The Effect of Fluorine Substitution on the Molecular Interactions and Performance in Polymer Solar Cells

Abstract

Fluorine (F) substitution on conjugated polymers in polymer solar cells (PSCs) has a diverse effect on molecular properties and device performance. We present a series of three D-A type conjugated polymers (PBT, PFBT, and PDFBT) based on dithienothiophene and benzothiadiazole units with different numbers of F atoms to explain the influence of F substitution by comparing the molecular interactions of the polymers and the recombination kinetics in PSCs. The preaggregation behavior of PFBT and PDFBT in o-DCB at the UV-vis absorption spectra proves that both polymers have strong intermolecular interactions. Besides, more closely packed structures and change into face-on orientation of fluorinated polymers are observed in polymer:PCBM blends by GIXD which is beneficial for charge transport and, ultimately, for current density in PSCs (4.3, 13.0, and 14.5 mA cm for PBT, PFBT, and PDFBT, respectively). Also, the introduction of F atoms on conjugated backbones affects the recombination kinetics by suppressing bimolecular recombination, thereby improving the fill factor (0.41, 0.68, and 0.69 for PBT, PFBT, and PDFBT, respectively). Consequently, the PCE of PSCs reached 7.3% without any additional treatment (annealing, solvent additive, etc.) in the polymer containing difluorinated BT (PDFBT) that is much higher than nonfluorinated BT (PBT ∼ 1%) and monofluorinated BT (PFBT ∼ 6%).

Syntheses and optical, electrochemical, and photovoltaic properties of polymers with 6‐(2‐thienyl)‐4H‐thieno[2,3‐b]indole with a variety of electron‐deficient units

“…The highest PCE was achieved in the PTTIDOMBI device with CN additive; this gave a PCE of 2.84% with the best J SC of 9.16 mA/cm 2 because its blend film for the OPV device had a preferred orientation along the in‐plane direction. The open‐circuit voltage ( V OC ) values of the devices were generally matched with the relationship between the HOMO energy level of a donor and the LUMO energy level of the acceptor . Compared to that of the previously reported PTTIDTBT, the introduction of dialkoxyl groups in the electron‐deficient BT unit of PTTIDOBT resulted in a deeper HOMO level and a higher V OC .…”

New Conjugated Polymers Based on Dithieno[2,3‐e:3′,2′‐g]Isoindole‐7,9(8H)‐Dione Derivatives for Applications in Nonfullerene Polymer Solar Cells

“…Monomers 4,7‐bis(5‐(trimethylstannyl)thiophen‐2‐yl)benzo[c][1,2,5] thiadiazole (M2) and 5,6‐difluoro‐4,7‐bis(5‐(trimethylstannyl) thiophen‐2‐yl)benzo[c] [1,2,5]thiadiazole (M3)were prepared according to the procedure reported in previous studies …”

“…Monomers 4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c] [1,2,5] thiadiazole (M2) and [52,53] 5,6-difluoro-4,7-bis(5-(trimethylstannyl) thiophen-2-yl)benzo[c] [1,2,5]thiadiazole (M3)were prepared according to the procedure reported in previous studies. [54,55] The general synthetic routed and molecular structure of dithieno[2,3-e:3 0 ,2 0 -g]isoindole-7,9(8H)-dione (DTID) (M1) monomer is shown in Scheme 1, and the details of the synthesis are described in the Supporting Information (the experimental part).…”

Printed Large-Area Photovoltaic Modules Based on Small Molecules with Different Alkyl Terminal Chains

“…Solution-processed organic photovoltaics (OPVs) have been regarded as next-generation photovoltaics owing to their key advantages such as low-cost manufacturing, mass production, and easy fabrication of flexible devices. , During the past decade, continuous efforts have been devoted to advancing the field of OPVs, such as synthesis of numerous organic semiconductor materials − and development of device engineering techniques. − With these tremendous exertions, power conversion efficiency (PCE) has consequently increased up to 15% for polymer OPVs and 13% for small-molecule OPVs . The efficiency of OPVs is now high enough for commercial viability.…”