CH3NH3PbI3 (MAPbI3) perovskite materials hold considerable promise for future low cost, high-efficiency solar cells, and replacement materials for toxic lead have also been in demand. In this study, the optical constants, absorption coefficients, and interband electron transitions of MAPb1−xSnxI3 (x = 0, 0.4, 0.8, and 1) films have been analyzed by spectroscopic ellipsometry in the photon range of 1 eV–5 eV. The bandgaps of MAPb1-xSnxI3 (x = 0, 0.4, 0.8, 1) are 1.54 eV, 1.51 eV, 1.49 eV, and 1.46 eV, respectively. With the increase in Sn, the s–p antibonding coupling becomes stronger, and the bandgap energy decreases, owing to the shallower and more active lone-pair states of Sn-5s than Pb-5s near the valence band maximum (VBM). According to the x-ray diffraction patterns, doping Sn does not change the material structures, which makes the shape of VBM more fluctuating, resulting in a similar band structure. Moreover, band structures and interband electron transitions of all four samples are discussed in terms of solid-state physics and can be assigned to the direct transition between the valence band and the conduction band at R, M, and X symmetry points.

中文翻译：

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Sn掺杂的CH3NH3PbI3钙钛矿薄膜的光学常数、带间电子跃迁和带隙的演变

CH3NH3PbI3 (MAPbI3) 钙钛矿材料在未来低成本、高效率的太阳能电池方面具有相当大的前景，并且也需要有毒铅的替代材料。在这项研究中，MAPb1−xSnxI3 (x = 0、0.4、0.8 和 1) 薄膜的光学常数、吸收系数和带间电子跃迁已通过光谱椭偏法在 1 eV–5 eV 的光子范围内进行了分析。MAPb1-xSnxI3 (x = 0, 0.4, 0.8, 1) 的带隙分别为 1.54 eV、1.51 eV、1.49 eV 和 1.46 eV。随着Sn的增加，s-p反键耦合变得更强，带隙能量降低，这是由于Sn-5s在价带最大值（VBM）附近比Pb-5s更浅且更活跃的孤对态。根据 X 射线衍射图，掺杂 Sn 不会改变材料结构，这使得 VBM 的形状更加波动，导致类似的能带结构。此外，所有四个样品的能带结构和带间电子跃迁都根据固态物理学进行了讨论，并且可以分配到价带和导带之间在 R、M 和 X 对称点处的直接跃迁。