Antimony oxide buffer layer for single- and double-junction perovskite-based solar cells

Domain: biology
Published: 2026-03-25
Editorial outcome: major_revision

Abstract
Atomic layer-deposited tin oxide serves as an effective buffer layer in perovskite/silicon tandem solar cells due to its
efficient charge extraction and sputtering tolerance. Nevertheless, its unavoidable chemical erosion effect of atomic layer-
deposited tin oxide on perovskite requires thicker fullerene charge transport layers, leading to increased parasitic optical
absorption. Herein, we firstly integrated thermal evaporated antimony oxide into solar cells to effectively replace atomic
layer-deposited tin oxide, enabling a thinner fullerene to minimize optical losses and prevent damage to the perovskite.
The unique amorphous-nanocrystalline structure of, antimony oxide facilitates ultrafast carrier transport via its embedded
nanocrystalline network. The antimony oxide-based tandem solar cells demonstrated a significant improvement in power
conversion efficiency compared to tin oxide-based devices, primarily due to an enhanced short-circuit current density of
approximately 1 mA/cm² in the perovskite top cell. Remarkably, even at 64.64 cm2 scale, the antimony oxide-based
encapsulated large-area tandem solar cell retains an efficiency of 28.16% (with a certified value of 27.70%), attesting
the scalability of this approach.

Introduction
Monolithic perovskite/silicon tandem solar cells (PSTs) have emerged as highly promising photovoltaic devices,
demonstrating exceptional power conversion efficiency (PCE) with a certified value of 34.85%1. Nevertheless, the
considerable gap relative to the 42% theoretical limit points to critical unresolved losses in optical absorption and charge
carrier transport2. The engineered functional layers in light-facing front contact architectures, featuring controlled
nanoscale thickness3, present significant potential for improving photovoltaic performance through enhanced short-
circuit current density (J ).
SC
Currently, thermal evaporated (TE) fullerene (C ) and atomic layer deposited (ALD) tin oxide (SnO ) films are
60 X
widely used as electron transport layer (ETL) and buffer layer, respectively, in nearly all p-i-n structured PSTs 4-13.
However, the intrinsic ligand exchange reaction between tetrakis(dimethylamino)tin(IV) (TDMASn) precursor in ALD
and formamidinium (FA+) in the perovskite is one of the main sources of the collapse of perovskite structure14. Therefore,
it is essential to enhance the thickness and mechanical strength of C layer to avoid adverse erosion dominated by ALD-
60
SnO . However, this exacerbates the parasitic optical absorption at 300-550 nm wavelength which is a harbinger of the
X
current loss in PSTs15,16. Besides, the additional ALD technology further complicates the tandem solar cell fabrication
equipment. Thus, it is urgently desirable to develop a gentler technology to prepare the buffer layer to overcome the
drawbacks of state-of-the-art SnO .
X
Herein, we firstly developed TE-antimony oxide (Sb O ) film as an innovative alternative to ALD-SnO for buffer
2 3 X
layer applications. Through comprehensive characterization, we identified an amorphous-nanocrystalline hybrid
structure in the Sb O film and elucidated its unique electron transport mechanism, mediated by percolating
2 3
nanocrystalline channels. Compared to ALD-SnO , TE-Sb O demonstrates superior process window and minimized
X 2 3
adverse effects on perovskite materials. This enhanced compatibility enables the reduction of the C layer thickness
60
from 15 to 5 nm without compromising perovskite device performance. Consequently, the C /Sb O stacked functional
60 2 3
layer achieves both excellent carrier extraction efficiency and minimized optical parasitic absorption losses. We
employed a vacuum-solution hybrid deposition method to fabricate perovskite films with tunable bandgaps (1.59, 1.62,
1.64 and 1.68 eV) and integrated an ultra-thin C /Sb O film into perovskite solar cells (PSCs), demonstrating universal
60 2 3
bandgap applicability. The 1.64 eV-bandgap PSCs achieved a champion PCE of 23.18%, comparable to that of SnO -
X
based PSCs (23.17%). Notably, the 23.18% PCE achieved here represents the highest reported value for mid-/wide-
bandgap PSCs fabricated using a vacuum-solution hybrid method. Furthermore, Sb O -based PSTs exhibited an
2 3
enhanced PCE of 30.28% with an aperture area of 1.0 cm², compared to the 28.59% efficiency of SnO -based PSTs,
X
primarily due to a J improvement of ~1 mA/cm². The scalability of this approach was successfully demonstrated
SC
through the fabrication of 64.64 cm² encapsulated PSTs, which achieved a certified PCE of 27.70%—ranking among the
highest reported efficiencies for larger-area PSTs (>10 cm²) in the literature.

Results
Antimony oxide thin film
Materials located at the junction of metallic and non-metallic elements in the periodic table are typically used as
functional layers in semiconductor devices. N-type metal oxides, e.g. SnO and titanium oxide (TiO )17, have been
X X
widely applied in perovskite-based tandem solar cells. However, the high melting points of most metal oxides complicate
their preparation via TE (Supplementary Table 1). In contrast, Sb O is an n-type semiconductor with a low sublimation
2 3
temperature (~490 ℃ under ambient pressure), owing to its molecular crystal structure18. Given this unique advantage,
we proposed to prepare Sb O film with evaporation method, as shown in Figure 1a.
2 3
Atomic force microscope (AFM) image based on Sb O shows a flat and homogenous morphology at the
2 3
micrometer scale, without discernible voids or bumps (Supplementary Figure 1). The morphology of 15 nm Sb O
2 3
coated on perovskite (PVK)/C multilayer further validates its homogeneity and flatness by scanning electron
60
microscope (SEM) and AFM (Supplementary Figures 2-3). However, only 5 nm Sb O fails to fully cover the substrate
2 3
(Supplementary Figure 3). Transmission electron microscope (TREM) and X-ray diffraction (XRD) measurements
indicate that the Sb O forms an amorphous-nanocrystalline film19,20 (Figure 1b-c, Supplementary Figure 4). The
2 3
nanocrystalline structure was identified as cubic with an interplanar spacing of d=3.2 Å. The XRD data further reveals
that the crystallites are preferentially oriented with the (222) planes parallel to the glass substrate21,22.
To investigate the vertical conductivity of Sb O , we performed conductive atomic force microscopy (c-AFM),
2 3
applying a 3 V bias to the longitudinal side of silicon/Sb O 23 (Figure 1d-f). The c-AFM mapping clearly distinguishes
2 3
between amorphous and nanocrystalline regions in the Sb O layer (Figure 1e). Our findings demonstrate that the
2 3
nanocrystalline regions enable vertical conduction, whereas the amorphous regions remain insulation (Figure 1f).
