Improved Cathode Interlayer Based on an N-Type Organic Semiconductor for ITO-Free Organic Photovoltaics

ITO-free organic photovoltaics (OPVs) utilizing a PEDOT:PSS PH1000 (PH1000) transparent electrode offer industrial compatibility, but achieving high efficiency and reproducibility remains challenging. This work systematically investigates n-type organic semiconductor cathode interlayers for PH1000-based ITO-free OPVs, employing PDINN as a model system. Pristine PDINN exhibits poor charge transport, insufficient solvent resistance, and interfacial morphology disruption, which compress the built-in field, aggravate non-radiative recombination, and degrade the active layer, resulting in limited open-circuit voltage, fill factor, and reproducibility. To overcome these limitations, a synergistic interface engineering strategy combining low-temperature thermal annealing and F16CuPc molecular doping is developed. This approach simultaneously enhances PDINN uniformity, charge transport, and solvent resistance while inducing favorable molecular packing, optimized phase separation, and improved exciton dissociation in the PM6:Y6DT active layer. Consequently, non-radiative voltage losses are suppressed, the built-in potential is increased, and both efficiency and reproducibility are significantly improved. Optimized ITO-free OPVs achieve average efficiency surpassing conventional ITO-based reference devices. The strategy is fully compatible with non-halogenated solvents and blade-coating processes, demonstrating excellent scalability. This work establishes the n-type organic semiconductor interlayer with the PH1000 electrode as a viable, industrially compatible alternative to inorganic cathodes, offering a paradigm for high-performance ITO-free OPVs.