Polymorphic Organic Crystals of P(NDI2O-T2): Impact of Microstructure on The Charge Transport Properties

The electronic charge transport characteristics of organic semiconductors (OSCs) are intricately linked to their solid-state morphology. Deciphering the complex interplay of these OSC polymer properties with the supramolecular organizations in their (semi)crystalline structure is of importance in the pursuit of high-performance materials for next-generation optoelectronic technologies. However, currently available <i>in-situ</i> experimental characterization techniques offer limited nano-scale insight, making it challenging to comprehensively describe the microstructure of fabricated films in terms of crystallinity and polymer conformations and orientations, and thus to rationalize the relationship of structure with associated electronic properties. In this study, we present an in-depth characterization of the supramolecular crystal organization and its impact on the electronic charge transport properties of polymorphic crystalline forms of the n-type hairy-rod polymer P(NDI2O-T2); this material can have low energetic disorder and high electron mobility, making it well-suited for a wide range of electronic device applications. Based on available experimental data from X-ray scattering techniques and infra-red spectroscopy, we derive the crystal unit-cell structures of the three reported polymorphic forms at the atomistic scale, through a meticulously parameterized classical molecular dynamics force field in conjunction with periodic density functional theory (DFT) calculations. Furthermore, we extend our simulations to investigate the diverse morphological aspects of the semicrystalline structure following thermal treatment and account for the factors governing the polymorphic interconversion and selectivity. We sample the nano- to microstructure of the simulated thin films and quantify charge carrier transport through density functional theory calculations. These results serve as the foundation to establish critical and fundamental correlations between crystal transport properties and the nano- and microstructure of the polymer, as well as the associated disorder. This, in turn, allows the determination of the dominant transport microscopic parameters and provides insight into how these parameters can be tuned through precise processing techniques.