Solution processed, aligned arrays of TCNQ micro crystals for low-voltage organic phototransistor

A simple approach is developed to prepare periodic arrays of large, elongated crystals of p-conjugated organic molecules, viz, 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) through a solution based method. The ordered crystalline array is successfully used to fabricate low-voltage organic phototransistors (OPT). The OPT with polymeric gate dielectric exhibits very stable n-type characteristics with a low threshold voltage (<0.5 V). Under illumination, the devices produce a current gain (I-light/I-dark) of 31 at V-G = 0.3 V. Photoswitching occurs within 10 ms and photosensitivity is greater than 1 mA W-1 at low driving voltages and low optical powers. The drain current increases gradually with increasing the illumination intensity resulting in typical output FET characteristics. The one-step, solution-based, self-assembly method for highly ordered organic crystals in large area could have significant potential for future large-scale and low-cost optoelectronic devices. In addition, this study aims to aid the development of organic semiconductor materials with high quality crystalline structures for various optoelectronic applications

Polymer-Gated Transistors with Only One Solution-Processed, Single Crystalline Organic Microwire for Light and Oxygen Detection

Organicsemiconductors employed in single crystalline form haveseveral advantages over polycrystalline films, such as higher chargecarrier mobility and better environmental stability. Herein, we reportthe fabrication and characterization of a solution-processed microsizedsingle-crystalline organic wire of n-type N,N '-dipentyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C-5). The crystal was appliedas an active layer in polymer-gated organic field-effect transistors(OFETs) and organic complementary inverter circuits. The single crystaiilinenature of PTCDI-C-5 wires were characterized using two-dimensionalgrazing incidence wide-angle X-ray diffraction (2D-GIXD) and polarizedoptical microscopy. OFETs with the PTCDI-C-5 crystals exhibitedhigh n-type performance and air stability under ambientconditions. To investigate the electrical properties of the single-crystallinePTCDI-C-5 wire more precisely, OFETs with only one PTCDI-C-5 microwire in the channel were fabricated, and clear n-type characteristics with satisfactory saturation behaviorwere observed. The device with only one crystal wire exhibited characteristicswith significantly lower variation compared to the multicrystal devices,which shows that the density of crystal wires is a critical factorin precisely investigating device performance. The devices exhibiteda reversible threshold voltage shift under vacuum and oxygen conditions,without changing the charge carrier mobility. Light-sensitive characteristicswere also observed. Additionally, this solution-processed, highlycrystalline organic semiconductor can be used in high-performanceorganic electronic circuits as well as in gas or light sensors

Polymer binder assisted, solution processed cyanophenyl functionalized diketopyrrolopyrrole microwire for n-channel field-effect transistors

A cyanophenyl functionalized diketopyrrolopyrrole molecular semiconductor, DPP-PhCN, is used as an nchannel active material for organic field-effect transistors (FETs) with a polymer gate dielectric. Two types of DPP-PhCN active layer are prepared for the formation of the FET devices; 1) thin-film formed through a thermal vacuum deposition at different substrate temperatures and 2) microwire (single and multiple), prepared through a polymer binder assisted solution process. Both types of devices show electron dominant charge transport behavior. The device based on the polymer assisted solution processed microwire exhibit higher performance than the device with a thin-film. The highest electron mobility of 0.23 cm(2)/Vs in ambient condition is achieved from a device with only one microwire of DPP-PhCN, and is 30 times higher than that of the device with DPP-PhCN thin-film (0.008 cm(2)/Vs)

Solution‐Processed PTCDI‐C8 Crystalline Wire: Dual Role as Mask and Active Layer for Organic Transistors with Increased Switching Speeds

Abstract Organic field‐effect transistors (OFETs) have been extensively studied over the past decades because of their suitability for low‐cost, large‐area, and flexible electronics. However, improvements are needed to satisfy the demands of high‐speed applications. The switching speed of a logic device is affected by the charge‐carrier mobility (µ) and the square of the channel length (L) at a given gate–source bias. Therefore, increasing µ and/or reducing L are crucial for achieving high‐speed OFET‐based digital circuits. In this study, an n‐type OFET is fabricated with increased switching speed via a dual‐role approach involving solution‐grown, highly ordered single‐crystalline N,N'‐dioctyl‐3,4,9,10‐perylenetetracarboxylic diimide (PTCDI‐C8) wires, which serve as a mask for short‐channel formation up to the microscale and an active layer with enhanced charge mobility. Additionally, the performance of the n‐type short‐channel OFET and resistive‐load‐type inverters is evaluated. For comparative purposes, long‐channel (50 µm) devices with PTCDI‐C8 wires and short‐channel devices with a PTCDI‐C8 film are fabricated and the device performance is analyzed. The short‐channel device with the PTCDI‐C8 wires exhibits a significantly higher switching speed. Thus, the dual‐role approach is a simple and straightforward method for fabricating short‐channel devices, paving the way for further advancements in OFET technology requiring high switching speeds

