Multiple exciton generation for photoelectrochemical hydrogen evolution reactions with quantum yields exceeding 100%

Multiple exciton generation (MEG) in quantum dots (QDs) has the potential to greatly increase the power conversion efficiency in solar cells and in solar-fuel production. During the MEG process, two electron–hole pairs (excitons) are created from the absorption of one high-energy photon, bypassing hot-carrier cooling via phonon emission. Here we demonstrate that extra carriers produced via MEG can be used to drive a chemical reaction with quantum efficiency above 100%. We developed a lead sulfide (PbS) QD photoelectrochemical cell that is able to drive hydrogen evolution from aqueous Na2S solution with a peak external quantum efficiency exceeding 100%. QD photoelectrodes that were measured all demonstrated MEG when the incident photon energy was larger than 2.7 times the bandgap energy. Our results demonstrate a new direction in exploring high-efficiency approaches to solar fuels. Multiple exciton generation has been shown to improve the performance of quantum-dot-based solar cells. Yan et al. now apply it to photoinduced hydrogen production and present a system using PbS quantum-dot photoelectrodes that yields an external quantum efficiency of over 100%.