Solar RRL, 2019, vol 0, 0, pp. 1800333
For the preparation of flexible organic solar cells (OSCs), the Roll-to-Roll slot-die coating technique is preferable. Herein, a sequential slot-die (SSD) coating strategy to fabricate flexible OSCs using non halogenated solvent under ambient atmosphere, is developed. The coating order of the active layer materials shows great influence on the performance of OSCs. It is found that, compared with the one-step coating, the power conversion efficiency (PCE) of devices with an area of 0.75 cm2, and fabricated by SSD coating process with the polymer as the first layer, is enhanced from 4.86 to 5.51% for the binary system, whereas from 6.09 to 7.32% for the ternary system, showing an increase of 13 and 20% in PCE, respectively. For the devices with a standard small area of 4 mm2 and large area of 1 cm2, PCE as high as 9.36 and 7.11% are obtained, respectively, which are among the top value for flexible devices fabricated by slot-die coating. It turns out that the SSD coating process with the polymer as the first layer assists pre-aggregation of the polymer to form better crystal domains with face-on orientation. Therefore, a sequential deposition strategy could provide a new means for manufacturing the high efficiency flexible OSCs.