High Throughput Characterization of Organic Thin Film Transistors.

Automation is vital to accelerating research. In recent years, the application of self-driving labs to materials discovery and device optimization has highlighted many benefits and challenges inherent to these new technologies. Successful automated workflows offer tangible benefits to fundamental science and industrial scale-up by significantly increasing productivity and reproducibility all while enabling entirely new types of experiments. However, it's implemtation is often time-consuming and cost-prohibitive and necessitates establishing multidisciplinary teams that bring together domain-specific knowledge with specific skillsets in computer science and engineering. This perspective article provides a comprehensive overview of how the research group has adopted "hybrid automation" over the last 8 years by using simple automatic electrical testers (autotesters) as a tool to increase productivity and enhance reproducibility in organic thin film transistor (OTFT) research. From wearable and stretchable electronics to next-generation sensors and displays, OTFTs have the potential to be a key technology that will enable new applications from health to aerospace. The combination of materials chemistry, device manufacturing, thin film characterization and electrical engineering makes OTFT research challenging due to the large parameter space created by both diverse material roles and device architectures. Consequently, this research stands to benefit enormously from automation. By leveraging the multidisciplinary team and taking a user-centered design approach in the design and continued improvement of the autotesters, the group has meaningfully increased productivity, explored research avenues impossible with traditional workflows, and developed as scientists and engineers capable of effectively designing and leveraging automation to build the future of their fields to encourage this approach, the files for replicating the infrastructure are included, and questions and potential collaborations are welcomed.

Poly(ionic liquid) Gating Materials for High-Performance Organic Thin-Film Transistors: The Role of Block Copolymer Self-Assembly at the Semiconductor Interface.

The widespread realization of wearable electronics requires printable active materials capable of operating at low voltages. Polymerized ionic liquid (PIL) block copolymers exhibit a thickness-independent double-layer capacitance that makes them a promising gating medium for the development of organic thin-film transistors (OTFTs) with low operating voltages and high switching speed. PIL block copolymer structure and self-assembly can influence ion conductivity and the resulting OTFT performance. In an OTFT, self-assembly of the PIL gate on the semiconducting polymer may differ from bulk self-assembly, which would directly influence electrical double-layer formation. To this end, we used poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) as a model semiconductor for our OTFTs, on which our PILs exhibited self-assembly. In this study, we explore this critical interface by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) of P(NDI2OD-T2) and a series of poly(styrene)-b-poly(1-(4-vinylbenzyl)-3-butylimidazolium-random-poly(ethylene glycol) methyl ether methacrylate) (poly(S)-b-poly(VBBI+[X]-r-PEGMA)) block copolymers with varying PEGMA/VBBI+ ratios and three different mobile anions (where X = TFSI-, PF6-, or BF4-). We investigate the thin-film self-assembly of block copolymers as a function of device performance. Overall, a mixed orientation at the interface leads to improved device performance, while predominantly hexagonal packing leads to nonfunctional devices, regardless of the anion present. These PIL gated OTFTs were characterized with a threshold voltage below 1 V, making understanding of their structure-property relationships crucial to enabling the further development of high-performance gating materials.

Ionic Liquid Containing Block Copolymer Dielectrics: Designing for High-Frequency Capacitance, Low-Voltage Operation, and Fast Switching Speeds.

Polymerized ionic liquids (PILs) are a potential solution to the large-scale production of low-power consuming organic thin-film transistors (OTFTs). When used as the device gating medium in OTFTs, PILs experience a double-layer capacitance that enables thickness independent, low-voltage operation. PIL microstructure, polymer composition, and choice of anion have all been reported to have an effect on device performance, but a better structure property relationship is still required. A library of 27 well-defined, poly(styrene)-b-poly(1-(4-vinylbenzyl)-3-butylimidazolium-random-poly(ethylene glycol) methyl ether methacrylate) (poly(S)-b-poly(VBBI+[X]-r-PEGMA)) block copolymers, with varying PEGMA/VBBI+ ratios and three different mobile anions (where X = TFSI-, PF6 - or BF4 -), were synthesized, characterized and integrated into OTFTs. The fraction of VBBI+ in the poly(VBBI+[X]-r-PEGMA) block ranged from to 100 mol % and led to glass transition temperatures (T g) between -7 and 55 °C for that block. When VBBI+ composition was equal or above 50 mol %, the block copolymer self-assembled into well-ordered domains with sizes between 22 and 52 nm, depending on the composition and choice of anion. The block copolymers double-layer capacitance (C DL) and ionic conductivity (σ) were found to correlate to the polymer self-assembly and the T g of the poly(VBBI+[X]-r-PEGMA) block. Finally, the block copolymers were integrated into OTFTs as the gating medium that led to n-type devices with threshold voltages of 0.5-1.5 V while maintaining good electron mobilities. We also found that the greater the σ of the PIL, the greater the OTFT operating frequency could reach. However, we also found that C DL is not strictly proportional to OTFT output currents.

Conjoint use of Naphthalene Diimide and Fullerene Derivatives to Generate Organic Semiconductors for n-type Organic Thin Film Transistors.

In this paper, we described the design, synthesis, and characterization of two novel naphthalene diimide (NDI) core-based targets modified with terminal fullerene (C60 ) yield - so called S4 and S5, in which NDI bearing 1 and 2 molecules of C60 , respectively. The absorption, electrochemical and thin-film transistor characteristics of the newly developed targets were investigated in detail. Both S4 and S5 displayed broad absorption in the 450-500 nm region, owing to the effect of conjugation due to fullerene functionalities. The electrochemical measurement suggested that the HOMO and the LUMO energy levels can be altered with the number of C60 units. Both S4 and S5 were employed as organic semiconductor materials in n-channel transistors. The thin film transistor based on S4 exhibited superior electron mobility (µe) values ranging from 1.20×10-4 to 3.58×10-4  cm2  V-1 s-1 with a current on-off ratio varying from 102 to 103 in comparison with the performance of S5 based transistor, which exhibited µe ranging from 8.33×10-5 to 2.03×10-4  cm2  V-1 s-1 depending on channel lengths.

Air and temperature sensitivity of n-type polymer materials to meet and exceed the standard of N2200.

N-type organic semiconductors are notoriously unstable in air, requiring the design of new materials that focuses on lowering their LUMO energy levels and enhancing their air stability in organic electronic devices such as organic thin-film transistors (OTFTs). Since the discovery of the notably air stable and high electron mobility polymer poly{[N,N'-bis (2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,29-bisthiophene)} (N2200), it has become a popular n-type semiconductor, with numerous materials being designed to mimic its structure. Although N2200 itself is well-studied, many of these comparable materials have not been sufficiently characterized to compare their air stability to N2200. To further the development of air stable and high mobility n-type organic semiconductors, N2200 was studied in organic thin film transistors alongside three N2200-based analogues as well as a recently developed polymer based on a (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b']difuran-2,6(3 H,7 H)-dione (IBDF) core. This IBDF polymer has demonstrated promising field-effect mobility and air stability in drop-cast OTFTs. While N2200 outperformed its analogues, the IBDF-based polymer displayed superior air and temperature stability compared to N2200. Overall, polymers with more heteroatoms displayed greater air stability. These findings will support the development of new air-stable materials, and further demonstrate the persistent need for the development of novel n-type semiconductors.