Bi(2)Te(3)/Bi(2)Se(3)/Bi(2)S(3) Cascade Heterostructure for Fast‐Response and High‐Photoresponsivity Photodetector and High‐Efficiency Water Splitting with a Small Bias Voltage

Large‐scale multi‐heterostructure and optimal band alignment are significantly challenging but vital for photoelectrochemical (PEC)‐type photodetector and water splitting. Herein, the centimeter‐scale bismuth chalcogenides‐based cascade heterostructure is successfully synthesized by a sequential vapor phase deposition method. The multi‐staggered band alignment of Bi(2)Te(3)/Bi(2)Se(3)/Bi(2)S(3) is optimized and verified by X‐ray photoelectron spectroscopy. The PEC photodetectors based on these cascade heterostructures demonstrate the highest photoresponsivity (103 mA W(−1) at −0.1 V and 3.5 mAW(−1) at 0 V under 475 nm light excitation) among the previous reports based on two‐dimensional materials and related heterostructures. Furthermore, the photodetectors display a fast response (≈8 ms), a high detectivity (8.96 × 10(9) Jones), a high external quantum efficiency (26.17%), and a high incident photon‐to‐current efficiency (27.04%) at 475 nm. Due to the rapid charge transport and efficient light absorption, the Bi(2)Te(3)/Bi(2)Se(3)/Bi(2)S(3) cascade heterostructure demonstrates a highly efficient hydrogen production rate (≈0.416 mmol cm(−2) h(−1) and ≈14.320 µmol cm(−2) h(−1) with or without sacrificial agent, respectively), which is far superior to those of pure bismuth chalcogenides and its type‐II heterostructures. The large‐scale cascade heterostructure offers an innovative method to improve the performance of optoelectronic devices in the future.