Deciphering the Role of Fluorination: Morphological Manipulation Prompts Charge Separation and Reduces Carrier Recombination in All-Small-Molecule Photovoltaics

Hua Tang, Cenqi Yan, Safakath Karuthedath, Hang Yin, Yajun Gao, Jie Gao, Lerun Zhang, Jiaming Huang, Shu Kong SO, Zhipeng Kan*, Frédéric Laquai, Gang Li*, Shirong Lu*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

24 Citations (Scopus)


Fluorination has proven effective in increasing the absorption, downshifting the energy levels, and enhancing the crystallinity of high-performance fused-ring electron acceptors (FREAs). However, an in-depth understanding of the effects of fluorination is still lacking, as research efforts have mainly focused on increasing the power conversion efficiency (PCE). In addition, fluorination on FREAs has rarely been reported in all-small-molecule organic solar cells (ASM OSCs). Herein, fluorination on FREAs is systematically studied in ASM OSCs using the popular FREA 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile and its fluorinated analog paired with DRCN5T, an oligothiophene donor seldom investigated in ASM OSCs to date. (Photo)physical studies are conducted on both systems and it is identified that, along with the aforementioned ones, fluorination exerts several additional effects, including the following. First, it optimizes the morphology, thereby accelerating charge separation and reducing geminate recombination charge pairs; second, it suppresses energetic disorder; and third, it prolongs the carrier lifetime and thus aids charge extraction. Consequently, the short-circuit current density and fill factor are significantly enhanced, and in turn, the PCE yields a 36% improvement, climbing to 9.25% and rivaling that of the current state-of-the-art oligothiophene-donor/nonfullerene ASM OSCs. The insights decipher the working mechanism of ASM OSCs that use fluorinated FREAs, paving the way toward high-performance ASM OSCs.

Original languageEnglish
Article number1900528
JournalSolar RRL
Issue number4
Publication statusPublished - 1 Apr 2020

Scopus Subject Areas

  • Atomic and Molecular Physics, and Optics
  • Energy Engineering and Power Technology
  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering

User-Defined Keywords

  • carrier lifetime
  • charge separation
  • energetic disorders
  • fluorination
  • organic solar cells


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