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.