Nanomanufacturing of Emerging 2D Materials for Thin-Film Photovoltaic Applications

2D layered transition metal dichalcogenides (LTMDs) attracted a great deal of interests because of their attractive electronic, optoelectronic and mechanical properties, versatile chemistry, and large natural abundance. Especially, a single semiconducting LTMD (e.g., WSe 2 , WS 2 , and MoS 2) layer (~0.5 nm thick) can absorb as much sunlight as 50 nm of Si (or 12 nm of GaAs) and generate currents as high as 4.5mA/cm 2. Therefore, 2D LTMD films hold a significant potential to be used for making ultrathin flexible photovoltaic (PV) cells with 1-3 orders of magnitude higher power densities than the best existing thin-film solar cells. In addition, LTMD-based PV cells are anticipated to have extra advantages, including (1) excellent chemical stability (i.e., LTMDs are naturally stable 2D crystals); (2) good flexibility; (3) superior transport property (i.e., high-quality heterojunctions free of tangling bonds and charge traps can be formed by simply stacking LTMD layers with other 2D materials), and (4) low production cost (i.e., such ultrathin PV cells can be manufactured on low-cost flexible substrates by using roll-to-roll processes). In spite of such optimistic anticipation, highly efficient LTMD-based PV cells have not been created yet. In particular, although single and few-layer LTMD PV devices (including photodetectors) exhibit strong light-matter interaction in terms of a high photocurrent density (J sc) per unit photoactive layer thickness, multilayer LTMD PV devices still exhibit relatively poor total values of J sc , extrinsic quantum efficiency (EQE), responsivity, open-circuit voltage (V oc), fill factor (FF), and power-conversion efficiency (PCE). Such poor performance is because of the fact that people still lack knowledge and technology for tailoring the band structures of LTMD PV cells to optimize critical PV parameters and their trade-off against the total thickness of LTMD-based photoactive layers as well as the flexibility of PV cells. We are looking for the collaboration in areas of plasmonics, nanophotonics, and photovoltaics to create and study flexible PV cell arrays based on vertically stacked 2D hetero-structures consisting of LTMD and graphene few-layer films, and plasmonic nanostructures. The implementation of LTMD/graphene hetero-structures can improve the PV responsivity over a broader range of wavelengths as well as the collection efficiency of photo-generated carriers. Furthermore, it is expected to significantly enhance FF and V oc parameters, which can ultimately result in a high PCE. The PV characterization of such hetero-structures will also provide new knowledge for leveraging the unique optoelectronic properties of LTMDs for …