Two-dimensional heterojunction SnS₂/SnO₂ photoanode with excellent photoresponse up to near infrared region

Two-dimensional (2D) semiconductor materials have attracted much attention in solar energy utilization due to their unique structure and excellent photoelectrical properties. However, the band bending in the 2D materials-based photoelectrodes is limited when the thickness of 2D flakes are too thin, which normally leads to weak driving force for charge separation and transfer. Constructing heterojunction is an effective way to enhance the band bending by creating additional space charge layer in semiconductors. Herein we intentionally introduce a 2D SnS₂ layer on SnO₂ nanoflakes to design a new class of 2D heterojunction of SnS₂/SnO₂. The low lattice mismatch of two materials leads to intimate heterojunction contact with well-matched energy band alignment, which efficiently promote the charge carrier separation of SnS₂ photoelectrodes. Moreover, the conductive SnO₂ provides a good pathway for electron collection. Consequently, the photocurrent density of the SnS₂/SnO₂ heterojunction photoanode is largely improved by 2.8 times to 0.7 mA cm⁻² at 1.23 V vs RHE compared to the pristine SnS₂, which also shows significantly improved photocurrent density than others for wet-chemically prepared SnS₂ based photoanodes. Considerable near infrared (NIR) light photoresponse is also observed in the SnS₂/SnO₂ heterojunction which is mainly induced by the defects.