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Dong et al. Energy Mater. 2026, 6, 600026 Page 3 of 16

To address these challenges, we propose and experimentally validate an Nd doping strategy based on ionic
3+
antisite diffusion, enabling coordinated optimization of the crystal structure, interfacial electronic states, and
carrier dynamics of Sb Se thin films. Unlike conventional surface treatments or direct-doping approaches,
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this strategy combines Nd soaking on the CdS surface with a reverse-gradient diffusion process, allowing Nd
to penetrate the Sb Se bulk while avoiding significant lattice distortion or structural damage. Notably, the
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same process induces pronounced passivation within the CdS buffer layer, enabling synergistic regulation of
interfacial defect states, band bending, and interfacial barriers, thereby providing a conceptual pathway for
incorporating rare-earth ions into narrow-bandgap photovoltaic absorbers. The effectiveness of this strategy
is supported by the mutual corroboration of experimental results, first-principles calculations, and multiple
characterizations. Based on the synergistic optimization of structural and interfacial properties, the device
achieves a PCE of 9.17%, representing benchmark performance under comparable fabrication conditions.
Overall, the Nd -induced ionic antisite diffusion mechanism proposed in this work offers a new physical
3+
pathway and materials strategy for overcoming the performance bottlenecks of Sb Se devices.
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EXPERIMENTAL
Materials
Fluorine-doped tin oxide (FTO) glass substrates with an optical transmittance of around 80% and a sheet
resistance of 6 Ω/square were provided by Liaoning Advanced Electronic Technology Co., Ltd. (China).
Common organic solvents, including acetone (≥ 99.0%), isopropanol (≥ 99.7%), ethanol (≥ 95.0%), cadmium
sulfate hydrate (≥ 99.0%), aqueous ammonia (25%-28%), cadmium chloride hydrate (≥ 99.0%), thiourea
(≥ 99.0%), potassium antimony (III) L(+)-tartrate hemihydrate (≥ 99.0%), and sodium sulfite, were supplied
by Sinopharm Chemical Reagent Co., Ltd. (China). Selenourea (98%) was purchased from Sigma-Aldrich,
and elemental selenium powder was acquired from Beijing Loyaltarget Technology Co., Ltd.
4-tert-Butylpyridine (TBP, 96%), lithium bis (trifluoromethanesulfonyl)imide (Li-TFSI, 99%), and
spiro-OMeTAD (99.5%) were supplied by Advanced Electronic Technology Co., Ltd. (China). Acetonitrile
(99%) and chlorobenzene (99.5%) were purchased from Alfa Aesar. Neodymium (III) chloride hexahydrate
(99.9%) was obtained from Aladdin.

Fabrication of CdS film
FTO substrates (1.5 cm × 2.5 cm) were ultrasonically cleaned sequentially in glass-cleaning solution,
deionized water, isopropanol, acetone, and ethanol for 20 min each before film deposition. To enhance
surface cleanliness, ozone plasma treatment was applied to the substrates after they had dried. CdS electron
transport layers were deposited using chemical bath deposition. The deposition bath consisted of 20 mL of
CdSO solution (0.015 mol L ), thiourea solution (0.75 mol L ), NH OH solution (15.6 mol L ), and 140 mL
-1
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of deionized water. The pretreated FTO substrates were submerged in the bath and kept at 65 °C for 15 min.
Following deposition, the films underwent a thorough rinsing and nitrogen flow drying. For Nd
modification, the CdS-coated substrates were submerged in NdCl aqueous solutions at concentrations of
3
0.01, 0.03, 0.05, 0.07, or 0.10 mol L at 65 °C for 15 min, followed by washing and nitrogen drying. Finally,
-1
the films underwent a 10-min heat treatment at 400 °C.
Preparation of Sb 2 Se 3 layers and hole transport layer
Sb Se thin films were deposited directly on FTO/CdS substrates via chemical bath deposition. Potassium
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antimony tartrate (KSbC H O ·0.5H O) and Na Se SO were employed as the Sb and Se precursors,
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respectively. Thiourea (CH N S) or selenourea (CH N Se) was introduced as an additive to regulate film
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growth. Typically, 15 mmol of KSbC H O ·0.5H O was dissolved in 38 mL of deionized water under
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continuous stirring. Subsequently, either CH N S (2.62-10.51 mmol) or CH N Se (0.05-0.81 mmol), together
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with 2 mL of 0.1 M Na Se SO solution, was added. The FTO/CdS substrates were placed into the precursor
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2
solution, and the reaction was carried out in a thermostated water bath at 95 °C for 2 h. After deposition, the