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Solution-processed bulk heterojunction solar cells have experienced a remarkable acceleration in performances in the last two decades, reaching power conversion efficiencies above 10%. This impressive progress is the outcome of a simultaneous development of more advanced device architectures and of optimized semiconducting polymers. Several chemical approaches have been developed to fine-tune the optoelectronics and structural polymer parameters required to reach high efficiencies. Fluorination of the conjugated polymer backbone has appeared recently to be an especially promising approach for the development of efficient semiconducting polymers. As a matter of fact, most currently best-performing semiconducting polymers are using fluorine atoms in their conjugated backbone. In this review, we attempt to give an up-to-date overview of the latest results achieved on fluorinated polymers for solar cells and to highlight general polymer properties' evolution trends related to the fluorination of their conjugated backbone. [ABSTRACT FROM AUTHOR]

The use of Non-Fullerene Acceptors (NFAs) in the active layer of organic solar cells (OSCs) has made it possible to exceed 18% conversion efficiency. However, OSCs still present stability issues under operational conditions that need to be surpassed for their industrialization. In this work, we investigated binary and ternary blends to examine their efficiency and their stability as active layers of OSCs. We used a fluorinated polymer (PF2) as an electron donor and two different electron acceptors, a fullerene derivative (PC 71 BM) and a NFA (EH-IDTBR). We demonstrated that using EH-IDTBR instead of PC 71 BM leads to a decrease in efficiency attributed to the low out-of-plane electron mobility measured in the blend. However, using EH-IDTBR as single electron-acceptor significantly enhanced the OSCs stability under continuous illumination. Ternary blends were tested to reach simultaneously a high efficiency and a long-term stability. The best efficiency/stability compromise appeared to be when using EH-IDTBR only as electron-acceptor. We identified changes in the main charge-carrier recombination mechanism in photo-degraded devices from bimolecular in low EH-IDTBR content blends to trap-assisted in high EH-IDTBR ones. Finally, the blend morphology at a nanometer scale appeared as stable in high EH-IDTBR content blends while photo-degradation impacted significantly the morphology of the low EH-IDTBR content blend. [Display omitted] • An electron-donor polymer (PF2) blended with PC 71 BM leads to a high power conversion efficiency with low stability. • PF2 blended with a non-fullerene acceptor (EH-IDTBR) leads to a high stability with a lower efficiency. • The higher stability is linked to an improved morphology despite a change in the main charge-carrier recombination mechanism. • The lower stability is linked to a slight modification of the nano-morphology. [ABSTRACT FROM AUTHOR]

A series of donor‐acceptor (D‐A) π‐conjugated polymers, based on indacenodithienothiophene (IDTT) as an electron‐donating unit and quinoxaline as an electron‐deficient moiety, are synthesized via a Pd‐catalyzed Stille cross‐coupling polymerization. Molecular characteristics, photovoltaic parameters, and optoelectronic properties are examined through structural differences corresponding to thienyl versus phenyl side group substitutions on the IDTT and the non‐fluorinated versus the monofluoro quinoxaline derivatives. One of the most important outcome is that the power conversion efficiency (PCE) in the studied polymers is more device architecture dependent (conventional vs inverted) rather than chemical structure dependent. From single junction solar cells based on bulk heterojunction polymer:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) systems as the active layer, a maximum PCE of 5.33% has been achieved from the polymer containing the thienyl substituent on the IDTT and one fluorine atom on the quinoxaline. This demonstrates that finding the optimum molecular weight of ThIDTT‐QF or introducing the monofluoro‐quinoxaline in a regioregular motif in the polymer backbone significantly higher PCE can be expected versus the fully optimized high performance PhIDTT‐Q conjugated polymer. A correlation between polymer chemical structure—optoelectronic properties—organic solar cell performances has been performed in a series of donor‐acceptor (D‐A) π‐conjugated polymers, based on indacenodithienothiophene as an electron‐donating unit and quinoxaline as an electron‐deficient moiety. [ABSTRACT FROM AUTHOR]

Diketopyrrolopyrrole (DPP) derivatives are among the most efficient materials studied for both polymer solar cells (PSCs) and organic field-effect transistors (OFETs) applications. We report here the synthesis of new fluorinated dithienyldiketopyrrolopyrrole (fDT-DPP) monomers suitable for direct heteroarylation polymerization. fDT-DPP copolymers were then prepared to probe the effect of the fluorination. It was found that they feature deeper HOMO energy levels and smaller bandgaps than their non-fluorinated analogues. Moreover, some fDT-DPP copolymers show ambipolar behavior when tested in OFETs. For example, P2 shows hole mobility up to 0.8 cm2 V-1 s-1 and electron mobility up to 0.5 cm2 V-1 s-1. Inverted PSCs with power conversion efficiency (PCE) up to 7.5% were also obtained for P5. These results reported here (OFETs and PSCs) confirm that the fluorination of dithienyl-DPP moieties improves the performance of organic electronics devices. This study is also evidencing the strength of the direct heteroarylation polymerization and fDT-DPP as a new class of conjugated polymers. [ABSTRACT FROM AUTHOR]