A fully printed ultrafast Si/WS 2 quantum dot photodetector with very high responsivity over the UV to near-infrared region.

Two-dimensional (2D) semiconducting material-based photodetectors (PDs) with high responsivity and fast photo-response are of great interest for various applications such as optical communications, biomedical imaging, security surveillance, environmental monitoring, etc . Additive manufacturing such as 2D printing is a potentially less cumbersome and cost-effective alternative to conventional microdevice fabrication processes used in the production of PDs. Here, we have fabricated a Si/WS 2 quantum dot-based heterostructure PD with a very short electrode gap of 40 μm by a simple printing process. The printed p-Si/n-WS 2 PD shows an excellent photo-to-dark current ratio of 5121 under 405 nm illumination (23.8 mW cm -2 ). The printed photodetector exhibits a peak responsivity of 126 A W -1 and a peak detectivity of 9.24 × 10 12 Jones over a very broad wavelength range (300-1100 nm), which is much superior to commercial Si PDs. A high external quantum efficiency of 3.9 × 10 4 % and an ultrafast photoresponse (7.8 μs rise time and 9.5 μs fall time) make the device an attractive candidate as an efficient photodetector. The origin of high-performance photodetection is traced to a nearly defect-free interface at the heterojunction, leading to highly efficient charge separation and high photocurrent. Finally, the 2D-printed device exhibits good photodetection even in self-powered conditions, which is very attractive.