Core and π‐Bridge Engineering to Deconstruct Y6‐Series into Modular Non‐Fused Acceptors: DFT‐Guided Structure‐Property Map for Organic Solar Cells

ABSTRACT Non‐fullerene acceptors have propelled organic solar cells beyond 20% efficiency, yet the fused Y‐series backbones enabling high performance impose synthetic complexity and limited modularity. In this theoretical study, we propose a backbone deconstruction strategy, converting the BTP‐4Cl acceptor into an A‐π‐A′‐π‐A type non‐fused architecture to establish atomistic structure‐property relationships for core and bridge engineering. Six acceptors (Q1‐Q6) were designed by tuning the π‐bridge from thiophene to thienothiophene and the central BTD core to dithiophene‐based DT‐BTD, conjugation‐extended 4T‐BTD, and thiazole‐enriched TZT‐BTD. Density Functional Theory calculations show that the designed acceptors retain efficient Y‐class electronic structures and narrow energy gaps, yielding Scharber‐estimated V OC of 1.01–1.17 V against PM6 donor. Designed acceptors exhibited broad near‐IR absorption with λ max of 642–751 nm and achieved dominant charge‐transfer character, reaching 84% ICT excitations compared to 53% for BTP‐4Cl. Notably, the designs maintained tight solid‐state packing with significantly reduced reorganization energies (0.132–0.164 eV), achieving up to a four‐fold enhancement in electron mobility (9.43 × 10 − 1 cm 2 V − 1 s − 1 ) over the benchmark BTP‐4Cl. Interfacial calculations further indicated markedly strengthened PM6:acceptor electronic couplings for robust charge separation and low recombination losses. Overall, this study demonstrates that non‐fused engineering successfully preserves Y‐series optoelectronics while improving intrinsic electron transport and charge separation for efficient organic photovoltaics.