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.

For at least the past ten years printed electronics has promised to revolutionize our daily life by making cost-effective electronic circuits and sensors available through mass production techniques, for their ubiquitous applications in wearable components, rollable and conformable devices, and point-of-care applications. While passive components, such as conductors, resistors and capacitors, had already been fabricated by printing techniques at industrial scale, printing processes have been struggling to meet the requirements for mass-produced electronics and optoelectronics applications despite their great potential. In the case of logic integrated circuits (ICs), which constitute the focus of this Progress Report, the main limitations have been represented by the need of suitable functional inks, mainly high-mobility printable semiconductors and low sintering temperature conducting inks, and evoluted printing tools capable of higher resolution, registration and uniformity than needed in the conventional graphic arts printing sector. Solution-processable polymeric semiconductors are the best candidates to fulfill the requirements for printed logic ICs on flexible substrates, due to their superior processability, ease of tuning of their rheology parameters, and mechanical properties. One of the strongest limitations has been mainly represented by the low charge carrier mobility (μ) achievable with polymeric, organic field-effect transistors (OFETs). However, recently unprecedented values of μ ∼ 10 cm(2) /Vs have been achieved with solution-processed polymer based OFETs, a value competing with mobilities reported in organic single-crystals and exceeding the performances enabled by amorphous silicon (a-Si). Interestingly these values were achieved thanks to the design and synthesis of donor-acceptor copolymers, showing limited degree of order when processed in thin films and therefore fostering further studies on the reason leading to such improved charge transport properties. Among this class of materials, various polymers can show well balanced electrons and holes mobility, therefore being indicated as ambipolar semiconductors, good environmental stability, and a small band-gap, which simplifies the tuning of charge injection. This opened up the possibility of taking advantage of the superior performances offered by complementary "CMOS-like" logic for the design of digital ICs, easing the scaling down of critical geometrical features, and achieving higher complexity from robust single gates (e.g., inverters) and test circuits (e.g., ring oscillators) to more complete circuits. Here, we review the recent progress in the development of printed ICs based on polymeric semiconductors suitable for large-volume micro- and nano-electronics applications. Particular attention is paid to the strategies proposed in the literature to design and synthesize high mobility polymers and to develop suitable printing tools and techniques to allow for improved patterning capability required for the down-scaling of devices in order t...

Organic non‐volatile memory (ONVM) based on pentacene field‐effect transistors (FETs) has been fabricated using various chargeable thin polymer gate dielectrics—termed electrets—onto silicon oxide insulating layers. The overall transfer curve of organic FETs is significantly shifted in both positive and negative directions and the shifts in threshold voltage (VTh) can be systemically and reversibly controlled via relatively brief application of the appropriate external gate bias. The shifted transfer curve is stable for a relatively long time—more than 105 s. However, this significant reversible shift in VTh is evident only in OFETs with non‐polar and hydrophobic polymer electret layers. Moreover, the magnitude of the memory window in this device is inversely proportional to the hydrophilicity (determined from the water contact angle) and dielectric polarity (determined from the dielectric constant), respectively. Memory behaviors of ONVM originate from charge storage in polymer gate electret layers. Therefore, the small shifts in VTh in ONVM with hydrophilic and polar polymers may be due to very rapid dissipation of transferred charges through the conductive channels which form from dipoles, residual moisture, or ions in the polymer electret layers. It is verified that the surface or bulk conductivities of polymer gate electret layers played a critical role in determining the non‐volatile memory properties.

Organic field‐effect transistor (FET) memory is an emerging technology with the potential to realize light‐weight, low‐cost, flexible charge storage media. Here, solution‐processed poly[9,9‐dioctylfluorenyl‐2,7‐diyl]‐co‐(bithiophene)] (F8T2) nano floating gate memory (NFGM) with a top‐gate/bottom‐contact device configuration is reported. A reversible shift in the threshold voltage (VTh) and reliable memory characteristics was achieved by the incorporation of thin Au nanoparticles (NPs) as charge storage sites for negative charges (electrons) at the interface between polystyrene and cross‐linked poly(4‐vinylphenol). The F8T2 NFGM showed relatively high field‐effect mobility (µFET) (0.02 cm2 V−1 s−1) for an amorphous semiconducting polymer with a large memory window (ca. 30 V), a high on/off ratio (more than 104) during writing and erasing with an operation voltage of 80 V of gate bias in a relatively short timescale (less than 1 s), and a retention time of a few hours. This top‐gated polymer NFGM could be used as an organic transistor memory element for organic flash memory.

