title: Synthesis and characterization of benzodithiophene and benzotriazole-based polymers for photovoltaic applications.
abstract: Two high bandgap benzodithiophene-benzotriazole-based polymers were synthesized via palladium-catalysed Stille coupling reaction. In order to compare the effect of the side chains on the opto-electronic and photovoltaic properties of the resulting polymers, the benzodithiophene monomers were substituted with either octylthienyl (PTzBDT-1) or dihexylthienyl (PTzBDT-2) as side groups, while the benzotriazole unit was maintained unaltered. The optical characterization, both in solution and thin-film, indicated that PTzBDT-1 has a red-shifted optical absorption compared to PTzBDT-2, likely due to a more planar conformation of the polymer backbone promoted by the lower content of alkyl side chains. The different aggregation in the solid state also affects the energetic properties of the polymers, resulting in a lower highest occupied molecular orbital (HOMO) for PTzBDT-1 with respect to PTzBDT-2. However, an unexpected behaviour is observed when the two polymers are used as a donor material, in combination with PC61BM as acceptor, in bulk heterojunction solar cells. Even though PTzBDT-1 showed favourable optical and electrochemical properties, the devices based on this polymer present a power conversion efficiency of 3.3%, considerably lower than the efficiency of 4.7% obtained for the analogous solar cells based on PTzBDT-2. The lower performance is presumably attributed to the limited solubility of the PTzBDT-1 in organic solvents resulting in enhanced aggregation and poor intermixing with the acceptor material in the active layer.
authors: Future Industries Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia; Department of Chemistry and Chemical Engineering, Polymer Technology, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
authors: Desta
authors: D
authors: Gedefaw
authors: National Research Council (CNR) - Institute of Nanostructured Materials (ISMN), Via P. Gobetti, 101, 40129 Bologna, Italy.
authors: Marta
authors: M
authors: Tessarolo
authors: Laboratory MIST E-R, Via P. Gobetti, 101, 40129 Bologna, Italy.
authors: Margherita
authors: M
authors: Bolognesi
authors: National Research Council (CNR) - Institute of Nanostructured Materials (ISMN), Via P. Gobetti, 101, 40129 Bologna, Italy.
authors: Mario
authors: M
authors: Prosa
authors: Department of Chemistry and Chemical Engineering, Polymer Technology, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
authors: Renee
authors: R
authors: Kroon
authors: Department of Chemistry and Chemical Engineering, Polymer Technology, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
authors: Wenliu
authors: W
authors: Zhuang
authors: Department of Chemistry and Chemical Engineering, Polymer Technology, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
authors: Patrik
authors: P
authors: Henriksson
authors: Department of Chemistry and Chemical Engineering, Polymer Technology, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
authors: Kim
authors: K
authors: Bini
authors: Department of Chemistry and Chemical Engineering, Polymer Technology, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
authors: Ergang
authors: E
authors: Wang
authors: National Research Council (CNR) - Institute of Nanostructured Materials (ISMN), Via P. Gobetti, 101, 40129 Bologna, Italy.
authors: Michele
authors: M
authors: Muccini
authors: National Research Council (CNR) - Institute of Organic Synthesis and Photoreactivity (ISOF), Via P. Gobetti, 101, 40129 Bologna, Italy.
authors: Mirko
authors: M
authors: Seri
authors: Future Industries Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia; Department of Chemistry and Chemical Engineering, Polymer Technology, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
authors: Mats R
authors: MR
authors: Andersson
keywords: 2D conjugated polymers; alkyl side chains; benzodithiophene; bulk heterojunction solar cells; fluorinated benzotriazole