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采用第一性原理,研究三方及六方相FAPbI_3(FA=HC(NH_2)_2~+)钙钛矿的结构及光电特性.结果表明,FAPbI_3钙钛矿由三方到六方的形变能够扭转PbI_3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FAPbI_3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FAPbI_3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PbI_3骨架提供超过0.7 e的电荷.相比于六方相晶体,三方相FAPbI_3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FAPbI_3和四方相MAPbI_3(MA=CH3NH3+)钙钛矿.六方相FAPbI_3比三方相晶系更稳定,FA和PbI_3骨架之间的结合作用力强于MA和PbI_3骨架之间的作用力.
The structure and photoelectric properties of FAPbI_3 (FA = HC (NH_2) _2 ~ +) perovskite from tripartite and hexagonal phases were investigated by the first principle.The results show that the deformation of PbAP_3 can be reversed by trigeminal to hexagonal deformation of FAPbI_3 perovskite, Change the bonding properties of Pb-I and change their bandgap values.These two kinds of crystals belong to direct band gap semiconductors.The direct band gap point of the tripartite FAPbI_3 is located at the symmetry point of Z (0,0,0.5) in the Brillouin zone, Has a band gap of about 1.50 eV, and the direct bandgap point of the hexagonal phase FAPbI_3 is located at a symmetrical point of Γ (0,0,0) with a bandgap of about 2.50 e V. FA ions are not directly involved in the electronic transition Process, acting solely as a charge donor, provided a charge of more than 0.7 e for the PbI 3 framework.Triple phase FAPbI 3 has a smaller carrier effective mass compared to hexagonal crystals, a significant red shift in the absorption spectrum, and its absorption behavior Which is more stable than hexagonal phase FAPbI_3 and tetragonal phase MAPbI_3 (MA = CH3NH3 +) perovskite.The hexagonal phase FAPbI_3 is more stable than the ternary phase and the binding force between FA and PbI_3 framework is stronger than that between MA and PbI_3 framework .