4.1.3 Slot-die coating
Slot-die coating involves delivering a solution onto a substrate through a narrow slot situated in close proximity to the surface. Slot-die coating offers a greater advantage over spin-coating due to its superior efficiency in material conservation. Zhao et al. studied the film-forming kinetics of slot-die by introducing the third component.[91] Kinetic studies have unveiled that improved miscibility between BTR-Cl and D18 plays a pivotal role in the segregation of Y6 from the mixed phase with D18. Additionally, the presence of highly crystalline BTR-Cl accelerates the L-L phase separation of the D18:Y6 mixture, leading to a greater accumulation of Y6 molecules. The Y6 peak location redshift in the D18:BTR-Cl:Y6 blend shifts noticeably earlier compared to the D18:Y6 blend, as depicted in Figure 4a. This observation suggests that Y6 tends to aggregate more quickly. In 110 nm and 300 nm thick photoactive films, PCE reached 17.2% and 15.5%, respectively. The use of slot-die coating in conjunction with a ternary design approach has demonstrated its effectiveness in manufacturing thick, large-scale, and flexible OSCs with high efficiency. The utilization of industry-scale R2R fabrication techniques showcases the replicability of outcomes with this approach. Zhao et al. developed a sequential slot-die (SSD) coating method for the preparation of OSCs at room temperature using halogen-free solvents.[99] The device was prepared in ternary systems with PTB7-Th andp -DTS-(FBTTH2)2 as donors and PC71BM as acceptors. In the SSD coating process, PTB7-Th is used as the first coating. In fact, PTB7-Th molecules undergo two phases of aggregation (Figure 4b). The solvent from the second layer has the ability to dissolve some of the PTB7-Th molecules. During PCBM fabrication, these dissolved molecules move to the upper surface and reassemble into aggregates. Furthermore, when the polymer is coated with the first layer, the size of the area gradually expands, resulting in an appropriate phase separation. The power conversion efficiency (PCE) of devices produced using SSD coating is improved from 6.09 to 7.32%, indicating a 20% increase in PCE.