Elastic organic semiconducting single crystals for durable all-flexible field-effect transistors: insights into the bending mechanism

Ranita Samanta; Susobhan Das; Saikat Mondal; Tamador Alkhidir; Sharmarke Mohamed; Satyaprasad P Senanayak; C Malla Reddy

doi:10.1039/d2sc05217b

Elastic organic semiconducting single crystals for durable all-flexible field-effect transistors: insights into the bending mechanism

Chem Sci. 2022 Dec 22;14(6):1363-1371. doi: 10.1039/d2sc05217b. eCollection 2023 Feb 8.

Authors

Ranita Samanta¹, Susobhan Das¹, Saikat Mondal¹, Tamador Alkhidir², Sharmarke Mohamed^{2

3}, Satyaprasad P Senanayak⁴, C Malla Reddy¹

Affiliations

¹ Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata Mohanpur Nadia West Bengal 741246 India cmallareddy@gmail.com.
² Department of Chemistry, Green Chemistry & Materials Modelling Laboratory, Khalifa University of Science and Technology P.O. Box 127788 Abu Dhabi United Arab Emirates sharmarke.mohamed@ku.ac.ae.
³ Advanced Materials Chemistry Center (AMCC), Khalifa University of Science and Technology P.O. Box 127788 Abu Dhabi United Arab Emirates.
⁴ Nanoelectronics and Device Physics Lab, School of Physical Sciences, National Institute of Science Education and Research, An OCC of HBNI Jatni 752050 India satyaprasad@niser.ac.in.

Abstract

Although many examples of mechanically flexible crystals are currently known, their utility in all-flexible devices is not yet adequately demonstrated, despite their immense potential for fabricating high performance flexible devices. Here, we report two alkylated diketopyrrolopyrrole (DPP) semiconducting single crystals, one of which displays impressive elastic mechanical flexibility whilst the other is brittle. Using the single crystal structures and density functional theory (DFT) calculations, we show that the methylated diketopyrrolopyrrole (DPP-diMe) crystals, with dominant π-stacking interactions and large contributions from dispersive interactions, are superior in terms of their stress tolerance and field-effect mobility (μ _FET) when compared to the brittle crystals of the ethylated diketopyrrolopyrrole derivative (DPP-diEt). Periodic dispersion-corrected DFT calculations revealed that upon the application of 3% uniaxial strain along the crystal growth (a)-axis, the elastically flexible DPP-diMe crystal displays a soft energy barrier of only 0.23 kJ mol^-1 while the brittle DPP-diEt crystal displays a significantly larger energy barrier of 3.42 kJ mol^-1, in both cases relative to the energy of the strain-free crystal. Such energy-structure-function correlations are currently lacking in the growing literature on mechanically compliant molecular crystals and have the potential to support a deeper understanding of the mechanism of mechanical bending. The field effect transistors (FETs) made of flexible substrates using elastic microcrystals of DPP-diMe retained μ _FET (from 0.019 cm² V^-1 s^-1 to 0.014 cm² V^-1 s^-1) more efficiently even after 40 bending cycles when compared to the brittle microcrystals of DPP-diEt which showed a significant drop in μ _FET just after 10 bending cycles. Our results not only provide valuable insights into the bending mechanism, but also demonstrate the untapped potential of mechanically flexible semiconducting crystals for designing all flexible durable field-effect transistor devices.