Synergistic Effect of Fluorine Substitution and Thio-Alkylation on Photovoltaic Performances of Alternating Conjugated Polymers Based on Alkylthio-Substituted Benzothiadiazole-Quaterthiophene

Abstract

Three low bandgap polymers (PSDTBT-DFDT, PSDTfBT-DFDT, and PSDTffBT-DFDT) based on fluorine and alkylthio-substituted benzothiadiazole-quaterthiophene alternating units are synthesized and applied in polymer solar cells. The effects of fluorination and thio-alkylation on photophysical, electrochemical, and photovoltaic properties of the polymers are comparatively investigated. The results indicate that PSDTfBT-DFDT and PSDTffBT-DFDT show better light-harvesting abilities, lower HOMO energy levels, and better morphology than that of PSDTBT-DFDT. Bulk heterojunction (BHJ) organic photovoltaic devices based on the three polymers as donor materials were fabricated. The power conversion efficiencies (PCE) of 6.94% for PSDTfBT-DFDT and 7.50% for PSDTffBT-DFDT were attained, respectively, both of which are higher than that of PSDTBT-DFDT (4.48%) due to the increase in the numbers of fluorine atoms. This work demonstrates that both fluorine substitution and thio-alkylation are efficient to improve photovoltaic performances of polymers.

Chalcogen-bond driven molecular recognition at work

“…The same principle was then extended to different oligothiophenyl substrates, including oligothiophene, [129] bulk-heterojunction materials, [130] and conjugated polymers. [131] 4. Conclusions.…”

Chlorination strategy on polymer donors toward efficient solar conversions

“…To enhance photovoltaic performances, the strategy of fluorine (F) substitution has been investigated in detail in polymer solar cells, and many reports have demonstrated that the fluorine atom, a strong electron-withdrawing group, can simultaneously downshift both the LUMO and HOMO energy levels [46][47][48][49][50][51] . In addition, benefiting from the smallest atomic radius and the strongest electronegativity in the halogen family, the introduction of fluorine atoms could improve the molecular absorption, increase intermolecular interaction, crystallinity as well as charge mobility, and obtain desired morphology [52][53][54][55] .…”

Fluorination effects on bithiophene unit in benzodithiophene-4,8-dione based D–A type alternating copolymers for highly efficient polymer solar cells

“…29 The homogeneous phase separation indicates good miscibility between PDFTB and ITIC, which contributes to exciton dissociation, charge separation and transport and promotes J SC of the devices. 18,30 The AFM and TEM images reveal that uorination on the polymer backbone can effectively promote the surface morphology and the miscibility between donor and acceptor simultaneously, which may be favorable for higher J SC .…”