Optical and Electronic Properties of Atomically Thin Organic-WSe2 Hybrid Structures

Abstract

Two-dimensional (2D) transition metal dichalcogenides such as WSe2 have garnered much attention due to their extraordinary layer-number-dependent optoelectronic properties. To exploit the unique properties for novel optoelectronic applications, it is important to construct heterojunctions and understand their layer-number-dependent characteristics. In this work we have investigated heterojunctions made of 2D WSe2 flakes decorated with organic dye molecules elucidated the optical and electronic properties as a function of layer number. We introduce a facile one-step approach to deposit a uniform layer of eosin Y (EY) molecules on various number of WSe2 layers, forming hybrid heterojunctions. Photoconductive atomic force microscopy (PC-AFM), Kelvin probe force microscopy (KPFM), and photoluminescence (PL) spectroscopy probed the organic/inorganic heterojunctions. The hybrid structures show drastically enhanced photocurrents due to the lowered barrier height by the staggered band alignment. The barrier heights of the hybrid structures monotonically decrease as the layer number increases. The surface potential measurements reveal that the work functions of the hybrids are smaller than those of the pristine WSe2 samples. Moreover, the hybrid samples show spatially uniform current and photocurrent responses, indicating the high quality and uniform heterojunctions. Lastly, the hybrid samples show a drastic PL quenching due to p-doing on WSe2. These findings will open new opportunities for novel WSe2-based 2D heterostructured optoelectronics.