 1 These authors contributed equally to this work. Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig http://dx.doi.org/10.1016/j.dyepig.2015.06.026 0143-7208/© 2015 Elsevier Ltd. All rights reserved. Dyes and Pigments 122 (2015) 213e223