Flexible broadband photodetectors based on 2D MoS 2 have gained significant attention due to their superior light absorption and increased light sensitivity. However, pristine MoS 2 has absorption only in visible and near IR spectrum. This paper reports a paper-based broadband photodetector having ZnS-MoS 2 hybrids as active sensing material fabricated using a simple, cost effective two-step hydrothermal method wherein trilayer MoS 2 is grown on cellulose paper followed by the growth of ZnS on MoS 2 . Optimization in terms of process parameters is done to yield uniform trilayer MoS 2 on cellulose paper. UV sensing property of ZnS and broadband absorption of MoS 2 in visible and IR, broadens the range from UV to near IR. ZnS plays the dual role for absorption in UV and in the generation of local electric fields, thereby increasing the sensitivity of the sensor. The fabricated photodetector exhibits a higher responsivity toward the visible light when compared to UV and IR light. Detailed studies in terms of energy band diagram are presented to understand the charge transport mechanism. This represents the first demonstration of a paper-based flexible broadband photodetector with excellent photoresponsivity and high bending capability that can be used for wearable electronics, flexible security, and surveillance systems, etc.

This paper describes an approach to the fabrication of flexible electronics i.e., a wearable temperature sensor and infrared (IR) photodetector on flexible polyimide (PI) substrate. Solar exfoliated reduced graphene oxide (SrGO) and graphene flakes are used as the sensing materials for developing the sensors on a PI substrate. PI, apart from being flexible and compatible with microfabrication processes, also helps in reducing the mobility and recombination of the photo-generated electrons of graphene due of its dielectric nature, thus enabling IR detection. Current responsivity and external quantum efficiency of IR photodetector for graphene flakeand SrGO-based devices were found to be 0.4 A W −1 , 16.53% and 0.8 A W −1 , 33.06% respectively which are higher than those of commercially available photodetectors. In addition, we demonstrate an ultrasensitive wearable human body temperature sensor in the temperature range of 35 °C to 45 °C, wherein both graphene flakeand SrGO-based devices exhibited a negative temperature coefficient of −41.30 × 10 −4 °C−1 and −74.29 × 10 −4 °C−1 respectively, which are higher than commercially available counterparts. Plausible underlying mechanisms to both IR sensing and temperature sensing have been studied. Furthermore, as a proof of concept, we investigated the effect of IR radiation emitted by a human hand on the device. Interestingly it was found that the device was very sensitive to it, indicating that the sensor can be used for motion detection which has potential applications in security, surveillance etc. The strategy presented here provides a new, simple, cost effective approach for the fabrication of nextgeneration wearable and bio-implantable devices based on a polyimide substrate that can be easily integrated onto the surface of a leaf, skin, paper, clothes etc owing to its versatile nature.

In this work, we demonstrate the high-yield synthesis of carbon quantum dots using a one-step eco-friendly, low-cost thermal treatment of a renewable biomass, i.e. natural chia seeds.

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The synthesis of vanadium oxide family compounds is challenging because of their affinity to exist in different oxidation states and is further intensified by the lack of suitable techniques for their direct growth on flexible substrates, thus limiting their applications in flexible electronics. In this report, we demonstrate the one-step fabrication of a two-dimensional (2D) V2O5-based versatile papertronics (paper electronics) platform on a low-cost cellulose paper substrate and its application toward broadband photodetection and resistive memories. The porous nature of cellulose paper helps in the uniform growth of 2D V2O5 not only on the surface but also in bulk, thereby assisting in the easy diffusion of silver ions (Ag+) in the defect sites of V2O5, unlike in conventional flexible polymeric substrates, thereby assisting in the resistive switching mechanism. 2D V2O5 on a cellulose-paper-based memory exhibited an ON/OFF ratio of 3.5 × 102 and V set and V reset voltages of ∼+1 and −1 V, respectively, with excellent endurance and retention capacity of up to 500 cycles. The synthesized 2D V2O5 nanosheets exhibited broadband absorption ranging from ultraviolet (UV) to visible with an optical band gap calculated as 2.4 eV, making it suitable for broadband photodetection. Responsivities under UV- and visible-light illumination were found to be 31.5 and 20.2 mA/W, respectively, which are better than those of V2O5-based photodetectors fabricated using sophisticated methods. The fabricated broadband photodetector exhibited excellent mechanical stability with excellent retention in responsivity values over 500 cycles. The strategy outlined here presents a novel, low-cost, and one-step approach for fabricating devices on paper that find wide applications in flexible electronics.

