Six novel carbon and silicon allotropes with their potential application in photovoltaic field.

By stacking up five novel cagelike structures, three novel three-dimensional (3D) sp 3 bonding networks, named hP24, hP30 and hP36, were predicted in this work for the first time. These three newly discovered structures have trigonal unit cell with the space groups of P-3m1, P-3m1 and P3m1, respectively. Using first-principle calculations, the physical properties, including structural, mechanical, electronic and optical properties of C and Si in hP24, hP30 and hP36 phases were systematically studied. All these newly discovered carbon and silicon allotropes were proven to be thermodynamically and mechanically stable. The wide indirect bandgap value in range of 3.89-4.03 eV suggests that C in hP24, hP30 and hP36 phases have the potential to be applied in high frequency and high power electronic devices. The direct bandgap value in range of 0.60-1.16 eV, the smaller electron and hole effective mass than diamond-Si, and the significantly better photon absorption characteristics than diamond-Si suggest that hP24-Si, hP30-Si and hP36-Si are likely to have better performance in photovoltaic applications than diamond-Si. hP24-Si also has the potential to be applied in infrared detectors.