Mechanoelectronics: Flexible Organic Semiconducting Single Crystals for Durable All-Flexible Field-Effect Transistors

Although many examples of mechanically flexible crystals are currently known, their utility in all-flexible devices is not yet demonstrated, despite their immense potential for fabricating high-performance flexible devices. 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 (µFET) when compared to the brittle crystals of ethylated diketopyrrolopyrrole derivative (DPP-diEt). The field effect transistors (FETs) made of flexible substrates using elastic microcrystals of DPPdiMe retained µFET (from 0.019 cm2/Vs to 0.014 cm2/Vs ) more efficiently even after 40 bending cycles when compared to the brittle microcrystals of DPP-diEt which showed a significant drop in µFET just after 10 bending cycles. Our results not only provide valuable insights into bending mechanism but also demonstrate the untapped potential of mechanically flexible semiconducting crystals for designing all flexible durable devices.