Directional Photogenerated Charge Transfer in Bi ₂ S ₃ /In _2.77 S ₄ /In(OH) ₃ Heterostructure for Solar Water Oxidation

ABSTRACT Photoelectrochemical (PEC) water splitting provides a viable pathway for green hydrogen production, but the carrier regulation synergy of heterostructures remains elusive. Herein, an effective Bi 2 S 3 /In 2.77 S 4 /In(OH) 3 is constructed, the ‌Bi 4f orbital shifts to lower binding energy (0.2 eV)‌, forming the In−S−Bi to reduce the energy barriers for both hydroxyl dissociation and O─O coupling. ‌As the surface potential of bulk Bi 2 S 3 is higher than surface In 2.77 S 4 /In(OH) 3 , the free electrons will flow from Bi 2 S 3 to In 2.77 S 4 /In(OH) 3 when the two semiconductors are contacted. This charge redistribution results in positive and negative charges are accumulated at ‌ Bi 2 S 3 and In 2.77 S 4 /In(OH) 3 sides, inducing the upward and downward band bending. The band bending induces an outward built‐in electric field originating from the surface potential gap (102 mV), and the density functional theory calculations evidence integrated type‐II band alignment. This heterostructure achieves a 2.15‐fold increase in photocurrent compared to Bi 2 S 3 , reaching 5.4 mA cm −2 . ‌Hall effect reveals the Bi 2 S 3 /In 2.77 S 4 /In(OH) 3 has a resistivity of 9.25 Ω cm, which is much less than Bi 2 S 3 , further enhancing the directional charge transfer.‌