Complementary lateral c-AFAM measurements further reveal poor lateral conductivity in Sb O in Supplementary
2 3
Figure 5. These results suggest that the nanocrystals can serve as conductive channels for longitudinal electrical transport,
making the Sb O potentially suitable as a buffer layer (Figure 1g). However, as a wide-bandgap material (~4.25 eV),
2 3
Sb O tends to form high energy barriers at interface (Supplementary Figure 6). We found that the presence of Sb-
2 3
interstitial-induced defects generates a quasi-continuum of gap states in Sb O nanocrystalline (Supplementary Notes
2 3
1, 2 and Supplementary Figures 7-13). These states form a conductive pathway across the interface, allowing electrons
to traverse the barrier via defect-mediated transport.
Cross-sectional TEM of the PVK/C /Sb O /indium zinc oxide (IZO) structure was performed to investigate the
60 2 3
interlayer behavior of Sb O (Figure 1h and Supplementary Figures 14-15). A uniform 15 nm Sb O film exhibits
2 3 2 3
favorable interfacial contact with the amorphous C , owing to their low mutual chemical reactivity and residual stress
60
(Supplementary Note 3 and Supplementary Figures 15-17). Notably, energy dispersive spectrometer (EDS) mapping
confirms a well-defined layer structure and reveals negligible indium diffusion into the underlying layers, displaying the
qualified sputtering tolerance of the Sb O film (Figure 1h and Supplementary Figure 14). As shown in
2 3
Supplementary Figure 15, the nanocrystalline also exhibits a cubic structure, aligning with the planar TEM and XRD
results (Figure 1b-c). The structural stability also indicates its excellent sputtering tolerance and simple physic contact
style with C layer via van der Waals forces. Furthermore, we conducted dark photocurrent density-voltage (J-V) tests
60
with device structure of ITO/Me-4PACz/PVK/C /with or without Sb O /IZO/Al (Supplementary Figure 18). The
60 2 3
Sb O sample exhibits weaker leakage current, proving the excellent sputtering tolerance of Sb O 24.
2 3 2 3

Buffer layer in PSCs
We applied Sb O and SnO as buffer layer in p-i-n PSCs (Figure 2a), respectively, utilizing triple-cation
2 3 X
Cs (MA FA )Pb(I Br ) perovskite with a bandgap of 1.64 eV fabricated via vacuum-solution hybrid method.
0.05 0.05 0.95 0.88 0.12 3
Notably, the configuration represents the first implementation of Sb O as a charge-transport layer in photovoltaics. We
2 3
modulated the C thickness via fixing the metal oxide thickness to 15 nm, as shown in Figure 2b and Supplementary
60
Figure 19. The result of PV parameter distribution reveals a performance degradation with thinner C in the SnO -
60 X
based PSCs, marked by a sharp drop in fill factor (FF) at 5 nm. We attribute this primarily to the ligand exchange reaction
between the TDMASn precursor and the perovskite (Supplementary Note 4 and Supplementary Figures 20-22).
Besides, the 15 nm C layer functions as an effective barrier, preventing the irreversible interfacial reaction in the SnO -
60 X
based PSCs. In contrast, the Sb O -based PSCs present a broader process window for C thickness, owing to the non-
2 3 60
destructive nature of TE-Sb O .
2 3
The Sb O thickness is further adjusted to 15 nm by using 5 nm C . We observed poor performance and repeatability
2 3 60
for 5 nm Sb O samples (Supplementary Figure 23), which is ascribed to leakage current induced by non-denser 5 nm
2 3
Sb O (Supplementary Figure 3). From reverse-scan J-V curve (Figure 2c), the champion PSC, using 5 nm C and 15
2 3 60
nm Sb O , obtains a PCE of 23.18% with open-circuit voltage (V ) of 1.227 V, J of 22.34 mA/cm-2 and FF of 84.55%,
2 3 OC SC
which has similar PV parameter with 23.17% of champion PSC with 15 nm C and 15 nm SnO . Amazingly, the PCE
60 X
marks the highest efficiency reported for mid/wide-bandgap PSCs using vacuum-solution hybrid method6,25-39. The
stabilized power output (SPO) of the champion PSCs with SnO and Sb O also can be maintained at 22.74 and 23.02%
X 2 3
after 600 s maximum power point (MPP) tracking, respectively (Figure 2d). It illustrates that the Sb O samples used
2 3
by thin C layer still have excellent photovoltaic performance. We assess its universality via fabricated PSCs with 1.59,
60
1.62 and 1.68 eV-bandgaps perovskite absorbers. The 1.59, 1.62, 1.68 eV-bandgaps PSCs deliver notable performance
with champion PCEs of 22.28, 22.50 and 22.29%, respectively (Figure 2e and Supplementary Table 2), which are also
among the highest PCE for the hybrid deposited PSCs6,25-39, as shown in Figure 2f and Supplementary Table 3. All
cells have achieved prominent FF, showing excellent generality in gently nature of Sb O . As shown in Supplementary
2 3
Figure 24, the integrated J from the external quantum efficiency (EQE) spectra of PSCs with 1.59, 1.62, 1.64 and 1.68
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eV-bandgaps matched well with the J values from J-V curves (Figure 2c, 2e).
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To gain a deep insight in the electrical transport mechanism of Sb O , the transient photocurrent (TPC) and transient
2 3
photovoltage (TPV) measurements were performed in Figure 2g-h. The comparable photoelectron lifetimes of SnO
X
and Sb O -based PSCs confirm the excellent efficiency of the defect-assisted carrier mechanism in Sb O . The similar
2 3 2 3
photovoltage lifetimes of them indicates that the defect-assisted transport enables efficient charge extraction without
introducing additional non-radiative recombination.

Optical benefit in PSTs
To verify the adaptability of Sb O in PSTs, we integrated the Sb O film in 1 cm2 PSTs, which manufactured double-
2 3 2 3
textured silicon heterojunction bottom cells and p-i-n structured perovskite top cells with 1.64 eV of bandgap (Figure
3a and Supplementary Figure 25).
Based on the electrical feasibility in single junction devices (Figure 2b), we fabricated PSTs by varying the
thickness of C layers while fixing 15 nm Sb O film. For direct comparison, control devices with 15 nm C and 15 nm
60 2 3 60
SnO were prepared under identical conditions. The performance statistics of PSTs are summarized in Figure 3b-c and
X
Supplementary Figure 26, wherein the gradually increased J with thinning C for the tandem devices with Sb O ,
SC 60 2 3
and more enhanced J than the tandem device with SnO can be observed, facilitating to improving PCE. Among, the
SC X
champion tandem device with Sb O display a reverse-scan PCE of up to 30.28%, with a higher J of 20.26 mA/cm2
2 3 SC
than that of tandem device with SnO (19.22 mA/cm2), and almost the same V of 1.894 V and FF of 78.67% (Figure
X OC
3d and Supplementary Table 4). The SPO of 30.1% was also recorded after 2400 s MPP tracking (Figure 3e).
