Synthesis and photovoltaic performance of nitrogen-bridged star-shaped fused-ring electron acceptors

Abstract

<p indent="0mm">A new nitrogen-bridged star-shaped fused-ring electron acceptor (BTDTP-C8C9-6Cl) with benzo[1,2-<italic>b</italic>:3,4-<italic>b</italic>′-5,6-<italic>b</italic>′′]tri(4-<italic>H</italic>-dithieno[3,2-<italic>b</italic>:2′,3′-<italic>d</italic>]pyrrole) as a fused ring skeleton and 5,6-dichloro-3-(dicyano methylene)indone as end groups has been designed and synthesized. The electron acceptor shows an strong intramolecular charge transfer absorption in the range of 500~<sc>800 nm</sc> with the molar extinction coefficient of 3.2×10⁵ M⁻¹ cm⁻¹ and the optical bandgap of <sc>1.56 eV.</sc> Two wide bandgap polymer donors, PM6 and D18, which have complementary absorption spectra with BTDTP-C8C9-6Cl, are blended with BTDTP-C8C9-6Cl to fabricate organic solar cell devices, respectively. Compared with the blend film based on PM6 and BTDTP-C8C9-6Cl, the blend film based on D18 and BTDTP-C8C9-6Cl shows stronger crystallinity and more suitable fibrous interpenetrating network phase separation morphology. The investigation of the charge transport and recombination behaviors reveals that the device based on D18:BTDTP-C8C9-6Cl exhibits more balanced charge transport, weakened recombination, and effective exciton dissociation and charge collection. Finally, the organic solar cell device based on D18:BTDTP-C8C9-6Cl achieves power conversion efficiencies of 12.00%.