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Xia et al. Energy Mater. 2026, 6, 600022 Page 5 of 13

Figure 1. Surface and cross-sectional morphologies of Sb 2 S 3 thin films (A) without ZnO and with ZnO deposited with (B) 20 s, (C) 40 s,
(D) 80 s, (E) 200 s and (F) 400 s. SEM: Scanning electron microscope; W/O: without ZnO.

To evaluate the photovoltaic impact of ZnO incorporation, Sb S solar cells were fabricated using a
2 3
hydrothermally deposited PbS HTL, paste-coated carbon and Ag contacts. The statistical results of the
average values of J-V measurements [Figure 2A and Table 1] show that the enhancement effect of the ZnO
modified devices is consistent. The V remained above 700 mV for all ZnO-treated samples, peaking at 40 s
oc
due to reduced Sb S degradation and minimized leakage pathways. The optimal 40 s ZnO condition
2 3
coincides with minimized resistive Sb O formation and improved bulk conductivity, facilitating efficient
3
2
carrier extraction. The J increased by 17% at 40 s ZnO (14.6 mA/cm ) compared to the control, then
2
sc
declined with thicker ZnO layers. Similarly, the FF reached an optimal average of 59% at 40 s, but dropped to
~50% at ≥ 80 s, consistent with increased series resistance and impeded hole transport from thicker ZnO
layers. Consequently, the highest PCE of 7.00% was attained under 40 s ZnO conditions (V = 729 mV, J =
sc
oc
15.6 mA/cm , FF = 61.5%), representing a 20% improvement over the unmodified reference device. Although
2
this device performance still lags behind that of Spiro-OMeTAD/metal electrodes and Sb S -based tandem
2 3
devices [17,18] , this study provides a practical strategy for the low-cost fabrication of solar cells employing
all-inorganic carbon electrodes.

X-ray diffraction (XRD) analysis [Figure 2B] verified the crystallographic composition of annealed films,
identifying orthorhombic Sb S (PDF#42-1393) as the dominant phase, with minor peaks corresponding to
2 3
cubic Sb O (PDF#71-0365). Notably, the intensity of the Sb O (222) peak at 27.68° decreased systematically
3
2
2
3
with longer ZnO deposition [Supplementary Figure 3A and B], indicating suppressed secondary oxide
formation. A weak ZnO (100) peak appeared only at 80 s ZnO, while no ZnO diffraction was detectable at
shorter deposition times (≤ 40 s), underscoring the ultrathin and amorphous nature of ZnO in those cases.
These results confirm that the ZnO interlayer effectively retards Sb O phase formation during air annealing.
3
2
To understand the origin of these enhancements, grazing-incidence XRD (GIXRD) at 2 incidence
o
[Supplementary Figure 4] revealed no residual ZnO phase in the 40 s ZnO film post-annealing, suggesting
Zn substitution within the Sb S or Sb O lattices. Detailed peak analysis [Figure 2C] showed systematic shifts
2 3
2
3
of major Sb S and Sb O peaks toward higher angles, consistent with lattice contraction per Bragg’s law
2 3
3
2
(d = λ/2sinθ). When larger Zn (134 pm) replaces Sb (140 pm), the smaller ionic radius causes lattice
2+
3+
contraction, which is the direct origin of the aforementioned peak shift. Further observation also reveals that