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Page 4 of 16 Dong et al. Energy Mater. 2026, 6, 600026

Sb Se films were washed with deionized water, dried under nitrogen flow, and annealed at 375 °C for 5 min
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in a nitrogen environment to enhance crystallinity. The hole transport layer was prepared by dissolving
36.6 mg of spiro-OMeTAD in 1 mL of chlorobenzene, followed by the addition of Li-TFSI acetonitrile
solution (9.5 μL, 520 mg mL ) and TBP (14.5 μL). The resultant solution (20 μL) was spin-coated onto the
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Sb Se layer.
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Calculation methods
First-principles computations based on density functional theory were performed using the Vienna Ab initio
Simulation Package (VASP). A 2 × 3 × 2 supercell (25.30 Å × 11.96 Å × 23.29 Å, 240 atoms) was constructed
using Γ-point sampling. Projector augmented-wave pseudopotentials were employed with a plane-wave
cutoff energy of 350 eV. Structural optimizations were carried out until residual forces on all atoms were less
than 0.001 eV Å . Based on PBE-optimized geometries, electronic structure computations were performed
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using the Heyd-Scuseria-Ernzerhof hybrid functional (HSE06). The valence band maximum of bulk Sb Se 3
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was set as the reference point for the Fermi level when evaluating defect production energies using existing
formalisms. For charged flaws, potential alignment and image-charge adjustments were incorporated.

Characterization
X-ray diffraction (XRD) of crystalline formations was performed using a Smart Apex II Duo diffractometer
(DMX2500, Cu-Kα, Rigaku Corporation, Japan). Surface morphology and roughness were assessed using
atomic force microscopy (AFM; Nano Man VS, Veeco, United States) and field-emission scanning electron
microscopy (FESEM; NOVA NANOSEM 4800, FEI Company, United States). Optical transmittance and
absorbance spectra were recorded with a UV-Vis spectrophotometer (UV-3600iPlus, Shimadzu Corporation,
Japan). Chemical composition and electronic structure were examined by X-ray photoelectron spectroscopy
(XPS; K-Alpha, Thermo Fisher Scientific, United States) and ultraviolet photoelectron spectroscopy (UPS;
PHI 5000 VersaProbe III, ULVAC-PHI, Inc., Japan). Surface conductivity was measured using Kelvin probe
force microscopy (KPFM; Dimension Icon, Bruker Corporation, United States). Current-voltage
characteristics under AM 1.5G illumination (100 mW cm ) were evaluated using a solar simulator
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(3A-94023A, Newport, United States) and a Keithley 2400 source meter (Keithley, United States). External
quantum efficiency (EQE) spectra were collected using a QEXL system (PV Measurements, United States).
Capacitance-voltage measurements in the dark at 25 °C and 10 kHz were conducted with a Keysight
E4980AL LCR meter (Keysight Technologies, United States). Electrochemical impedance spectroscopy (EIS)
was performed over a frequency range of 1 Hz to 4 MHz. Transient absorption spectroscopy (TAS) was
measured using a pump-probe system (Helios, Ultrafast Systems, United States).

RESULTS AND DISCUSSION
To address critical bottlenecks in Sb Se solar cells - namely insufficient crystallinity, high defect density, and
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suboptimal interfacial band alignment - an Nd-enabled ionic antisite diffusion strategy is proposed to
simultaneously optimize crystal growth and the heterojunction band structure. The working hypothesis is
that effective Nd incorporation can facilitate lattice-level doping and a more favorable band alignment,
thereby enhancing carrier transport, suppressing interfacial recombination, and improving device
performance. To validate this hypothesis, a standard FTO/CdS/Sb Se architecture was used as the
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experimental platform. In the control group, CdS films underwent Sb Se deposition and post-annealing
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without any pretreatment. In the Nd-treated group, CdS films were immersed in NdCl solutions with
3
varying concentrations and then annealed under identical thermal conditions to drive Nd diffusion and
incorporation. To quantitatively elucidate the role of Nd incorporation in regulating crystal-growth kinetics,
band-structure evolution, and carrier-transport behavior, systematic structural, optical, and electrical
characterizations were performed on both treated and untreated films and devices.