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

Abstract

Two asymmetric thiophene (T)/pyridine (Py) flanked diketopyrrolopyrrole (DPP) polymers with a regiorandom and regioregular conjugated backbone are synthesized via a Stille polycondensation to investigate the effect of regioregularity on their optoelectronic properties and photovoltaic performance in fullerene-based polymer solar cells. Surprisingly, both polymers possess very similar optical bandgap, energy levels, and photovoltaic performance. These findings, combined with a factor of 19 reactivity difference between the two end groups of the asymmetric DPP monomer, intuitively suggest the formation of regular chain segments in the random polymer. However, by modeling the random polymerization reaction with a kinetic Monte Carlo (KMC) simulation, evidence is obtained for exclusive formation of a fully random polymer structure. UV–vis–NIR absorption spectra of three extended DPP chromophores, containing the donor segments (T-T-T, Py-T-Py, and Py-T-T) present in the regiorandom polymer, confirm that regioregularity of the backbone has a negligible influence on the optical properties.

Impact of π-Conjugated Linkers on the Effective Exciton Binding Energy of Diketopyrrolopyrrole–Dithienopyrrole Copolymers

“… 47 , 49 , 50 The Py-DPP-T units are randomly incorporated in the conjugated backbone of P(DPP-Py-DTP-T), despite a reactivity difference at both ends of the asymmetric monomer. 44 Before polymerization, monomers 1 and 2 were purified by recrystallization in methanol. The commercial distannyl-DTP monomer ( 3 ) (purity ≈98.5%) was used as received because recrystallization in methanol was not possible.…”

Local structuring of diketopyrrolopyrrole (DPP)-based oligomers from molecular dynamics simulations

“…The combination of these studies point to a coherent qualitative picture: DPP polymers form short range aggregates with the size of the aggregate being modulated by changes in the polymer backbone and side chain. [55][56][57] The conjugated portions in the more ordered phases are co-planar with measurable π-stacking distance but there is no other information available on the local structure and therefore on the driving force for aggregation and the microscopic effect of chemical changes.…”

Structurally‐tuned benzo[1,2‐b:4,5:b']dithiophene‐based polymer as a dopant‐free hole transport material for perovskite solar cells

“…Thus, the blue‐shift of around 45 nm was observed in the transitioning from Py0 to Py4, indicating that the frontier energy levels are changed upon the pyridine replacement within the respective HTMs. Moreover, it could be inferred from this observation that the progressive substitution of pyridine in our polymers would generate the gradually twisting of polymer chain out of conjugated planarity, resulting in a steady reduction in conjugation length 37,38 . All polymers showed the appearance of strong shoulder protrusions in both solution and film states, suggesting the presence of polymer aggregates due to the strong interchain couplings within the chains of synthesized BDT‐based polymers.…”