Apart from being a unique material for efficient solar cells, hybrid halide perovskites possess more mysteries than ever. An anomalous bandgap behavior in CH3NH3Sn1−xPbxI3 alloys has been reported recently [Hao et al., J. Am. Chem. Soc. 136, 8094 (2014)], in which the composition-dependent optical bandgap follows nonmonotonic and nonlinear characteristics instead of a linear trend or Vegard's law; the bandgap of the intermediate compounds was lower than that of the end members. In this article, we study composition-dependent conduction and valence band energies through scanning tunneling spectroscopy to deliberate on the role of the two bands in the bandgap bowing phenomenon and the underlying mechanism. We observe a nonlinear behavior of the two bands with respect to the alloy composition, leading to an anomalous behavior in the transport gap as well. We confirm that two competing events, namely, a spin–orbit coupling parameter appearing due to inclusion of a high-Z material and structural distortion affecting molecular orbitals responsible for the formation of the valence and the conduction bands, result in bandgap bowing in CH3NH3Sn1−xPbxI3 alloys.Apart from being a unique material for efficient solar cells, hybrid halide perovskites possess more mysteries than ever. An anomalous bandgap behavior in CH3NH3Sn1−xPbxI3 alloys has been reported recently [Hao et al., J. Am. Chem. Soc. 136, 8094 (2014)], in which the composition-dependent optical bandgap follows nonmonotonic and nonlinear characteristics instead of a linear trend or Vegard's law; the bandgap of the intermediate compounds was lower than that of the end members. In this article, we study composition-dependent conduction and valence band energies through scanning tunneling spectroscopy to deliberate on the role of the two bands in the bandgap bowing phenomenon and the underlying mechanism. We observe a nonlinear behavior of the two bands with respect to the alloy composition, leading to an anomalous behavior in the transport gap as well. We confirm that two competing events, namely, a spin–orbit coupling parameter appearing due to inclusion of a high-Z material and structural distortion aff...

中文翻译：

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混合卤化物钙钛矿合金（CH3NH3Sn1−xPbxI3）中传输间隙的弯曲：哪个带负责？

除了作为高效太阳能电池的独特材料之外，混合卤化物钙钛矿比以往任何时候都具有更多的奥秘。最近报道了 CH3NH3Sn1-xPbxI3 合金中的异常带隙行为 [Hao 等人，J. Am. 化学 社会。136, 8094 (2014)]，其中依赖于成分的光学带隙遵循非单调和非线性特性，而不是线性趋势或 Vegard 定律；中间体化合物的带隙低于末端成员的带隙。在本文中，我们通过扫描隧道光谱研究了与成分相关的导带和价带能量，以探讨这两个带在带隙弓形现象中的作用及其潜在机制。我们观察到关于合金成分的两个带的非线性行为，也会导致传输间隙中的异常行为。我们确认两个相互竞争的事件，即由于包含高 Z 材料而出现的自旋轨道耦合参数和影响负责形成价带和导带的分子轨道的结构畸变，导致 CH3NH3Sn1− 中的带隙弯曲。 xPbxI3 合金。除了作为高效太阳能电池的独特材料之外，混合卤化物钙钛矿比以往任何时候都具有更多的奥秘。最近报道了 CH3NH3Sn1-xPbxI3 合金中的异常带隙行为 [Hao 等人，J. Am. 化学 社会。136, 8094 (2014)]，其中依赖于成分的光学带隙遵循非单调和非线性特性，而不是线性趋势或 Vegard 定律；中间体化合物的带隙低于末端成员的带隙。在本文中，我们通过扫描隧道光谱研究了与成分相关的导带和价带能量，以探讨这两个带在带隙弓形现象中的作用及其潜在机制。我们观察到关于合金成分的两个带的非线性行为，导致传输间隙中的异常行为。我们确认两个相互竞争的事件，即由于包含高 Z 材料和结构畸变而出现的自旋轨道耦合参数... 也会导致传输间隙中的异常行为。我们确认两个相互竞争的事件，即由于包含高 Z 材料和结构畸变而出现的自旋轨道耦合参数... 也会导致传输间隙中的异常行为。我们确认两个相互竞争的事件，即由于包含高 Z 材料和结构畸变而出现的自旋轨道耦合参数...