Effects of Monofluorinated Positions at the End-Capping Groups on the Performances of Twisted Non-Fullerene Acceptor-Based Polymer Solar Cells

Abstract

Recently, main-chain twisted small molecules are attractive as electron-acceptors in polymer solar cells (PSCs) for their upshifted molecular energy levels, enhanced extinction coefficients, and better charge extraction properties along with longer carrier lifetimes and lower recombination rates relative to their planar analogues, which are conducive to the power conversion efficiency (PCE) promotion of PSCs. To further probe the “structure–performance” correlation of main-chain twisted acceptors, in particular the monofluorine-substituted sites on the performances of the resultant acceptors, two new main-chain twisted small molecules were synthesized, in which a fluorine atom was introduced at different sites on the end-capping group 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)­malononitrile (INCN). Although fine structural modification was adopted, quite different performances were obtained for the two acceptors. Compared to the 3-fluorinated analogue (i-IEICO-F3), a mixture of 4-fluorinated and 5-fluorinated isomers (i-IEICO-2F) exhibited a higher dipole moment, enlarged molar extinction coefficient with a bathochromic-shifted absorption region, suppressed charge recombinations with balanced charge mobilities, and slightly enhanced crystallinity. In combination with a fluorobenzotriazole-based medium-band gap polymer (J52), a high efficiency of 12.86% was resultantly achieved in an i-IEICO-2F-based device, which is superior to the result (7.65%) of the i-IEICO-F3 device, revealing the importance of monofluorinated positions on the performances of main-chain twisted non-fullerene acceptors.

Design of Thienothiophene-Based Copolymers with Various Side Chain-End Groups for Efficient Polymer Solar Cells

“…Nonfullerene acceptors have attracted much attention owing to their strong visible-near-infrared light-harvesting capability and tunable energy levels. In addition, they exhibit higher short-circuit current density (J sc ) and PCE in PSCs than fullerene acceptors, leading to a PCE of 18% that was reported recently [6][7][8]. In most PSCs with high efficiency, the conjugated polymer donor material often contains electron-rich and electron-deficient units in the polymer backbone, creating a push-pull effect that results in intraor intermolecular charge transfer (ICT) and gives rise to a polymer with a low bandgap and broad absorption band [9,10].…”

“…-b ]dithiophene (ITIC) and [6,6]-phenyl C 71 butyric acid methyl ester (PC 71 BM) used for polymer solar cells fabrication were purchased from Sigma-Aldrich and Solenne, respectively.…”

“…Among all kinds of solar cells, polymer solar cells (PSCs) have attracted extensive attention and become an emerging technology due to their benefits, such as light weight, low cost, easy solution processing, and potential for use in large-area flexible devices through roll-to-roll or printing technologies [1][2][3]. Typically, a PSC device structure comprises a conjugated polymer as an electron donor and a fullerene derivative [e.g., [6,6]-phenyl C 71 butyric acid methyl ester (PC 71 BM)] as an electron acceptor and features nanoscale, phase-separated bulk heterojunction (BHJ) morphology between the two electrodes. Through the great efforts of many researchers, power conversion efficiencies (PCEs) of PSCs have 2 of 16 attained over 13% for traditional single-junction PSCs and over 14% for tandem PSCs [4,5].…”

Boron(iii) β-diketonate-based small molecules for functional non-fullerene polymer solar cells and organic resistive memory devices

“…5 and S9 †). [68][69][70] For comparison, the surface morphology of the ascast J52:4 blend lm was also studied, in which a rather large RMS of 11.11 nm with excessive phase separation is observed (Fig. S9 †).…”

Tetrabromination versus Tetrachlorination: A Molecular Terminal Engineering of Nonfluorinated Acceptors to Control Aggregation for Highly Efficient Polymer Solar Cells with Increased Voc and Higher Jsc Simultaneously

“…Halogenation at the core unit or at the end group of the NF‐SMAs with different number of halogen atoms or in different substituted position/aromatic groups is a significantly effective strategy to modulate molecular energy levels and absorption range and improve the blend morphology and device performance. [ 66–80 ] Compared with the popular fluorinated or chlorinated IC functionalized NF‐SMAs, although brominated NF‐SMAs show lower synthesis cost and are much easier for postmodification, the brominated IC has been less incorporated into NF‐SMAs. [ 14,69,70,79,80 ] Until recently, Prof. Li's and Prof. Chen's groups independently reported the monobrominated IC functionalized NF‐SMAs with different core unit, which both exhibited slightly higher PCE in comparison with corresponding monofluorinated IC functionalized NF‐SMAs.…”