First-principles analysis of the structural, electronic, and elastic properties of cubic organic-inorganic perovskite HC(NH₂)₂PbI₃

The structural, electronic, and elastic properties of cubic HC(NH₂)₂PbI₃ perovskite are investigated by density functional theory using the Tkatchenko-Scheffler pairwise dispersion scheme. Our relaxed lattice parameters are in agreement with experimental data. The hydrogen bonding between NH₂ and I ions is found to have a crucial role in FAPbI₃ stability. The first calculated band structure shows that HC(NH₂)₂PbI₃ has a direct bandgap (1.02 eV) at R-point, lower than the bandgap (1.53 eV) of CH₃NH₃PbI₃. The calculated density of states reveals that the strong hybridization of s(Pb)-p(I) orbital in valence band maximum plays an important role in the structural stability. The photo-generated effective electron mass and hole mass at R-point along the R-Γ and R-M directions are estimated to be smaller:m_e^*=0.06m₀ and m_h^*=0.08m₀ respectively, which are consistent with the values experimentally observed from long range photocarrier transport. The elastic properties are also investigated for the first time, which shows that HC(NH₂)₂PbI₃ is mechanically stable and ductile and has weaker strength of the average chemical bond. This work sheds light on the understanding of applications of HC(NH₂)₂PbI₃ as the perovskite in a planar-heterojunction solar cell light absorber fabricated on flexible polymer substrates.