Organic photovoltaic cells with water-based ink offer many advantages, especially in terms of the environment, but are compromised by their lower photovoltaic performance. As part of an international collaboration, scientists have managed to produce such cells with a yield close to their equivalents based on halogenated or aromatic inks and requiring the use of toxic solvents. This work, published in the journal Advanced Energy Materials, indicates a conversion of 9.98% of the solar energy received.
Organic photovoltaic cells (OPV) can be manufactured entirely through printing processes, applying an active layer of semiconductor inks. For example, OPVs are manufactured at low temperatures on flexible substrates, can be semi-transparent, and because they require little energy to produce, they offer a faster return on investment than silicon cells despite energy conversion. Less solar energy.
The most efficient OPV cells are made with halogenated solvents such as chloroform or aromatic compounds, whose toxic fumes pose various environmental restrictions. An alternative using water-based inks would solve these problems. Since organic semiconductors are not soluble in water, the strategy is to develop dispersions of nanoparticles. In this type of cells, energy conversion has so far remained less than half compared to those based on halogenated solvents, which is due to poorer organization of the nanoparticles, especially in the form of too strong phase separation.
Researcher from the Laboratory “Integration of Materials into the System” (IMS, CNRS/Bordeaux INP/University of Bordeaux), the Institute of Analytical Sciences and Physical-Chemistry of Environment and Materials (IPREM, CNRS/University of Pau – Pays de l’) Adour ), the Charles Sadron Institute (ICS, CNRS), the Laboratory for Integrated Micro Mechatronics Systems (LIMMS, CNRS/University of Tokyo), the Paul Scherrer Institute (Switzerland), the Lawrence-Berkeley National Laboratory (USA) and the Universities of Tokyo and Sydney have developed the first-ever water-based ink OPVs, enabling up to 10% conversion of solar energy into electricity. This yield is very close to that of reference cells made from halogenated solvent inks, at 11.2%.
In this work, carried out as part of the ANR WATER-PV project, scientists have circumvented the problems of solubility of semiconductors in water. To do this, they used nanoparticles that disperse in the water without having to dissolve. They consist of two organic semiconductors: an electron donor and an electron acceptor. These two materials were integrated into the nanoparticle in such a way that their domain sizes, i.e. the width of the areas of the donor and acceptor materials, are only a few tens of nanometers apart. Importantly, they maintain these minimum domain sizes, which improve energy conversion, during the various heat treatment phases of OPV cell fabrication. The cells obtained in this way are strictly organized and offer an energy conversion of 9.98%.
This work has narrowed the gap between solar cells made with halogenated or aromatic inks and those made with aqueous inks. They thus open the way to the development of cleaner processes for organic photovoltaics, but also for organic electronics in general. The team now plans to completely compensate for this difference and lower the heat treatment temperature, which would reduce the time and energy required to produce these cells.
References
Towards highly efficient water-processed organic photovoltaics: Controlling nanoparticle morphology with surface energies.
Laval, H., Holmes, A., Marcus, MA, Watts, B., Bonfante, G., Fehl, M., Deniau, E., Szymanski, R., Lartigau-Dagron, C., Xu, X. , Cairney, JM, Hirakawa, K., Awai, F., Kubo, T., Wantz, G., Bousquet, A., Holmes, NP, Chambon, S..
Adv. energy matter. 2023, 13, 2300249.
https://doi.org/10.1002/aenm.202300249