Toward Mass Production of Transition Metal Dichalcogenide Solar Cells: Scalable Growth of Photovoltaic-Grade Multilayer WSe by Tungsten Selenization.

Semiconducting transition metal dichalcogenides (TMDs) are promising for high-specific-power photovoltaics due to their desirable band gaps, high absorption coefficients, and ideally dangling-bond-free surfaces. Despite their potential, the majority of TMD solar cells to date are fabricated in a nonscalable fashion, with exfoliated materials, due to the lack of high-quality, large-area, multilayer TMDs. Here, we present the scalable, thickness-tunable synthesis of multilayer WSe films by selenizing prepatterned tungsten with either solid-source selenium at 900 °C or HSe precursors at 650 °C. Both methods yield photovoltaic-grade, wafer-scale WSe films with a layered van der Waals structure and superior characteristics, including charge carrier lifetimes up to 144 ns, over 14× higher than those of any other large-area TMD films previously demonstrated. Simulations show that such carrier lifetimes correspond to ∼22% power conversion efficiency and ∼64 W g specific power in a packaged solar cell, or ∼3 W g in a fully packaged solar module. The results of this study could facilitate the mass production of high-efficiency multilayer WSe solar cells at low cost.