## 3 Polystyrene in TIPS Pentacene Crystallization
### High Molecular Weight PS (Greater than 250k)  
High Mw PS (Mw greater than 250k) leads to larger crystalline domains and improved long-range order due to its higher viscosity and slower solvent evaporation rates. This results in better film coverage and fewer grain boundaries, significantly boosting charge \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Author** & **PS Mw** & **Result** & **Mobility** \\ \hline [PERSON] et al. & 48k & \begin{tabular}{c} PS additive greatly reduce the film roughness of \\ TIPS pentacene grown with a scanning \\ corona-discharge coating method \\ \end{tabular} & 0.23 cm\({}^{2}\)/Vs \\ \hline [PERSON] et al. & 140k & \begin{tabular}{c} Crosslinked PS served as a modifier layer to \\ optimize semiconductor crystallization \\ \end{tabular} & 0.48 cm\({}^{2}\)/Vs \\ \hline [PERSON] et al. & 180k & \
\begin{tabular}{c} Electrostatic spray deposition of TIPS \\ pentacene/PS blends, resulting in vertical phase \\ stratification with a flat charge transport \\ interface \\ \end{tabular} & 0.95 cm\({}^{2}\)/Vs \\ \hline [PERSON] et al. & 230k &
\begin{tabular}{c} PS acts as an insulating polymer, and influences \\ the phase separation and crystallization modes, \\ thereby enhancing the structural and electrical \\ properties \\ \end{tabular} & 0.653 cm\({}^{2}\)/Vs \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Overview of the studies on TIPS pentacene blended with PS of medium Mw, highlighting the author, Mw, result and mobility from each study. transport efficiency and overall device performance. However, very high Mw PS can also introduce challenges such as increased phase separation and reduced solubility, potentially affecting the uniformity and electrical properties of the thin films. [PERSON] et al. reported the inkjet printing of TIPS pentacene/polymer mixture for transistor fabrication on flexible substrate. In order to modify the threshold voltage, two types of polymers including PS (Mw 280k) and poly(vinylphenol) (PVA) (Mw 25k) were inkjet printed onto the substrate prior to the printing of the organic semiconductor TIPS pentacene. A low saturation mobility of 0.13 cm\({}^{2}\)/Vs and a threshold voltage of \(-\)1.49V was obtained from the thin film transistors without incorporating the pre-deposited polymer material. In contrast, the devices based on the PS and PVA polymer layer showed a hole mobility of 0.85 cm\({}^{2}\)/Vs and 0.14 cm\({}^{2}\)/Vs, and a threshold voltage of \(-\)0.02V and 4.1V, respectively. The degradation of electrical performance of the devices with PVA polymer was attributed to the existent of hydroxyl groups on the PVP surface which induces trapping sites for the hole charge carriers. [PERSON] et al. reported the employment PS (Mw 280k) and PMMA (Mw 996K) polymer additive as a passivation and crystallization assistance layer in order to modify the wetting condition of the substrate and to realize controlled growth of the organic semiconductor TIPS pentacene [115]. In this work, a blade coating technique was combined with a \"non-isotropic solvent evaporation\" method to control the drying process and crystal alignment. Solvent with a low boiling point such as chloroform yielded spherulite structure of crystals whereas solvent with a higher boiling point such as dichlorobenzene led to thick crystals. Without the polymer additive, the neat TIPS pentacene formed poor coverage with nonideal crystal grain orientations. Figure 8a,b display the polarized optical microscopic (POM) images of typical blade-coated TIPS pentacene films deposited on PS or PMMA interlayers through \"nonisotropic solvent evaporation\". The distinct birefringence signifies that well-oriented crystalline structures were successfully formed. Furthermore, the consistent brightness and color of the crystals suggest good thickness uniformity. POM measurements (Figure 8c) were obtained for crystalline films grown on the PVP layer.