Organic Solar Cell Interface Engineering

Organic solar cells rely critically on engineered interfaces to facilitate efficient charge generation, separation and extraction. At the junction between photoactive layers and electrodes, interfacial layers govern energy level alignment, carrier selectivity and suppression of recombination. Organic–inorganic hybrid interlayers such as transition metal oxides (for example MoO₃, NiOₓ or MoOₓ) are widely employed to match work functions and enhance stability. Similarly, polymeric or small-molecule interlayers can tune surface energetics, morphology and chemical compatibility under low-temperature or solution-processing conditions. Advances in interface design encompass novel deposition methods—inkjet printing, lamination or aqueous sol–gel routes—alongside the introduction of insulating additives to reduce voltage losses. Optimised interfaces have yielded significant improvements in open-circuit voltage, fill factor and long-term operational life, paving the way for scalable, roll-to-roll production of organic photovoltaics with efficiencies approaching those of emerging perovskite or inorganic technologies.

Research from Nature Portfolio

Systematic studies of vapour-deposited MoO₃ on diverse organic semiconductors have revealed that interfacial diffusion and new core-level states arise from electron transfer at the oxide–organic boundary, with the degree of oxide penetration inversely related to molecular mass. Energy level alignment follows universal rules for molecules on metal oxides, informing selection of oxide thickness and deposition sequence to minimise energy offset losses. Separately, inkjet-printed NiO films have been integrated as hole-transporting layers in polymer solar cells, demonstrating controlled thickness and high transmittance alongside power conversion efficiencies comparable to spin-coated counterparts. Optimisation of droplet spacing, substrate treatment and annealing temperature allowed uniform films with matched energy levels and suppressed recombination, underscoring the potential of printed metal-oxide interlayers for large-area device manufacturing.

Organic Solar Cell Interface Engineering publication trend

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

Technical terms

Bulk heterojunction: A blend of donor and acceptor materials forming interpenetrating networks for efficient exciton dissociation.

Hole transport layer (HTL): A selective interfacial layer that facilitates extraction of holes and blocks electrons toward the anode.

Electron transport layer (ETL): A selective interlayer that extracts electrons and blocks holes toward the cathode.

Work function: The minimum energy required to remove an electron from a solid to vacuum, critical for energy level matching.

Energy level alignment: The relative positioning of molecular or semiconductor frontier orbitals and electrode Fermi levels at an interface.

Open-circuit voltage (Voc): The maximum voltage obtainable from a solar cell under illumination when no current flows.

References

1. Overcoming the voltage losses caused by the acceptor‐based interlayer in laminated indoor OPVs. SmartMat (2023).
2. 17% Non‐Fullerene Organic Solar Cells with Annealing‐Free Aqueous MoOx. Advanced Science (2020).
3. Interface Structure of MoO3 on Organic Semiconductors. Scientific Reports (2016).
4. Inkjet printing of NiO films and integration as hole transporting layers in polymer solar cells. Scientific Reports (2017).
5. PEG-assisted Sol-gel Synthesis of Compact Nickel Oxide Hole-Selective Layer with Modified Interfacial Properties for Organic Solar Cells. Polymers (2019).