Investigation of the efficiency of non-toxic RbGeX₃ (X = I, Br, Cl) perovskites as absorption layer in solar energy converters based on thickness dependency

Abstract To promote green environmental protection, we explore Ge-based perovskites i.e., RbGeX 3 (X= I, Br, or Cl) as alternatives to Pb-based perovskites for efficient solar cells. Their properties are analyzed using density functional theory (DFT). The phonon dispersion curve and cohesive energies are utilized to determine the dynamic stability of RbGeX 3 perovskite materials. The mechanical stability was validated through Born stability criteria, while thermodynamic stability was confirmed despite the lower entropy and large specific heat capacity. The direct bandgaps of the perovskites RbGeI 3 , RbGeBr 3 , and RbGeCl 3 are located at R-point and indicate their semiconducting nature at 0.49 eV, 0.65 eV, and 0.87 eV, respectively. We performed Boltzmann transport calculations to explore the thermoelectric properties of these compounds. Our observations of the high Seebeck coefficients and power factors of these materials indicate their suitability as excellent candidates for thermoelectric device applications. The RbGeI 3 exhibits an impressive static dielectric constant value indicating the material’s property of possessing low carrier recombination. The absorption coefficients of RbGeX 3 depict a red shift while moving in the direction Cl→Br→I. We examined how the substitution of various halogen atoms in RbGeX 3 materials impacts their electronic, optical, thermodynamic, and thermoelectric properties. Based on their thickness, we have employed a spectroscopic limited maximum efficiency (SLME) to predict the solar cell parameters for each perovskite used as an absorber layer. Using the SLME approach, the efficiencies of the RbGeI 3 , RbGeBr 3 , and RbGeCl 3 absorber layers at a thickness of 1 μm are approximately shown 15.67%, 22.08%, and 28.93%, respectively.