Hello all.
I work with Organic-Inorganic Perovskite CH3NH3PbI3. There are papers describing the energies of Highest Occupied Molecular Orbitals (HOMO) and Lowest Unoccupied Molecular Orbitals (LUMO), and constructing the band alignment diagram. For this perovskite, HOMO = -5.4 eV and LUMO = -3.9 eV.
There are also papers describing the band structure calculated by Density Functional Theory softwares, like Quantum Espresso. But the energies of HOMO and LUMO don't match with the known values, and they consider that the valence band is the zero energy, not the vacuum, as experiments consider.
I can replicate the results from Quantum Espresso bands calculation, but is it possible to obtain HOMO = -5.4 eV and LUMO =-3.9 eV through QE calculations? At least an approximated value?
The values of HOMO and LUMO shown in the diagram are usually not obtained from the band structures (usually levelled up to the Fermi level, thus 0 eV is the Fermi level). The values of HOMO and LUMO needed to be reference to the Vacuum level. Therefore, you need to obtain the vacuum potential from you calculations, and later subtract the potential value from your HOMO and LUMO which are exactly VB and CB edges of bands. Hope above are useful.
I also recommend some of our latest publications on perovskite as below:
1. Hongfei Chen, Hejin Yan, and Yongqing Cai*, Effects of defect on work function and energy alignment of PbI2: Implications for solar cell applications. Chem. Mater. 34, 1020–1029 (2022)
2. Tingting Yin*, Hejin Yan, Ibrahim Abdelwahab, Yulia Lekina, Xujie Lü, Wenge Yang, Handong Sun, Kai Leng, Yongqing Cai*, Ze Xiang Shen*, and Kian Ping Loh*, Pressure driven rotational isomerism in 2D hybrid perovskites. Nat. Commun. 14, 411 (2023)
3. Yan Shao, Wei Gao, Hejin Yan, Runlai Li, Ibrahim Abdelwahab, Xiao Chi, Lukas Rogée, Lyuchao Zhuang, Wei Fu, Shu Ping Lau, Siu Fung Yu*, Yongqing Cai*, Kian Ping Loh*, and Kai Leng*, Unlocking surface octahedral tilt in two-dimensional Ruddlesden-Popper perovskites. Nature Commun. 13, 138 (2022)
4. Hejin Yan, Bowen Wang, Xuefei Yan, Qiye Guan, Hongfei Chen, Zheng Shu, Dawei Wen, and Yongqing Cai*, Efficient passivation of surface defects by Lewis base in lead-free tin-based perovskite solar cells. Mater. Today Energy 27, 101038 (2022)
5. Devesh R. Kripalani, Yongqing Cai*, Jun Lou, and Kun Zhou*, Strong edge stress in molecularly thin organic–inorganic hybrid Ruddlesden–Popper perovskites and modulations of their edge electronic properties. ACS Nano 16, 1, 261–270 (2022)
6. Hongfei Chen, Hejin Yan, and Yongqing Cai*, Recipe for the design of mixed cation lead halide perovskites: adsorption and charge transfer from A-site cations to PbI2. J. Mater. Chem. A (2023) Accepted
7. Hongfei Chen, Qiye Guan, Hejin Yan, Xiangyue Cui, Zheng Shu, and Yongqing Cai*, Additive Molecules Adsorbed on Monolayer PbI2: Atomic Mechanism of Solvent Engineering for Perovskite Solar Cells. ACS Appl. Mater. Interfaces 15, 32475–32486 (2023)
Hello Yongqing Cai ,
Thanks for the advise of the vacuum level, but I don't know how do it correctly. I have seen tutorials about creating a slab of the structure and leave an empty space in the structure to simulate the vacuum. I did it with a silicon structure, made a SCF calculation, but it's very expensive even for a simple silicon structure. Is this the correct method to calculate vacuum potential?
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