Atomic Sandwiched p-n Homojunctions.

Semiconductor p-n junctions have been explored and applied in photoelectrochemical (PEC) water splitting, but serious carrier recombination and sluggish oxygen evolution reaction (OER) dynamics have demanded further progress in p-n junction photoelectrode design. Here, via a controllable NH3 treatment, we construct sandwiched p-n homojunctions in three-unit-cells n-type SnS2 (n-SnS2 ) nanosheet arrays using nitrogen (N) as acceptor dopants. The optimal N-doped n-SnS2 (pnp-SnS2 ) with such unique structure achieves a record photocurrent density of 3.28 mA cm-2 , which is 21 times as high as that of n-SnS2 and the highest value among all the SnS2 photoanodes reported so far. Moreover, the stoichiometric O2 and H2 evolution from water was achieved with Faradaic efficiencies close to 100 %. The superior performance could be attributed to the facilitated electron-hole separation/transfer, accelerated surface OER kinetics, prolonged carrier lifetime, and improved structural stability.