Strain-engineered photogalvanic anisotropy in SnP2X6 (X = S, Se) monolayers for high-performance optoelectronics

The photogalvanic effect (PGE) in non-centrosymmetric materials can generate stable currents without external bias, holding significant potential for optoelectronic applications. However, the limited absorption range and weak photoresponse in conventional materials have hindered practical applications. Herein, we investigate the strain-engineered PGE in SnP2X6 (X = S, Se) monolayers, a class of chalcogenophosphate materials featuring strong visible-to-near-infrared absorption and intrinsic anisotropy. First-principles calculations reveal that both uniaxial and biaxial strain significantly modulate the electronic structure and lattice asymmetry, leading to a remarkable enhancement in PGE. Notably, the photocurrent exhibits remarkable anisotropy, with the armchair direction response being ∼40 times and ∼4 times stronger than that along the zigzag direction in SnP2Se6 and SnP2S6 monolayers, respectively. Additionally, a 2% tensile strain along the armchair direction enhances the photocurrent by one order of magnitude compared to the unstrained state. These findings not only reveal the underlying mechanism of strain-tuned PGE but also establish SnP2X6 as a versatile platform for designing polarization-sensitive, broadband, and high-efficiency optoelectronic devices.