The Effect of α‐Branched Side Chains on the Structural and Opto‐Electronic Properties of Poly(Diketopyrrolopyrrole‐alt‐Terthiophene)

Abstract

Introducing solubilizing α‐branched alkyl chains on a poly(diketopyrrolopyrrole‐alt‐terthiophene) results in a dramatic change of the structural, optical, and electronic properties compared to the isomeric polymer carrying β‐branched alkyl side chains. When branched at the α‐position the alkyl substituent creates a steric hindrance that reduces the tendency of the polymer to π–π stack and endows the material with a much higher solubility in common organic solvents. The wider π–π stacking and reduced tendency to crystallize, evidenced from grazing‐incidence wide‐angle X‐ray scattering, result in a wider optical band gap in the solid state. In solar cells with a fullerene acceptor, the α‐branched isomer affords a higher open‐circuit voltage, but an overall lower power conversion efficiency as a result of a too well‐mixed nanomorphology. Due its reduced π–π stacking, the α‐branched isomer fluoresces and affords near‐infrared light‐emitting diodes emitting at 820 nm.

Influence of Regioregularity on the Optoelectronic Properties of Conjugated Diketopyrrolopyrrole Polymers Comprising Asymmetric Monomers

“…The vibrational splitting is characteristic for aggregated DPP polymers. 55 Comparison of the temperature-dependent absorption spectra of both polymers (Figure S1, Supporting Information ) in TCE shows that the regioregular polymer retains this higher ratio between the 0–0 and 0–1 vibronic peaks at elevated temperatures. This indicates that the regioregular polymer has a higher degree of aggregation than the regiorandom polymer.…”

Tuning the Optical Characteristics of Diketopyrrolopyrrole Molecules in the Solid State by Alkyl Side Chains

“… 48 The low reaction yield for a is related to the use of a secondary bromoalkane, rather than a primary one and is typical for the synthesis of α-branched DPP molecules. 49 Subsequent bromination to c gave a yield of 86%. The yield of the bromination reaction with NBS is not strongly influenced by the branching of the alkyl side chain.…”

Recent progress of ultra-narrow-bandgap polymer donors for NIR-absorbing organic solar cells

“…42 Janssen et al reported α-and β-branched alkyl sidechain-substituted DPP-based polymer donors (1'HD-PDPP3T and 2'HD-PDPP3T) to investigate the effect of sidechains on the structural and optoelectronic properties. 43 backbones. 49 The synthesized region-regular asymmetric polymer (P(TDPPPy-T)-reg) showed a stronger vibronic peak and narrower bandgap (1.49 eV) than those of the random polymer (P(TDPPPy-T)-ran, E g = 1.53 eV).…”