TL;DR: In this article, the authors combine a large band gap organic semiconductor dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene with polystyrene electret to form an optical sensor with memory effect.
Abstract: Polymer electret transistor memory device has stable charge storage and memory properties. Here, we combine a large band gap organic semiconductor dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene with the polystyrene electret to form an optical sensor with memory effect. The blue light combined with programming bias leads to a positive threshold voltage shift for more than 100 V while the drain-source current shows a variation of seven orders of magnitude. The dynamic range of current device is up to 23 bits and the photo responsivity is 420 A W−1. The optically programmed transistor can be directly used for high-resolution optical sensor and multi-level data storage applications.
TL;DR: Herein, the applications of organic 2D materials for optoelectronic devices are a main focus and an introduction to what is known and suggestions for the potential of many exciting developments are presented.
Abstract: The remarkable merits of 2D materials with atomically thin structures and optoelectronic attributes have inspired great interest in integrating 2D materials into electronics and optoelectronics. Moreover, as an emerging field in the 2D-materials family, assembly of organic nanostructures into 2D forms offers the advantages of molecular diversity, intrinsic flexibility, ease of processing, light weight, and so on, providing an exciting prospect for optoelectronic applications. Herein, the applications of organic 2D materials for optoelectronic devices are a main focus. Material examples include 2D, organic, crystalline, small molecules, polymers, self-assembly monolayers, and covalent organic frameworks. The protocols for 2D-organic-crystal-fabrication and -patterning techniques are briefly discussed, then applications in optoelectronic devices are introduced in detail. Overall, an introduction to what is known and suggestions for the potential of many exciting developments are presented.
TL;DR: Flexible nonvolatile optical memory devices developed based on the bisbenzothieno[3,2-b];2',3'-d']naphtho[2,3-b;6,7-b']dithiophene (BBTNDT) organic field-effect transistors with charge trapping centers induced by the inhomogeneity (nanosprouts) of the organic thin film are revealed.
Abstract: Organic optical memory devices keep attracting intensive interests for diverse optoelectronic applications including optical sensors and memories. Here, flexible nonvolatile optical memory devices are developed based on the bisbenzothieno[2,3-d;2',3'-d']naphtho[2,3-b;6,7-b']dithiophene (BBTNDT) organic field-effect transistors with charge trapping centers induced by the inhomogeneity (nanosprouts) of the organic thin film. The devices exhibit average mobility as high as 7.7 cm2 V-1 s-1 , photoresponsivity of 433 A W-1 , and long retention time for more than 6 h with a current ratio larger than 106 . Compared with the standard floating gate memory transistors, the BBTNDT devices can reduce the fabrication complexity, cost, and time. Based on the reasonable performance of the single device on a rigid substrate, the optical memory transistor is further scaled up to a 16 × 16 active matrix array on a flexible substrate with operating voltage less than 3 V, and it is used to map out 2D optical images. The findings reveal the potentials of utilizing benzothieno[3,2-b]benzothiophene (BTBT) derivatives as organic semiconductors for high-performance optical memory transistors with a facile structure. A detailed study on the charge trapping mechanism in the derivatives of BTBT materials is also provided, which is closely related to the nanosprouts formed inside the organic active layer.
TL;DR: For the first time, an electret-based synaptic transistor (EST) is presented, which successfully performs synaptic behaviors including excitatory/inhibitory postsynaptic current (EPSC/IPSC), paired-pulse facilitation/depression (PPF/PPD), long-term plasticity (LTP) and high-pass filtering.
Abstract: Neuromorphic computing inspired by the neural systems in human brain will overcome the issue of independent information processing and storage. An artificial synaptic device as a basic unit of a neuromorphic computing system can perform signal processing with low power consumption, and exploring different types of synaptic transistors is essential to provide suitable artificial synaptic devices for artificial intelligence. Hence, for the first time, an electret-based synaptic transistor (EST) is presented, which successfully shows synaptic behaviors including excitatory/inhibitory postsynaptic current, paired-pulse facilitation/depression, long-term memory, and high-pass filtering. Moreover, a neuromorphic computing simulation based on our EST is performed using the handwritten artificial neural network, which exhibits an excellent recognition accuracy (85.88%) after 120 learning epochs, higher than most reported organic synaptic transistors and close to the ideal accuracy (92.11%). Such a novel synaptic device enriches the diversity of synaptic transistors, laying the foundation for the diversified development of the next generation of neuromorphic computing systems.
TL;DR: In this paper, high-performance, lowvoltage organic thin-film transistors based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) are thoroughly characterized with respect to their optical functionality.
Abstract: Photosensitive elements based on organic thin-film transistors readily integrated into flexible, large-area organic circuits open up new scopes in light-sensing applications In this work, high-performance, low-voltage organic thin-film transistors based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) are thoroughly characterized with respect to their optical functionality The fundamental light-dependent effect, ie, a large but slow threshold-voltage shift based on charge trapping in the aluminum oxide of the gate dielectric or at the semiconductor–dielectric interface, is analyzed depending on various parameters, such as biasing conditions, integration time, wavelength and power of the incoming light as well as the channel length An optimized 3-phase operation consisting of reset, integration and read-out is proposed in order to maximize reproducibility, sensitivity and responsivity of the phototransistors Two distinct regimes, an absorption-limited and a trapping-limited regime, are identified depending on the density of available trappable electrons, which is determined by the optical input power and the integration time The maximum operation frequency is found to be larger in phototransistors with shorter channel lengths Based on these results, an organic gesture recognition system with a refresh rate of 1 Hz was designed, implemented and successfully tested
...Furthermore, proper biasing sequences and read-out techniques have to be developed, which distinguish these opto-electric transducers from memory-type organic transistors [9,10]....
