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Flexographic printing is promising for large-area electronics due to high print-speed and roll-to-roll capability. There have been recent attempts in using graphene as an active pigment in inks, most notably for slower techniques such as inkjet and screen printing. However, formulation of graphene-enhanced inks for high-speed printing and its effect on key metrics have never been investigated. Herein, graphene nanoplatelets (GPs) are incorporated to a conductive flexographic ink without compromising the rheological properties. An industrial scale at 100 m min−1 is printed on paper and polyethylene terephthalate (PET) substrates using a commercial flexographic press, and statistical performance variations are investigated across entire print runs. It is shown that GP-incorporation improves sheet-resistance (Rs) and uniformity, with up to 54% improvement in average Rs and 45% improvement in the standard-deviation on PET. The adhesion on both the substrates improves with GP-incorporation, as verified by tape/crosshatch tests. The durability of GP-enhanced samples is probed with a 1000 cyclic bend-test, with 0.31% average variation in resistance in the flat state on PET between the first and last 100 bends, exhibiting a robust print. The statistically scalable results show that GP-incorporation offers a cost-performance advantage for flexographic printing of large-area conductive patterns without modifications to traditional high-speed graphics printing presses. Published version We acknowledge funding from the Engineering and Physical Sciences Research Council (EP/L016087/1) and Alphasense Limited in United Kingdom.

We present a stable inkjet printable graphene ink, formulated in isopropyl alcohol via liquid phase exfoliation of chemically pristine graphite with a polymer stabilizer. The rheology and low deposition temperature of the ink allow uniform printing. We use the graphene ink to fabricate counter electrodes (CE) for natural and ruthenium-based dye-sensitized solar cells (DSSCs). The repeatability of the printing process for the CEs is demonstrated through an array of inkjet-printed graphene electrodes, with ∼5% standard deviation in the sheet resistance. As photosensitizers, we investigate natural tropical dye extracts from Pennisetum glaucum, Hibiscus sabdariffa and Caesalpinia pulcherrima. Among the three natural dyes, we find extracts from C. pulcherrima exhibit the best performance, with ∼0.9% conversion efficiency using a printed graphene CE and a comparable ∼1.1% efficiency using a platinum (Pt) CE. When used with N719 dye, the inkjet-printed graphene CE shows a ∼3.0% conversion efficiency, compared to ∼4.4% obtained using Pt CEs. Our results show that inkjet printable graphene inks, without any chemical functionalization, offers a flexible and scalable fabrication route, with a material cost of only ∼2.7% of the equivalent solution processed Pt-based electrodes.

The widespread use of printing of 2D materials in their relevant applications is highly dependent on the cost and scalability of their methods of production. This chapter serves as an introduction to the key methods for 2D material production and characterisation. Methods such as chemical vapour deposition, plasma cracking of hydrocarbons, intercalation, chemical exfoliation and liquid phase exfoliation are described and their relative merits are discussed. Particular emphasis is given to the 2D materials relevant to ink production. The latter half of the chapter discusses commonly used processing steps and characterisation methods for the 2D materials and their respective roles in qualifying and quantifying the material produced.

The primary goal of this book is to comprehensively review 2D materials that have gained research interest and present the use of printing as a low-cost, high-throughput method of exploiting 2D materials in mass produced devices and components. This chapter covers the existing demonstrations of printed 2D materials in a wide variety of devices and summarises their current status. In addition, this chapter also discusses the state-of-the-art literature on the trends and development stages, future technology directions and their likely convergence for next generation of applications, devices and systems.

Early scientific investigations into graphene date back to the 1950s. The interest in graphene intensified when Konstantin Novosolev and Andre Geim were awarded the Nobel prize in physics for ‘groundbreaking experiments regarding the two-dimensional material graphene’. Since then, other two-dimensional (2D) materials have (re)gained increasing research interest. The most studied 2D materials to date include transition metal dichalcogenides (TMDs), black phosphorus (BP), hexagonal boron nitride (h-BN) and transition metal carbides and/or carbonitrides (MXenes). This chapter introduces these key material groups, and provides a review of the current understanding of their structures and properties. In particular, this chapter will focus on the (opto)electronic properties of the individual 2D materials and their potential applications.

