Hello, Kamal Assiouan

I have been trying to find how to calculate VB and CB values, but didn't find either yet. However, calculate bandgap is quite trivial. So, my question is: is it really possible to obtain VB energy from XPS?

If you can determine this, you are halfway your goal, because with VB from XPS and bandgap calculated from DFT, you can apply Bandgap = CB - VB (remember that CB and VB are negative by convention).

Also, Bandgap is easily determined by UV-Vis spectroscopy, and you have to be careful about bandgaps calculated from DFT. Ideally, obtain absorbance spectra, calculate experimental bandgap, and try to obtain similar values with QE. If you need help with QE, let me know.

Best regards,

Ricardo Tadeu

Cs2BX6 double halide perovskites have garnered significant attention in the fields of materials science, physics, and optoelectronics. They hold great promise as potential candidates for light-absorbing layers in solar cells and ultrafast scintillators. This is primarily due to their notable advantages, such as cost-effectiveness, ease of processing, adjustable bandgaps, high absorption coefficients, enhanced mobility, and rapid response to excitation. To provide preliminary information for developing multijunction devices using Cs2BX6, it is crucial to determine the band alignment of Cs2BX6. Therefore, we thoroughly investigated the surface physics of Cs2BX6, where B = Ti, Zr, Hf, and X = Cl, Br, I, utilizing the electron affinity rule. We extracted all the natural band offsets between Cs2BX6 and TiO2. Our findings revealed that the band alignment of Cs2BX6 is of type-I, regardless of whether they were categorized based on the same transition metal or halide. The positions of the conduction band minimum in Zr and Hf compounds are relatively close to each other due to the positioning of Zr and Hf d states. The shift in the valence band has a more significant impact on the variation of band gaps in Ti compounds compared to the change in the conduction band. We anticipate that the knowledge of the band alignment of Cs2BX6 will not only aid in the design of heterostructures but also contribute to a better understanding of the behavior of alloy bandgap tuning among Cs2BX6, whether through the mixing of B or X atom