TL;DR: This work has successfully developed conformable, flexible, large-area networks of thermal and pressure sensors based on an organic semiconductor, and, by means of laminated sensor networks, the distributions of pressure and temperature are simultaneously obtained.
Abstract: Skin-like sensitivity, or the capability to recognize tactile information, will be an essential feature of future generations of robots, enabling them to operate in unstructured environments. Recently developed large-area pressure sensors made with organic transistors have been proposed for electronic artificial skin (E-skin) applications. These sensors are bendable down to a 2-mm radius, a size that is sufficiently small for the fabrication of human-sized robot fingers. Natural human skin, however, is far more complex than the transistor-based imitations demonstrated so far. It performs other functions, including thermal sensing. Furthermore, without conformability, the application of E-skin on three-dimensional surfaces is impossible. In this work, we have successfully developed conformable, flexible, large-area networks of thermal and pressure sensors based on an organic semiconductor. A plastic film with organic transistor-based electronic circuits is processed to form a net-shaped structure, which allows the E-skin films to be extended by 25%. The net-shaped pressure sensor matrix was attached to the surface of an egg, and pressure images were successfully obtained in this configuration. Then, a similar network of thermal sensors was developed with organic semiconductors. Next, the possible implementation of both pressure and thermal sensors on the surfaces is presented, and, by means of laminated sensor networks, the distributions of pressure and temperature are simultaneously obtained.
TL;DR: This review 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.
Abstract: 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.
TL;DR: A sensor matrix is realized that detects the spatial distribution of applied mechanical pressure and stores the analog sensor input as a two-dimensional image over long periods of time by integrating a flexible array of organic floating-gate transistors with a pressure-sensitive rubber sheet.
Abstract: Using organic transistors with a floating gate embedded in hybrid dielectrics that comprise a 2-nanometer-thick molecular self-assembled monolayer and a 4-nanometer-thick plasma-grown metal oxide, we have realized nonvolatile memory arrays on flexible plastic substrates. The small thickness of the dielectrics allows very small program and erase voltages (≤6 volts) to produce a large, nonvolatile, reversible threshold-voltage shift. The transistors endure more than 1000 program and erase cycles, which is within two orders of magnitude of silicon-based floating-gate transistors widely employed in flash memory. By integrating a flexible array of organic floating-gate transistors with a pressure-sensitive rubber sheet, we have realized a sensor matrix that detects the spatial distribution of applied mechanical pressure and stores the analog sensor input as a two-dimensional image over long periods of time.
TL;DR: Infrared photodetectors based on single-layer CVD-grown graphene and PbS quantum dots, which are fabricated by solution processing, show ultrahigh responsivities of up to 10(7) A/W under infrared light illumination.
Abstract: 12 ] Therefore, graphene-based IR detectors have much lower responsivities than photoconductors based on QDs. It is reasonable to consider that the responsivity of a graphene-based IR detector can be improved substantially by modifying the graphene ﬁ lm with QDs, which can absorb IR light more efﬁ ciently. On the other hand, if the carriers gener-ated by IR light can transfer to the graphene ﬁ lm, their mobility will be much higher and thus the responsivity will be dramati-cally improved for a QD-based IR detector. Moreover, an array of graphene devices can be easily patterned by state-of-the-art techniques and this could possibly lead to elimination of the crosstalk between neighboring pixels that occur in silicon devices.
TL;DR: In this paper, a poly(a-methylstyrene) (PaMS) layer was added to the SiO2 gate insulator and the pentacene channel in the typical OFET structure, and the results indicated reasonably good OFET behavior, suggesting the additional PaMS layer does not degrade the performance of the devices.
Abstract: electrets. In this Communication, we report on OFET memory devices built on silicon wafers and based on films of pentacene and an SiO2 gate insulator that are separated by a thin layer of poly(a-methylstyrene) (PaMS), which acts as a polymeric gate dielectric. This OFET memory device displayed reversible shifts in the threshold voltage (VTh) when an appropriate gate voltage (Vg) was applied above a certain threshold via a relatively short switching time. Based on these reversible shifts in VTh, a non-volatile organic memory was demonstrated that takes advantage of the simple configuration of a typical OFET. This device showed a large memory window (about 90 V), a high on/off ratio (IOn/IOff) (10 5 ), a short switching time (less than 1 ls), and a long retention time (more than 100 h). These memory characteristics were obtained only when an appropriate polymeric gate electret layer (e.g., PaMS) was inserted between the SiO2 gate insulator and the pentacene channel in the typical OFET structure. Therefore, it is possible that this behavior originates from the modulation of the gate field by stored charges in the polymeric gate electret. Detailed reasons for these results and a possible operating mechanism for our OFET memory device are discussed. A cross-sectional view of the fabricated device structure is shown in Figure 1a. Further details concerning the fabrication of this device are discussed in the Experimental section. Figure 1b and c shows the output and transfer characteristics of the devices, respectively. The results indicate reasonably good OFET behavior, suggesting the additional PaMS layer does not degrade the performance of the devices.  From the conventional characterization equation,  the measured values of the typical field-effect mobility (lFET), VTh, and IOn/IOff were 0.51 cm 2 V –1 s –1 (maximum value, 0.89 cm 2 V –1 s –1 ), – 19 V, and 10 5 , respectively. These transistor properties could