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

Abstract

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 (MoTe 2 )/pentacene heterostructure to boost the carrier density via efficient triplet transfer from pentacene to MoTe 2 using ultrafast transient absorption spectroscopy. We observe carrier multiplication by nearly four times by doubling carriers in MoTe 2 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 MoTe 2 /pentacene film. This puts a step forward to enhancing photovoltaic conversion efficiency beyond the S-Q limit in the organic/inorganic heterostructures.