The use of two-dimensional (2D) materials in low-cost, high-throughput printing as a scalable production method relies heavily on its successful incorporation into printable ink systems. However, industrial scale production of 2D material printing inks has proven to be a significant challenge. This chapter begins with a brief history of inks and progresses to the basic ink formulations and the techniques used in traditional printing technologies. This chapter also discusses ink properties, processing techniques and optimisation of formulation parameters using methods such as Design of Experiments (DOE), and useful characterisation techniques when formulating 2D material inks. Finally, the chapter covers ink–substrate interaction and optimisation strategies for ink formulation.

We demonstrate a long-term stable, all-fiber, erbium-doped femtosecond laser mode-locked by a black phosphorus saturable absorber. The saturable absorber, fabricated by scalable and highly controllable inkjet printing technology, exhibits strong nonlinear optical response and is stable for long-term operation against intense irradiation, overcoming a key drawback of this material. The oscillator delivers self-starting, 102 fs stable pulses centered at 1555 nm with 40 nm spectral bandwidth. This represents the shortest pulse duration achieved from black phosphorus in a fiber laser to date. Our results demonstrate the great potential for black phosphorus as an excellent candidate for long-term stable ultrashort pulse generation.

openaire: EC/H2020/645241/EU//TransFlexTeg | openaire: EC/FP7/631610/EU//GrabFast Graphene-based organic nanocomposites have ascended as promising candidates for thermoelectric energy conversion. In order to adopt existing scalable printing methods for developing thermostable graphene-based thermoelectric devices, optimization of both the material ink and the thermoelectric properties of the resulting films are required. Here, inkjet-printed large-area flexible graphene thin films with outstanding thermoelectric properties are reported. The thermal and electronic transport properties of the films reveal the so-called phonon-glass electron-crystal character (i.e., electrical transport behavior akin to that of few-layer graphene flakes with quenched thermal transport arising from the disordered nanoporous structure). As a result, the all-graphene films show a room-temperature thermoelectric power factor of 18.7 µW m−1 K−2, representing over a threefold improvement to previous solution-processed all-graphene structures. The demonstration of inkjet-printed thermoelectric devices underscores the potential for future flexible, scalable, and low-cost thermoelectric applications, such as harvesting energy from body heat in wearable applications.

Graphene and related two-dimensional materials provide an ideal platform for next generation disruptive technologies and applications. Exploiting these solution-processed two-dimensional materials in printing can accelerate this development by allowing additive patterning on both rigid and conformable substrates for flexible device design and large-scale, high-speed, cost-effective manufacturing. In this review, we summarise the current progress on ink formulation of two-dimensional materials and the printable applications enabled by them. We also present our perspectives on their research and technological future prospects.

We use liquid phase exfoliation to produce dispersions of molybdenum disulfide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical structures of the bile salt surfactants play a crucial role in the exfoliation and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched in single and few (6) layer flakes with large edge to surface area ratio. We use the dispersions to fabricate free-standing polymer composite wide-band saturable absorbers to develop mode-locked and Q-switched fiber lasers, tunable from 1535 to 1565 and 1030 to 1070 nm, respectively. We attribute this sub-bandgap optical absorption and its nonlinear saturation behavior to edge-mediated states introduced within the material band-gap of the exfoliated MoS2 nanoflakes.

We report self-starting mode-locking in all-fiber erbium-doped lasers utilizing inkjet-printed transition metal dichalcogenide saturable absorbers, exhibiting highly optical uniformity, with

We demonstrate an inkjet-printed temperature- and humidity-resistant black phosphorus saturable absorber, enabling stable continuous mode-locking over 210 hours. Our work highlights the potential of BP-based devices for photonic applications operating under challenging environmental conditions.

We demonstrate a wavelength tunable dual-wavelength fiber laser using black phosphorus (BP) saturable absorber. By controlling the tunable filter together with a polarization controller to adjust intra-cavity birefringence, dual-wavelength pulses tunable from 1532 nm to 1545 nm are observed.

