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

In this work, a TCAD based approach is presented to model electrical behavior of TIPS-Pentacene: polymer blend organic field-effect transistors (OFETs). Stress induced and temperature induced effects are also captured, thereby accurately modeling the device behavior under different operating conditions. The framework is validated against experimental results and is then used to estimate the effect of temperature on characteristics of inverter circuit using this device.

Comprehensive analysis of TIPS-Pentacene: Polymer blend organic field-effect transistor for device and circuit simulation

Flexible electronics offers advantages over conventional electronics on this aspect with the possibility of fabrication on unconventional and biodegradable substrates. Organic field-effect transistors (OFETs) receive significant attention because of their potential use in flexible electronics, specifically for circuit and sensing applications. These devices can be used as a building block for applications in electronic skin (E-skin), health monitoring, and biomimetic applications due to flexibility or stretchability. However, during the operation, these devices are encountered with various electrical, mechanical, and thermal stimulations. Thus, for reliable operation in practical applications, OFETs must be operationally stable. In this chapter, firstly, the area of flexible electronics is introduced and the historical perspective along with various potential applications are summarized. The structure and operation of OFETs are discussed along with some crucial aspects. OFETs on various flexible substrates including plastic and paper are discussed. High performing OFET devices fabricated on unconventional substrates such as paper can pave the way toward biodegradable or green electronics. In addition, these devices have shown the potential to be used for real-time health monitoring and e-skin applications. OFETs with biodegradable gelatin dielectric had shown the possibility to be used as a breath rate analyzer. These devices will eventually be useful for low-cost self-health monitoring systems.

Flexible Organic Field-Effect Transistors for Biomimetic Applications

Effect of UV irradiation $( \lambda _{Peak} \quad =365$ nm) on the electrical performance of the OFETs with CuPc as active layer is demonstrated. The devices have shown stable electrical performance under dark with avg. and max. field effect mobility of $( 1.0 \pm 0.3 ) \times 10 ^{-2}$ and $1.4 \times 10 ^{-2}$ cm $^{2}\, \mathrm {V}^{-1}\, \mathrm {s}^{-1}$ respectively. Under UV illumination there found a shift in threshold voltage and change in ON current along with fast response and recovery time of 0.4 s and 2 s respectively with periodic UV ON-OFF pulses.

Copper (II) Phthalocyanine based Organic Field-Effect Transistors for UV Photo-detection

We report on the fabrication of bottom gate top contact organic field effect transistors with hybrid gate dielectric and TIPS-Pentacene:PS blend as active layer on PowerCoat™ HD 230 paper substrate. The hybrid dielectric layer leads the devices operated at relatively low voltage of −10 V with avg. and maximum field effect mobility of $0.52(\pm 0.16)$ and 0.78 cm2 V−1 S−1 respectively, with near zero threshold voltage and on-off current ratio approaching ~104. The devices have shown excellent operational stability when tested with DC bias stress of $\mathrm{V}_{\mathrm{DS}}=\mathrm{V}_{\mathrm{GS}}=-10\ \mathrm{V}$ for 1 h and minuscule changes in electrical characteristics were observed with continuous multiple transfer cycle scans. In addition, we have demonstrated a resistive load inverter circuit with varying the load resistance with these paper OFETs.

TIPS-Pentacene:PS Blend Organic Field-Effect Transistors with Hybrid Gate Dielectric on Paper Substrate

In this work, high performance organic thin-film transistors (OTFTs) are demonstrated based on an eco- friendly gate dielectric consisting of a bilayer combination of two biodegradable nature-based materials chitosan and gelatin. TIPS-pentacene and Polystyrene (PS) blend was used as an active layer to obtain highly stable OTFT devices. Fabricated p-type devices exhibited excellent electrical characteristics with maximum field-effect mobility of 1.6 cm2 V-1s-1 with average of 1.1 cm2 V-1s-1 and a relatively low threshold voltage of −0.5V for a low operating voltage of −5 V. Various electrical tests, including repeatability and bias-stress stability were performed to evaluate the device's operational and electrical stability. Further, circuit applicability was also evaluated by the external resistive load connected inverter characteristics.

Vivek Raghuwanshi

Papers

Comprehensive analysis of TIPS-Pentacene: Polymer blend organic field-effect transistor for device and circuit simulation

Flexible Organic Field-Effect Transistors for Biomimetic Applications

Copper (II) Phthalocyanine based Organic Field-Effect Transistors for UV Photo-detection

TIPS-Pentacene:PS Blend Organic Field-Effect Transistors with Hybrid Gate Dielectric on Paper Substrate

High Performance Flexible Organic Transistors with Biodegradable Natural-Protein based Gate Dielectrics