Nonfullerene Polymer Solar Cells Based on a Main-Chain Twisted Low-Bandgap Acceptor with Power Conversion Efficiency of 13.2%

A new acceptor–donor–acceptor-structured nonfullerene acceptor, 2,2′-((2<i>Z</i>,2′<i>Z</i>)-(((4,4,9,9-tetrakis­(4-hexylphenyl)-4,9-dihydro-<i>s</i>-indaceno­[1,2-<i>b</i>:5,6-<i>b</i>′]­dithiophene-2,7-diyl)­bis­(4-((2-ethylhexyl)­oxy)­thiophene-4,3-diyl))­bis­(methanylylidene))­bis­(5,6-difluoro-3-oxo-2,3-dihydro-1<i>H</i>-indene-2,1-diylidene))­dimalononitrile (<b>i-IEICO-4F</b>), is designed and synthesized via main-chain substituting position modification of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1<i>H</i>-indene-2,1-diylidene)­dimalononitrile. Unlike its planar analogue <b>IEICO-4F</b> with strong absorption in the near-infrared region, <b>i-IEICO-4F</b> exhibits a twisted main-chain configuration, resulting in 164 nm blue shifts and leading to complementary absorption with the wide-bandgap polymer (J52). A high solution molar extinction coefficient of 2.41 × 10⁵ M^–1 cm^–1, and sufficiently high energy of charge-transfer excitons of 1.15 eV in a J52:<b>i-IEICO-4F</b> blend were observed, in comparison with those of 2.26 × 10⁵ M^–1 cm^–1 and 1.08 eV for <b>IEICO-4F</b>. A power conversion efficiency of 13.18% with an open-circuit voltage (0.849 V), a short-circuit current density of 22.86 mA cm^–2, and a fill factor of 67.9% were recorded in J52:<b>i-IEICO-4F</b>-based polymer solar cells (PSCs), demonstrating that this main-chain twisted strategy can be a guideline that facilitates the development of new acceptors to maximize the efficiency in PSCs