Active enhancement of the optical absorption coefficient to improve the light converting efficiency of thin-film solar cell materials is crucial to develop the next-generation solar cell devices. Here we report first-principles calculations with generalized gradient approximation to study the optoelectronic properties of pristine and divacancy blue phosphorene thin films under structural deformation. We show that instead of forming sp-like covalent bonds as in the pristine blue phosphorene layer, a divacancy introduces two particular dangling bonds between the voids. Using a microscopic (non-) affine deformation model, we reveal that the orbital hybridization of these dangling bonds is strongly modified in both the velocity and vorticity directions depending on the type of deformation, creating an effective light trap to enhance the material absorption efficiency. Furthermore, this successful light trap is complemented by a clear signature of sigma + pi plasmon when a divacancy blue phosphorene layer is slightly compressive. These results demonstrate a practical approach to tailor the optoelectronic properties of low-dimensional materials and to pave a novel strategy to design functionalized solar cell devices from the bottom-up with selective defects.

Improvement of the optical absorption coefficient is essential to enhance the light conversion efficiency of thin-film organic solar cells. Here we report the use of an external electric field as a novel switch to improve the optical absorption capacity of two-dimensional defect blue phosphorene (BlueP) systems. Using the density functional theory with van der Waals functionals, we investigate the structural, electronic, magnetic and optical absorption properties of the pristine, single-vacancy (SV) BlueP thin films, and a BlueP system absorbing a Vanadium adatom. We demonstrate that a SV BlueP layer would exhibit half-metallic and its absorption spectrum under an electric field parallel to the material plane is significantly enhanced in the ultra-violet region. More interestingly, when a Vanadium transition metal is absorbed on a pristine BlueP, the applied electric field perpendicular to the BlueP plane not only doubles the optical absorption coefficient, but also switches ON/OFF the magnetic moments of this system. The prominent red shift of the absorption spectra towards the visible light range under selected polarized directions paves a novel way to engineer solar cell devices with BlueP materials.