Theoretical study on photoelectric properties of ferroelectric photovoltaic perovskite CsGeBr₃ based on first-principle calculations

Abstract

Ferroelectric photovoltaic materials with intrinsic spontaneous polarization have attracted great attention because the ferroelectric polarization can promote the directional migration of electrons and holes, and reduce the trend of carrier recombination. Recently, the evidence of ferroelectricity in the typical three-dimensional all-inorganic halide perovskites CsGeX3, with band gaps of 1.6 eV to 2.3 eV has been confirmed. But the spontaneous polarization of ferroelectric perovskite CsGeX3 is ~10 to 20 μc/cm2 which is weaker than that of ABO3 (~26 to 75 μc/cm2). Strain engineering has a significant influence on the ferroelectric polarization of semiconductor materials by controlling the lattice scaling and the internal atomic spacing. Hence, in this work, strain engineering is introduced to enhance the ferroelectric polarization and maintain the photovoltaic properties of ferroelectric perovskite CsGeBr3. In this paper, we studied the ferroelectric polarization and photoelectric properties of ferroelectric perovskite CsGeBr3 under different triaxial compressive strain based on first-principle calculations. The calculated results show that when the applied compressive strain increases from 0% to -4%, the spontaneous polarization of ferroelectric perovskite CsGeBr3 increases from 14.23 μc/cm2 to 51.61 μc/cm2, and the band gap reduces from 2.3631 eV to 1.5310 eV. The effective mass of electrons and holes gradually reduces, exciton binding energies decrease from 48 meV to 5 meV, and the optical absorption coefficient is strongly enhanced from 3×105 cm-1 to 5×105 cm-1 in visible range. Besides, the power conversion efficiency(PCE) of CsGeBr3 is significantly increased from 16.95% to 26.77%. Therefore, the results indicate that the application of compressive strain can increase the ferroelectric polarization and even improve the original photovoltaic performance of ferroelectric perovskite CsGeBr3. Our theoretical calculations can provide useful insights and beneficial guidance into experimental studies of ferroelectric perovskites in photoelectric applications.