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Wide‐bandgap (WBG) nonfullerene acceptors (NFAs) with nonfused conjugated structures play a critical role in organic photovoltaic (OPV) cells. Here, NFAs named GS‐OEH, GS‐OC6, and GS‐ISO, with optical bandgaps larger than 1.70 eV, are synthesized without using the fused ring structures. Compared with GS‐OEH and GS‐OC6, GS‐ISO exhibits much stronger crystallinity, leading to a smaller energetic disorder and a larger exciton diffusion coefficient. GS‐ISO also possesses a higher electroluminescence external quantum efficiency of 1.0 × 10⁻². The OPV cell based on PBDB‐TF:GS‐ISO demonstrates a power conversion efficiency (PCE) of 11.62% under the standard one sun illumination. Besides, the PBDB‐TF:GS‐ISO‐based cell with effective area of 1.0 cm² exhibits a PCE of 28.37% under 2700 K illumination of 500 lux. A tandem OPV cell using PBDB‐TF:GS‐ISO as the front subcell shows an …