Effects of Processing-Induced Contamination on Organic Electronic Devices

Organic semiconductors are often touted as ‘defect tolerant’, however to date there have been relatively few systematic studies of the role of impurities on device performance. In particular, little attention has been paid to processing-induced contaminants, originating from e.g. the glovebox atmosphere or solvents, even though anecdotal reports have long indicated that such factors may be important.<br/>Here,[1] we present a systematic study of processing-induced contamination on the performance of indacenodithiophene-co-benzothiadiazole (IDTBT) organic field effect transistors (OFETs). We observe that glovebox vapor can result in film contamination, but that in gloveboxes with a typical carbon-based solvent trap, the dominant impurities are typically aliphatics such as vacuum pump oil, rather than aromatics typically used for spin coating. In clean gloveboxes, we observe that the solvent content in films is largely determined by the residual solvent vapor in the atmosphere, rather than annealing, due to the large surface to volume ratio of thin films.<br/>In addition, we find that most common plastic laboratory consumables, such as pipette tips, syringes, and even metal needles, leach contaminants into organic semiconductor solutions. In some cases, such as poly(dimethylsiloxane) (PDMS) coatings on metal needles, contamination leads to improvements in film wetting and device performance. However, in other cases, such as leachates from micropipettes, we observe strongly degraded device performance. Using NMR, we identify two primary contaminants (oleamide and glycerol monostearate) leaching from micropipette tips. These chemicals are both ampiphilic, and therefore could plausibly lead to increased electrostatic disorder, or the formation of hydrophilic inverse micelles. Tellingly, quartz crystal microbalance measurements reveal that uncontaminated IDTBT films are entirely hydrophobic, while contaminated films swell by 20% upon exposure to water, suggesting that previous studies on the role of water uptake in IDTBT may have been dominated by impurities. Our results promisingly suggest that intrinsic OFET performance may actually be more stable than previously thought. However, they are also broadly relevant to a wide range of materials and devices fabricated from solution, and suggest important strategies to limit contamination and increase experimental reproducability,<br/><br/>[1] D. Simatos,* I.E. Jacobs,* et al. Small Methods, 2023, 2300476