Further, we conducted EQE and ultraviolet-visible (UV-vis) measurements to explain the reason of improving J
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and colour difference in aperture area (Figure 3f-g and Supplementary Figures 27-28). The UV-vis shows reflection,
transmittance and absorbance spectra of different thicknesses of C . We detected that the average transmission (T )
60 avg
decreases from 81.17 to 63.87% in the wavelength range from 300 to 560 nm, with increasing C film thickness from 5
60
to 15 nm. As expected, the intensity of absorption increases with increasing film thickness. Therefore, the stronger EQE
response of top sub-cell at the 300-560 nm wavelength is exhibited with thinning C film, resulting in a higher
60
photocurrent of 20.45 mA/cm2 for C (5 nm)/Sb O tandem device of top sub-cell and well-matched photocurrent of
60 2 3
20.54 mA/cm2 for bottom sub-cell (Figure 3f). Next, UV-vis was employed to investigate the optical properties of
C /SnO and C /Sb O stacks (Figure 3g and Supplementary Figure 28). The C (5 nm)/Sb O (15 nm) sample
60 X 60 2 3 60 2 3
shows an T of 74.85%, exceeding that of PVK/C (15 nm)/SnO (15 nm) sample (62.68%) in the wavelength range
avg 60 X
from 300 to 560 nm. Similarly, the intensity of absorption for C (5 nm)/Sb O (15 nm) sample is lower than C (15
60 2 3 60
nm)/SnO (15 nm) sample, suggesting the achievement of lower parasitic light absorption by thinning C .
X 60
To evaluate devices stability under operational conditions (Supplementary Note 5 and Supplementary Figures
29-39), we performed MPP tracking on encapsulated Sb O -based PST (Figure 3h). After 500 h under white light
2 3
emitting diode (LED) illumination (100 mW/cm2), The Sb O -based device exhibited negligible efficiency degradation.
2 3
Furthermore, both encapsulated devices conducted the accelerated aging tests (LED illumination or 65 °C over 1000 h),
retained over 90% of their initial PCE (Supplementary Figures 37-38).

Application in encapsulated large-area PSTs
Scaling up aperture area in tandem devices represent a necessary trend for commercial development. To examine the
homogeneity of Sb O , we deposited a 45 nm Sb O film on a 10×10 cm2 glass substrate, which was subsequently divide
2 3 2 3
it into 25 sub-samples, each measuring 2×2 cm2 (Figure 4a). The results indicate nearly identical thickness across all
samples, revealing superior uniformity of the large-area Sb O film deposition in a 100 cm2 region (Figure 4b and
2 3
Supplementary Figure 40). Besides, we further selected five representative positions to verify the uniformity of C
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and the thinner Sb O (15 nm) layers (Supplementary Note 6 and Supplementary Figures 41-43, Supplementary
2 3
Table 5). The normalized PCE distribution of 100 sub-cells on a 10×10 cm2 substrate was also shown in Figure 4c.
Similarly, we fabricated Sb O films as buffer layer in 100 sub-cells, adopting the device structure illustrated in Figure
2 3
2a. The high similarity of the PCE for all sub-cells further proves the homogeneity of Sb O film.
2 3
Furthermore, we used vacuum-solution hybrid method to fabricate 110.25 cm2 encapsulated PSTs with an aperture
of 64.64 cm2 and achieved an enhanced PCE from 27.29 to 28.16% for Sb O -based PST, which is attributed to an
2 3
improvement of J from 18.61 to 18.96 mA/cm2 (Figure 4d, Supplementary Figure 44 and Supplementary Table 6).
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Crucially, The PCE of 28.16% is currently among the highest PCE for larger-area PSTs with the aperture area over 10
cm2 in published literature33,39-49 (Figure 4e and Supplementary Table 7). Moreover, the encapsulated large-area PST
was further certified by a third party (National Institute of Metrology) showed a reverse-scan PCE of 27.70%
(Supplementary Figure 45). Furthermore, a SPO of 27.66% was confirmed following 1800 s of stabilization at the MPP
(Supplementary Figure 46). In addition, the process demonstrates excellent reproducibility across multiple independent
fabrication, indicating promising scalability (Supplementary Note 7, Supplementary Figure 47 and Supplementary
Table 8). Notably, the development of Sb O achieves dual breakthroughs in performance and cost, which reduces
2 3
fabrication cost to ~70% of conventional ALD-SnO , demonstrating significant commercial potential (Supplementary
X
Note 8 and Supplementary Table 9).

Methods
Materials
Me-4PACz (>99%) and C were purchased from Lumtec. Ethanol (99.5% anhydrous) and isopropyl alcohol (IPA) (99.5%
60
anhydrous) were purchased from Alfa Aesar. Lead iodide (PbI , >99.99%) and antimony trioxide (Sb O , >99.9%) were
2 2 3
purchased from Sigma-Aldrich. Formamidine bromide (FABr), formamidine iodide (FAI), methylamine hydrochloride
(MACl), Cesium chloride (CsCl), 4-fluorobenzylamine hydroiodide (F-PMAI) and 1,3-propanediammonium iodide
(PDADI) were purchased from Xi’an Polymer Light Technology (China).

Fabrication of Silicon Bottom Cells
We employed a fabrication process for the silicon heterojunction (SHJ) bottom cell that closely followed established
methods reported in the literature5. The procedure is as follows: an n-type <100> CZ Si wafer with a resistivity of 1–5
Ω·cm was used. An initial etching step was conducted to remove saw damage and polish the wafer. Subsequently, both
the front and rear surfaces of the wafer were mildly textured using a relatively low-concentration alkaline solution to
ensure uniform small-pyramid structures with a size of 300–500 nm on both sides. After standard cleaning and a hydrogen
fluoride dip, hydrogenated intrinsic amorphous silicon layers (~5 nm thick) were deposited on both sides. Then, an n-
type hydrogenated nanocrystalline silicon oxide layer (~15 nm) and a p-type hydrogenated nanocrystalline silicon (nc-
Si:H) layer (~20 nm) were deposited on the front and rear, respectively. To complete the bottom cell, an 80-nm-thick
In O -based transparent conductive oxide followed by silver was deposited on the rear, while a 10-nm-thick TCO film
2 3
was deposited on the front. The electrode area was 1.1 × 1.1 cm2, and the silicon cells were laser-cut to 2.03 × 2.03 cm2
substrates for tandem fabrication.

