While organic electronics is mostly dominated by light-emitting diodes, photovoltaic cells and transistors, optoelectronics properties peculiar to organic semiconductors make them interesting candidates for the development of innovative and disruptive applications also in the field of light signal detection. In fact, organic-based photoactive media combine effective light absorption in the region of the spectrum from ultraviolet to near-infrared with good photogeneration yield and low-temperature processability over large areas and on virtually every substrate, which might enable innovative optoelectronic systems to be targeted for instance in the field of imaging, optical communications or biomedical sensing. In this review, after a brief resume of photogeneration basics and of devices operation mechanisms, we offer a broad overview of recent progress in the field, focusing on photodiodes and phototransistors. As to the former device category, very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, and even though the simultaneous optimization of all these relevant parameters is demonstrated in a limited number of papers, real applications are within reach for this technology, as it is testified by the increasing number of realizations going beyond the single-device level and tackling more complex optoelectronic systems. As to phototransistors, a more recent subject of study in the framework of organic electronics, despite a broad distribution in the reported performances, best photoresponsivities outperform amorphous silicon-based devices. This suggests that organic phototransistors have a large potential to be used in a variety of optoelectronic peculiar applications, such as a photo-sensor, opto-isolator, image sensor, optically controlled phase shifter, and opto-electronic switch and memory.

Organic light detectors: photodiodes and phototransistors.

Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...

Organic Optoelectronic Materials: Mechanisms and Applications

The basic units in our brain are neurons, and each neuron has more than 1,000 synapse connections. Synapse is the basic structure for information transfer in an ever-changing manner, and short-term plasticity allows synapses to perform critical computational functions in neural circuits. Therefore, the major challenge for the hardware implementation of neuromorphic computation is to develop artificial synapse network. Here in-plane lateral-coupled oxide-based artificial synapse network coupled by proton neurotransmitters are self-assembled on glass substrates at room-temperature. A strong lateral modulation is observed due to the proton-related electrical-double-layer effect. Short-term plasticity behaviours, including paired-pulse facilitation, dynamic filtering and spatiotemporally correlated signal processing are mimicked. Such laterally coupled oxide-based protonic/electronic hybrid artificial synapse network proposed here is interesting for building future neuromorphic systems.

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Artificial synapse network on inorganic proton conductor for neuromorphic systems

Major growth in the image sensor market is largely as a result of the expansion of digital imaging into cameras, whether stand-alone or integrated within smart cellular phones or automotive vehicles. Applications in biomedicine, education, environmental monitoring, optical communications, pharmaceutics and machine vision are also driving the development of imaging technologies. Organic photodiodes (OPDs) are now being investigated for existing imaging technologies, as their properties make them interesting candidates for these applications. OPDs offer cheaper processing methods, devices that are light, flexible and compatible with large (or small) areas, and the ability to tune the photophysical and optoelectronic properties − both at a material and device level. Although the concept of OPDs has been around for some time, it is only relatively recently that significant progress has been made, with their performance now reaching the point that they are beginning to rival their inorganic counterparts in a number of performance criteria including the linear dynamic range, detectivity, and color selectivity. This review covers the progress made in the OPD field, describing their development as well as the challenges and opportunities.

Organic Photodiodes: The Future of Full Color Detection and Image Sensing

An organic light-emitting diode (OLED) display is disclosed. In one aspect, the display includes a stretchable substrate, a thin film transistor (TFT) formed over the stretchable substrate and including a plurality of electrodes, an OLED electrically connected to the TFT and including a plurality of electrodes, and a plurality of interconnection lines connected to the electrodes of the OLED and the TFT. At least one of the interconnection lines is configured to move in a stretching direction and rotate an electrode selected from the electrodes of the OLED and the TFT connected to the at least one interconnection line.

Organic light-emitting diode display

Non-invasive ammonia sensors are attractive alternatives for the diagnoses of a variety of chronic diseases such as liver cirrhosis and renal failure. A low cost pentacene-based organic thin film transistor (OTFT) fabricated by a novel and simple process was demonstrated to be highly sensitive and specific for ammonia gas. Various measurement parameters that reflected OTFT device characteristics for ammonia detection were investigated. Significant variations of the turn-on current, intrinsic mobility, and threshold voltage (Vth) were observed while subthreshold swing (S.S.) was almost unchanged to the alteration of ammonia concentration. The OTFT device detected 0.5 ~ 5 ppm concentration ammonia gas at room temperature, which is in the critical range that can distinguish between healthy person and paticents with liver cirrhosis and renal failure. The sensitivity of the device was further enhanced following a simple UV irradiation treatment to modify the functional groups on poly(methyl methacrylate) (PMMA) dielectric layer. Possible interference for ammonia detection such as humidity effect and selectivity among nitrogen, alcohol, carbon dioxide, acetone, methane and ammonia were also examined. We concluded that the proposed pentacene-based OTFT is a promising device for the future application in non-invasive medical diagnoses.

