Key Takeaways & Executive Findings
- •• • The AZnO-F3N hybrid cathode interlayer achieves a PCE of 20.6% in binary PM6:L8-BO devices, surpassing conventional ZnO-based interlayers by >1% absolute, attributed to enhanced electron extraction and reduced trap-assisted recombination. • • Incorporating BTP-eC9 as a third component in a ternary blend elevates PCE to 21.0% (certified 20.8%), with a fill factor of ~82.5%, representing the highest certified efficiency for single-junction OSCs to date. • • The ternary OSCs exhibit good operational stability, maintaining >80% of initial PCE after 1000 hours of continuous illumination under 1-sun equivalent, addressing the chronic stability bottleneck of OSCs. • • The AZnO-F3N CIL is universally effective across multiple donor–acceptor systems, thick-film (>300 nm) active layers, and flexible substrates, demonstrating compatibility with roll-to-roll manufacturing and mechanical flexibility requirements.
Abstract
Organic solar cells (OSCs) have emerged as a promising photovoltaic technology, yet their power conversion efficiency (PCE) and operational stability remain critical bottlenecks for commercialization. Here, we report a hybrid cathode interlayer (CIL) comprising aluminum-doped zinc oxide (AZnO) modified with a perylene diimide-based conjugated polyelectrolyte (PNDIT-F3N, simplified as F3N). This AZnO-F3N CIL effectively enhances electron extraction and suppresses charge recombination, yielding a PCE of 20.6% in binary devices based on the PM6:L8-BO active layer. By incorporating a third component, BTP-eC9, as a second acceptor in a ternary blend, the PCE is further boosted to 21.0% (certified 20.8%), the highest certified value reported to date for OSCs. The ternary devices also exhibit an impressive fill factor of approximately 82.5% and good operational stability. The AZnO-F3N CIL demonstrates broad applicability across various donor–acceptor systems, thick-film architectures, and flexible substrates, underscoring its potential for future OSC manufacturing. This work provides a robust interfacial engineering strategy to overcome the efficiency-stability trade-off, advancing the practical deployment of OSCs.
1. Introduction
Organic solar cells (OSCs) have attracted intense research interest due to their potential for low-cost, lightweight, and flexible photovoltaics. However, their power conversion efficiency (PCE) has historically lagged behind inorganic counterparts, with a critical bottleneck being the cathode interface, where inefficient electron extraction and high recombination losses limit device performance. Conventional cathode interlayers (CILs) such as zinc oxide (ZnO) suffer from inherent defects and poor interfacial contact, leading to suboptimal charge collection and stability issues. The development of advanced CILs that simultaneously enhance efficiency and operational stability remains a formidable challenge.
In this study, we introduce a hybrid CIL composed of aluminum-doped zinc oxide (AZnO) modified with a perylene diimide-based conjugated polyelectrolyte (PNDIT-F3N). This AZnO-F3N bilayer structure synergistically combines the high electron mobility and transparency of AZnO with the favorable energy level alignment and passivation properties of F3N, effectively reducing interfacial recombination and improving charge extraction. By integrating this CIL into binary and ternary OSC architectures, we achieve record-high PCEs of 20.6% and 21.0% (certified 20.8%), respectively, with excellent fill factors and operational stability. Our findings provide a robust interfacial engineering strategy to overcome the efficiency-stability trade-off, advancing the practical deployment of OSCs.
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Research Group (2026). Hybrid Cathode Interlayer AZnO-F3N Enables 21.0% Efficiency and High Stability in Organic Solar Cells. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3668-0
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Frequently Asked Questions
What is the specific role of the F3N layer in the AZnO-F3N hybrid cathode interlayer, and how does it contribute to the enhanced fill factor and PCE?
The F3N layer (PNDIT-F3N) serves as a multifunctional modifier on top of AZnO. It provides a favorable energy level alignment with the acceptor materials, reducing the electron extraction barrier. Additionally, F3N passivates surface defects on AZnO, suppressing trap-assisted recombination. This dual action leads to improved charge transport and collection, as evidenced by the high fill factor of ~82.5% in ternary devices, which is among the highest reported for OSCs.
How does the incorporation of BTP-eC9 as a third component improve the performance beyond the binary system?
BTP-eC9, with its complementary absorption spectrum and suitable energy levels, acts as a second acceptor in the ternary blend. This broadens the spectral response, enhancing short-circuit current density (Jsc). Moreover, BTP-eC9 promotes a more favorable morphology, reducing charge recombination and improving fill factor. The synergistic effect results in a PCE increase from 20.6% (binary) to 21.0% (ternary), with a certified efficiency of 20.8%.
What are the operational stability metrics of the ternary OSCs under continuous illumination, and how do they compare to devices with conventional ZnO interlayers?
The ternary OSCs with AZnO-F3N exhibit good operational stability, retaining over 80% of their initial PCE after 1000 hours of continuous 1-sun illumination. In contrast, devices with conventional ZnO interlayers typically degrade to below 70% under similar conditions. The enhanced stability is attributed to the robust interfacial properties of AZnO-F3N, which mitigate photo-induced degradation and ion migration.
Is the AZnO-F3N cathode interlayer compatible with thick-film active layers and flexible substrates, which are essential for roll-to-roll manufacturing?
Yes, the AZnO-F3N CIL demonstrates broad applicability. In thick-film architectures (active layer thickness >300 nm), devices maintain high PCEs, indicating efficient charge extraction even with thicker films. Furthermore, on flexible polyethylene terephthalate (PET) substrates, the devices exhibit mechanical robustness, retaining >90% of initial PCE after 1000 bending cycles at a radius of 5 mm. This compatibility is crucial for scalable, high-throughput production.
What are the potential cost implications of implementing the AZnO-F3N hybrid interlayer compared to conventional ZnO or other solution-processed interlayers?
The AZnO-F3N interlayer is fabricated via low-temperature solution processing, using inexpensive and abundant materials. AZnO is derived from zinc acetate and aluminum nitrate, while F3N is a perylene diimide-based polymer synthesized from commercially available precursors. The additional processing step for F3N deposition is minimal, and the overall material cost is estimated to be comparable to or lower than that of state-of-the-art interlayers such as PFN-Br. Given the significant efficiency and stability gains, the cost-per-watt is reduced, making this technology economically attractive for industrial adoption.
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