Optoelectronic and solar cell applications of Janus monolayers and their van der Waals heterostructures
Optoelectronic and solar cell applications of Janus monolayers and their van der Waals heterostructures
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DOI：
10.1039/c9cp02648g
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发表时间：
2019-09-14
影响因子：
3.3
通讯作者：
Amin, B.
中科院分区：
文献类型：
--
作者：
Idrees, M.;Din, H. U.;Amin, B.
通过混合密度泛函理论计算研究了 Janus 单层及其范德华异质结构。 MoSSe、WSSe、MoSeTe 和 WSeTe 被发现是直接带隙半导体。外部电场用于将间接 MoSTe 和 WSTe 转变为直接带隙半导体。 MoSSe-WSSe、MoSeTe-WSeTe 和 MoSTe-WSTe vdW 异质结构也是具有 II 型能带排列的间接带隙半导体。与相应的单层类似，在上述一些 vdW 异质结构中，外部电场和拉伸应变可以将间接带隙转变为直接带隙，同时维持 II 型能带排列。 Janus 单层的功函数 (phi) 值低于其 vdW 异质结构对应物。此外，还计算吸收光谱、吸收效率和价（导）带边缘电势，以了解这些系统的光学和光催化行为。由于 Janus 单层中的诱导应变，在激子峰位置观察到红移和蓝移。在可见光、红外和紫外区域，WSeTe、MoSTe 和 WSTe 单层具有很强的器件吸收效率 (80-90%)。 Janus 单分子层中能量有利的能带边缘位置使其适合在零 pH 下进行水分解。我们发现 MoSSe-WSSe 异质结构和 MoSTe 单层是水分解的有希望的候选者，其导带和价带边缘位于氧化还原区间之外。
Janus monolayers and their van der Waals heterostuctures are investigated by hybrid density functional theory calculations. MoSSe, WSSe, MoSeTe and WSeTe are found to be direct band gap semiconductors. External electric fields are used to transform indirect MoSTe and WSTe to direct band gap semiconductors. MoSSe-WSSe, MoSeTe-WSeTe and MoSTe-WSTe vdW heterostructures are also indirect band gap semiconductors with type-II band alignment. Similar to the corresponding monolayers, in some of the above mentioned vdW heterostructures an external electric field and tensile strain can transform indirect to direct band gaps, while sustaining type-II band alignment. Janus monolayers have lower values of the work function (phi) than their vdW heterostructure counterparts. Furthermore, absorption spectra, absorption efficiency, and valence(conduction) band edge potentials are calculated to understand the optical and photocatalytic behavior of these systems. Red and blue shifts are observed in the position of excitonic peaks due to the induced strain in Janus monolayers. Strong device absorption efficiencies (80-90%) are observed for the WSeTe, MoSTe and WSTe monolayers in the visible, infra-red and ultraviolet regions. Energetically favourable band edge positions in Janus monolayers make them suitable for water splitting at zero pH. We find that the MoSSe-WSSe heterostructure and the MoSTe monolayer are promising candidates for water splitting with conduction and valence band edges positioned just outside of the redox interval.