Optical constants of MoTe2from reflectivity measurements. (Brillouin zone transitions)

Boosting internal quantum efficiency via ultrafast triplet transfer to 2H-MoTe2 film

Organic systems often allow to create two triplet spin states (triplet excitons) by converting an initially excited singlet spin state (a singlet exciton). An ideally designed organic/inorganic heterostructure could reach the photovoltaic energy harvest over the Shockley-Queisser (S-Q) limit because of the efficient conversion of triplet excitons into charge carriers. Here, we demonstrate the molybdenum ditelluride (MoTe₂)/pentacene heterostructure to boost the carrier density via efficient triplet transfer from pentacene to MoTe₂ using ultrafast transient absorption spectroscopy. We observe carrier multiplication by nearly four times by doubling carriers in MoTe₂ via the inverse Auger process and subsequently doubling carriers via triplet extraction from pentacene. We also verify efficient energy conversion by doubling the photocurrent in the MoTe₂/pentacene film. This puts a step forward to enhancing photovoltaic conversion efficiency beyond the S-Q limit in the organic/inorganic heterostructures.

Two-dimensional transition metal dichalcogenides as an emerging platform for singlet fission solar cells

Singlet fission, a rapid exciton doubling process via inverse Auger recombination, is recognized as one of the most practical and feasible means for overcoming the Shockley-Queisser limit. Singlet fission solar cells are generally developed by integrating photon downconversion organic semiconductors into conventional photovoltaic devices to break the maximum photovoltaic response of the host semiconductors by virtue of extra triplet excitons. In this regard, proper matching of two different semiconductors and heterointerface engineering are both crucial for highly efficient singlet fission solar cells. Therefore, the aim of this study is to review the prerequisite conditions for efficient triplet transfer at the heterointerfaces and thus highlight the robust spin and valley degrees of freedom of transition metal dichalcogenides with the ultimate goal of stimulating research into next-generation singlet fission solar cells.