The complex nonlinear dynamics of mode-locked fibre lasers, including a broad variety of dissipative structures and self-organization effects, have drawn significant research interest. Around the 2 μm band, conventional saturable absorbers (SAs) possess small modulation depth and slow relaxation time and, therefore, are incapable of ensuring complex inter-pulse dynamics and bound-state soliton generation. We present observation of multi-soliton complex generation in mode-locked thulium (Tm)-doped fibre laser, using double-wall carbon nanotubes (DWNT-SA) and nonlinear polarisation evolution (NPE). The rigid structure of DWNTs ensures high modulation depth (64%), fast relaxation (1.25 ps) and high thermal damage threshold. This enables formation of 560-fs soliton pulses; two-soliton bound-state with 560 fs pulse duration and 1.37 ps separation; and singlet+doublet soliton structures with 1.8 ps duration and 6 ps separation. Numerical simulations based on the vectorial nonlinear Schr¨odinger equation demonstrate a transition from single-pulse to two-soliton bound-states generation. The results imply that DWNTs are an excellent SA for the formation of steady single- and multi-soliton structures around 2 μm region, which could not be supported by single-wall carbon nanotubes (SWNTs). The combination of the potential bandwidth resource around 2 μm with the soliton molecule concept for encoding two bits of data per clock period opens exciting opportunities for data-carrying capacity enhancement.

We demonstrate a long-term stable fiber laser mode-locked by a solution deposited and encapsulated black phosphorus (BP) saturable absorber. Our work highlights the potential of BP-based devices for photonic applications when operating under ambient conditions.

Understanding of the fundamental photoresponse of carbon nanotubes has broad implications for various photonic and optoelectronic devices. Here, Z-scan and pump-probe spectroscopy performed across 600-2400 nm were combined to give a broadband 'degenerate' mapping of the nonlinear absorption properties of single-wall carbon nanotubes (SWNTs). In contrast to the views obtained from non-degenerate techniques, sizable saturable absorption is observed from the visible to the near-infrared range, including the spectral regions between semiconducting excitonic peaks and metallic tube transitions. In addition, the broadband mapping unambiguously reveals a photobleaching to photoinduced absorption transition feature within the first semiconducting excitonic band ∼2100 nm, quantitatively marking the long-wavelength cut-off for saturable absorption of the SWNTs investigated. Our findings present a much clearer physical picture of SWNTs' nonlinear absorption characteristics, and help provide updated design guidelines for SWNT based nonlinear optical devices.

We demonstrate a simple and compact, all-fiber thulium-based CPA system, delivering 136 fs pulses with ∼6 nJ energy at 50.8 MHz pulse repetition rate.

We discuss the emerging role of solution processing and functional ink formulation in the fabrication of devices based on two dimensional (2d) materials. By drawing on examples from our research, we show that these inks allow 2d materials to be exploited in a wide variety of applications, including in photonics and (opto)electronics.

Z-scan spectroscopy is used to reveal ultra-broadband nonlinear absorption across different orders of resonant transitions in single-wall carbon nanotube ensembles, demonstrating the potential of nanotubes for nonlinear optics beyond the conventional NIR range.

We demonstrate an all-normal dispersion ytterbium-doped fiber laser Q-switched by using a solution processed few-layer tungsten disulfide (WS 2 )-polymer composite saturable absorber at 1030 nm.

We demonstrate a ytterbium (Yb) and an erbium (Er)-doped fiber laser Q-switched by a solution processed, optically uniform, few-layer tungsten disulfide saturable absorber (WS2-SA). Nonlinear optical absorption of the WS2-SA in the sub-bandgap region, attributed to the edge-induced states, is characterized by 3.1% and 4.9% modulation depths with 1.38 and 3.83 MW/cm2 saturation intensities at 1030 and 1558 nm, respectively. By integrating the optically uniform WS2-SA in the Yb- and Er-doped laser cavities, we obtain self-starting Q-switched pulses with microsecond duration and kilohertz repetition rates at 1030 and 1558 nm. Our work demonstrates broadband sub-bandgap saturable absorption of a single, solution processed WS2-SA, providing new potential efficacy for WS2 in ultrafast photonic applications.

