## 3 Polystyrene in TIPS Pentacene Crystallization
### High Molecular Weight PS (Greater than 250k)
These visualizations further corroborate that the inclusion of anisole as an auxiliary solvent results in a marked reduction in surface irregularities, with the average root mean square roughness decreasing from 20 nm (for the single-solvent case) to 2.5 nm (in the dual-solvent scenario). Additionally, a notable expansion in the size of the crystalline domains is observed for films cast from the dual-solvent mixture  
Figure 8: POM images, along with the corresponding AFM topographies (insets), of self-organized TIPS pentacene crystals on (**a**) PS and (**b**) PMMA surfaces. The white arrow in the POM images points to the primary direction of crystal growth. (**c**) POM image within the transistor’s channel area illustrates the remarkable directionality of the crystalline domains. The white arrow denotes the vapor flow direction. Reproduced from reference [115], with permission from The Royal Society of Chemistry. compared to those deposited using only mesitylene. At an equimolar mixing ratio (1:1) of TIPS pentacene and PS in the binary solvent system of anisole and mesitylene, a peak mobility of 1.16 cm\({}^{2}\)/Vs was achieved, which was ascribed to the expansion of crystallite dimensions owing to the inclusion of anisole. Furthermore, when the mixing ratio was adjusted to 3:1 (TIPS pentacene to PS), an enhanced saturation mobility of 1.82 cm\({}^{2}\)/Vs was observed, primarily due to the diminished surface irregularities and the enlargement of crystal domains. [PERSON] et al. investigated the phase separation mechanisms in small molecule-polymer blends, particularly focusing on how different polymer architectures, including linear, 4-arm star, and centipede PS, affect film morphology and electrical performance [119]. The linear, 4-arm star, and centipede PS has a Mw of 486k, 483k and 540k, respectively, with molecular structures shown in Figure 11d. Utilizing an ultrasonic spray technique, the researchers discovered that phase separation is driven by kinetic factors, with polymer chain mobility playing a crucial role. Figures 10 and 11 provide a detailed examination of the phase morphologies both within the plane of the film and across its thickness. In Figure 10, energy-filtered transmission electron microscopy (EFTEM) reveals the in-plane distribution of TIPS pentacene and PS domains. The blend with 4-arm star PS shows well-defined domain boundaries that resemble crystal edges, signifying pronounced lateral  
Figure 9: The structural configuration of TIPS pentacene films, deposited from solutions prepared in a 3:1 proportion using both mono- and binary-solvent methodologies, is depicted. Figures (**a**,**c**) provide optical micrographs and height-mode AFM scans, respectively, derived from a mono-solvent system (mesitylene). In stark contrast, Figures (**b**,**d**) exhibit analogous visualizations from a mesitylene–anisole binary solvent formulation, elucidating the pronounced disparities in film morphology between the two distinct solvent strategies. Reproduced from reference [118], with permission from The Royal Society of Chemistry. phase separation, where distinct regions rich in TIPS pentacene or PS are clearly separated. In contrast, the linear PS blend displays more diffuse, indistinct boundaries, indicating that the phase separation is more vertical, with layers forming throughout the film rather than separating laterally. The centipede PS blend presents a more complex scenario, where the domain boundaries are somewhat blurred but still discernible, suggesting a combination of both lateral and vertical phase separations. This results in a gradient where both types of phase separations coexist within the film. Figure 11 builds on these observations by analyzing the distribution of TIPS pentacene through the film's thickness using cross-sectional EFTEM silicon element mapping.