Achieve panchromatic absorption for all-small-molecule organic solar cells based on mono-porphyrin molecules by π-bridge modification

Porphyrin small molecules have been widely used in organic solar cells in recent years. However, further improvement of device efficiency is restricted owing to the absorption defects between Soret and Q bands of porphyrin donors and the limitation of application. The aim of this study was to compensate for its inherent defects and explore the photoelectric properties combined with the non-fused non-fullerene acceptor (NFA) to increase its universality. To achieve this goal, seven mono-porphyrin donor molecules with A-π-D-π-A configuration (SM1-SM7) were designed by modifying the π-bridges. The results indicate that π-bridge and side chains can lead to different ways of intramolecular charge transfer, which obtaining a new absorption peak between Soret and Q bands while the absorption range was extended to a near-infrared region (up to 1200 nm). When combined with the NFA, the larger ratios of intermolecular charge transfer and recombination rates (kinter-CT/kinter-CR) exceed 1011, which is conducive to obtaining higher short circuit current (JSC). At the same time, the open-circuit voltages (VOC) of devices were close to and/or higher than 1.0 V, indicating that the imbalance between JSC and VOC will be broken. Finally, we hope that this work can provide a strategy for designing potential panchromatic absorption donor molecules.