We fabricate a free-standing few-layer molybdenum disulfide (MoS2)-polymer composite by liquid phase exfoliation of chemically pristine MoS2 crystals and use this to demonstrate a wideband tunable, ultrafast mode-locked fiber laser. Stable, picosecond pulses, tunable from 1,535 nm to 1,565 nm, are generated, corresponding to photon energies below the MoS2 material bandgap. These results contribute to the growing body of work studying the nonlinear optical properties of transition metal dichalcogenides that present new opportunities for ultrafast photonic applications.

We demonstrate Q-switched pulses with 13.6 and 179.6 nJ pulse energy in Yb- and Er-doped fiber lasers using a few-layer WS2-PVA saturable absorber. We attribute the saturable absorption to edge-induced sub-bandgap states in WS2.

We present the characterisation of a hydrogel forming family of benzene 1,3,5-tricarboxamide (BTA) aromatic carboxylic acid derivatives. The simple, easy to synthesise compounds presented here exhibit consistent gel formation at low concentrations through the use of a pH trigger.

We fabricate a free-standing molybdenum diselenide (MoSe2) saturable absorber by embedding liquid-phase exfoliated few-layer MoSe2 flakes into a polymer film. The MoSe2-polymer composite is used to Q-switch fiber lasers based on ytterbium (Yb), erbium (Er) and thulium (Tm) gain fiber, producing trains of microsecond-duration pulses with kilohertz repetition rates at 1060 nm, 1566 nm and 1924 nm, respectively. Such operating wavelengths correspond to sub-bandgap saturable absorption in MoSe2, which is explained in the context of edge-states, building upon studies of other semiconducting transition metal dichalcogenide (TMD)-based saturable absorbers. Our work adds few-layer MoSe2 to the growing catalog of TMDs with remarkable optical properties, which offer new opportunities for photonic devices.

Few-layer molybdenum disulfide (MoS2) is emerging as a promising quasi-two-dimensional material for photonics and optoelectronics, further extending the library of suitable layered nanomaterials with exceptional optical properties for use in saturable absorber devices that enable short-pulse generation in laser systems. In this work, we catalog and review the nonlinear optical properties of few-layer MoS2, summarize recent progress in processing and integration into saturable absorber devices, and comment on the current status and future perspectives of MoS2-based pulsed lasers.

openaire: EC/FP7/631610/EU//GrabFast Ultrafast lasers with tunable parameters in wavelength and time domains are the choice of light source for various applications such as spectroscopy and communication. Here, we report a wavelength and pulse-duration tunable mode-locked Erbium doped fiber laser with single wall carbon nanotube-based saturable absorber. An intra-cavity tunable filter is employed to continuously tune the output wavelength for 34 nm (from 1525 nm to 1559 nm) and pulse duration from 545 fs to 6.1 ps, respectively. Our results provide a novel light source for various applications requiring variable wavelength or pulse duration.

We demonstrate an all-fiber erbium-doped laser mode-locked by an inkjet-printed black phosphorus saturable absorber, delivering 102 fs pulses with 40 nm spectral width. Our work highlights the potential of BP-based devices for future photonic technologies.

A binary solvent ink exploiting solutal Marangoni flows to suppress the coffee-ring effect for uniform printing of 2D crystals., Recent advances in inkjet printing of two-dimensional (2D) crystals show great promise for next-generation printed electronics development. Printing nonuniformity, however, results in poor reproducibility in device performance and remains a major impediment to their large-scale manufacturing. At the heart of this challenge lies the coffee-ring effect (CRE), ring-shaped nonuniform deposits formed during postdeposition drying. We present an experimental study of the drying mechanism of a binary solvent ink formulation. We show that Marangoni-enhanced spreading in this formulation inhibits contact line pinning and deforms the droplet shape to naturally suppress the capillary flows that give rise to the CRE. This general formulation supports uniform deposition of 2D crystals and their derivatives, enabling scalable and even wafer-scale device fabrication, moving them closer to industrial-level additive manufacturing.