Atomically thin two-dimensional (2D) materials have gained significant attention from the research community in the fabrication of high-performance optoelectronic devices. Even though there are various techniques to improve the responsivity of the photodetector, the key factor limiting the performance of the photodetectors is constrained photodetection spectral range in the electromagnetic spectrum. In this work, a mixed-dimensional 0D/2D SnS2-QDs/monolayer MoS2 hybrid is fabricated for high-performance and broadband (UV–visible–near-infrared (NIR)) photodetector. Monolayer MoS2 is deposited on SiO2/Si using chemical vapor deposition (CVD), and SnS2-QDs are prepared using a low-cost solution-processing method. The high performance of the fabricated 0D/2D photodetector is ascribed to the band bending and built-in potential created at the junction of SnS2-QDs and MoS2, which enhances the injection and separation efficiency of the photoexcited charge carriers. The mixed-dimensional structure also suppresses the dark current of the photodetector. The decorated SnS2-QDs on monolayer MoS2 not only improve the performance of the device but also extends the spectral range to the UV region. Photoresponsivity of the device for UV, visible, and NIR region is found to be ∼278, ∼ 435, and ∼189 A/W, respectively. Fabricated devices showed maximum responsivity under the visible region attributed to the high absorbance of monolayer MoS2. The response time of the fabricated device is measured as ∼100 ms. These results reveal that the development of a mixed-dimensional (0D/2D) SnS2-QDs/MoS2-based high-performance and broadband photodetector is technologically promising for next-generation optoelectronic applications.

development of flexible electronics, especially in the biomedical field, which has led to an exploration of flexible substrate photodetectors. [7,8] These devices are far more compact and cost-effective compared to the conventional bulk substrate devices and reduce the expenditure on material as well as fabrication. [9] Still, several issues need to be addressed. [10] Some of the issues are surface roughness, thermal stability, and cleanroom compatibility. Almost all of the flexible substrates utilized (polymers, paper, textile, etc.) have a rough surface which not only affects the charge carrier mobility but also increases the recombination rate. Further, the rise time is also affected which affects the gain of the photodetector. The second is thermal stability, that is, most of the flexible substrates cannot withstand high temperatures, and hence performing high-temperature processes is not possible which restricts limited fabrication methodologies. [11] Last, the flexible substrates are not cleanroom compatible and novel methodologies need to be developed for integrating novel functional nanomaterials onto the flexible substrates. Novel functional materials ranging from 0D to 2D, and hybrids (0D-1D, 0D-2D, and 1D-2D) based on these materials have been explored for this purpose. [12-15] Piezotronics is another means to improve the responsivity upon application of external strain which modulates the depletion region width and increases the electric field and thereby the responsivity. But the issue with piezotronics is that, the application of strain leads to permanent damage in the device, thereby decreasing the reliability of the photodetector. Localized surface plasmon resonance (LSPR) is another means of increasing the absorption, and hence the responsivity and speed, and is a widely researched domain for conventional rigid substrate devices with the decoration of noble nanoparticles (NPs). [16-19] However, reports on the use of metal NPs for high-performance flexible devices using LPSR are few. Moreover, the reports on the comparative performance of different NPs also remain limited. Hence, there is a need to explore Plasmonic enhancement in flexible substrate devices. Transition metal dichalcogenides (TMDs) are a popular class of 2D materials because of their outstanding optical and mechanical properties and tunable bandgap. [20] Of these, MoS 2 is of special interest due to its superior electrical properties, high Even though there are reports on flexible photodetectors, one of the main issues that still needs to be resolved is the lower values of responsivity arising due to the use of non-conventional substrates such as polymers, cellulose paper, etc. There are ways to improve the responsivity, such as piezotronics and surface plasmonic resonance, but studies on utilizing the same for flexible substrates remain limited. Further, the comparative performance of different nanoparticles (NPs) remains unexplored. This report demonstrates the fabrication of flexible visible/near-infrared (NIR) photodetectors by...