The incorporation of non-hexagonal rings into nanographenes (NGs) would significantly alter their geometry and electronic structures, unlocking new application potential. However, the precise integration of consecutive pentagon–octagon into NGs remains synthetically challenging due to the associated high strain and the limitation in design strategy. Herein, we report an unprecedented horse-saddle non-benzenoid NG (HN1) embedding four pairs of pentagon–octagon units. The synthesis proceeds through two key steps: a tetramerization of 3-bromoacenaphthylen-1(2H)-one, followed by a three-fold Pd-catalyzed annulation with a diacetylene derivative. Single-crystal X-ray diffraction confirms that HN1 adopts a unique horse-saddle geometry induced by the four adjacent octagons. The fused pentagon–octagon pairs of NG impart configurational stability, high solubility, multiple reversible redox behavior, and a distinct antiaromatic character arising from the core structure. Notably, the incorporation of HN1 as an additive in the perovskite active layer significantly enhanced the power conversion efficiency (PCE) of perovskite solar cells from 20.60% to 22.61%. This work not only provides a synthetic approach to negatively curved NGs with contiguous nonhexagonal motifs but also explores their promising application in emerging optoelectronic devices.