4.1.4 Other film-forming methods
In addition to the deposition methods above mentioned, meniscus-assisted-coating (MAC) are also effective strategies. The meniscus coating is done by pumping paint into the applicator roller. The paint flows through the porous surface of the applicator roll, forming a film on the substrate that is transported by the coating roller. The configuration and dimensions of the meniscus established within the gap between the rollers are influenced by variables such as the gap distance, the speed, and the rotational direction of the rollers.[100-103] Different flow regions will be formed inside the liquid, and coating speed and temperature have significant effects on the formation of film thickness. Yue et al. used MAC strategy to prepare a PM6:PY-IT film with high crystallinity and nano interpenetrating networks.[88] As shown in Figure 4c, the researchers investigated the crystallization kinetics of the polymer blend film. The results revealed a straightforward linear correlation between the rate of meniscus movement and the extent of crystallinity in the polymer. With the increase of V a, the absorption peak intensity of PM6 and PY-IT decreased significantly, indicating that the crystallinity of the blend film decreased with the increase ofV a. But when the speed is reduced to 1 mm/s, it leads to excessive crystallization of the polymer. The results show that by using MAC strategy and precisely controlling the propulsion rate, the active layer can obtain finer nanofiber networks. In the end, the PCE exceeded 15%.