Effects of K- or Ge-additions to formamidinium-based perovskite crystals on electronic structures and photovoltaic properties

Abstract

The effects of potassium (K) or germanium (Ge)-addition to methylammonium-formamidinium-based perovskite crystals were investigated on the device performance and electronic structures. The Ge-addition increased the short-circuit current density for the as-prepared device, and the K-addition improved the open-circuit voltage and conversion efficiency by room temperature aging. Crystallite sizes and (100)-orientations of perovskite crystals increased by the K-addition, and the lattice constants of K- and/or Ge-doped perovskites increased with time. The first-principles calculations indicated that the formation energies of the perovskite crystals were reduced by the K- or Ge-addition, which would contribute to the stability of the perovskite crystals.