Flexible Vertical p-n Diode Photodetectors with Thin N-type MoSe Films Solution-Processed on Water Surfaces.

Two-dimensional (2D) nanosheets of transition metal dichalcogenides (TMDs) are of significant interest for potential photoelectronic applications. However, the fabrication of solution-processed arrays of mechanically flexible thin TMD films-based vertical type p-n junction photodetectors over a large area is a great challenge. Our method is based on controlled solvent evaporation of MoSe suspension spread on water surface. Single or few-layered MoSe nanosheets modified with the dispersant amine-terminated poly(styrene) (PS-NH) were homogeneously deposited and stacked on water upon solvent evaporation, giving rise to uniform MoSe/PS-NH composite films that can be readily transferred onto other substrates. A p-n junction vertical diode of Al/p-type Si/p-type poly(9,9-di- n-octylfluorenyl-2,7-diyl)/n-type MoSe composite/Au stacked from bottom to top exhibited characteristic rectifying current behavior upon voltage sweep with a rectification ratio of 10. Subsequent illumination of near-infrared light on the device resulted in a substantially enhanced dark current of approximately 10 times greater than that of the nonexposed device. The photodetection performance, that is, switching time, responsivity, and detectivity, were 100.0 ms, 2.5 AW, and 2.34 × 10, respectively. Furthermore, the performance of mechanically flexible photodetectors devices was comparable with that of the devices fabricated on the hard Si substrate even after 1000 bending cycles at a bending diameter of 7.2 mm.