Ultrasmall Nanoplatelets: The Ultimate Tuning of Optoelectronic Properties

2D semiconducting nanoplatelets (NPLs) are an emerging class of photo-active materials. They can be used as building blocks in optoelectronic devices thanks to their large absorption coefficient, high carrier mobility, and unique thickness-dependent optical transitions. The main drawback of NPLs is their large lateral size, which results in unfavorable band energy levels and low quantum yield (QY). Here, ultrasmall lead chalcogenide PbSe1-xSx NPLs are prepared, which exhibit an unprecedented QY of approximate to 60%, the highest ever reported for this structure. The NPLs are applied as light absorber in a photoelectrochemical system, leading to a saturated photocurrent density of approximate to 5.0 mA cm(-2) (44 mL cm(-2) d(-1)), which is a record for NPL-based photo-electrodes in solar-driven hydrogen generation. Ultrasmall NPLs hold the potential for breakthrough developments in the field of optically active nanomaterials.