Photo-response modulation of organic transistors for multi-level light sensing using active layer microstructure control

Annealing processes are widely used to alter the morphology of organic films and optimize the electrical properties of organic field-effect transistors (OFETs). However, the impact of annealing processes on the photo-response characteristics of phototransistors is not widely studied. We analyze the photo-response modulation of OFETs functioning as multi-level light sensors using active layer microstructure control through annealing processes. We apply solvent vapor annealing with dichloromethane vapor or thermal annealing to an N,N '-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide film, a widely used photosensitive n-type active layer. The annealing processes lead to significant changes in the morphology of the film, altering the charge transport and trapping processes. These changes affect the charge carrier mobility and photo-response characteristics of the device. The difference in static and dynamic photo-response of the OFET devices with respect to the processing conditions is believed to be due to changes in the mechanism of charge transport and the trapping of photogenerated charge carriers in the active layers with altered morphologies. We analyze the active layer morphologies considering the processing conditions and explain their impact on device characteristics based on the charge transport and photo-response characteristics. We demonstrate that simple annealing processes enable the control of charge carrier mobility and photosensitivity of OFETs which highlights the importance of morphology control in the semiconductor film when fabricating multi-level light sensor

Flexible complementary inverter with low-temperature processable polymeric gate dielectric on a plastic substrate

We report low-temperature processability of poly(4-vinylphenol) based gate dielectric by investigating the effect of composition and processing temperature on the thermal, mechanical and electrical characteristics of the gate dielectric. We found that the processing temperature of the gate dielectric could be reduced up to 70 degrees C by optimizing the composition of the gate dielectric solution. Based on this finding, we have fabricated a flexible organic complementary inverter by integrating n- and p-type organic thin-film transistors (OTFTs) with the low-temperature processable gate dielectric on a plastic substrate. Pentacene and F16CuPc were used as p-type and n-type semiconductor, respectively. The inverter shows that the swing range of V-out is same as V-DD, which ensures "zero" static power consumption in digital circuits. The logic threshold of the inverter with G5 gate dielectric cured at 70 degrees C is 21.0 V and the maximum voltage gain (partial derivative V-our/partial derivative V-in) of 8.1 is obtained at V-in = 21.0 V. In addition, we have discussed in more detail the characteristics of the OTFTs and the complementary inverter with respect to the process condition of the gate dielectric. (C) 2009 Elsevier B.V. All rights reserved

Synthesis and structural analysis of dimethylaminophenyl-end-capped diketopyrrolopyrrole for highly stable electronic devices with polymeric gate dielectric

Herein, we report the synthesis and structural analysis of 3,6-bis(5-(4-(dimethylamino)phenyl)thiophen-2-yl)-2,5-dihexadecylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione [DPP(PhNMe2)(2)], a stable diketopyrrolopyrrole derivative end-capped with a strongly electron-donating dimethylaminophenyl moiety. Optical and electrochemical characterization determined the band gap, HOMO, and LUMO energies of the above compound as 1.63, -4.65, and -3.02 eV, respectively. The prepared DPP(PhNMe2)(2) was fabricated into thin films to construct field-effect transistors and resistance load-type inverters, the responses of which to static/dynamic electrical stimuli were analyzed in detail. Specifically, field-effect transistors demonstrated stable output/transfer characteristics during 100 sweeping cycles and showed excellent performance stability (over 300 days) under ambient conditions, with the corresponding dynamic switching characteristics being well maintained during 500 on-off cycles. The above inverters also showed good performance under ambient conditions. To clarify the origin of this performance enhancement, the above thin films were subjected to structural analysis by atomic force microscopy, density function theory calculations, and two-dimensional grazing incidence X-ray diffraction, which revealed that DPP(PhNMe2)(2) molecules were stacked over the surface of the gate dielectric via their NMe2 groups. Based on the obtained results, the improved device performance was ascribed to the end-on orientation and close packing of DPP(PhNMe2)(2) molecules along the - stacking direction