【摘要】 采用第一性原理,研究三方及六方相FAPbI₃（FA=HC（NH₂）₂⁺）钙钛矿的结构及光电特性.结果表明,FAPbI₃钙钛矿由三方到六方的形变能够扭转PbI₃骨架,改变Pb—I键合特性,进而改变其禁带宽度值.两种晶体均属于直接带隙半导体,三方相FAPbI₃的直接带隙点位于布里渊区Z（0,0,0.5）对称点,具有较为理想的约1.50 e V的禁带宽度;六方相FAPbI₃的直接带隙点位于Γ（0,0,0）对称点,具有约2.50 e V的禁带宽度.FA离子不直接参与电子跃迁过程,仅仅充当电荷供体为PbI₃骨架提供超过0.7 e的电荷.相比于六方相晶体,三方相FAPbI₃具有更小的载流子有效质量,吸收光谱发生了显著的红移,并且其吸收特性优于六方相FAPbI₃和四方相MAPbI₃（MA=CH3NH3+）钙钛矿.六方相FAPbI₃比三方相晶系更稳定,FA和PbI₃骨架之间的结合作用力强于MA和PbI₃骨架之间的作用力.更多还原

【Abstract】 Formamidinium lead halide perovskite FAPbI₃（FA=HC（NH₂）₂⁺） has drawn wide attention as efficient photoelectronic conversion material. First-principles calculations were performed by using the Vienna ab initio simulation package（VASP） based on density functional theory. The structure configuration, electronic property, absorption spectrum, and bonding energy were analyzed to elucidate the structural and photoelectronic properties of trigonal and hexagonal FAPbI₃ perovskites. Results showed that the crystal deformation from trigonal to hexagonal crystal would distort the PbI₃ framework, change the covalent/ionic Pb—I bonds, and eventually alter the semiconductor bandgaps. The trigonal and hexagonal FAPbI₃ perovskites are both direct-bandgap semiconductors. The direct-bandgap nature of trigonal crystal locates at Z（0, 0, 0.5） symmetry point with the ideal bandgap of ca. 1.50 e V; the direct-bandgap nature of hexagonal crystal locates at Γ（0, 0, 0） symmetry point with the wide bandgap of ca. 2.50 e V. For the both crystals, the main contributions to VBM（valence band maximum） are I 5p orbitals with a little overlapping of Pb 6s orbitals, and the main components of CBM（conduction band minimum） are Pb 6p orbitals. The FA cations do not directly participate into the electron transition process, just acting as charge donors to supply PbI₃ framework with more than 0.7 e. There exists both covalent and ionic interactions between Pb and I ions. Compared with the hexagonal crystal, the trigonal FAPbI₃ possesses smaller electron and hole effective masses. It exhibits dramatic red shifted absorption spectrum and a better absorption efficiency than hexagonal FAPbI₃ and tetragonal MAPbI₃（MA=CH）3NH)3⁺) perovskites. Bonding energy analyses showed that the hexagonal FAPbI₃ was more stable than the trigonal crystal, and interaction between FA and PbI₃ framework was stronger than that between MA and PbI₃ framework. Our results could provide theoretical guidance for the experimental design and synthesis of FAPbI₃ perovskite solar cells.更多还原