Boosting power conversion efficiency (PCE) of organic solar cells (OSCs) has been restricted by its undesirably high energy loss, especially for those nonhalogenated solvent-processed ones. Here,a dichloro-methoxylated terminal group in an asymmetric small molecular acceptor design, which realizes a significantly reduced non-radiative energy loss (0.179 eV) compared to its symmetric counterpart (0.202 eV), is reported. Consequently, the device efficiency is improved by up to 20% for PM6:BTP-eC9-4ClO, without sacrificing the photon harvest or charge transport ability of the control system PM6:BTP-eC9. Further characterizations reveal the asymmetric acceptor BTP-eC9-4ClO's blend film demonstrates a suppressed triplet state formation, enabled by an enhanced electron delocalization. In addition, the asymmetric BTP-eC9-4ClO is found to be thermally stabler than BTP-eC9, and thus providing an improved device stability, whose T80 value reaches > 7800 h under 80 °C anneal in N2 via linear extrapolation. This work represents state-of-the-art device performance for nonhalogenated solvent-processed binary OSCs with certified results (19.45%).
Keywords: energy loss; nonhalogenated solvent; organic solar cell; power conversion efficiency; triplet state suppression.
© 2025 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.