Center for Functional Nanomaterials Seminar

Two-dimensional (2D) semiconductors have attracted much attention for ultrathin optoelectronics due to their exceptional optical properties and the ability to build artificial heterostructures. Nevertheless, the large and uncontrollable Schottky barrier at the metal-semiconductor interface still impedes the realization of high-performance optoelectronic devices. Therefore, it is highly demanding to develop the appropriate strategies to engineer contact interfaces for effective charge transport and collection. In this talk, I would like to introduce two facile approaches to boost optoelectronic device performance by utilizing monolithically formed WOx and self-assembled monolayers (SAMs) [1,2]. The atomically thin WOx layer, which is monolithically formed by layer-by-layer oxidation of WSe2, is used as a hole transport layer. When the WOx interlayer was introduced at the semiconductor/electrode interface, the power conversion efficiency of the WSe2-MoS2 p-n junction devices increased by about an order of magnitudes, maintaining the response time. The enhanced characteristics can be understood by the formation of the low Schottky barrier and favorable interface band alignment resulting from the monolithic phase transition. And, the dipole-induced SAMs on the metal surface leading the work function difference and the built-in potential across the vdW metal-semiconductor junction. As a result, when the SAMs interlayer was introduced at the interface, the photovoltaic characteristics were tuned depending on differently polarized molecules. Our work suggests a new route to achieve contact engineering in the heterostructures toward realizing high-performance 2D optoelectronics.