A non-destructive n-doping method for graphene with precise control of electronic properties via atomic layer deposition.

Graphene applications require high precision control of the Fermi level and carrier concentration via a nondestructive doping method. Here, we develop an effective n-doping technique using atomic layer deposition (ALD) of ZnO thin films on graphene through a reactive molecular layer. This ALD doping method is nondestructive, simple, and precise. The ZnO thin films on graphene are uniform, conformal, of good quality with a low density of pinholes, and finely tunable in thickness with 1 Å resolution. We demonstrate graphene transistor control in terms of the Dirac point, carrier density, and doping state as a function of the ZnO thickness. Moreover, ZnO functions as an effective thin-film barrier against air-borne water and oxygen on the graphene, resulting in extraordinary stability in air for graphene devices. ZnO ALD was also applied to other two-dimensional materials including MoS2 and WSe2, which substantially enhanced electron mobility.

Highly efficient and stable DSSCs of wet-chemically synthesized MoS2 counter electrode.

A competitive power conversion efficiency of 7.01% is achieved for TiO2-based dye-sensitized solar cells (DSSCs) using a chemically stable and mechanically robust molybdenum di-sulfide (MoS2) counter electrode, synthesized using a simple, scalable and low-temperature wet-chemical process, owing to its good redox reaction stability.