Elastic, electronic and optical properties of stable pentagonal ZnO 2

Using first-principles calculations, we predict the existence of two dimensional (2D) pentagonal ZnO 2 (penta-ZnO 2 ) sheet and confirm that penta-ZnO 2 is dynamically and mechanically stable. Due to its unique atomic configuration, penta-ZnO 2 has intrinsic negative Possion's ratio, contrary to the most existing materials. Furthermore, Penta-ZnO 2 is much more flexible than graphene-like ZnO and penta-graphene in elasticity. Using the Heyd-Scuseria-Ernzerhof (HSE06) functional, the calculated indirect energy band gap is 4.53 eV, which is corresponding with optical gap (4.54 eV). More interesting, in the visible range of light, we find that penta-ZnO 2 has very low reflectance (0.0035%). Together with the expected zero absorption below the band gap, the light transmittance of penta-ZnO 2 is almost 100% in a broad spectral range. Our study demonstrates that penta-ZnO 2 possesses unique stable structure and promising mechanical, electronic and optical properties, which offers great potential in a wide range of applications in optoelectronics. Especially, the high flexibility and high light transmission make the penta-ZnO 2 to be a promising candidate for transparent electrodes.