Doping effect on the electronic and optical properties of all-inorganic CsGeBr _3-x I _x

The excitonic effect of metal halide perovskites as an important indicator on their optoelectronic and photovoltaic characteristics has been widely studied. Here, we investigate doping effects on the electronic and optical properties of CsGeBr_3-<i>x</i>I<i>_x</i> (<i>x</i> = 0,1, 2, 3) by first-principles methods. The calculated band gap and electron effective mass at the band-edge are observed to decrease with increasing doping proportion, suggesting enhanced charge transport properties for efficient solar cells. Considering the excitonic effect in halide perovskites, we further investigate the absorption spectra of CsGeBr_3-<i>x</i>I<i>_x</i>, including the electron-hole interactions. Our results show the pronounced excitonic resonances and low exciton binding energies in mixed halide perovskites. This study establishes doped ferroelectric halide perovskites as a novel class of functional materials, characterized by an ideal band gap, low exciton binding energy, and strong optical absorption, providing a platform for advanced optoelectronic and photovoltaic applications.