Organic photovoltaics (OPV) have the advantage of possible fabrication by energy-efficient and cost-effective deposition methods, such as solution processing. Solvent additives can provide fine control of the active layer morphology of OPVs by influencing film formation during solution processing. As such, solvent additives form a versatile method of experimental control for improving organic solar cell device performance. This review provides a brief history of solution-processed bulk heterojunction OPVs and the advent of solvent additives, putting them into context with other methods available for morphology control. It presents the current understanding of how solvent additives impact various mechanisms of phase separation, enabled by recent advances in in situ morphology characterization. Indeed, understanding solvent additives' effects on film formation has allowed them to be applied and combined effectively and synergistically to boost OPV performance. Their success as a morphology control strategy has also prompted the use of solvent additives in related organic semiconductor technologies. Finally, the role of solvent additives in the development of next-generation OPV active layers is discussed. Despite concerns over their environmental toxicity and role in device instability, solvent additives remain relevant morphological directing agents as research interests evolve toward nonfullerene acceptors, ternary blends, and environmentally sustainable solvents.

Solvent Additives: Key Morphology‐Directing Agents for Solution‐Processed Organic Solar Cells

Paper, as a flexible, low-cost, lightweight, tailorable, environmental-friendly, degradable, and renewable material, is emerging in electronic devices Especially, many kinds of paper-based (PB) sensors have been reported for wearable applications in recent years Among them, the PB gas, humidity, and strain sensors are widely studied for monitoring gas, humidity, and strain from the human body and the environment However, gas, humidity, and strain often coexist and interact, and the paper itself is hydrophilic and flexible, resulting in that it is still challenging to develop high-performance PB sensors specialized for gas, humidity, and strain detections Therefore, it is necessary to summarize and discuss them systematically In this review, we focus on summarizing the state-of-art studies of the PB gas, humidity, and strain sensors Specifically, the fabrications (electrodes and sensing materials) and applications of PB gas, humidity, and strain sensors are summarized and discussed The current challenges and the potential trends of PB sensors for gas, humidity, and strain detections are also outlined This review not only can help readers to understand the development status of the PB gas, humidity, and strain sensors but also is helpful for readers to find out and solve the problems in this field through comparative reading

Paper-Based Sensors for Gas, Humidity, and Strain Detections: A Review.

Flexible sensors have the potential to be seamlessly applied to soft and irregularly shaped surfaces such as the human skin or textile fabrics. This benefits conformability dependant applications including smart tattoos, artificial skins and soft robotics. Consequently, materials and structures for innovative flexible sensors, as well as their integration into systems, continue to be in the spotlight of research. This review outlines the current state of flexible sensor technologies and the impact of material developments on this field. Special attention is given to strain, temperature, chemical, light and electropotential sensors, as well as their respective applications.

Flexible Sensors—From Materials to Applications

Resistive random access memory (RRAM) devices are receiving increasing extensive attention due to their enhanced properties such as fast operation speed, simple device structure, low power consumption, good scalability potential and so on, and are currently considered to be one of the next-generation alternatives to traditional memory. In this review, an overview of RRAM devices is demonstrated in terms of thin film materials investigation on electrode and function layer, switching mechanisms and artificial intelligence applications. Compared with the well-developed application of inorganic thin film materials (oxides, solid electrolyte and two-dimensional (2D) materials) in RRAM devices, organic thin film materials (biological and polymer materials) application is considered to be the candidate with significant potential. The performance of RRAM devices is closely related to the investigation of switching mechanisms in this review, including thermal-chemical mechanism (TCM), valance change mechanism (VCM) and electrochemical metallization (ECM). Finally, the bionic synaptic application of RRAM devices is under intensive consideration, its main characteristics such as potentiation/depression response, short-/long-term plasticity (STP/LTP), transition from short-term memory to long-term memory (STM to LTM) and spike-time-dependent plasticity (STDP) reveal the great potential of RRAM devices in the field of neuromorphic application.

https://www.mdpi.com/2079-4991/10/8/1437/pdf

Advances of RRAM Devices: Resistive Switching Mechanisms, Materials and Bionic Synaptic Application.

Organic transistors are being developed for a variety of flexible electronics applications. They are usually fabricated on polymeric substrates, but considering the significant negative impact of plastic waste on the global environment and taking into account the many desirable properties of paper, there have also been efforts to use paper as a substrate for organic transistors. In this review we provide a brief overview of these efforts.

