Fluid Control of Dip Coating for Efficient Large-Area Organic Solar Cells.

As a classical low-cost technique, dip coating has not been used for printable electronics. Here, the study demonstrates large-area organic solar cells can be made by dip coating. The correlation is revealed among Van der Waals forces in precursor film, aggregation state of polymer, and fibrous orientation in active layer; the relationship is also expounded between fluid mechanics of the confined liquid in polymer scaffold and the continuity of the acceptor phase. By controlling the fluid characteristics, the ideal nanoscale bicontinuous interpenetrating network forms. As a result, the 1.0 cm rigid and 10.0 cm flexible cells exhibit efficiencies of 17.9% and 13.7%, respectively. Moreover, the method for predicting the optimal coating speed for the dip coating of given inks is proposed. Overall, this work not only demonstrates the superiority of dip coating for organic solar cell fabrication but also provides guidance for its application in printable electronics.