Many attempts have been made to realize a universal memory, [1] that is, an ideal memory device comprising new, fast, non-volatile, inexpensive methods for storing information. Compared to its inorganic counterparts, organic memory has attracted a great deal of interest because of its remarkable progress in organic electronics and its unique advantages: it is inexpensive, lightweight, and capable of printing ubiquitous components onto plastic substrates. [2][3][4] In an attempt to create a novel organic memory, several types of memory devices based on organic and polymeric materials have been evaluated, including organic electrical bistable devices, [5] organicinorganic hybrid memory using a polymeric fuse, [6] and organic field-effect transistors (OFETs) based on ferroelectric gate insulators and chargeable gate dielectrics. [7][8][9][10][11] Among these types of organic memory devices, a memory element based on FETs is especially attractive because of its non-destructive readout and single-transistor applications. [12] In this case, the functionality arises from the field-effect modulation by the spontaneous polarization that occurs in ferroelectrics or the trapped charges in chargeable dielectrics, which are referred to as electrets.While an OFET memory has many potential advantages, state-of-the-art results of OFET memory devices are in a less favorable position, compared to other types of organic memories. [7][8][9][10][11] With respect to the case of organic ferroelectrics, Naber et al. recently demonstrated an on/off ratio of 10 4 with a programming time of 0.3 ms and a memory effect stability of more than one week. [8] However, when compared to ferroelectrics, only a small amount of attention has been given to electret-charged OFET memory, in spite of the similar field-effect modulation. Moreover, the characteristics of OFET memory based on electrets are less well understood than those of ferroelectric-based OFET memory devices due to a lack of research. Katz et al. demonstrated an OFET memory with a polarizable gate insulator that induced a floating-gate-like behavior, [9] and Singh et al. also demonstrated an OFET memory using poly(vinyl alcohol) as a gate electret.[10] However, these devices still do not sufficiently satisfy the criteria demanded in order to compete with other types of memory devices. [13] Furthermore, details of the operating mechanisms of these devices are not well understood. Therefore, the mechanism should be further investigated to successfully develop a high-performance OFET memory based on electrets.In this Communication, we report on OFET memory devices built on silicon wafers and based on films of pentacene and an SiO 2 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 (V Th ) when an appropriate gate voltage (V g ) was applied above a certain threshold via a relatively short switching time. Based on these reversible shifts in...

Understanding the relationship between molecular/macromolecular architecture and organic thin film transistor (TFT) performance is essential for realizing next-generation high-performance organic electronics. In this regard, planar π-conjugated, electron-neutral (i.e., neither highly electron-rich nor highly electron-deficient) building blocks represent a major goal for polymeric semiconductors, however their realization presents synthetic challenges. Here we report that an easily accessible (minimal synthetic steps), electron-neutral thienyl-vinylene (TVT)-based building block having weak intramolecular S···O "conformational locks" affords a new class of stable, structurally planar, solution-processable, high-mobility, molecular, and macromolecular semiconductors. The attraction of merging the weak TVT electron richness with supramolecular planarization is evident in the DFT-computed electronic structures, favorable MO energetics, X-ray diffraction-derived molecular structures, experimental lattice coehesion metrics, and excellent TFT performance. TVT-based polymer TFTs exhibit stable carrier mobilities in air as high as 0.5 and 0.05 cm(2)/V·s (n- and p-type, respectively). All-TVT polymer-based complementary inverter circuitry exhibiting high voltage gains (~50) and ring oscillator circuitry with high f(osc)(~1.25 kHz) is readily fabricated from these materials by simple inkjet printing.

The effects of using a blocking dielectric layer and metal nanoparticles (NPs) as charge‐trapping sites on the characteristics of organic nano‐floating‐gate memory (NFGM) devices are investigated. High‐performance NFGM devices are fabricated using the n‐type polymer semiconductor, poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} (P(NDI2OD‐T2)), and various metal NPs. These NPs are embedded within bilayers of various polymer dielectrics (polystyrene (PS)/poly(4‐vinyl phenol) (PVP) and PS/poly(methyl methacrylate) (PMMA)). The P(NDI2OD‐T2) organic field‐effect transistor (OFET)‐based NFGM devices exhibit high electron mobilities (0.4–0.5 cm2 V−1 s−1) and reliable non‐volatile memory characteristics, which include a wide memory window (≈52 V), a high on/off‐current ratio (Ion/Ioff ≈ 105), and a long extrapolated retention time (>107 s), depending on the choice of the blocking dielectric (PVP or PMMA) and the metal (Au, Ag, Cu, or Al) NPs. The best memory characteristics are achieved in the ones fabricated using PMMA and Au or Ag NPs. The NFGM devices with PMMA and spatially well‐distributed Cu NPs show quasi‐permanent retention characteristics. An inkjet‐printed flexible P(NDI2OD‐T2) 256‐bit transistor memory array (16 × 16 transistors) with Au‐NPs on a polyethylene naphthalate substrate is also fabricated. These memory devices in array exhibit a high Ion/Ioff (≈104 ± 0.85), wide memory window (≈43.5 V ± 8.3 V), and a high degree of reliability.

Large-area polymer FET arrays and integrated circuits (ICs) are successfully demonstrated via a simple wire-bar-coating process. Both a highly crystalline conjugated polymer layer and very smooth insulating polymer layer are formed by a consecutive wire-bar-coating process on a 4-inch plastic substrate with a short processing time for application as the active and dielectric layers of OFET arrays and ICs.