The mechanical bending effect and mechanism of high performance and low-voltage flexible organic thin-film transistors with a cross-linked PVP dielectric layer

Low operational voltage flexible organic thin-film transistors (OTFTs) have been achieved using two layers of cross-linked PVP as the dielectric layer on a flexible polyimide (PI) substrate. At low operating voltages of -4 V, the flexible OTFTs showed good performances with high field-effect mobility (∼0.56 cm² V^-1 s^-1), low threshold voltage (∼-0.82 V), high on/off current ratio (∼10⁵) and excellent electrical stability (∼2 months). During a severe mechanical bending test (10⁴ bending cycles and a bending radius of 0.75 mm) under ambient conditions, the flexible OTFTs still showed excellent electrical performance at the low operational voltage. Moreover, the effects of the mechanical bending on the electrical parameters of the flexible OTFTs were also systematically investigated. We found that the variations of the electrical parameters of the flexible OTFTs during the mechanical bending process were closely related to the distance effect of the spacing between stretched pentacene molecules and the doping effect of H₂O and O₂ which were induced by the mechanical bending strains. In comparison with previously reported flexible OTFTs, the research results showed that the distance effect and doping effect were mutually independent as well as mutually related during the mechanical bending process of the flexible OTFTs.