Extrusion of a nano-ordered active layer for organic photovoltaic cells
For the first time, an extrusion process is used to produce a perfectly nanostructured organic photoactive layer. Extrusion is an interesting, inexpensive and environment-friendly (solventless) option allowing an industrial production scale for polymer solar cell technology. In this paper, this plausible alternative to the usual large scale wet-processing techniques (inkjet printing, roll-to-roll coating…) was considered in order to elaborate bulk lamellar ordered heterojunctions employing polythiophene and fullerene based materials, as the electron donor and acceptor respectively, which were specifically elaborated for this work. An alternating donor/acceptor (D/A) lamellar structure close to the ideal interpenetrating system was targeted and successfully realized. Continuous D and A domains of about 24 nm were obtained, i.e. size close to the exciton diffusion length (20 nm) for π-conjugated organic materials; a photovoltaic response was evidenced under AM1.5 light simulator conditions. This photovoltaic effect, observed in spite of the presence of insulating polymers (∼61 wt%) added in both semi-conductor materials in order to adjust their viscosities, proves the possible achievement of such a perfect working nano-architectured structure via the extrusion process. The next step, consisting in the use of pure D and A extrudable polymers, should thus lead to high and durable photovoltaic performances. Therefore, this paper opens the way to a new promising OPV processing method: extrusion.