A GGA + vdW study on electronic properties and optoelectronic functionality of Cd-doped tetragonal CH₃NH₃PbI₃ for photovoltaics

The electronic properties and optoelectronic functionalities of tetragonal CH₃NH₃PbI₃ doped with different concentrations (6.25%, 12.5% and 25%) of Cd have been investigated using the the generalized gradient approximation with the correction of van der Waals interactions (GGA + vdW). First, we examine the dependence of band gap on the Cd doping concentration, and find that the increased Cd content narrows the band gap up to 1.41 eV, extending the photoabsorption wavelength of CH₃NH₃PbI₃ into the range of near-infrared spectrum. Furthermore, the electron mobility is found to be enhanced by 28%, which is beneficial for separating and collecting the photo-excited carriers. The effects of band-gap reduction and electron-mobility enhancement jointly contribute to the promotion in optoelectronics of CH₃NH₃PbI₃. The detailed analyses on the thermodynamic stabilities of doped structures have been made through examining their phonon dispersions and decomposition energies. This work has implications in offering guidance for broadening the photovoltaic applications of CH₃NH₃PbI₃.