A DFT Study of Alkaline Earth Metal-Doped FAPbI[sub.3] Surfaces

Density functional theory calculations have been performed to study the effect of replacing lead by alkaline earth metals on the stability, electronic and optical properties of the formamidinium lead triiodide (FAPbI[sub.3] ) (111) and (100) surfaces with different terminations in the form of FAPb[sub.1-x] AE[sub.x] I[sub.3] structures, where AE is Be, Mg or Ca. It is revealed that the (111) surface is more stable, indicating metallic characteristics. The (100) surfaces exhibit a suitable bandgap of around 1.309 and 1.623 eV for PbI[sub.5] and PbI[sub.6] terminations, respectively. Increases in the bandgaps as a result of Mg- and Ca-doping of the (100) surface were particularly noted in FAPb[sub.0.96] Ca[sub.0.04] I[sub.3] and FAPb[sub.0.8] Ca[sub.0.2] I[sub.3] with bandgaps of 1.459 and 1.468 eV, respectively. In the presence of Be, the band gap reduces critically by about 0.315 eV in the FAPb[sub.0.95] Be[sub.0.05] I[sub.3] structure, while increasing by 0.096 eV in FAPb[sub.0.96] Be[sub.0.04] I[sub.3] . Optimal absorption, high extinction coefficient and light harvesting efficiency were achieved for plain and doped (100) surfaces in the visible and near UV regions. In order to improve the optical properties of the (111)-PbI[sub.3] surface in initial visible areas, we suggest calcium-doping in this surface to produce FAPb[sub.0.96] Ca[sub.0.04] I[sub.3] , FAPb[sub.0.92] Ca[sub.0.08] I[sub.3] , and FAPb[sub.0.88] Ca[sub.0.12] I[sub.3] structures.