Elastic, electronic and optical properties of stable pentagonal ZnO2

Using first-principles calculations, we predict the existence of two dimensional (2D) pentagonal ZnO2 (penta-ZnO2) sheet and confirm that penta-ZnO2 is dynamically and mechanically stable. Due to its unique atomic configuration, penta-ZnO2 has intrinsic negative Possion's ratio, contrary to the most existing materials. Furthermore, Penta-ZnO2 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-ZnO2 has very low reflectance (0.0035%). Together with the expected zero absorption below the band gap, the light transmittance of penta-ZnO2 is almost 100% in a broad spectral range. Our study demonstrates that penta-ZnO2 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-ZnO2 to be a promising candidate for transparent electrodes.