New insights into the electronic structures and optical properties in the orthorhombic perovskite MAPbI3: a mixture of Pb and Ge/Sn

Abstract

As a new type of promising photovoltaic material, organic–inorganic hybrid perovskites (OIHPs) have attracted particular attention owing to their rapid increase in power conversion efficiency (PCE). It is quite remarkable that within several years PCEs have speedily exceeded the value of 20% from the original 3.8% in 2009. Nevertheless, the existence of heavy metal lead in the prototype perovskite MAPbI₃ poses a great threat to human health and the living environment. To explore potential alternatives, we choose the congener elements of Ge and Sn as partial substituents for lead. By virtue of density functional theory calculations, the electronic structures and optical properties of Ge/Sn-doped perovskite compounds have been investigated involving GGA-PBE and DFT-SOC levels. The simulations indicate that the optical absorption coefficient is significantly enhanced due to the use of Ge/Sn dopants. Moreover, it is revealed that the absorption spectra shift towards the near infrared and even the middle infrared, and meanwhile, the band gap can be tuned by means of the Ge/Sn doping. Additionally, optical property analyses imply that the effect of spin–orbit coupling (SOC) plays a positive role for the application of OIHP materials in the photovoltaic field. These results shed a new light on a deep understanding of the nature of a range of functional materials constituted of OIHPs.