Fabrication of Single-junction PSCs
The single-junction devices were fabricated with the structure: ITO/Me-4PACz/Perovskite/PDADI/C /SnO or
60 X
Sb O /Al. Glass substrates with ITO coating were cleaned with three solvents in the sequence of deionized water, acetone,
2 3
and ethanol. The Me-4PACz solution in ethanol solution was spin-coated at 3000 rpm for 30 s, following an annealing
treatment at 100 ℃ for 10 min in N glovebox. Then, the Me-4PACz film was clean up via spin-coating 100 µL ethanol
2
at 5000 rpm for 30 s. CsCl was evaporated in a Lesker mini Spectros system chamber (working pressure <5×10-6 mbar,
evaporation rates of 0.4 Å/s). Next, PbI was co-evaporated with CsCl to form inorganic precursor in same chamber
2
(working pressure <5×10-6 mbar, evaporation rates of 2 Å/s for PbI and of 0.1 Å/s for CsCl). The substrate temperature
2
was kept at 30 ℃. Subsequently, a solution of FABr and FAI with different molar ratio of 1:5.2, 4.6, 1.5, 0.8 (bandgaps
of 1.59, 1.62, 1.64, 1.68 eV) dissolved in ethanol and containing 10 mol% of MACl and 5 mol% of F-PMAI, was spin-
coated at 5000 rpm for 30 s in N glovebox, following by the annealing step at 150 ℃ for 20 min in ambient air with a
2
30-35% humidity. PDADI dissolved in IPA (1 mg mL-1) was spin-coated onto perovskite layer at 5000 rpm for 30 s,
following an annealing treatment at 100 ℃ for 5 min in N glovebox. Afterward, different thicknesses of C (5, 10, 15
2 60
nm) and of Sb O (5, 15, 25 nm) were sequentially evaporated in a homemade evaporation system to fabricate Sb O -
2 3 2 3
based PSCs (working pressure <5×10-6 mbar, substrate holder at 30 ℃). For the PSCs with SnO , the Sb O is replaced
x 2 3
by 15 nm SnO through ALD at 80 ℃ using TDMASn and hydrogen peroxide as precursors. Finally, the metal grids
x
were fabricated by depositing a 80 nm thick layer of Al (Angstrom Engineering) through thermal evaporation, using a
shadow mask. Besides, the active area was 0.0755 cm2 for single-junction devices.

Fabrication of PSTs
20 nm nickel oxide (NiO ) layer was sputtered using a nickle target at room temperature in pure Ar at 80 W to cap the
X
ITO recombination layer on the top of SHJ bottom cells. Then, Me-4PACz, perovskite, PDADI, C and Sb O or are
60 2 3
deposited on NiO substrate using same process as the single-junction PSCs, where the perovskite with 1.64 eV bandgap
X
is used in small-area tandem devices (1 cm2), the perovskite with 1.59 eV bandgap is used in large-area tandem devices
(64.64 cm2). Subsequently, 50 nm of IZO transparent electrode was sputtered in a Lesker sputtering system using a 6-in.
target (90% In O and 10% ZnO) with a radio frequency power of 38 W (sheet resistance of 40 Ω/sq). Afterward, 200
2 3
nm of Ag was evaporated through a shadow mask to form the metal electrode for small-area tandem devices (1 cm2),
and the screen-printing metal grids instead of the evaporated Ag electrode for large-area tandem devices (64.64 cm2),
following the curing of silver paste was annealing at 85 °C for 20 min.

Device Characterization
J-V curves of single-junction PSCs and tandem solar cells were measured by a Keithley 2400 Source meter under Enli
Solar Simulator (AM 1.5G, 100 mW cm-2), calibrated by a standard silicon reference cell. The devices were measured
with a scan rate of 20 mV/s, the voltage step of 0.02 V, and delay time of 40 ms. During the J-V test, shadow masks with
area of 0.0755 cm2 for single-junction and of 1 or 64.64 cm2 for tandem solar cells were used, respectively. EQE of
single-junction PSCs were measured using an Enli Tec (Taiwan) system. For tandem solar cells, EQE spectra were
measured by a QEX10 PV Measurement system in the wavelength from 300 to 1200 nm with a scanning rate of 10 nm.
SPO was measured in N glovebox at room temperature with multichannel system (Enli. Tech.) under AM 1.5G
2
illumination by a xenon-lamp. Device stability was evaluated through aging tests under LED illumination using a high-
power LED light source system (CEL-LED100HA-96, AuLight) and full-spectrum AM 1.5G illumination provided by a
xenon lamp solar simulator (FG-MN001-ACA-AM1.5G-100, FengGuan), each calibrated to 100 mW/cm2. Encapsulated
tandem devices were subjected to continuous light soaking at ~40 °C under both illumination conditions, with periodic
J-V measurements to track the evolution of MPP efficiency over time.

Other Characterization:
XPS and UPS were performed by Thermo Scientific ESCALAB 250Xi spectrometer. UV-vis spectra was carried out
through a Varian Cary 500 spectrophotometer. SEM images was characterized by FEINanoSEM650 with an acceleration
voltage of 1 kV. AFM, kelvin probe force microscopy (KPFM) and c-AFM tested by Bruker Dimension Icon with Pt/Ir
coated conductive probes. Grazing-incidence X-ray diffraction (GIXRD) patterns of films were obtained by a
multifunctional diffractometer (Rigaku, ATX-XRD) with Cu Kα radiation (λ=1.5405 Å). The cross-sectional TEM
samples were prepared using a focused ion beam (FIB) lift-out technique on a ZEISS Crossbeam 540 FIB-SEM system.
