Benzothiadiazole Halogenation Impact in Conjugated Polymers, a Comprehensive Study

Abstract

The rise of halogenated organic semiconducting materials has led to a significant increase of organic photovoltaic power conversion efficiencies in recent years. However, the impact of halogen atoms on optoelectronic, structural and photovoltaic properties is not yet fully understood. In particular, because of different physico-chemical properties, the design of polymers using chlorine atoms instead of fluorine atoms still needs to be rationalized. In this paper, we investigate a series of 4 halogenated D-A electron donor copolymers, by varying not only the number of halogen atoms, but also their nature. The in-depth experimental and theoretical study of these new polymers, using the non-halogenated polymer as a reference, allowed us to rationalize the impact of these chemical modifications. In particular, we found that the structural properties and blending morphologies are mainly influenced by the nature of the halogen in this series of polymers. We have also demonstrated that a reasonable reduction in the number of fluorine atoms along the polymer backbone can be a good strategy to improve thin film processing conditions while keeping efficiencies at an acceptable level.

Non‐Fullerene Acceptors with an Extended π‐Conjugated Core: Third Components in Ternary Blends for High‐Efficiency, Post‐Treatment‐Free Organic Solar Cells

“…Such effect of the fluorine substitution was already evidenced in various families of NFAs including ITIC and in polymer series. [35] Overall, the values deduced from CV experiments are consistent with the ones obtained from density functional theory (DFT) calculation (see the Supporting Information). Despite a shift of 0.2-0.4 eV a similar trend is observed (Figure 2).…”

On the Impact of Linear Siloxanated Side Chains on the Molecular Self‐Assembling and Charge Transport Properties of Conjugated Polymers

“…[ 17 ] However, this effect is not observed in PF2‐C 20 , that is attributed to the strong intermolecular coulombic dipole–dipole interactions provided by fluorine atoms maintaining a close π‐stacking distance between polymer backbones whatever the side‐chain nature is. [ 27,36,73 ] Another aspect of interaction strength is the degree of overlapping of facing backbones, which is in first approximation reproduced by the intensity of h π peak. [ 71 ] Intensity of (100) peak is a relevant reference since electronic densities of siloxane and alkyl chains coincide within 1–2% and only the overall chain layer thickness needs to be considered: if π‐stacking was not affected by siloxane chains, their introduction would reduce I ( h π )/ I (100) ratios by roughly 20%.…”

Identifying the Trade-off between Intramolecular Singlet Fission Requirements in Donor–Acceptor Copolymers

“…For instance, the backbone fluorination of thiophene moieties, either alone [33][34][35][36] or as a component of more complex units [37][38][39][40] is a widely-reported approach to tuning the electronic properties of the heterocycle and the resulting extended material. 30 The chlorination of monomers [41][42][43][44][45] has also been used experimentally to modify the electronic and steric properties of conjugated polymers, as has esterification, cyanation and alkoxylation. [46][47][48][49][50][51] Nsubstituted side-chains on the amide and imide moieties found on isoindigo (iI), diketopyrrolopyrrole (DPP), naphthalene diimide (NDI) and thienopyrroledione (TPD) acceptors are readily accessible through the condensation of anhydrides with amines and substitutions reactions.…”