(Invited) Strain Sensing Inverter and Photovoltaic Circuits Based on Novel Heptazole Organic Thin Film

Abstract

Following solid pentacene films and other p-type small molecules, in the present work, we show a new small molecule, 8,16-dihydrobenzo[a]benzo[6,7]indolo[2,3-h]carbazole (heptazole; C26H16N2) which has almost the same HOMO level as that of pentacene but with a higher HOMO-LUMO gap of ~2.95 eV, so as to be photostable under visible light except deep blue-to-violet range. The field-effect mobility of our new OTFT turns out to be ~0.21 cm2/V s which is lower than that of the pentacene OTFT on the same dielectric layer, however our new OTFT on flexible substrate is found to work as a strain sensor because organic heptazole layer changes its electric resistance under tensile strain but such change appears elastically recoverable by removing the strain. We here display an inverter which is composed of two OTFTs but with 90 drgree different channel orientations each other: one would work as a strain sensor while the other works as a load under static and dynamic tensile bending strain conditions. Moreover, we also found that our heptzole organic film has very small exciton binding (~40 meV) properties under deep blue photons (wave length~410 nm). Taking advantages of such small exciton binding energy, we developed a Schottky diode circuit which can dynamically measure the photovoltaic effects without any assistacnce of electric power. Based on above-mentioned benefits of our heptazole layer in TFT and Schottky diode, we demonstrate in the meeting the dynamic strain sensing of the organic inverter on flexble substrate, and dynamic photovoltaic switching of the Schottky diode circuits as briefly shown below. Figure 1