TEM imaging and selected area electron diffraction analysis were performed using an FEI Tecnai F20 field-emission
transmission electron microscope operating at an acceleration voltage of 200 kV. Dark J-V curve measurement was
conducted in dark in dark by Keithley 2400 Source meter at a scan rate of 20 mV/s with a delay time of 20 ms, where
the bias scan ranged from -2 to 2 V. TPC and TPV were obtained with a digital oscilloscope (DOS-X 304A).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript investigates the application of antimony trioxide (Sb₂O₃) thin films as buffer layers in perovskite/silicon tandem solar cells, comparing them with conventional atomic layer deposition-based tin oxide (SnOₓ). The findings indicate that Sb₂O₃ thin films exhibit excellent optical transmittance, high sputtering resistance, and compatibility with ultrathin C60, effectively reducing optical parasitic losses and enhancing device performance. Overall, the concepts and results presented herein are promising. Reducing the optical parasitic absorption of functional layers has been a significant research direction in this field; however, several issues require further consideration:\n1. Given the proximity of the constituent oxides in the periodic table, what is the underlying mechanism of perovskite film chemical etching by SnOₓ? Moreover, what mechanism allows Sb₂O₃ to resist such chemical etching?\n2. Does the thermal evaporation of Sb₂O₃ result in the formation of metallic antimony? The presence of metallic antimony could potentially contribute to the n-type characteristics of Sb₂O₃.\n3. Based on the current experimental data, the amorphous-nanocrystalline vertical conduction mode in Sb₂O₃ is not entirely convincing. Could the authors provide additional supporting evidence?\n4. Reducing the fullerene thickness is crucial for minimizing optical parasitic absorption. However, what is the coverage of a 5 nm C60 layer? Does this affect electron extraction efficiency?\n5. Figure S8 contains a clear error; please review it thoroughly. Additionally, the valence band edge truncation in Figure S6 appears questionable. It is recommended to increase the number of experimental samples to ensure statistically robust results.\n6. Since the primary advantage of Sb₂O₃ over SnOₓ in this study is the reduced chemical etching of perovskite films, the results of various stability tests are critical. Stability data under continuous illumination at maximum power point tracking, temperature, and electrical bias should be included for devices incorporating Sb₂O₃ buffer layers, along with appropriate explanations.", "reviewer_2": "This work reports a promising strategy of replacing ALD-deposited SnOx layer with an Sb2O3 layer to reduce optical losses in the C60/SnOx stacked layer. This approach reduces the thickness of the C60 layer, decreases the parasitic absorption and finally increases the Jsc, and protects the perovskite layer. This strategy is universal to a broad range of perovskite solar cells with various bandgaps and to large-area tandem solar cells. This work is of great interest and significance to the community of perovskite single-junction and tandem solar cells, especially this work provides an alternative thermal evaporation deposition technique to the existing ALD technique, which could reduce the fabrication cost. Therefore, I would recommend publication of this manuscript after addressing the following minor issues.\n(1) As well known, C60 could increase the fabrication cost of perovskite solar cells. Completely substituting C60 seems a great challenge for perovskite solar cells. Could the authors comment on whether Sb2O3 can replace C60 and work as an ETL in tandem cells?\n(2) The authors claim that the higher mobility of Sb2O3 is attributed to more favorable energy level alignment. Please explain more on this.\n(3) In Figure 2d and 2f, please clarify the voltage scan direction. In Figure 2h, please clarify what the current densities correspond to.\n(4) Section 5 of Page 10: to examine the homogeneity of Sb2O3, the authors deposited a 45 nm Sb2O3 layer on 10×10 cm2 glass substrate. Could the authors comment on uniformity of the 15 nm thick Sb2O3 for scaling up cells?\n(5) Page 8: to evaluate the optical benefits of Sb2O3 layer and reduced C60 thickness, the authors should compare the average transmittance of C60/Sb2O3 and C60/SnOx stacked layers.", "reviewer_3": "Shi et al. introduce an antimony oxide as buffer layer for perovskite based single junction and tandem solar cells. This approach enhances the power conversion efficiency (PCE) and stability of perovskite/silicon tandem cells. The optimized tandem device achieves a PCE of 30.1%. These results underscore the strategy’s potential for industrial-scale applications. However, the stability and efficiency of the devices in the article is not that impressive to garentee its publicaiton in Nature Communications. Overall, this work demonstrates interesting result with good material design. Therefore, I recommend this paper to be reconsidered after revisions and suggest some points for further improvement.\n1. The maximum power point testing should be incorporated in the manuscript with certain duration. Additionally, post-aging microstructural analysis using SEM, XRD and TOF-SIMS should be applied correspondingly.\n2. The TEM image in Fig. 1g appears blurred, and the interfaces are difficult to distinguish. A low-magnification TEM image should be provided to clearly demonstrate the long-range behavior of the interlayer.\n3. The AFM results show that the RMS roughness decreases after Sb2O3 deposition compared to the reference film. Does this imply that Sb2O3 does not form a uniformly coverage?\n4. The explanation of the electron transfer mechanism remains unclear. Additional characterizations are necessary to elucidate the underlying charge transfer behavior in the Sb2O3 layer.\n5. The nature of the Sb2O3/C60 interface is not well defined. It should be clarified whether the interface is governed by simple physical contact or involves specific chemical interactions.\n6. It should be specified whether the XPS and UPS measurements were conducted on the Sb2O3 film alone or on the C60/Sb2O3 stack, considering the limited detection depth of these techniques. Any potential band bending effects at the interface should also be discussed.\n7. Although the IZO layer thickness is claimed to exceed 50 nm, it is not clearly visible in the SEM image of the perovskite/IZO film. TOF-SIMS measurements may provide more insightful information to correlate potential IZO damage with changes in the perovskite morphology.\n8. The reference device employing a SnO2 buffer layer shows a PCE of only ~28%, which is noticeably lower than previously reported values from the same research group. The reason for this performance decline should be clarified.\n9. The intrinsic stability of the Sb2O3 layer has not been discussed. Additionally, its potential impact on the long-term stability (under thermal treatment, light illumination, and moisture) of the underlying perovskite film remains unclear and should be addressed.\n10. Related to 9, the device stability under various stresses should also be addressed. At least, for the single junction devices.\n11. The mechanical toughness of the developed interface remains unclear. Additional analysis is needed to evaluate its resistance to delamination or mechanical stress, particularly in the context of scalable device fabrication and long-term operation.