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Xia et al. Energy Mater. 2026, 6, 600022 Page 7 of 13

of ZnO deposition and subsequent annealing, Zn elements enter both the Sb S and Sb O lattices in the form
3
2
2 3
of substitutional doping, providing atomic-scale insights into the performance enhancement mechanism.
X-ray photoelectron spectroscopy (XPS) was employed to elucidate the Zn chemical state. Survey scans
[Supplementary Figure 5] confirmed elemental presence of C, Sb, S, O, and Zn. High-resolution Sb 3d
spectra [Figure 2D] revealed that ZnO deposition reduced Sb O content from 79% (control) to 65% (40 s
3
2
ZnO), consistent with SEM/XRD trends. The S 2p spectrum [Figure 2E] showed typical spin-orbit splitting
indicative of S in Sb S , with a shift to higher binding energies upon ZnO deposition, suggesting reduced
2-
2 3
sulfur vacancies. Zn 2p peaks [Figure 2F] were absent in the control but faintly detected at 1,022.11 eV and
1,045.50 eV in the 40 s ZnO sample. This chemically shift relative to crystalline ZnO indicates incorporation
rather than phase separation. Concurrent shifts in Sb MNN Auger peaks further suggest Zn-S bonding and
altered Sb electronic environments.

To probe the depth distribution of Zn doping, XPS depth profiling was performed on the Zn-doping sample
(40 s ZnO) versus the control (W/O ZnO) using Ar sputtering at 0.03 nm/s. The Sb 3d binding energy
+
5/2
[Figure 2G] decreased with sputtering time, stabilizing beyond 200 s (~6 nm depth). Quantifying the Sb 3d 5/2
shift relative to the unsputtered surface (Supplementary Figure 6, red spheres) showed an exponential decay
(y = -0.91 + 0.73e ), with stabilization beyond 200 s (~6 nm depth). This confirms a thin Sb O surface layer
-x/60
2
3
serving as a hole-blocking but tunnel-permissive oxide. This structure is beneficial for suppressing interfacial
recombination while enabling charge extraction. Concurrently, smaller S 2p shifts [Figure 2H and
Supplementary Figure 6] and analogous Sb MNN Auger peak displacements (Figure 2I, Supplementary
Figure 6, fit: y = -1.52 + 1.72e -x/42 ) indicate Zn substitutional doping confined primarily to the top ~10 nm.
Sb
Zn substitution was confined to the top ~10 nm, supported by S 2p and Sb MNN trends [Figures 2H and I,
Sb
Supplementary Figure 6]. This confirms that the ZnO cap limits Sb O formation to an ultrathin ~6 nm layer,
3
2
functioning as a wide-bandgap hole-blocking layer. Then it suppresses interfacial recombination while
enabling efficient hole tunneling due to its minimal thickness, consistent with enhanced J . Collectively,
sc
these depth-resolved analyses demonstrate the dual role of the ZnO interlayer: (1) restricting Sb O to
2
3
nanoscale surface regions, and (2) enabling shallow Zn doping in Sb S .
2 3
To correlate these interfacial modifications with carrier dynamics, light-intensity-dependent J and V oc
sc
measurements were conducted [Figure 3]. According to the power-law relationship [Equation 1] , the
[19]
fitting can obtain the α value.

(1)
∝
Where I represents the percentage of irradiation light intensity, and α is the power exponent. As shown in the
J and irradiation light intensity relationship graph in Figure 3A, yielded α = 0.90 (control) versus 0.91
sc
(Zn-doping), indicating marginally improved carrier collection efficiency. More significantly, the function
relationship between V and light intensity satisfies :
[20]
oc

= + (2)

where T, k (1.38 × 10 J/K), and q (1.60 × 10 C) are the Kelvin temperature, Boltzmann constant, and
-23
-19
B
elementary charge, respectively, and n is the ideality factor related to recombination. The diode ideality
factor n extracted from decreased from 2.43 (control) to 1.87 (Zn-doping), demonstrating substantial
suppression of Shockley-Read-Hall (SRH) recombination via Zn-induced defect passivation. These carrier
transport enhancements directly explain the observed performance gains.