Effect of side chains on solubility and morphology of poly(benzodithiohene-alt-alkylbithiophene) in organic photovoltaics

It was reported that the side chains play especially an important role in enhancing physical properties and energy levels. Polythiophene based on benzodithiophene has excellent carrier mobility, but high HOMO level. We synthesized polythiophenes, PBDTBiTh(2EH) and PBDTBiTh(12C), were polymerized using the Stille coupling reaction and had thiophene with a 2-ethylhexyl or n-dodecyl side chain. Upon introducing the 2-ethylhexyl side chain, the absorption coefficients of the monomers and polymers were enhanced. Also, the edge-on orientation was fortified and the HOMO level was decreased to -5.37 eV. PBDTBiTh(2EH) showed a power conversion efficiency (PCE) of 2.1%, which was double that of PBDTBiTh(12C). (C) 2015 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.