2-(5,6-Difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)-malononitrile and Naphtho[2,3-b]thiophene Diimide End-Capped Porphyrin Derivatives as Panchromatic Light-Harvesting Absorbers and Non-Fullerene Acceptors in Organic Solar Cells.

Porphyrin-based nonfullerene acceptors (NFAs) are one of the most promising photoactive components in organic solar cells (OSCs) due to their excellent light-harvesting properties, featuring a high absorption coefficient of the Soret band in the ultraviolet-visible (UV-vis) region and an adjustable Q-band in the near-infrared (NIR) region, respectively. Moreover, the Acceptor-Donor-Acceptor (A-D-A) architecture is the most successful design strategy for constructing efficient NFAs. Herein, two porphyrin-based NFAs, named S-NPN-EH and T-NPN-OD, having naphtho-[2,3-b]-thiophene diimide (NTI) as the terminal acceptor units and porphyrin as a central core, are constructed with and without an acetylene linkage to elucidate the impact of linkage chemistry. For comparison, a 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2FIC) end-capped porphyrin derivative, denoted as POR6-4FIC, with acetylene-bridged alkylthiophene as the π-spacers, is reported. The impact of the terminal NTI acceptor and acetylene linkage on structural, optoelectronic, and photovoltaic properties of S-NPN-EH and T-NPN-OD is systematically studied. The film-state UV-vis absorption of T-NPN-OD shows a more red-shifted spectrum with intensified Soret-/Q-bands in the NIR region over 1000 nm because acetylene bridges enhance intermolecular stacking and coplanarity compared to S-NPN-EH. In addition, T-NPN-OD exhibits a down-shifted lowest unoccupied molecular orbital (LUMO) energy level compared with S-NPN-EH, indicating that the S-NPN-EH-based device improves V oc values. As expected, the reference POR6-4FIC shows strong red-shifted absorption over 1000 nm in the NIR region and down-shifted LUMO energy levels because of the strong intermolecular interactions between the donor and acceptors. The optimized device based on PTB7-Th/S-NPN-EH blend delivers a higher PCE of 2.19%, whereas the optimized PBDB-T:T-NPN-OD-based device shows a lower PCE of 1.01%. The reference PTB7-Th/POR6-4FIC-based device delivers a poor PCE of 0.32%. These results indicate that fine-balanced blend film morphology, well-matched energy levels, and solubility are critical for enhancing device performance.