Increasing sustainability in organic solar cells fabrication through the synthesis of polymer-based water-processable blend nanoparticles

Organic photovoltaic (OPV) technology has been intensively investigated over the last decades as an intriguing alternative for electrical power generation. Even if recently the power conversion efficiencies have been increased, its market penetration is still limited by some drawbacks making expensive their industrial production, as in particular the use of huge amount of halogenated and aromatic solvents, which are toxic and harmful (1,2). Three main strategies have been developed in order to increase the sustainability of the active layer production processes: (i) using other organic solvents that are less harmful for human life and environment; (ii) functionalization of donor and acceptor structure with polar groups and so the use of less hazardous solvents as methanol; (iii) production of polymer-based water-processable nanoparticles (WPNPs). We have focused our attention on this latter strategy because, in addition to reduce halogenated wastes, it allows the control of the final film morphology and the optimization of the interpenetrating electron donor/acceptor networks ensuring good performances in the final device (3,4,5). Particularly, our research group developed the preparation of polymer-based WPNPs using amphiphilic rod-coil block copolymers (ABCPs), bearing a rigid block and a hydrophilic flexible segment. Thanks to these features, ABCPs are able to self-assemble through miniemulsion method generating organized nanostructures under specific conditions. The hydrophilic flexible block works as surfactant and assures the colloidal suspension stability interacting with aqueous medium (6,7). Also, it interacts with the electron-acceptor material (n-type), leading to the formation of pre-aggregated domains, suitable to achieve the charge percolation into the final device (8,9). We synthetized a well-known low band-gap polymer PTB7, in order to connect it to a tailored segment of P4VP producing a new ABCP, the PTB7-b-P4VP. We tested its capability to self-assemble in aqueous medium to produce nanoparticles, both neat and in blend with fullerene derivatives. The obtained WPNPs were characterized by dynamic light scattering (DLS) and UV-Vis spectroscopy, deposited in films topologically characterized by atomic force microscopy (AFM) to confirm the compactness of the obtained active layer. Now we will employ them as active layers for the fabrication of sustainable OPV devices. References 1.Holmes P., Marks M., Kumar P., Kroon R., Barr M. G., Andersson R., Dastoor P. C., Belcher W. J. Nano Energy 2016, 19, 495-510 2.Zhang S., Ye L., Zhang H., Hou J. Materials Today 2016, 19, 533-543 3.Thromholt T., Gevorgyan S. A., Jørgensen M., Krebs F. C., Sylvester-Hvid K. O., ACS Appl. Mater. Interfaces 2009, 1, 2768 4.Ulum S., Holmes N., Barr M., Kilcoyne A. L. D., Gong B. B., Zhou X., Belcher W., Dastoor P., Nano Energy, 2013, 2, 897 5.Gärtner S., Christmann M., Sankaran S., Röhm H., Prinz E. M., Penth F., Pütz A., Türeli A. E., Penth B., Baumstümmler B., Colsmann A., Adv. Mater., 2014, 26, 6653 6.Zappia S., Mendichi R., Battiato S., Scavia G., Mastria R., Samperi F., Destri S. Polymer 2015, 80, 245-258 7.Ferretti A. M., Zappia S., Scavia G., Giovanella U., Villafiorita F., Destri S., Polymer 2019, 174, 61-69 8.Zappia S., Scavia G., Ferretti A. M., Giovanella U., Vohra V., Destri S. Adv Sustainable Syst. 2018, 2, 1700155 9.Ganzer L., Zappia S., Russo M., Ferretti A. M., Vohra V., Diterlizzi M., Antognazza M. R., Destri S., Virgili T., Manuscript submissed to PCCP. Acknowledgements: This work was funded by ENI Corporate University