Simple near-Infrared Nonfullerene Acceptors Enable Organic Solar Cells with >9% Efficiency.

Nonfullerene acceptors (NFAs) based on calamitic-shaped small molecules are being developed rapidly to improve the photoelectron conversion efficiencies (PCEs) of organic solar cells. NFAs with light absorption extended to the near-infrared (NIR) region are of interest because they play a pivotal role in both organic tandem cells and semitransparent devices. In this work, two simple acceptor-donor-acceptor-structured NFAs (CPDT-4Cl and CPDT-4F) have been designed and synthesized. Featured with dimerized 4H-cyclopenta[1,2-b:5,4-b']dithiophene (CPDT) as the electron-donating core and Cl- or F-substituted 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile as the electron-accepting unit, the absorption spectra of two NFAs are extended to the NIR region with an absorption edge at approximately 910 nm. In conjunction with the polymer donor material PBDB-T, a PCE of 9.47% was achieved by using a CPDT-4F-based device with a short-circuit current density of up to 20.1 mA/cm2, which slightly outperforms its counterpart CPDT-4Cl (PCE = 9.28%) under the same condition. This work broadens the scope of developing new NIR NFAs with both high efficiency and easy accessibility.