Spin orbit coupling effect band gaps engineering of the lead-free perovskites FABI3 (B= Sn, Ge or Pb) materials for Tandem Solar Cells: first principle investigation of structural and electronic properties

Abstract Pb-free perovskites are novel compounds that are currently studied, essentially for their photovoltaic applications. In this paper, we are studying the Hybrid-Organic-Inorganic perovskite (HOIP) for photovoltaic application. In fact, we study and discuss the structural and electronic properties of the perovskite FABI3 (B= Sn, Ge or Pb and FA= formamidinium: CH(NH2)2) applying the density functional theory DFT method executed in the Quantum Espresso framework. The band structure these perovskites has been presented; it is showed that these perovskits has a semi-conductor nature, with a band gap value 1.36eV for FASnI3, 1.72eV for FAGeI3 and 1.61eV for FAPbI3. Also, The DOS and PDOS have been presented and discussed for each of these materials. Indeed, we investigate the structural properties of these perovskites and demonstrated that the optimized value of lattice parameter is 6.35Å for the FASnI3, While, for the FAGeI3, this value is 6.3Å. And 6.5Å for FAPbI3. Moreover, the impact of the lattice parameter on the band gap value of FABI3 (B =Sn, Ge or Pb) has been investigated, it is demonstrated that the lattice parameter increases, the band gap increases. The results of this work can be utilized as a guideline for the development of new efficient, lead-free perovskite devices including tandem solar cells.