Layer-by-Layer Processing in Organic Photovoltaics

Layer-by-layer processing, also known as sequential deposition, has emerged as a powerful method for fabricating the active layers of organic photovoltaic devices. Unlike the conventional bulk heterojunction approach, which blends donor and acceptor materials in a single solution, layer-by-layer techniques deposit the donor and acceptor in separate steps. This controlled assembly promotes well-defined vertical phase separation, optimising exciton dissociation and charge transport pathways. By tuning inter-layer interactions—through choice of solvent, additives or preformed nanostructures—researchers achieve precise control over morphology, crystallinity and stratification. Such control leads to enhanced power conversion efficiencies, improved thermal and mechanical stability, and reproducible device performance that is largely insensitive to small variations in processing conditions. Moreover, sequential deposition is inherently compatible with large-area and roll-to-roll manufacturing, offering a route towards scalable, eco-friendly production of high-performance organic solar cells.

Research from Nature Portfolio

Recent studies have demonstrated that pre-assembling a polymer fibril network as the first layer, followed by infiltration of a non-fullerene acceptor, yields highly uniform morphologies and robust devices. The sequentially formed fibril mesh ensures optimal donor–acceptor interfaces and reduces batch-to-batch variability, enabling certified efficiencies above 16 %. A pseudo-bilayer architecture has further advanced this concept by creating an ordered crystalline donor layer beneath a selectively deposited acceptor film. The enhanced crystallinity extends the exciton diffusion length and balances dissociation and transport, resulting in power conversion efficiencies approaching 17.5 %. These findings highlight the critical role of vertical stratification and microstructural control in maximising device performance.

Layer-by-Layer Processing in Organic Photovoltaics publication trend

The graph below shows the total number of articles in layer-by-layer processing in organic photovoltaics across all publications each year (not limited to Nature Index journals).

Technical terms

Bulk heterojunction: A blend of electron-donor and electron-acceptor materials cast together, forming an interpenetrating network for exciton dissociation and charge transport.

Vertical phase separation: Stratification of donor and acceptor domains along the film thickness, optimising exciton cleavage near interfaces and directing charges toward respective electrodes.

Sequential deposition: A fabrication method in which donor and acceptor layers are deposited in discrete steps, enabling precise morphological and interfacial control.

Exciton diffusion length: The average distance an exciton travels before returning to the ground state; longer diffusion lengths increase the likelihood of reaching a dissociation interface.

Non-fullerene acceptor: A class of electron-accepting molecules that serve as an alternative to fullerene derivatives, offering tunable absorption and energy levels for improved device efficiency.

References

1. Solid Additive-Assisted Layer-by-Layer Processing for 19% Efficiency Binary Organic Solar Cells. Nano-Micro Letters (2023).
2. Optimized active layer morphology toward efficient and polymer batch insensitive organic solar cells. Nature Communications (2020).
3. Pseudo-bilayer architecture enables high-performance organic solar cells with enhanced exciton diffusion length. Nature Communications (2021).
4. Layer-by-layer fabrication of organic photovoltaic devices: material selection and processing conditions. Journal of Materials Chemistry C (2021).
5. Sequentially Deposited versus Conventional Nonfullerene Organic Solar Cells: Interfacial Trap States, Vertical Stratification, and Exciton Dissociation. Advanced Energy Materials (2019).
6. Highly Efficient Layer-by-Layer Organic Photovoltaics Enabled by Additive Strategy. Energies (2024).