Twist‐Angle Engineering of Atomically Thin Halide Perovskite/WSe ₂ Van der Waals Heterojunctions for Enhanced Optoelectronic Performance

ABSTRACT The development of atomic‐level heterojunctions between halide perovskites and 2D van der Waals semiconductors offers a promising route to boost optoelectronic performance by tailoring interfacial coupling, yet achieving deterministic control of interlayer alignment at the atomic scale remains challenging. Here, we report atomically thin (PEA) 2 PbBr 4 /WSe 2 van der Waals heterojunctions with precisely defined twist angles (0°, 5°, 7°, 10°, 12° and 15°), and systematically investigate their twist‐angle‐dependent and optoelectronic responses. Twist‐dependent Raman, PL and density‐functional‐theory analyses consistently show that increasing twist strengthens interlayer coupling, leading to phonon hardening, PL redshift and quenching, and a pronounced narrowing of the effective type‐II bandgaps via enhanced interlayer hybridization and band‐edge density of states. In line with this microscopic picture, the 15° heterojunction delivers a high photoresponsivity of 2.8 A W −1 , an on/off ratio of 2.33 × 10 5 , and a mobility of 117.1 cm 2 V −1 s −1 under 405 nm. Our results establish twist angle as a programmable, atomic‐scale knob for jointly tuning band structure and device performance in perovskite/2D heterostructures, providing a general strategy for high‐performance optoelectronic devices.