\n12. The manuscript lacks a detailed comparison with other potential buffer layer materials that are frequently used. A discussion on how Sb2O3 performs relative to these commonly used alternatives would strengthen the manuscript.\n13. A thorough evaluation, supported by quantitative data, is necessary to assess the economic and technical feasibility of implementing the Sb2O3 interlayer in large-scale manufacturing, especially in comparison with commonly adopted strategies.\n14. For the certification of the large-area tandem device, data on hysteresis behavior and steady-state power output are missing. These measurements are essential to validate the reliability and performance consistency of the device.\n15. The device performance results using different bandgaps perovskites primarily serve to demonstrate generality and would be more appropriate in the Supplementary Information. In contrast, the comparison of electronic properties should be presented in the main manuscript to support the core scientific discussion.\n16. The light stability results show no significant difference between the SnO2- and Sb2O3-based tandem devices. If SnO2 were causing substantial damage to the perovskite surface, a corresponding impact on device stability would be expected. This apparent inconsistency should be addressed and clarified."}, "author_response": "Point-by-point response to the reviewer comments\nReviewer #1 (Remarks to the Author):\nThis manuscript investigates the application of antimony trioxide (Sb O ) thin films as buffer layers in\n2 3\nperovskite/silicon tandem solar cells, comparing them with conventional atomic layer deposition-based\ntin oxide (SnO ). The findings indicate that Sb O thin films exhibit excellent optical transmittance, high\nX 2 3\nsputtering resistance, and compatibility with ultrathin C , effectively reducing optical parasitic losses\n60\nand enhancing device performance. Overall, the concepts and results presented herein are promising.\nReducing the optical parasitic absorption of functional layers has been a significant research direction in\nthis field; however, several issues require further consideration:\nComment #1. Given the proximity of the constituent oxides in the periodic table, what is the underlying\nmechanism of perovskite film chemical etching by SnO ? Moreover, what mechanism allows Sb O to\nX 2 3\nresist such chemical etching?\nResponse: Thank you for the valuable comments. ALD-SnO is typically fabricated using TDMASn and H O\nX 2\nas precursors. The whole ALD process involves a high-temperature and water-rich environment, which is\nextremely unfavorable to perovskite. Critically, the TDMASn precursor undergoes a severe ligand exchange\nreaction with the perovskite, driven by the displacement of its dimethylamine groups by formamidinium ions1.\nAs evidenced by the N 1s XPS spectrum (Fig. R1), the emergence of a distinct peak at ~398.5 eV alongside the\ncharacteristic perovskite signal at ~400.6 eV confirms the formation of reduced nitrogen species via Sn–N\nbonding.2,3. In addition, the emergence of PbI characteristic peak confirms this result in the XRD pattern (Fig.\n2 3\nwithout complex precursors or post-deposition annealing. This inherent simplicity prevents any chemical\ninteraction with the perovskite layer, as confirmed by XPS and XRD results (Fig. R1-2).\nFig. R1 XPS spectra of N 1s, I 3d, Pb 4f, Sb 3d, Sn 3d core levels for the pristine PVK and PVK/SnO or Sb O .\nX 2 3\nFig. R2 XRD patterns of pristine PVK and PVK/SnO or Sb O . at different incidence angles (θ =0.3, 0.4 and\nX 2 3 inc\n1°).\nReferences\nphotovoltaics. Advanced Energy Materials 8, 1800591 (2018).\nhttps://doi.org/10.1002/aenm.201800591\nfilms. Journal of Alloys and Compounds 604, 106-111 (2014).\nhttps://doi.org/10.1016/j.jallcom.2014.03.098\nx\ndynamics, interface chemistry, and solar cell performance. ACS Applied Energy Materials 4, 510-522\n(2021). https://doi.org/10.1021/acsaem.0c02405\nNature Electronics 4, 906-913 (2021). https://doi.org/10.1038/s41928-021-00683-w\nComment #2. Does the thermal evaporation of Sb O result in the formation of metallic antimony? The\n2 3\npresence of metallic antimony could potentially contribute to the n-type characteristics of Sb O .\n2 3\nResponse: Thank you for the valuable comments regarding the potential formation of metallic antimony (Sb0)\nand its contribution in the n-type character for Sb O film. Our XPS data confirm the presence of a small fraction\n2 3\n(~4%) of a Sb0 (Fig. R3). However, it is unlikely in the form of segregated metallic nanocrystals. The key basis\nis described as follows:\nOur XRD and TEM results show no evidence of crystalline Sb0 phases (Fig. R4 and R5). Crucially, the\nspatial extent of conductive channels revealed by longitudinal c-AFM significantly surpasses 4% (Fig. R6).\nThese results suggests that the limited quantity of Sb0 atoms does not form a continuous metallic phase but may\ninstead contribute to electronic transport in a more localized manner.\nIn subsequent analysis, we confirm that some of the Sb0 can incorporate into the Sb O nanocrystal lattice\n2 3\nas interstitial defects (I ), which may play a critical role in facilitating charge transport across the film, as\nSb\ndetailed in our response to Comment #3.\nFig. R3 XPS spectrum of Sb 3d of Sb O film.\n3/2 2 3\nFig. R4 TEM images of Sb O film.\n2 3\nFig. R5 XRD spectrum of Sb O film.\n2 3\nFig. R6 AFM and corresponding c-AFM images of the Sb O film under a bias voltage of 3 V.\n2 3\nReferences\nantimony oxide films by ellipsometry and XPS. Journal of Electroanalytical Chemistry 645, 143-148\n(2010). https://doi.org/10.1016/j.jelechem.2010.04.023\nComment #3. Based on the current experimental data, the amorphous-nanocrystalline vertical\nconduction mode in Sb O is not entirely convincing. Could the authors provide additional supporting\n2 3\nevidence?\nResponse: Thank you for the valuable comments. We have systematically investigated the conduction\nmechanism in thermally evaporated Sb O films by integrating structural, electrical, and energy-level analyses,\n2 3\nwhich collectively support a defect-mediated transport model through embedded nanocrystals.\nStructurally, TEM and XRD confirm that the Sb O consists of α-Sb O nanocrystals embedded within an\n2 3 2 3\namorphous film without Sb nanocrystals (Fig. R4-5). This provides direct structural evidence for the existence\nof \"nanocrystalline pathways\" at the microscopic level.\nElectrically, the longitudinal c-AFM image reveals that the current does not flow uniformly but is\nconcentrated at numerous discrete \"hotspots\" associated with these nanocrystals (Fig. R6). Furthermore, the\nsingle-junction solar cells with the structure of ITO/Me-4PACz/Perovskite/C /Sb O /Al maintains excellent\n60 2 3\nperformance across a wide range of Sb O thickness from 15 to 25 nm (Fig. R7).\n2 3\nFig. R7 Statistics of PCE, V , J and FF of the PSCs with different Sb O thicknesses.\nOC SC 2 3\nDespite being a wide-bandgap material (~4.25 eV, Fig. R8) that creates a substantial interfacial energy\nbarrier of ~1.2 eV at the C /Sb O interface (as revealed by UPS, Fig. R9), Sb O still allows efficient electron\n60 2 3 2 3\ninjection across thick layers. Besides, UV–Vis spectra of 100 nm Sb O show significant sub-bandgap\n2 3\nabsorption, indicating abundant in-gap states (Fig. R10). These results rule out quantum tunneling5 or\nhomogeneous amorphous conduction6, possibly indicating an efficient defect-assisted and nanocrystal-\nmediated percolative transport mode.\nFig. R8 Tauc-plot of Sb O film.\n2 3\nFig. R9 UPS spectra of C and Sb O films.