Reel-to-reel wet coating by variation of solvents and compounds of photoactive inks for polymer solar cell production

In this paper we report about some aspects and the progress reached in the reel-to-reel (R2R) solvent-based production of polymer solar cells. In awareness of the huge advantages in energy and material savings the hole-injection and the photoactive layer were successfully prepared by continuous slot-die wet coating of low viscosity inks. The objective was to obtain higher values of light power conversion efficiencies for reducing the gap between production under optimal laboratory conditions via spin-coating on rigid substrates in comparison to the more robust and practically significant large-scale coating of flexible substrates. For this purpose, solvent systems were varied and a new fullerene used as electron–acceptor, leading to the highest light power conversion efficiencies (η=4.55%) described for polymer solar cells (PSCs) on flexible substrates up to now. PSCs manufactured from continuously coated foils by using a small-scale laboratory R2R-coating machine yield a maximum value of η=3.2%. With respect to environmental, safety and technological demands, reel-to-reel wet coating with a change to non-halogenated inks was also successfully carried out in order to learn more about its technological suitability and to allow the transfer of the results afterwards to other, more efficient material systems.