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Abstract Side‐chain symmetry‐breaking strategy plays an important role in developing photovoltaic materials for high‐efficiency all‐small‐molecule organic solar cells (ASM OSCs). However, the power conversion efficiencies (PCEs) of ASM OSCs still lag behind their polymer‐based counterparts, which can be attributed to the difficulties in achieving favorable morphology. Herein, two asymmetric porphyrin‐based donors named DAPor‐DPP and DDPor‐DPP were synthesized, presenting stronger intermolecular interaction and closer molecular stacking compared to the symmetric ZnP‐TEH. The DAPor‐DPP:6TIC blend afforded a favorable morphology with nanoscale phase separation and more ordered molecular packing, thus achieving more efficient charge transportation and suppressed charge recombination. Consequently, the DAPor‐DPP:6TIC‐based device exhibited superior photovoltaic parameters, yielding a champion PCE of 16.62% higher than that of the DDPor‐DPP‐based device (14.96%). To our knowledge, 16.62% can be ranked as one of the highest PCE values among the binary ASM OSC filed. This work provides a prospective approach to address the challenge of ASM OSCs in improving film morphology and further achieving high efficiency via side‐chain symmetry‐breaking strategy, exhibiting great potential in constructing efficient ASM OSCs.