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′-((2Z,2′Z)-(((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(4-((2-ethylhexyl)oxy)thiophene-4,3-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (i-IEICO-4F), is designed and synthesized via main-chain substituting position modification of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)dimalononitrile. Unlike its planar analogue IEICO-4F with strong absorption in the near-infrared region, i-IEICO-4F 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:i-IEICO-4F blend were observed, in comparison with those of 2.26 × 105 M–1 cm–1 and 1.08 eV for IEICO-4F. 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:i-IEICO-4F-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.