Malgorzata Nguyen1,Ulrike Kraft2,Katharina Broch3,Wen Liang Tan4,Ian Jacobs1,Illia Dobryden5,Weimin Zhang6,Deepak Venkateshvaran1,Iain McCulloch7,6,Chris McNeill4,Henning Sirringhaus1
Cambridge University1,Max Planck Institute for Polymer Research2,University of Tübingen3,Monash University4,Research Institutes of Sweden5,King Abdullah University of Science and Technology6,University of Oxford7
Malgorzata Nguyen1,Ulrike Kraft2,Katharina Broch3,Wen Liang Tan4,Ian Jacobs1,Illia Dobryden5,Weimin Zhang6,Deepak Venkateshvaran1,Iain McCulloch7,6,Chris McNeill4,Henning Sirringhaus1
Cambridge University1,Max Planck Institute for Polymer Research2,University of Tübingen3,Monash University4,Research Institutes of Sweden5,King Abdullah University of Science and Technology6,University of Oxford7
With the promise of low-cost solution-processing and the reported mobilities surpassing the industrial standard of amorphous Si, OFETs are now close to becoming ubiquitous circuit components of flexible electronics such as wearable devices, display matrices and biosensors. The bottleneck for OFETs to outperform their inorganic counterpart is their issues with environmental, thermal and operational stability, and the general poor understanding of mechanisms involved in these processes. The instabilities can be quantified by voltage threshold shifts, changes in mobility, ON/OFF current ratio or subthreshold swing as a function of applied condition. This can result in a variety of device shortcomings such as erroneous extraction of measured quantities in sensors or an unstable pixel brightness of an OLED display. Device instabilities are widely attributed to trapping of charges due to intrinsic properties such as conformational defects, or external effects related to atmospheric conditions or induced by bias stress.<br/>Here, we focus on the operational stability of the devices, i.e. under a prolonged bias. While a lot of research has been done into understanding and reducing the ON-state bias stress instabilities (such as addition of molecular additives [1], molecular doping [2] or encapsulation [3]), work on the OFF-state bias stress effects is scarce [4]. Since most OFET devices stay in in the depletion mode for longer times, excellent OFF-state stability is an equally important industrial requirement.<br/>In this work, we introduce a novel method of improving OFF-state stability of solution-processed polymeric OFETs, using an anti-solvent treatment on an Indacenodithiophene-co-benzothiadiazole (IDT-BT) film. We demonstrate an improvement across both voltage threshold (4-fold) and mobility (10-fold) stability that suggests a decrease in the density of both deep and shallow charge traps. Moreover, the anti-solvent treated devices exhibit superior long-term stabilisation of the device as well as OFF-state bias stability when exposed to atmospheric species or light. We also show the microscopic and crystallographic morphology change induced by the treatment, which we believe is crucial for understanding of the underlying mechanism. Our results show a simple and effective way of minimising the OFF-state instability of OFETs that can contribute to the future advancement of organic electronics in industrial applications.<br/>[1] M. Nikolka, I. Nasrallah, B. Rose, M. K. Ravva, K. Broch, A. Sadhanala, D. Harkin, J. Charmet, M. Hurhangee, A. Brown, S. Illig, P. Too, J. Jongman, I. McCulloch, J. L. Bredas, H. Sirringhaus, <i>Nat. Mater.</i> <b>2017</b>, <i>16</i>, 356.<br/>[2] M. P. Hein, A. A. Zakhidov, B. Lüssem, J. Jankowski, M. L. Tietze, M. K. Riede, K. Leo, <i>Appl. Phys. Lett.</i> <b>2014</b>, <i>104</i>.<br/>[3] H. F. Iqbal, Q. Ai, K. J. Thorley, H. Chen, I. McCulloch, C. Risko, J. E. Anthony, O. D. Jurchescu, <i>Nat. Commun.</i> <b>2021</b>, <i>12</i>, 2352.<br/>[4] M. Kettner, M. Zhou, J. Brill, P. W. M. Blom, R. T. Weitz, <i>ACS Appl. Mater. Interfaces</i> <b>2018</b>, <i>10</i>, 35449.