Cathode Interlayer Engineering in Organic Solar Cells

Cathode interlayer engineering has emerged as a pivotal strategy to boost the performance and longevity of organic solar cells. Positioned between the photoactive layer and the cathode electrode, ultrathin interlayers serve to tune energy alignment, facilitate electron extraction and suppress unwanted interfacial reactions. Designing effective interlayers demands precise control over work function modulation, interfacial dipole formation and physical contact with the active blend. Recent advances exploit tailored molecular structures—such as hydrogen-bonding motifs, sterically hindered units and dipole-inducing substituents—to optimise both efficiency and stability. Organic or hybrid organic–inorganic materials can be processed from benign solvents, enabling scalable manufacturing and tandem-device integration. By mitigating dark current leakage and recombination pathways, refined interlayers have driven power conversion efficiencies beyond 18% while maintaining operational stability under thermal stress and prolonged illumination. The global significance of these developments lies in the prospect of cost-effective, flexible photovoltaic modules for decentralised power generation and building-integrated applications.

Research from Nature Portfolio

Recent studies have demonstrated that phenanthroline-carbolong conjugates form robust interlayers that suppress chemical reactions at the cathode interface. By introducing double-phenanthroline-carbolong units with enhanced steric hindrance and electron-withdrawing character, devices achieved efficiencies of 18.2% and retained over 80% of initial performance after thousands of hours under inert conditions or elevated temperatures. The same interlayer chemistry enabled thermal post-treatment of subcells in perovskite–organic tandem architectures, yielding tandem efficiencies above 21% with excellent thermal resilience. Earlier pioneering work introduced an aliphatic amine-functionalised perylene-diimide derivative that leverages hydrogen bonding to lower the work function of air-stable metals while ensuring conformal contact with the active layer. Single-junction devices incorporating this material reached certified power conversion efficiencies above 17% and exhibited remarkable operational stability, highlighting the feasibility of intermolecular interactions as a design principle for high-performance interlayers.

Cathode Interlayer Engineering in Organic Solar Cells publication trend

The graph below shows the total number of articles in cathode interlayer engineering in organic solar cells across all publications each year (not limited to Nature Index journals).

Technical terms

Cathode interlayer: A nanometre-thick layer between the photoactive blend and cathode electrode that adjusts energy levels and interfacial properties to facilitate electron extraction.

Work function: The minimum energy needed to remove an electron from the surface of a solid to a point in the vacuum just outside the solid.

Interfacial dipole: An electric dipole formed at an interface due to asymmetric charge distribution, which shifts the effective work function of the electrode.

Non-fullerene acceptor: A class of organic electron-accepting materials used in place of fullerene derivatives to improve light absorption and device stability.

Perylene diimide (PDI): An aromatic organic compound with high electron affinity and mobility, commonly employed as an electron-transporting interlayer in organic photovoltaics.

References

1. Phenanthroline-carbolong interface suppress chemical interactions with active layer enabling long-time stable organic solar cells. Nature Communications (2023).
2. Cathode engineering with perylene-diimide interlayer enabling over 17% efficiency single-junction organic solar cells. Nature Communications (2020).
3. Double‐Dipole Induced by Incorporating Nitrogen‐Bromine Hybrid Cathode Interlayers Leads to Suppressed Current Leakage and Enhanced Charge Extraction in Non‐Fullerene Organic Solar Cells. Advanced Science (2023).
4. Environmentally friendly cathode interlayer modification on edible bio‐acids with enhanced electron extraction and improved power conversion efficiency. EcoMat (2022).
5. Solution‐Processed Semiconductor Materials as Cathode Interlayers for Organic Solar Cells. Advanced Science (2023).