Guided by a semi-empirical model, two small-molecule acceptors were rationally designed and an impressive PCE of 15.05% was achieved.

It has been proposed that isotope effects could effectively downshift intramolecular vibrational frequencies of lightharvesting materials, thereby reducing the non-radiative recombination from the charge-transfer (CT) state to the ground state (GS) and achieving a smaller non-radiative energy loss (ΔE loss non-rad ) theoretically in organic solar cells (OSCs). However, there are no systematic experimental studies to address such a crucial issue: can isotope effects enable OSCs to achieve a smaller ΔE loss non-rad and why? Herein, we constructed 29 non-fullerene acceptors (NFAs) by isotope substitution on different functional groups based on four high-performance NFA systems and further investigated their photovoltaic performance systematically. Large-scale statistical experimental and theoretical analyses indicate no significant difference of PCE and ΔE loss non-rad due to the intrinsically very weak electron-vibration coupling between the CT state and GS (EVC CT-GS ) and largely unimpacted coupling strength (t CT-LE ) between the CT and local exciton states. Also based on theoretical results from the Huang−Rhys factor, although different vibration modes could have different influences on the strength of EVC CT-GS , all are quite small. Both experimental and theoretical results suggest that an isotope strategy may not be a feasible way to significantly improve PCEs of high-performance OSCs by reducing ΔE loss non-rad at the current stage. Article pubs.acs.org/cm

Molecule engineering has been demonstrated as a valid strategy to adjust the active layer morphology in all‐small‐molecule organic solar cells (ASM‐OSCs). In this work, two non‐fullerene acceptors (NFAs), FO‐2Cl and FO‐EH‐2Cl, with different alkyl side chains are reported and applied in ASC‐OSCs. Compared with FO‐2Cl, FO‐EH‐2Cl is designed by replacing the octyl alkyl chains with branched iso‐octyl alkyl chains, leading to an enhanced molecular packing, crystallinity, and redshifted absorption. With a small molecule BSFTR as donor, the device of BSFTR:FO‐EH‐2Cl obtains a better morphology and achieves a higher power conversion efficiency (PCE) of 15.78% with a notable fill factor (FF) of 80.44% than that of the FO‐2Cl‐based device with a PCE of 15.27% and FF of 78.41%. To the authors’ knowledge, the FF of 80.44% is the highest value in ASM‐OSCs. These results demonstrate a good example of fine‐tuning the molecular structure to achieve suitable active layer morphology with promising performance for ASM‐OSCs, which can provide valuable insight into material design for high‐efficiency ASM‐OSCs.

Iron-catalyzed organic reactions have been attracting increasing research interest but still have serious limitations on activity, selectivity, functional group tolerance, and stability relative to those of precious metal catalysts. Progress...