\n60 2 3\nFig. R10 UV-vis absorption spectra of 100 nm Sb O films under different processing conditions: (i) as-\n2 3\ndeposited, (ii) after annealing in N at 350 °C, and (iii) after annealing in air at 350 °C; The difference in\n2\nabsorption spectrum (air-annealed minus as-deposited samples).\nWe further performed a series of correlated experiments and calculations to verify our hypothesis. We\nconducted a controlled annealing experiment (Fig. R11): the 100 nm Sb O film was annealed at 350 °C under\n2 3\nN atmosphere, which resulted in negligible change in its sub-bandgap absorption. In contrast, the Sb O film\n2 2 3\nannealed in air dramatically suppressed the sub-bandgap absorption. This distinct response identifies oxygen-\nrelated defects (including interstitial Sb, I ) as the primary source of the sub-gap states. Meanwhile, XPS\nSb\nconfirmed the presence of a reduced Sb species (Fig. R3), originating from I (detailed in our response to\nSb\nComment #2)7. We further calculated the density of states (DOS) for various defect types (Fig. R11-12). DFT\ncalculations further identify I -induced donor (E of 2.90 eV) and acceptor levels (E of 1.06 eV and E of\nSb D A1 A2\n1.86 eV) within the gap (Fig. R13), with the donor level aligned closely with the C LUMO, enabling efficient\n60\ndefect-assisted injection. In contrast, oxygen vacancy-related states were less favorably positioned, pointing to\nI as the dominant functional defect.\nSb\nTo bridge theory calculation and experiment, we correlate the measured absorption difference spectrum\n(Δα, the difference between the two absorption spectra) with the defect energy levels identified by theoretical\ncalculations (Fig. R10 and R13). The inflection points in the Δα spectrum at 2.2, 2.74, and 3.27 eV correspond\nto optical transitions from EA to CBM, from VBM to E , and from EA to CBM, respectively. The nearly\nlinear evolution of the absorption difference between 2.2 and 3.27 eV signifies the formation of quasi-\ncontinuous defect state around these I . This band effectively bridges the ~1.2 eV interface energy barrier,\nSb\nenabling efficient electron transport from the LUMO of C via a defect-assisted percolation mechanism (Fig.\nresults from inhomogeneous broadening and state hybridization induced by high defect densities, local micro-\nenvironment fluctuations, and defect-defect interactions within the realistic film.\nFig. R11 Electronic band structures of perfect cubic Sb O and defective systems with various point defects\n2 3\ncalculated by DFT (e.g., Sb interstitials or oxygen vacancies).\nFig. R12 Top views of the Sb O crystal and defect structures (e.g. I and V ).\n2 3 Sb O\nFig. R13 Energy level structure and optical transitions induced by I defects. Schematic diagram of the Sb O\nSb 2 3\nenergy levels upon introduction of I , obtained from DFT calculations. The optical transition energies E and\nSb 1\nE from the acceptor levels E and E to the CBM, and E from the VBM to the donor level E are indicated.\nFig. R14 Schematic energy level alignment and electron transport mechanism at the C /Sb O interface. The\n60 2 3\nenergy level diagram of C and Sb O , based on UPS results, illustrates that electrons can be efficiently\n60 2 3\ntransported from the LUMO of C to the Sb O layer via a quasi-continuous defect band induced by I , despite\n60 2 3 Sb\nthe large conduction band offset (~1.2 eV).\nTo further evaluate this transport mechanism, TPC/TPV analyses were performed on Sb O - and SnO -\n2 3 X\nbased devices (Fig. R15-16). The TPC decay dynamics show comparable lifetimes, confirming efficient\nelectron extraction via defect-assisted transport in Sb O . Meanwhile, the matching TPV decays indicate that\n2 3\nthese defect states do not introduce severe non-radiative recombination.\nIn conclusion, Sb O enables efficient vertical charge transport and extraction via defect-assisted\n2 3\nconduction through its nanocrystalline pathways. This mechanism successfully overcomes the high energy\nbarrier at the C /Sb O interface, providing a new material strategy for developing high-performance of devices.\n60 2 3\nFig. R15 TPC measurements of SnO - and Sb O -based PSCs.\nX 2 3\nFig. R16 TPV measurements of SnO - and Sb O -based PSCs.\nX 2 3\nReferences\nantimony oxide films by ellipsometry and XPS. Journal of Electroanalytical Chemistry 645, 143-148\n(2010). https://doi.org/10.1016/j.jelechem.2010.04.023\nMgFx. Science 377, 302-306 (2022). https://doi.org/10.1126/science.abn8910\n(2024). https://doi.org/10.1038/s41586-023-06892-x\nComment #4. Reducing the fullerene thickness is crucial for minimizing optical parasitic absorption.\nHowever, what is the coverage of a 5 nm C layer? Does this affect electron extraction efficiency?\nmicroscopy (TEM) image of the PVK/C /Sb O /IZO sample to intuitively demonstrate the higher coverage of\n60 2 3\na 5 nm C (Fig. R17). To further examine the coverage, we deposited a 5nm C film on a 100 cm2 large-area\n60 60\nsubstrate. Next, we selected five positions on the C film to conduct UV-vis measurement (Fig. R18 and Table\n60\narea scale. Besides, we fabricated 5 nm C films as electron transport layer in 100 sub-cells with the device\n60\nstructure illustrated in Fig. R19, showing uniform PCE distribution.\nFig. R17 Cross-sectional TEM image and the corresponding EDX mapping of PVK/C /Sb O /IZO stack\n60 2 3\nstructure.\nFig. R18 Photograph of a 5 nm C on a 10×10 cm2 glass substrate and transmittance spectra measured from\n60\nfive representative positions.\nFig. R19 Statistical distribution of normalized PCE with 100 sub-cells based on Sb O on a 10×10 cm2 substrate.\n2 3\nMeanwhile, we further investigated the potential influence of C thickness on electron extraction. We\n60\ndemonstrated slightly different energy level distributions and carrier lifetimes between the 5 and 15 nm C (Fig.\nImportantly, we provided favorable photovoltaic performance data of single-junction device with 5 nm C and\n60\n15nm Sb O , confirming the excellent extraction ability of 5 nm C (Fig. R23).\n2 3 60\nFig. R20 UPS spectra of 5 and 15 nm C .\n60 60\nFig. R23 The reverse-scan J-V curves of the 1.64 eV-bandgap champion PSCs with SnO or Sb O .\nX 2 3\nTable R1 The average transmittance of 5 nm C film in the wavelength range from 300 nm to 560 nm measured\n60\nfrom five representative positions.\nPosition 1 Position 2 Position 3 Position 4 Position 5\nAverage\n81.50 81.78 81.84 81.97 82.08\ntransmittance (%)\nTable R2 Extracted carrier lifetimes from TRPL measurements. The decay was modeled using a bi-exponential\nfunction, showing the fast (τ ) and slow (τ ) components, their amplitudes (A and A ).\n1 2 1 2\nτ (ns) A τ (ns) A\n1 1 2 2\nPVK/C -5 4.41 1205 16.07 235\nedge truncation in Figure S6 appears questionable. It is recommended to increase the number of\nexperimental samples to ensure statistically robust results.\nResponse: Thank you for pointing out these issues regarding Fig. S8 and S6. We sincerely apologize for the\nerror in Fig. S8 and any confusion it may have caused. We have conducted a systematic and thorough review\nof all supplementary figures. We have identified and corrected the specific error in Fig. S8 and have replaced it\nwith the revised version. The detailed analysis and calibration process are as follows:\nThe energy level structure of the Sb O has been established by combining DFT calculations with\n2 3\nconsistent results from multiple experimental characterizations, e.g. TEM, XRD. The electronic band structure\nof cubic Sb O was investigated using DFT calculations, which yielded a direct band gap of 4.20 eV (Fig. R11-\n2 3\n12). This theoretical value is well aligned with the optical band gap of approximately 4.25 eV determined from\nour UV-Vis measurements (Fig. R8), thereby validating both the computational model and the accuracy of UV-\nvis data. To further ensure the accuracy of the energy level diagram, UPS measurements were meticulously\nrepeated and cross-verified at three independent institutions (Fig. R24). The high consistent results confirm the\nreliability of the energy level structure of Sb O , as shown in Fig. R25.