Trion-induced current anomaly in organic polymer

• A current anomaly in OTFTs is found to result from strong many-body interactions.
• Trion formation is responsible for the observed anomaly.
• The trion forms when two polarons are captured by OH− in the H2O/O2 redox reaction.
• The metastable trion can dissociate to mobile polarons under external influences.
• The rate of trion formation is 1000 times higher than that of its dissociation.

In this report, an anomalous time-evolution of electrical current in organic thin-film transistors, OTFTs, is revealed by employing a specially tailored semiconductor composite channel. The composite is designed by controlling the density of carbon nanotubes dispersed in a host semiconducting polymer below electrical percolation. The current anomaly, which, to the best of our knowledge, has never been observed before, is directly correlated to strong many-body interactions instantaneously occurring in the system under investigation. In essence, two on-chain positively charged polarons are fused with an electrochemically generated negative hydroxyl ion, OH−, in the H2O/O2 redox reaction to form a trion. The trion, which is characteristic of the polymer, is intrinsically metastable and can dissociate to mobile polarons under the influence of electric field, temperature and/or light illumination. The rate of trion formation is almost three orders of magnitude higher than that of trion dissociation. The fast formation and slow dissociation of the trions is the cause responsible for the observed current anomaly. The metastable trion is, hence, of fundamental importance in the operation of OTFTs. Understanding the fundamentals pertaining to the anomalous phenomenon not only is crucial for design of more efficient devices but also can guide development of future, emerging applications of OTFTs.

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