record values exceeding 10 cm 2 V −1 s −1 have been reported. [3][4][5][6][7][8] Though these results are promising, some of these reported values suffer from overestimation, [9,10] require significant engineering efforts, [3] complex fabrication procedures, [4] or employ nonscalable fabrication techniques, [5] ultimately highlighting the need for alternative and potentially more industry-relevant processing methods. We believe that adjustments to existing solution coating methods rather than intensive technology engineering could result in a feasible and simple approach.Ink properties such as the solvents' boiling point, [11] solubility parameters, [12] or the solute concentration [13] can be tuned in order to control crystal growth and packing in a manner that provides favorable electrical characteristics. Such ink engineering has recently been shown to generate high mobility devices based on C8-BTBT. [14] In particular, a distinct increase of performance by utilizing a solvent mixture rather than a single solvent has been reported for a range of semiconductors, including TIPS-pentacene [15,16] or diketopyrrolopyrrole (DPP)-based polymers. [17] This approach has frequently been combined with another effective method -the addition of a polymer additive to the printing solution. This combination has been shown to significantly reduce the device-to-device variations and yielded improved transistor performances when applied to high-mobility small molecules, like TIPS-pentacene, [18] diF-TES-ADT, [8,19,20] or even C8-BTBT. [5,7,21,22] In this study, we explore various blends of the high-mobility semiconductor C8-BTBT with the inert polymer polystyrene (PS) with the objective of improving device-to-device uniformity and investigating the effect on device characteristics. We report improved film formation that results in the reduction of deviceto-device variations and the reliable fabrication of high-mobility organic field-effect transistors by a scalable, meniscus-guided coating method, and demonstrate OFETs based on C8-BTBT, that to the best of our knowledge show the highest intrinsic mobility so far reported. Results and Discussion Discussion of C8-BTBT-Based Devices in LiteratureIn the literature, the blending of C8-BTBT and PS led to improvements in the effective mobility of organic field-effect Organic field-effect transistors based on aligned small molecule semiconductors have shown high charge carrier mobilities in excess of 10 cm 2 V −1 s −1 . This makes them a viable alternative to amorphous inorganic semiconductors especially if a high reproducibility can be achieved. Here, the optimization of high mobility organic field-effect transistors based on the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C8-BTBT) via the addition of a polymer additive to the printing solution is reported. Specifically, films and devices are compared based on solutions of the neat semiconductor and the blend with polystyrene and shear-coated devices with excellent device characteristics and gate-voltage-ind...
Low‐voltage organic field‐effect transistors (OFETs) are of great interest for organic electronics applications that require low power consumption such as wearable electronics, biomedical applications, or mobile electronics. In this work, an approach leading to transistors fabricated from solution with high charge carrier mobilities operating at voltages < 1 V is presented. By blending the small‐molecule semiconductor 6,13‐bis(triisopropylsilyl‐ethynyl)pentacene (TIPS‐pentacene) with polystyrene it is possible to achieve good film coverage and uniformity as well as ultrathin semiconductor films. This reduction in thickness relative to neat films results in a high fraction of the high‐mobility polymorph of TIPS‐pentacene and excellent film morphologies with continuous highly crystalline domains. OFETs using SiO2 as the dielectric with average hole mobilities as high as 8.3 cm2 V−1 s−1 and maximum mobilities of up to 12.3 cm2 V−1 s−1 which favorably compares with the previous record for TIPS‐pentacene, especially when considering the simplicity of the approach, are demonstrated. By depositing the optimized semiconductor blends on solution‐based polymer dielectric layers of polyvinylphenol, cross‐linked with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, a record‐high mobility of 4.2 cm2 V−1 s−1 for solution‐processed, ultralow‐voltage OFET devices (operating at <1 V) is obtained.
In recent decades, organic memory devices have been researched intensely and they can, among other application scenarios, play an important role in the vision of an internet of things. Most studies concentrate on storing charges in electronic traps or nanoparticles while memory types where the information is stored in the local charge up of an integrated capacitance and presented by capacitance received far less attention. Here, a new type of programmable organic capacitive memory called p‐i‐n‐metal‐oxide‐semiconductor (pinMOS) memory is demonstrated with the possibility to store multiple states. Another attractive property is that this simple, diode‐based pinMOS memory can be written as well as read electrically and optically. The pinMOS memory device shows excellent repeatability, an endurance of more than 104 write‐read‐erase‐read cycles, and currently already over 24 h retention time. The working mechanism of the pinMOS memory under dynamic and steady‐state operations is investigated to identify further optimization steps. The results reveal that the pinMOS memory principle is promising as a reliable capacitive memory device for future applications in electronic and photonic circuits like in neuromorphic computing or visual memory systems.
Understanding the degradation mechanism of perovskite solar cells (PSCs) is of particular importance to solve their instability issue, which is one of the major hindrances toward commercialization. Here, it is shown that a halide diffusion equilibrium exists at the heterointerface of perovskite devices, which strongly impacts the evolution of device performance. The combined experimental and theoretical studies reveal that halide components diffuse from perovskite to fullerene layers in a p‐i‐n PSC device and equilibrate with an iodine density of 1018–1019 cm−3 within 80 h under dark aging condition. It is found that there is a strong correction between the device efficiency and halide diffusion equilibrium of PSCs, as the diffused halides can chemically dope the transport layer and result in the nonstoichiometric perovskite surface, leading to both initial enhancement and long‐term loss of the photovoltaic efficiency of solar cells. In response to this issue, a predoping strategy is developed to attain the halide diffusion equilibrium once the device is fabricated, thereby avoiding the further halide migration and initial efficiency variations. As a result, the as‐prepared PSC achieved an efficiency of 23.13% as well as stable power output under continuous one sun illumination.
The emergence of lead halide perovskites as light absorbers has enabled low cost and efficient photovoltaics via a simple solution, high‐throughout process. However, the perovskite materials suffer from instability under various environmental stressors, including moisture, oxygen, heat, and irradiation, which heavily hinders the practical application of perovskite solar cells (PSCs). In this review, the structural and performance instability of perovskites and their degradation causes and mechanisms under different conditions are discussed. The state‐of‐the‐art strategies that stabilize the perovskite layer in solar cells are then summarized; moreover, the microscopic reasons for the improved environmental tolerance are elucidated. Due to the structural tunability of perovskites, the environmental tolerance, which is influenced by defects and extended imperfections in the polycrystalline films, can be enhanced by varying intrinsic factors of component, dimensionality, and crystallinity. Furthermore, the extrinsic factors to improve the environmental tolerance of perovskites are portrayed in terms of surface functionalized molecules, barrier layers, and encapsulants. The mechanism of each method in reducing the environmental sensitivity is highlighted to provide potential guidance in extending the lifetime of perovskite devices.
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