Polymeric semiconductor and transition-metal dichalcogenide nanocomposites for inkjet-printed thin-film transistor devices
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Date
2023-10-20
Authors
Choi, Hyunwoo
Journal Title
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Publisher
University of Waterloo
Abstract
Patterned using subtractive processes, conventional thin-film deposition techniques inevitably require high-vacuum deposition and photolithography to define functional layers to create a device structure. Inkjet printing technology has received considerable attention to realize low-cost and potential mass production of large-area electronics at low temperatures using an additive process approach. However, the materials used in the printing process are based on solution-based electronic inks formulated with organic electronic materials. Among them, conjugated polymers are widely used as a semiconductor for thin-film transistor (TFT) applications, but they possess poor charge transport properties compared to other single or polycrystalline inorganic semiconductors. Moreover, the inkjet printing method has a weakness for depositing polymeric solution that form thin films having a highly ordered molecular structure.
To overcome this limitation when using printed polymers, a hybrid organic/inorganic semiconductor ink was explored. The hybrid semiconductor ink was prepared by mixing two different materials, molybdenum disulfide (MoS₂) nanosheets and solution-based poly(3-hexylthiopene-2,5-diyl) (P3HT), the former is a two-dimensional semiconductor and the latter a conjugated polymer. To enhance the level of exfoliation and stability of MoS₂ nanosheets in P3HT, the surfactant trichloro(dodecyl)silane (DDTS), was used to functionalize the MoS₂ surface. Printed TFTs using the nanosheet suspension were found to enhance the field-effect mobility by approximately 3× compared to TFTs without the suspension. The introduced single-crystalline MoS₂ nanosheets in the P3HT matrix improved the electrical and structural properties of the inkjet-printed thin-film polymer.
Based on these findings and insights, the observed effects can be extended to second-generation polymeric semiconductors, specifically the donor-acceptor (D-A) co-polymers. These materials are renowned for exhibiting the highest mobilities among printable polymers while maintaining ambipolarity, a desirable trait for configuring complementary metal-oxide-semiconductor (CMOS) circuits. In light of this, novel nanocomposite semiconductor inks were developed to demonstrate the influence of 2D nanoparticles on the electronic properties of D-A copolymers, diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT). Printed TFTs using this new hybrid semiconductor showed that the field-effect mobility of the devices increased by 33 % and 140 % in both hole (p-type) and electron (n-type) transports, respectively. Atomic force microscopy (AFM) results of the printed hybrid thin film revealed that strongly aggregated polymer domains were observed in films containing the MoS₂ nanosheets. In ultraviolet–visible–near infrared spectroscopy (UV-vis-NIR) measurement, increased intensity of 0-0 and 0-1 peaks from hybrid film indicates improved charge transport was due to enhanced intermolecular charge transfer in the microstructure of the polymer film. Furthermore, the incorporation of hybrid nanocomposites proved particularly beneficial for inkjet-printed TFTs utilizing metal electrodes, as the latter had a tendency to augment contact resistance and thereby compromise device performance. However, the introduction of hybrid nanocomposites effectively counteracted the performance degradation arising from the printed metal electrodes by enhancing the crystallinity of the polymeric film. Moreover, these findings also highlight the feasibility of employing lower sintering temperatures for inkjet-printed metal electrodes. This is attributed to the fact that the result of increased contact resistance associated with lower sintering temperatures can be effectively mitigated by the nanocomposite semiconductor. Consequently, an overall enhancement in device performance was achieved by applying the hybrid nanocomposite ink. This study elucidated the advantageous influence of solution-processed MoS₂ nanosheets on the crystallinity and electrical properties of polymeric thin films, consequently leading to significant improvements in the performance parameters of inkjet-printed TFTs.
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Keywords
inkjet printing, polymer semiconductor, thin-film transistor, 2D materials, silver nanoparticle