/pdf/pentacene-based-organic-thin-film-transistors-for-ammonia-4232e2w8ej.pdf

Pentacene-Based Organic Thin Film Transistors for Ammonia Sensing

IO N With a high mobility ( > 10 cm 2 V − 1 s − 1 ) and a low threshold voltage ( < 5 V) in low-temperature processes, transparent oxide semiconductor thin-fi lm transistors (TOS TFTs) have drawn considerable attention due to their applications on fl exible displays, level shifters, drivers, and pixel-driving circuits for activematrix organic light-emitting-diode (AMOLED) displays. [ 1 − 3 ] In addition to display applications, amorphous indium gallium zinc oxide (a-IGZO) TFTs are also promising for the development of radio-frequency identifi cation (RFID) tags, smart cards, and other types of fl exible electronics. When TOS TFTs are developed for a low-power high-frequency circuit, high electron mobility and a low parasitic capacitance are required. Most TFTs fabricated with ZnO, SnO 2 , In 2 O 3 , IGZO, or other semiconducting oxide thin fi lms exhibit electron mobilities smaller than 35 cm 2 V − 1 s − 1 . [ 4–6 ] Recent reports on transparent oxide nanowire transistors (NWTs) have demonstrated high electron mobilities approximately 70 to 4000 cm 2 V − 1 s − 1 . [ 7–9 ] The quasi1D structure of NWTs may reduce low-angle carrier scattering to produce high electron mobility. [ 9 ] However, the fabrication process of NWTs has poor reproducibility and is still not practical for real-world applications. Because TOS transistors are transparent, developing TOS circuits on windows is appealing. Particularly, for modern buildings or trains with series of windows, TOS RFID circuits on windows can deliver various types of signals through a low-power transmission system. In this type of application, the dimension of the transparent transistor can be large because an integrated circuit on a small chip is not necessary. A low-cost production method for delivering a highperformance TOS transistor is a critical challenge. Here, a nanostructure to improve the effective mobility in a-IGZO TFTs is proposed. A large channel dimension of 1000 μ m, defi ned by a shadow mask, is utilized. The nanostructure is developed using a low-cost, lithography-free process to produce abundant nanometer-scale dot-like doping in a-IGZO channel. The new method, called nanodot doping (NDD) increases the effective electron mobility to a level 19 times higher than that of the control and the intrinsic electron mobility is also 10 times higher than that of the control. This study demo nstrates a process utilizing self-organized polystyrene spheres with a diameter of 200 nm to fabricate a porous gate structure. Ar plasma treatment through the porous gate performs dot-like doping on a-IGZO channel region. A top-gate

https://ir.nctu.edu.tw:443/bitstream/11536/14748/1/000296258900002.pdf

Effective mobility enhancement by using nanometer dot doping in amorphous IGZO thin-film transistors

This letter investigates the effect of repeated bending of flexible p-channel low-temperature polycrystalline–silicon thin-film transistors employing an ultra-low-temperature process (<673 K). Experimental results reveal that interface state density (Nit) and grain boundary trap density (Ntrap) after 10 000 width-axis tensile strain bending iterations are more pronounced than after equivalent width-axis compressive strain bending. Extracted interface and grain boundary traps both increase, which elevate trap assisted leakage. Furthermore, the bending distorts the Si–Si bonds in the polycrystalline silicon (Poly-Si) film, which causes more significant negative bias temperature instability (NBTI) degradation because strain-induced weak Si–Si bonds can react with dissociated H during NBTI stress.

Impact of repeated uniaxial mechanical strain on p-type flexible polycrystalline thin film transistors

The direct influence of the vertical carrier mobility on the frequency response of bilayered organic photodiodes (PDs) is investigated for the first time. With fullerene as the acceptor material, changing vertical hole mobility from 2.3×10−5 to 2.8×10−4 cm2/V s increases PD bandwidth from 10 to 80 MHz under a 4 V operation. The influence of deposition rate on vertical hole mobility of pentacene film is also discussed. Our results facilitate the application of bilayered organic PDs on the detection of very-high-frequency optical signals.

https://ir.nctu.edu.tw:443/bitstream/11536/6415/1/000272895100044.pdf

Increasing organic vertical carrier mobility for the application of high speed bilayered organic photodetector

We report the construction of a polymer space-charge-limited transistor (SCLT), a solid-state version of vacuum tube triode. The SCLT achieves a high on/off ratio of 3×105 at a low operation voltage of 1.5 V by using high quality insulators both above and below the grid base electrode. Applying a greater bias to the base increases the barrier potential, and turns off the channel current, without introducing a large parasitic leakage current. Simulation result verifies the influence of base bias on channel potential distribution. The output current density is 1.7 mA/cm2 with current gain greater than 1000.

https://ir.nctu.edu.tw:443/bitstream/11536/31914/1/000284965000082.pdf

Wu-Wei Tsai

Papers

Pentacene-Based Organic Thin Film Transistors for Ammonia Sensing

Effective mobility enhancement by using nanometer dot doping in amorphous IGZO thin-film transistors

Impact of repeated uniaxial mechanical strain on p-type flexible polycrystalline thin film transistors

Increasing organic vertical carrier mobility for the application of high speed bilayered organic photodetector

Polymer space-charge-limited transistor as a solid-state vacuum tube triode