Influence Of Regioregularity Research Articles

Regioregular Non‐Fused Polymerized Small Molecular Acceptors Enabling Efficient All‐Polymer Solar Cells†

Comprehensive SummaryThe regioregularity induced by the isomers of the end‐groups has been widely recognized as a key factor that determines the photovoltaic properties of polymerized small molecular acceptors (PSMAs) in all‐polymer solar cells (all‐PSCs). However, the influence of regioregularity on the photovoltaic properties of non‐fused PSMAs has not been explored yet. In this contribution, two regioregular non‐fused PSMAs, PFBTz‐T‐γ and PFBTz‐T‐δ, were synthesized for the first time by using the monomers with isomeric pure end‐groups. Compared with PFBTz‐T‐δ, PFBTz‐T‐γ has more compact and more ordered packing in solid state, which results in a more red‐shifted optical absorption and a higher electron mobility. More remarkably, PFBTz‐T‐γ and PFBTz‐T‐δ exhibited huge difference in photovoltaic performance in all‐PSCs, which offered the power conversion efficiencies (PCEs) of 9.72% and 0.52%, respectively. Further studies have unveiled that the higher PCE of PFBTz‐T‐γ is due to more efficient exciton dissociation, higher and more balanced electron/hole mobility, and less charge recombination as a result of favorable morphology of the blend film. This work demonstrates that the development of regioregular non‐fused PSMAs by tuning the polymerization sites is an effective strategy for obtaining high‐efficiency all‐PSCs.

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

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.

On the influence of regioregularity on electronic and optical properties of poly(alkylthiophenes)

Three types of alkyl substituted poly(thiophenes) were studied: regioregular head-to-head, tail-to-tail, regioregular head-to-tail and swith random couplings. The valence electron (band) spectra were determined by photoelectron spectroscopy (PES) and were interpreted with a reference to the conformation of the polymer chains. It is shown that the chain conformation drastically influences the luminescence and the optical properties of the polymers

On the influence of regioregularity on the structural properties of poly (alky Ithiophenes)

We present an overview of thorough, X-ray diffraction studies of the crystalline structure and conformation of the series of poly(alkylthiophenes) (PATs) samples. Three types of polymers have been subjected to these studies: “common” PATs, with ca 80% “head to tail” couplings; regioregular, pure “head to tail” PATs, and regioregular, pure “head to head, tail to tail” poly(4,4′-dialkyl-2,2′-bithiophenes). The samples containing n-hexyl, n-octyl and n-decyl groups have been investigated. The computer modelling has been intensively used in order to interpret the diffraction data. The results obtained show the importance of the coupling sequences on the structural properties of the polymers studied. The main effect is related to the average torsion angle-between two adjacent thiophene rings: it exhibits a rather low value for the “head to tail” and tail to tail” couplings, but it is remarkably higher for the “head to head” couplings. This leads to the important relations between the planarity and the crystallinity of all samples studied