Solid Additive Engineering in Organic Solar Cells

Solid additive engineering has emerged as a powerful strategy to tailor the microstructure and optoelectronic properties of the active layer in organic solar cells. By introducing small organic molecules into the donor–acceptor blend prior to film formation, researchers can regulate crystallisation dynamics, phase separation and molecular packing without the drawbacks associated with high-boiling-point liquid additives. Solid additives may volatilise during or after deposition, leaving an optimised morphology characterised by fine donor–acceptor interpenetration, enhanced π–π stacking and reduced energetic disorder. These improvements translate directly into elevated charge mobilities, suppressed non-radiative recombination losses and superior device stability. Recent advances have demonstrated record-breaking power conversion efficiencies through precise control of intermediate states during film crystallisation, the design of volatilizable and semi-permanent additives to boost reproducibility, and the deployment of electrostatic or non-covalent interactions to promote molecular ordering. The global significance of this approach lies in its compatibility with scalable, solvent-lean fabrication processes and its potential to unlock further gains in efficiency and operational lifetime of next-generation organic photovoltaics.

Research from Nature Portfolio

Recent studies have shown that non-monotonic manipulation of crystallisation intermediates via a chlorinated benzene additive can finely tune the aggregation of non-fullerene acceptors, achieving a certified efficiency exceeding 19%. In this work, the additive acts as a crystallisation regulator, first promoting and then relaxing acceptor aggregation to suppress non-radiative losses and optimise charge transport. Another investigation introduced volatilizable solid additives tailored to acceptor–donor–acceptor molecules, enhancing π–π stacking in the active layer and delivering devices with improved stability and reproducibility compared with those processed with liquid additives. More recently, a conjugated molecular bridge additive exploiting electrostatic complementarity with polymer donors has been implemented to strengthen donor stacking, shorten π–π distances and boost both efficiency (up to 19.4%) and operational stability through a layer-by-layer deposition protocol.

Solid Additive Engineering in Organic Solar Cells publication trend

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

Technical terms

Solid additive: A volatile or semi-volatile small molecule added to the active layer blend to control film formation and morphology.

Bulk heterojunction: A nanoscale interpenetrating network of donor and acceptor materials that facilitates exciton dissociation and charge transport.

Phase separation: The spatial distribution of donor and acceptor domains within the active layer, critical for balanced charge generation and extraction.

π–π stacking: Face-to-face interactions between conjugated molecular backbones that enhance carrier mobility.

Intermediate state manipulation: The deliberate control of transient molecular assemblies during film crystallisation to achieve an optimal final morphology.

Sequential deposition: A fabrication method in which donor and acceptor layers are coated separately, often with an additive to guide vertical phase distribution.

Layer-by-layer deposition: A variant of sequential deposition using the same solvent for both layers, allowing additive-mediated swelling and intermixing.

References

1. 19.31% binary organic solar cell and low non-radiative recombination enabled by non-monotonic intermediate state transition. Nature Communications (2023).
2. Design and application of volatilizable solid additives in non-fullerene organic solar cells. Nature Communications (2018).
3. Electrostatic force promoted intermolecular stacking of polymer donors toward 19.4% efficiency binary organic solar cells. Nature Communications (2023).
4. Volatile Solid Additive‐Assisted Sequential Deposition Enables 18.42% Efficiency in Organic Solar Cells. Advanced Science (2022).
5. Defining Solid Additive's Pivotal Role on Morphology Regulation in Organic Solar Cells Produced by Layer‐by‐layer Deposition. Advanced Energy Materials (2024).
6. Crossbreeding Effect of Chalcogenation and Iodination on Benzene Additives Enables Optimized Morphology and 19.68% Efficiency of Organic Solar Cells. Advanced Science (2024).