Styrenic polymer-additive engineering of crystalline defects and charge transport in TIPS-pentacene organic thin-film transistors

Abstract

Solution-processed organic thin-film transistors (OTFTs) are promising emerging platforms for flexible micro- and nano-electronics; however, crystalline defects, orientational disorder, and incomplete semiconductor coverage can severely limit charge transport. Here, styrenic polymer additives are investigated as a solution-processable strategy for engineering the crystallization and defect morphology of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene, TP). Polystyrene (PS) and poly (α-methylstyrene) (PαMS) were evaluated as styrenic polymer additives. Their effects on crystalline morphology and electrical performance were investigated using polarized optical microscopy, scanning electron microscopy, and transistor electrical characterization. While pristine TP films exhibited substantial orientational disorder and incomplete substrate coverage, PS reduced the misorientation angle but produced relatively narrow domains with pronounced dendritic boundaries. In contrast, TP/PαMS films exhibited nearly parallel crystalline domains, with an average misorientation angle of 1.07 ± 1.29°, a domain width of 75.13 ± 24.63 μm, and a crystal coverage of 83.17%. The simultaneous improvement in alignment, domain width, and coverage minimized morphological interruptions associated with grain-boundary-limited transport and created more continuous source-to-drain pathways. Consequently, TP/PαMS devices achieved a maximum extracted saturation mobility of approximately 0.5 cm 2 /Vs, more than three times that of pristine TP devices. Because the PS and PαMS used in this study differ in molecular weight and exhibit different optimized additive loadings, the observed differences are interpreted as reflecting the combined effects of polymer structure, molecular weight, and concentration rather than being assigned exclusively to α-methyl substitution. More broadly, this study demonstrates that polymer-additive engineering provides an effective strategy for controlling crystalline defects and charge transport in next-generation solution-processed flexible electronics.