Exploring novel two-dimensional penta-XY2 (X = C, Si; Y = C, N, P) monolayers: Promising candidates for optoelectronic applications

• A new class of stable 2D penta-XY 2 monolayers with pentagonal lattice is proposed. • The monolayers exhibit wide, tunable bandgaps and strong visible-UV absorption. • High photogalvanic responses with polarization-sensitive photocurrents are demonstrated. • Negative Poisson’s ratios and flexible mechanical properties are observed. The discovery of stable two-dimensional (2D) materials with intrinsic photogalvanic effects opens new avenues for developing low-power optoelectronic technologies. Here, we propose a novel family of penta-XY 2 (X = C, Si; Y = C, N, P) monolayers characterized by a unique Cairo pentagonal lattice. Based on first-principles calculations, we systematically investigate their structural stability, electronic characteristics, and optoelectronic performance. The results reveal that these dynamically stable semiconductors possess wide bandgaps spanning the visible to near-ultraviolet range, accompanied by strong optical absorption capabilities. Remarkably, the inherent inversion symmetry breaking in these monolayers gives rise to a pronounced intrinsic photogalvanic effect. As a result, photodetectors based on penta-XY 2 monolayers can generate robust photocurrent under low bias conditions, featuring high polarization sensitivity and large extinction ratios. Moreover, the penta-XY 2 monolayers display diverse mechanical properties, with Young’s modulus ranging from flexible to rigid, and even exhibit negative Poisson’s ratios. These findings underscore the potential of 2D penta-XY 2 monolayers for high-performance, flexible, and polarization-sensitive optoelectronic devices.