## 3 Polystyrene in TIPS Pentacene Crystallization
### Low Molecular Weight PS (Less than 20k)  
PS with Mw less than 20k, when incorporated in the organic semiconductors or OTFTs as an amorphous additive, typically results in smaller, more uniform crystalline domains. The lower viscosity of low Mw PS facilitates consistent spreading and crystallization of the semiconductor, enhancing charge transport properties and improving the interface quality between the semiconductor and dielectric layers. These organic semiconductor films comprising low-Mw PS often exhibit reduced grain boundaries and smoother surfaces, contributing to better device performance. [PERSON] et al. reported the mixing of PS (Mw 9.58k) with TIPS pentacene for fabricating thin film transistor based circuits [108]. In this work, the TIPS pentacene/PS mixture was deposited by using inkjet printing. The inkjet printed solvent formed circular shaped crystals due to the isotropic spreading of the ink. Different hole mobilities of 0.9 \(\pm\) 0.1 cm\({}^{2}\)/Vs and 1.17 \(\pm\) 0.15 cm\({}^{2}\)/Vs were obtained based on the on-center and off-center devices, respectively. In contrast, Transistors using pure TIPS pentacene showed much lower mobility (0.24 \(\pm\) 0.06 cm\({}^{2}\)/Vs) and exhibited hysteresis, a larger threshold voltage, and less steep sub-threshold slopes. This indicates that adding polystyrene improved charge transport by increasing mobility nearly fivefold, while also stabilizing the interface and reducing variability in performance. Besides, a threshold voltage of close to 0 V was measured, indicating the good interface quality between the semiconductor and the dielectric. Besides, a device design composed of four transistors was configured under the same inkjet printing, which allowed reducing the electrical performance variation from device to device. A device design composed of four transistors configured under the same inkjet printing allowed reducing the electrical performance variation from device to device. This work demonstrates the potential of combining PS with such advanced device design for high performance organic electronic applications. [PERSON] et al. studied the effect of mixing PS (Mw 9.58k) with TIPS pentacene on the crystalline film morphology of inkjet printed organic semiconductor by using angle-dependent polarized Raman spectroscopy, which provides the capability to characterize the crystal lateral morphology with a high spatial resolution [109]. Figure 5a,b displays the cross-polarized optical images of OTFTs printed using TIPS pentacene and TIPS pentacene/PS sinks, respectively. In the cross-polarized micrographs, both the coffee stain rims and the deposit centers appear brighter due to higher concentrations of crystals. The rectangular section topography within the film's plane (marked by the red dotted line) was analyzed using atomic force microscopy (AFM) in noncontact mode, shown in Figure 5c,d. The rim thickness was found to be between 80-100 nm, while the mean thickness of the polycrystalline region near the droplet's center was measured at 20-30 nm. The results showed that the addition of PS as a polymer additive improves the organic semiconductor morphology by enhancing the uniform coverage in the charge transport channel and reducing the variation in the backbone in-plane orientation. Accordingly, the loading of PS additive improves the hole mobility from 0.22 cm\({}^{2}\)/Vs for the neat TIPS pentacene thin film transistor to 0.73 cm\({}^{2}\)/Vs for the blend based transistor, representing a more than threefold improvement in mobility. This enhancement is attributed to the improved uniformity of the molecular morphology and the reduction in variation in pentacene backbone orientation. Additionally, the threshold voltage shifted closer to 0 V, and the subthreshold slope became significantly steeper in the blend devices, further indicating an improved interface between the semiconductor and dielectric.