Abstract
Spin-coating has been used extensively in the fabrication of electronic devices; however, the effects of the processing parameters have not been fully explored. Here, we systematically characterize the effects of the spin-coating time on the microstructure evolution during semiconducting polymer solidification in an effort to establish the relationship between this parameter and the performances of the resulting polymer field-effect transistors (FETs). We found that a short spin-coating time of a few seconds dramatically improve the morphology and molecular order in a conjugated polymer thin film because the π-π stacking structures formed by the polymer molecules grow slowly and with a greater degree of order due to the residual solvent present in the wet film. The improved ordering is correlated with improved charge carrier transport in the FETs prepared from these films. We also demonstrated the effects of various processing additives on the resulting FET characteristics as well as on the film drying behavior during spin-coating. The physical properties of the additives are found to affect the film drying process and the resulting device performance.
Highlights
Spin-coating techniques are remarkably easy to use, versatile, inexpensive, and highly effective for depositing a uniform thin film reproducibly[1,2,3]
In the majority of reports describing the fabrication of solution-processed organic field-effect transistors (OFETs), the spinning time ranges from 40s to 180s, depending on the volatility of the solvents[8,15,33,34]
We systematically investigated, for the first time, the effects of the spinning time on the microstructure evolution in polymer thin films to establish the relationship between the polymer field-effect transistors (FETs) device performances
Summary
Spin-coating techniques are remarkably easy to use, versatile, inexpensive, and highly effective for depositing a uniform thin film reproducibly[1,2,3]. The spinning speed may be tuned to alter the strength of the centrifugal force and shear force, thereby varying the final film thickness as well as the film roughness and crystalline structures[23,24] These features in turn affect the charge injection and transport properties in the OFETs28,29. The resultant polyaniline thin films showed high thickness-independent conductivities, which were attributed to the improved degree of crystallinity These results gave us a vital clue about the relationship between the spinning time and the OFET performance. The spin-coating process was optically monitored to obtain important information about the drying behavior of the solution during spin-coating and to help explain why the brief spinning time improved the charge transport characteristics of the semiconducting polymer films. Polymer FETs processed with various additives for a given spinning time were characterized, revealing that the effective spinning time range could be controlled using processing additives
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