## 3 Polystyrene in TIPS Pentacene Crystallization
### High Molecular Weight PS (Greater than 250k)
The linear PS blend shows a clear stratification with a significant accumulation of TIPS pentacene at the bottom of the film, supporting the vertical phase separation observed in Figure 3. This structure leads to a polymer-rich surface layer, with the small molecule semiconductor concentrated near the substrate, which is ideal for charge transport in certain device configurations. On the other hand, the 4-arm star PS blend exhibits a thin TIPS pentacene-rich layer at the very top of the film, consistent with a scenario where lateral phase separation dominates, leading to isolated, horizontally oriented TIPS pentacene domains. The centipede PS blend, however, displays a more gradual variation in TIPS pentacene concentration from the bottom to the top, forming a gradient. This indicates a combination of vertical and lateral phase separations, where TIPS pentacene is more concentrated at the upper layers but also well-distributed throughout. The study also reports significant variations in charge mobility depending on the polymer architecture. The blend with centipede PS achieved the highest mobility, reaching 0.45 cm\({}^{2}\)/Vs, which is more than four times greater than that of the neat TIPS pentacene reference (0.10 cm\({}^{2}\)/Vs). Figure 10: Planar view EFTEM images of blend films consisting of (**a,d**) TIPS pentacene with linear PS, (**b,e**) 4-arm-star PS, and (**c,f**) centipede PS at energy losses of (**a–c**) 0 \(\pm\) 5 eV and (**d–f**) 20 \(\pm\) 5 eV. While the 0 eV images primarily highlight mass-thickness contrast, the 20 eV images exhibit increased brightness in areas enriched with TIPS pentacene. Reproduced from reference [119] and no changes were made, with permission from Wiley ([[https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/)]([https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/))) (accessed on 1 September 2024). The linear PS blend showed a mobility of 0.37 cm\({}^{2}\)/Vs, while the 4-arm star PS blend had a mobility of 0.26 cm\({}^{2}\)/Vs. These findings demonstrate the critical impact of polymer architecture on both phase morphology and charge transport, providing valuable insights for optimizing blend-based organic electronic devices. [PERSON] et al. reported the mixing of PS polymer additive (Mw 524k) with TIPS pentacene to reduce the sub-gap density of states (DOS) in order to improve the electrical performance of low voltage thin film transistors [120]. Figure 12a displays a photographic image of an array of OTTFs fabricated on a polyethylene naphthalate (PEN) substrate. As illustrated in the inset of Figure 12a, the Ag gate, source, and drain electrodes are created by inkjet printing a metal-organic precursor ink, followed by annealing for 15 min at 145 \({}^{\circ}\)C. The AFM image in Figure 12b reveals a smooth surface with a root-mean-square roughness of approximately 0.28 nm, facilitating the formation of a high-quality semiconductor/dielectric interface. In the channel region, the AFM image of the semiconductor film demonstrates polycrystalline microstructures with elongated crystalline grains measuring several tens of micrometers, as shown in Figure 12c. Source and drain contact electrodes were deposited prior to the formation of TIPS pentacene/PS mixture active layer. Afterwards, a CYTOP layer was deposited as an encapsulation layer. The thin film transistor exhibited a low dielectric capacitance of 2.97 nF/cm\({}^{2}\) and thereby improved power efficiency. A hole mobility of up to 0.4 cm\({}^{2}\)/Vs was demonstrated from the thin film transistors with the TIPS pentacene/PS mixture serving the active channel. [PERSON] et al. reported the effect of atactic PS additive (Mw 900k) at different weight ratios on the thin film morphology, crystal growth and charge carrier mobility of TIPS pentacene organic semiconductor [121].