Impact of Symmetric vs Asymmetric Conjugated Extensions in Acceptors on the Photovoltaic Performance of Organic Solar Cells

Abstract

To enhance efficiencies of OSCs, it is essential to minimize the 𝐸loss or maximize Voc while ensuring that the short-circuit current density (Jsc) and fill factor (FF) are not sacrificed. In this work, we design two small-molecule acceptors (SMAs), named CHSPh and CHAPh, which incorporate fused 2-bromobenzene units symmetrically and asymmetrically within the central unit of the Y-series SMAs. The asymmetric π-extending 2-bromobenzene block enhances π–π stacking, thereby facilitating efficient charge transport and improving luminous efficiency while minimizing non-radiative recombination. As a result, CHAPh demonstrates a significantly reduced Δ𝐸nr of 0.180 eV and 𝐸loss of 0.508 eV. Consequently, OSCs based on CHAPh achieve a PCE of 19.35%, representing a substantial improvement over the 10.06% PCE of OSCs based on CHSPh. This result provides a promising molecular strategy for enhancing the performance of high-efficiency OSCs.

Keywords: Organic solar cells, non-fullerene acceptors, energy loss, asymmetric, symmetric