A Filterless, Visible Blind, Flexible, and Highly Photosensitive Near Infrared Photodetector

Monika Kataria^1,2,3,4*, Wei-Hua Wang^1,3, Yang-Fang Chen^4,5

¹Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
²Department of Physics, National Central University, Chung-Li, Taiwan
³Molecular Science and Technology Program, Taiwan International Graduate Program, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
⁴Department of Physics, National Taiwan University, Taipei, Taiwan
⁵Advanced Research Centre for Green Materials Science and Technology, National Taiwan University, Taipei, Taiwan

* Presenter:Monika Kataria, email:simplymonika05@gmail.com

Filterless visible blind near infrared (NIR) photodetection is crucial when it comes to artilleries used by the military workforces, optical fire detection systems, narrow band detectors used in space navigation and communication systems, medicine and research. With abundant availability of broadband photodetectors, there is a dearth of NIR photodetectors capable of detecting only and only NIR light while completely filtering out visible light. Filtering out visible light is generally achieved by adding visible light filters onto the devices which adds on to the cost and bulkiness of the device. So, the challenge lies towards fabricating a light weight, robust and wearable NIR photodetector capable of harvesting NIR light without being affected by the presence of visible light in its surroundings. Lanthanides-based upconversion nanoparticles (UCNPs) exhibit a nonlinear optical phenomenon, in which a sequential absorption of two or more photons of higher wavelength leads to wide range of absorption spectrum. The lanthanides-doped UCNPs can be designed such that the maximum narrow band detection of NIR is easily accomplished by the photodetector even in the presence of visible light sources. Along with this, UCNPs have a multi-energy level system that provides metastable states for photogenerated charge carriers. These metastable states provide for longer lifetime for photogenerated charge carriers in the excited state thus catalyzing the process of photodetection. Graphene is a 2D material with high carrier mobility, good optical transmittance, great flexibility and low density of states around the Dirac point, making its conductance influenced by external perturbations from associated materials (which is UCNPs in the present case). Flexible micro-pyramidical poly (dimethylsiloxane) (PDMS) substrate provides an excellent platform for highly sensitive omnidirectional NIR light detection. By the combination of unique properties of each constituent materials, we develop for the first time a highly sensitive, visible blind, wearable and omnidirectional NIR photodetector. This hybrid device exhibits ultra-high responsivity of ≈ 800 A/W at V(drain-source) = 1 V under 0.07 µW of 980 nm laser illumination. The novel design of the device makes it user friendly, light weight, durable and transparent.

Keywords: visible blind, near infrared photodetector, upconversion nanoparticles, flexible photodetector, 2D hybrid system