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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