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Dong et al. Energy Mater. 2026, 6, 600026 Page 7 of 16

Figure 2. (A-C) Effect of W Nd-CdS and W/O Nd-CdS layers on the orientation of Sb 2 Se 3 thin films, (D) XRD patterns of Sb 2 Se 3 films with
W Nd-CdS and W/O Nd-CdS layers, (E) Texture coefficients of Sb 2 Se 3 films with W Nd-CdS and W/O Nd-CdS layers, (F) Raman spectra
of Sb 2 Se 3 films with W Nd-CdS and W/O Nd-CdS layers, (G-I) XPS spectra of Sb 3d, Se 3d, and Nd 3d for Sb 2 Se 3 films prepared with
W Nd-CdS and W/O Nd-CdS layers.

Sb Se films. Figure 2G-I shows the XPS data for untreated and NdCl -treated Sb Se films. The results
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3
2
3
3
indicate that the positions of the Sb 3d and Se 3d peaks are consistent with previously reported data, and the
two peaks for Nd 3d may correspond to Nd-O bonding. These findings confirm that the Nd element
successfully diffuses into the Sb Se films .
[38]
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3
Figure 3A-D shows the relationship between the formation energy of point defects, where Nd substitutes for
Sb, and the Fermi level under different chemical potential conditions (Sb-rich and Sb-poor). Lower
formation energies indicate that a defect is more likely to form under a given Fermi level and chemical
environment . Under Sb-rich conditions [Figure 3A and B], the formation energy for Nd doping is
[39]
significantly lower, suggesting that an Sb-rich environment is more favorable for Nd incorporation at the Sb
site. This effect arises from the influence of the Sb chemical potential on the formation energy of Nd doping:
in Sb-rich conditions, the higher Sb chemical potential reduces the energy barrier for Nd substitution at the
Sb site. In contrast, under Sb-poor conditions [Figure 3C and D], the formation energy increases
significantly, indicating that Sb-depleted environments are less favorable for Nd doping. The intersections of
the curves corresponding to different charge states indicate the defect’s charge state transition points as the
Fermi level varies. Under Sb-rich conditions (Nd ), when the Fermi level increases from 0 eV (the valence
Sb1