/pdf/organic-transistors-on-paper-a-brief-review-2hzhqa9208.pdf

Organic transistors on paper: a brief review

UV assisted non-volatile memory behaviour using Copper (II) phthalocyanine based organic field-effect transistors

A PMMA based Ag/PMMA/Ti/Glass RRAM devices are reported for their resistive switching behavior. Switching performance was tested on three samples fabricated at different PMMA annealing temperatures. The switching voltages have shown a down trend with increasing annealing temperature. The Current on/off ratio and retention time also degrades with annealing temperature. The devices exhibited significantly low switching voltages (<1 V) and retention time upto 103 s. Annealing of PMMA at higher temperatures may result in softening of films resulting in lower switching voltages due to defects generation and easy charge migration. The conduction mechanism has been investigated by double log plot of I-V characteristics of device suggesting ohmic conduction at lower voltages in in HRS and in LRS. At higher voltages in HRS, space charge limited conduction dominates the conduction mechanism.

Effect of Annealing on Resistive Switching Behavior of PMMA Based RRAM

Flexible organic field-effect transistors (OFETs) based on solution-processed TIPS-Pentacene as semiconductor and high-<inline-formula> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> P(VDF-TrFE) gate dielectric are successfully demonstrated on fabric for future electronic textile (e-textile) applications. These devices exhibited very high electrical performance with maximum (<inline-formula> <tex-math notation="LaTeX">$\mu _{{\mathrm {max}}}$ </tex-math></inline-formula>) and average (<inline-formula> <tex-math notation="LaTeX">$\mu _{{\mathrm {avg}}}$ </tex-math></inline-formula>) field-effect mobility values of ~1.2 and ~0.5(±0.3) <inline-formula> <tex-math notation="LaTeX">${\mathrm {cm}}^{2}\cdot {\mathrm {V}}^{-1}\cdot {\mathrm {s}}^{-1}$ </tex-math></inline-formula>, respectively, in the saturation regime and <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> of ~10<sup>3</sup> for a low operating voltage of −5 V, along with excellent electromechanical stability. Furthermore, these devices showed excellent environmental stability with almost unchanged electrical characteristics for 26 weeks. Moreover, devices showed high cyclic stability with stable ON/ OFF switching characterized up to 500 cycles.

Lamination of Flexible Organic Transistors on Fabric for E-Textile

We report the effect of varying the semiconductor:polymer blend ratio on the electrical performance and bias-stress stability of the organic field effect transistors (OFETs) with TIPS-Pentacene and polystyrene as semiconductor and polymer combination. Device performance was found to improve with increasing polymer content in the solution. Devices with 1:3 TIPS-Pentacene:polystyrene blend outperformed the other counterparts with high performance, and demonstrated least performance variation with regular 100 transfer measurement cycles. In addition, 1:3 blend devices have shown the least normalized drain current decay of $\sim$ 8.5 % with the bias stress condition of V DS = V GS = -30 V for 2 h, as compared to the 1:1, 3:1 and neat devices with the decay of 15 %, 37 % and 71 % respectively. Additionally, a better recovery of electrical characteristics was observed in blend devices with larger polymer fractions from the deteriorating effects of gate bias stress.

Effect of TIPS-Pentacene:Polystyrene Blend Ratio on Electrical Performance and Stability of Solution Processed Organic Field-Effect Transistors

In this work, we have explored the effect of TIPSpentacene: polystyrene (PS) blend on electrical performance and photo-response of solution processed organic field-effect transistors (OFETs). It was observed that though the blend OFETs show better electrical performance, the photo-responsivity (R) of neat TIPS-pentacene OFETs was significantly better. This study was performed for different color lights such as blue, red, and green, as well as for ultraviolet light (UV). R was highest for blue color (~2600 mA/W for neat, ~230 mA/W for blend), and smaller for other cases. Low R value in blend devices is attributed to less trapping of photo-generated charge carriers during photo-illumination compared to their neat counterparts.

Vivek Raghuwanshi

Papers

UV assisted non-volatile memory behaviour using Copper (II) phthalocyanine based organic field-effect transistors

Effect of Annealing on Resistive Switching Behavior of PMMA Based RRAM

Lamination of Flexible Organic Transistors on Fabric for E-Textile

Effect of TIPS-Pentacene:Polystyrene Blend Ratio on Electrical Performance and Stability of Solution Processed Organic Field-Effect Transistors

Effect of Polymer Blend on Electrical Performance and Photo-Response of TIPS-Pentacene OFETs