Benzotrithiophene Copolymers: Influence of Molecular Packing and Energy Levels on Charge Carrier Mobility

The planar benzotrithiophene unit (<b>BTT</b>) was incorporated into four different donor polymers, and by systematically changing the nature and positioning of the solubilizing alkyl side chains along the conjugated backbone, the polymers’ frontier energy levels and optoelectronic properties were controlled. Reducing the steric hindrance along the polymer backbone lead to strong interchain aggregation and highly ordered thin films, achieving hole mobilities of 0.04 cm²/(V s) in organic thin film transistors. In an attempt to increase the polymer’s processability and reduce chain aggregation, steric hindrance between alkyl side chains was exploited. As a result of the increased solubility, the film forming properties of the polymer could be improved, but at the cost of reduced hole mobilities in OFET devices, due to the lack of long-range order in the polymer films

Benzocarborano[2,1‑<i>b</i>:3,4‑<i>b</i>′]dithiophene Containing Conjugated Polymers: Synthesis, Characterization, and Optoelectronic Properties

We report the stannylation of a benzocarborano­[2,1-<i>b</i>:3,4-<i>b</i>′]­dithiophene monomer and its polymerization by Stille polycondensation with solubilized cyclopentadithiophene and diketopyrrolopyrrole derivatives. The physical, material, and optoelectronic properties of the resultant conjugated copolymers are reported, demonstrating that benzocarboranodithiophene acts as a mildly electron-withdrawing monomer

Fused Dithienogermolodithiophene Low Band Gap Polymers for High-Performance Organic Solar Cells without Processing Additives

We report the synthesis of a novel ladder-type fused ring donor, dithienogermolodithiophene, in which two thieno­[3,2-<i>b</i>]­thiophene units are held coplanar by a bridging dialkyl germanium. Polymerization of this extended monomer with <i>N</i>-octylthienopyrrolodione by Stille polycondensation afforded a polymer, <b>pDTTG-TPD</b>, with an optical band gap of 1.75 eV combined with a high ionization potential. Bulk heterojunction solar cells based upon <b>pDTTG-TPD</b>:PC₇₁BM blends afforded efficiencies up to 7.2% without the need for thermal annealing or processing additives

Isostructural, Deeper Highest Occupied Molecular Orbital Analogues of Poly(3-hexylthiophene) for High-Open Circuit Voltage Organic Solar Cells

We present the synthesis and characterization of two novel thiazole-containing conjugated polymers (<b>PTTTz</b> and <b>PTTz</b>) that are isostructural to poly­(3-hexylthiophene) (P3HT). The novel materials demonstrate optical and morphological properties almost identical to those of P3HT but with HOMO and LUMO levels that are up to 0.45 eV deeper. An intramolecular planarizing nitrogen–sulfur nonbonding interaction is observed, and its magnitude and origin are discussed. Both materials demonstrate significantly greater open circuit voltages than P3HT in bulk heterojunction solar cells. <b>PTTTz</b> is shown to be an extremely versatile donor polymer that can be used with a wide variety of fullerene acceptors with device efficiencies of up to 4.5%. It is anticipated that this material could be used as a high-open circuit voltage alternative to P3HT in organic solar cells