## 3 Polystyrene in TIPS Pentacene Crystallization
### High Molecular Weight PS (Greater than 250k)
Figure 12: **(a)** A digital photograph depicting a series of OTFTs on PEN. **(b)** The AFM image showing SU8. (c) The AFM image illustrating the semiconductor film across the contact areas and channel. Reproduced from reference [120], with permission from [PERSON]. We have discussed the role of PS as an amorphous polymer in improving the crystallization and morphology of organic semiconductors. Using PS as polymer additives in organic semiconductor crystallization, particularly with the benchmark semiconductor TIPS pentacene, offers several advantages, including enhanced crystallinity, improved charge transport, and controlled film morphology by promoting uniform crystal formation and reducing grain boundaries and defects. PS demonstrates several advantages over other types of polymers as discussed in this article, such as conjugated and semicrystalline polymers, in the crystallization process of organic semiconductors. While conjugated polymers such as P3 HT and PBTTT enhance charge transport by promoting molecular alignment, they often lead to more complex morphologies that can result in greater variability in device performance. Semicrystalline polymers such as PEO offer in-situ crystallization control, but their tendency for phase separation and reduced solubility at higher molecular weights can reduce the uniformity of the crystalline films. In contrast, PS, as an amorphous polymer, effectively minimizes misalignment and promotes uniform, parallel crystal orientation, which is crucial for achieving consistent charge transport. Additionally, PS can induce beneficial phase segregation and control film morphology without disrupting crystal integrity, which makes it a superior additive for enhancing the crystallization and electrical performance of organic semiconductors. PS, especially with low Mw, improves interface quality and device performance, while medium and high Mw PS enhance long-range order and stability. However, high Mw PS may introduce challenges such as increased phase separation and reduced solubility, which could potentially compromise film uniformity and electrical properties of the organic electronic devices. Therefore, the primary bottlenecks of implementing PS in organic electronic applications include optimizing the Mw of PS, selecting compatible solvent systems, and managing environmental sensitivities, all of which are crucial for achieving high-performance organic electronic devices. Another bottleneck in optimizing charge transport in organic semiconductor systems is the complex interplay of different factors such as crystal morphology, molecular alignment, grain boundaries, and phase separation. To address this, the large experimental parameter space, which comprises variables such as solvent types, polymer molecular weights, deposition methods, and post-processing techniques, can be employed to systematically explore and identify conditions that enhance charge transport. High-throughput experimentation combined with machine learning could accelerate this process by identifying patterns and correlations between different parameters and charge mobility outcomes [122; 123]. As PS is widely used in various industries, it has significant environmental impacts due to its long degradation time and resistance to natural decomposition [124; 125]. As a petroleum-based polymer, its production contributes to greenhouse gas emissions and the depletion of non-renewable resources [126]. Once discarded, PS tends to accumulate in landfills and the environment, where it can take hundreds of years to break down. It also poses a risk to wildlife, as small particles of PS can be ingested by animals, which leads to harmful health effects. From a sustainability perspective, PS is difficult to recycle efficiently, and its widespread use in single-use products further exacerbates its environmental