Water-oil interfacial kinetics control enables water-based organic solar cells with 12.59% certified efficiency

Organic solar cells (OSCs) are promising for clean-energy generation, but sustainable production remains constrained by hazardous organic solvents. Aqueous organic-semiconductor nanoparticle (NP) inks offer an environmentally friendly route to OSCs, yet low efficiency and limited stability hinder practical application. Here we report an interfacial-tension-mediated strategy that regulates NP structure and film formation. By tuning the liquid-liquid interfacial tension during NP synthesis, this strategy balances donor/acceptor segregation at the water/oil interface and converts a donor-dominated, highly ordered shell into a mixed polycrystalline surface region. The reconfigured surface promotes particle fusion, phase connectivity and packing uniformity, enhancing charge generation and transport while suppressing recombination. The resulting water-based OSCs achieve 12.64% efficiency (certified, 12.59%), surpassing the previous 11.1% benchmark for water-based OSCs, alongside a remarkable improvement in thermal stability and a T80 exceeding 2000 h at 85 °C. Interfacial-tension regulation thus provides a practical handle for NP structure control towards efficient, durable and sustainable printed photovoltaics. The practical applications of environmentally friendly water-based organic solar cells are hindered by low device performance. Bi et al. develop an interfacial-tension-mediated regulation strategy to improve nanoparticle-derived film formation, achieving a power conversion efficiency of 12.64%.