A more than six orders of magnitude UV-responsive organic field-effect transistor is developed using a benzothiophene (BTBT) semiconductor and strong donor-acceptor Disperse Red 1 as the traps to enhance charge separation. The device can be returned to its low drain current state by applying a short gate bias, and is completely reversible with excellent stability under ambient conditions.

sensors, re-writable memory devices, radio frequency identifi cation tags, etc. [ 1,2 ] Performance of OTFTs has been significantly improved in the last decade through engineering of the materials, interfaces, and architecture of devices. [3][4][5] Reported maximum charge carrier mobilities reached 17.2 cm 2 V −1 s −1 for vacuum-deposited asymmetric tridecyl (C 13 )-substituted [1]benzothieno [3,2-b][1]benzothiophene (C 13 -BTBT), [ 6 ] 31.3 cm 2 V −1 s −1 [ 7 ] and 43 cm 2 V −1 s −1 [ 8 ] for solution-processed OTFTs based on symmetric C 8 -BTBT, and 10.5 cm 2 V −1 s −1 for solution-processed conductive polymers. [ 9 ] Compared to the FETs made from the amorphous silicon (α-Si) that have a mobility of ≈1 cm 2 V −1 s −1 , these results are very promising for the massive commercialization of OTFTs. Moreover, an understanding of device physics has been achieved through simultaneous experimental and modeling analysis. [ 10 ] Finding new and specifi c functionalities and thus widening the applications of OTFTs is in the main research focus. One of the specifi c functionalities is optical control over OTFT electrical characteristics to attain air-stable photocontrolled transistors, i.e., organic thin-fi lm phototransistors (OTF-PT), with sensing and/ or memory properties. [ 14,15 ] OTF-PTs are four-terminal devices, namely, gate-source-drain-light electrodes where adjustment of the incident light intensity amplifi es the drain current. As a result, OTF-PTs have higher signal-to-noise ratio (higher sensitivity-lower noise), compared to photodiodes [ 14 ] and they are also suitable for application in optical transducers. [ 16 ] OTF-PTs have an advantage over their inorganic counterparts due to the ability to choose from a variety of organic materials to tune the sensing properties within the ultraviolet (UV) and visible light spectrum. However, response times are slower compared with inorganic UV sensors recently reported. [ 17 ] Therefore, the current challenge in the fabrication of OTF-PT with high photocurrent gain is to design and engineer organic sensors and memory devices with properties comparable to common inorganic devices. Important parameters for the fabrication of high quality OTF-PT are operational stability (electrical and photo-), photosensitivity, and retention times (long for memory and short for sensors).So far, photocontrol of OTFTs electrical properties has been achieved through the incorporation of photochromic organic

We have studied a UV responsive phototransistor and how the addition of various azobenzene derivatives alters the rise and relaxation times when exposed to and removed from UV light respectively. A three-component semiconductor system was studied consisting of a UV responsive material C5-BTBT, a polymer binder PMMA, and 1 of 5 different azobenzene materials for UV response enhancement. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were determined experimentally and found from DFT theory. Azobenzene units with a pendent nitro group have lower HOMO and LUMO levels than the semiconductor C5-BTBT. This combined with their electron withdrawing nature allow them to stabilize excited electrons, extending the lifetime of excitons, keeping the system at a high current longer. Using a bi-exponential model, we see the relaxation rate constant τ increase from 278 to 578 s when nitro-azobenzene was used. Meanwhile, when azobenzene contains the electron donating unit -NH2, the HOMO of the material was found to be higher than that of C5-BTBT. This allowed another pathway for excited electrons to decay to their ground state, causing hole pair recombination, reducing IDS. The relaxation curves when UV light is removed demonstrate a clear increase in decay rate over the control system, showing the charge donating aminoazobenzene assist in charge recombination.

A functional capacitive sensing device with five touch points was fabricated on the curved surfaces of polyvinyl chloride, polycarbonate and acrylonitrile butadiene styrene piping. The capacitive touch sensor points and conductive traces were printed with an Optomec™ Aerosol Jet printer using silver nanoparticle ink. We present a solution to a common problem with hybrid printed electronics of transitioning from the printed electronic components on a three-dimensional object to traditional rigid circuit board electronics. We highlight the need for CAD/CAM technology as an essential tool for printing on three-dimensional surfaces. The capacitive touch sensor library of an Arduino Uno Bard Rev 3 microcontroller enabled the detection of contact at the printed touch points. Corresponding LEDs attached to the surface of the pipe light up to indicate contact at the touch points. This hybrid printed electronic device presents a fully integrated and functioning electronic device printed on a three-dimensional surface and highlights the requirement of multidisciplinary knowledge for the field of hybrid printed electronics.