Tailoring donor-acceptor copolymer conformations to minimize non-radiative voltage loss in perovskite solar cells

Non-radiative recombination at interfaces remains a critical bottleneck for achieving high open-circuit voltage (V_OC) in perovskite solar cells (PVSCs). Here, we propose a molecular design strategy of non-equivalent electron donor-electron acceptor (D-A) copolymers, which effectively reduces the non-radiative voltage loss ($\Delta V_{\mathrm{nr}}$) from 0.176 V to 0.127 V through synergistic optimization of interfacial energy alignment and defect passivation. By tailoring the D:A ratio in indacenodithiophene-benzodithiophene-4,8-dione-based polymers, the optimal B-20 (D:A = 3:2) achieves the lowest $\Delta V_{\mathrm{nr}}$ in the series, directly attributed to its enhanced planar molecular conformation and tighter intermolecular packing (π-π spacing: 4.24 Å). Density functional theory calculations and grazing incidence wide-angle X-ray scattering reveal that the D-A-D-D segment in B-20 exhibits superior coplanarity and π-π stacking, boosting hole mobility to 8.31 × 10⁻⁴ cm² V⁻¹ s⁻¹ and reducing interfacial carrier accumulation. These structural advantages, coupled with effective defect passivation via Lewis base interactions, collectively suppress non-radiative recombination. Consequently, the PVSCs using B-20 achieve a champion power conversion efficiency (PCE) of 22.35 % with a V_OC of 1.19 V, and a leading V_OC of 1.20 V at the PCE of 22.09 %, representing one of the most impressive V_OC values among the organic-inorganic hybrid PVSCs employing dopant-free polymeric HTMs, and demonstrating the critical role of molecular conformation control in mitigating $\Delta V_{\mathrm{nr}}$ for high-performance PVSCs.