\n2 3\nFig. R24 UPS spectra of Sb O films from different test institutions.\n2 3\nFig. R25 Energy level scheme of Sb O films from different test institutions.\n2 3\nComment #6. Since the primary advantage of Sb O over SnO in this study is the reduced chemical\n2 3 X\netching of perovskite films, the results of various stability tests are critical. Stability data under\ncontinuous illumination at maximum power point tracking, temperature, and electrical bias should be\nincluded for devices incorporating Sb O buffer layers, along with appropriate explanations.\n2 3\nResponse: Thank you for the valuable comments. We fully agree that long-term device stability is indispensable\nfor practical applications. Thus, we systematically evaluated the thermal (65°C, N ) and optical stability (100\n2\nmW/cm2 white LED illumination, N ) of intrinsic Sb O , Sb O -based stack films and devices across different\n2 2 3 2 3\ntime dimensions.\nFor the intrinsic Sb O films, TEM and XRD results revealed no structural changes after thermal or\n2 3\noptical aging, demonstrating its robust microstructural stability (Fig. R26-27). XPS analysis demonstrated\nnearly consistent area of the I -related peak before and after aging, indicating excellent chemical stability of\nSb\nthe key defect species (Fig. R28).\nFig. R26 TEM images of Sb O films under different aging conditions. (i) Pristine film, and films aged after 40\n2 3\ndays in N atmosphere under (ii) 65 °C or (iii) a white LED source (100 mW/cm2).\ninc 60 2 3\nPristine film, and films aged after 40 days in N atmosphere under (ii) 65 °C or (iii) a white LED source (100\n2\nmW/cm2).\nFig. R28 XPS spectra of Sb O films under different aging conditions. (i) Pristine film, and films aged after 40\n2 3\ndays in N atmosphere under (ii) 65 °C or (iii) a white LED source (100 mW/cm2).\n2 3 60 2 3\nshow no interlayer cracks, warps, delamination, exhibiting excellent stress stability (Fig. R29). The GIXRD\nmeasurement further confirmed negligible stress gradient within the Sb O film and poor residual stress at the\n2 3\nC /Sb O interface8 (Fig. R27), attribute to simple physical interaction via van der Waals. Moreover, aging\n60 2 3\nstudies of PVK/C /SnO or Sb O /IZO structures demonstrate the excellent stability of both configurations\n(Fig. R30). SEM and XRD analyses confirm well-maintained structural integrity with no observable adverse\neffects of Sb O on the perovskite layer (Fig. R31-33)\n2 3\nFig. R29 Optical microscopy images of Glass/C /Sb O samples before and after thermal, light aged tests.\n60 2 3\nFig. R30 Photographs of Glass/Me-4PACz/PVK/C /SnO - or Sb O /patterned IZO stacks under different aging\nconditions. (i) Pristine film, and films aged after different days in N atmosphere under (ii) 65 °C or (iii) a white\ncharacterization.)\nFig. R31 SEM images of PVK/C /SnO or Sb O /IZO samples before and after thermal aging at 65℃ in a N\natmosphere.\nFig. R32 SEM images of PVK/C /SnO or Sb O /IZO samples before and after light aging under a white LED\nlamp illumination at 100 mW/cm2 in a N atmosphere.\nconditions. (i) Pristine film, and films aged after different days in N atmosphere under (ii) 65 °C or (iii) a white\nFor encapsulated full devices, Sb O -based PST were subjected to 500 hours of MPP tracking under white\n2 3\nLED lamp illumination at 100 mW/cm2 (Fig. R34). The device maintained their initial PCE without substantial\nloss. In addition, we continuously monitored the light and thermal stability for more than 1,000 hours under\nlight (white LED lamp illumination at 100 mW/cm2) and 65°C thermal aging tests, respectively (Fig. R35-36).\nBoth encapsulated devices demonstrated robust photothermal stability, retaining over 90% of their initial PCE.\nFig. R34 Normalized PCE, V , J , FF of encapsulated Sb O -based PST for MPP tracking under a white LED\nOC SC 2 3\nlamp illumination at 100 mW/cm2 in air.\nFig. R35 Normalized PCE, V , J , FF of encapsulated SnO - or Sb O -based tandem devices for thermal\nOC SC X 2 3\naging test at 65℃ in a N atmosphere.\nOC SC X 2 3\ntests under a white LED lamp illumination at 100 mW/cm2 in a N atmosphere.\nphotovoltage loss. Science 388, 88-95 (2025). https://doi.org/10.1126/science.adt3417\nReviewer #2 (Remarks to the Author):\nThis work reports a promising strategy of replacing ALD-deposited SnOx layer with an Sb O layer to\n2 3\nreduce optical losses in the C /SnO stacked layer. This approach reduces the thickness of the C layer,\ndecreases the parasitic absorption and finally increases the J , and protects the perovskite layer. This\nSC\nstrategy is universal to a broad range of perovskite solar cells with various bandgaps and to large-area\ntandem solar cells. This work is of great interest and significance to the community of perovskite single-\njunction and tandem solar cells, especially this work provides an alternative thermal evaporation\ndeposition technique to the existing ALD technique, which could reduce the fabrication cost. Therefore,\nI would recommend publication of this manuscript after addressing the following minor issues.\nComment #1. As is well known, C could increase the fabrication cost of perovskite solar cells.\n60\non whether Sb O can replace C and work as an ETL in tandem cells?\n2 3 60\nResponse: Thank you for the valuable comments. To verify whether Sb O can directly replace C as an ETL,\n2 3 60\nwe fabricated single-junction device with the ITO/Me-4PACz/perovskite/Sb O /Al structure. J-V curve shows\n2 3\na poor PCE only 14.63% (Fig. R1), which is attributed to the large Rs of the device. We further modified the\nperovskite/Sb O interface using PDADI, improving the PCE to 16.58%. However, it can be found that the FF\n2 3\nof the device is still relatively low, which may be determined by its higher density of interfacial defects and\npoorer electrical conductivity compared to C . Currently, Sb O cannot be directly used as an ETL in single-\n60 2 3\njunction or tandem devices. Nevertheless, it is feasible to conduct modifications in term of the electrical\nproperties of Sb O and the interface defects between perovskite and Sb O . Thus, Sb O material exhibits\n2 3 2 3 2 3\nsignificant promise as a future ETL, offering a combination of superior optical management and cost-\neffectiveness.\nFig. R1 The J-V curves of champion PSCs based on Sb O as ETL.\n2 3\nComment #2. The authors claim that the higher mobility of Sb O is attributed to more favorable energy\n2 3\nlevel alignment. Please explain more on this.\nResponse: Thank you for the valuable comments. In previous work, the conduction mechanism in Sb O was\n2 3\nmisinterpreted due to inaccuracies in the quantification of its energy levels, for which we apologize and take\nresponsibility for the provided data. To rectify this, we have ensured the accuracy of the Sb O energy level\n2 3\nalignment through cross-verification at three independent institutions (Fig. R2-4). The corrected energy level\ndiagram reveals a ~1.2 eV energy barrier at the C /Sb O interface (Fig. R5), in principle, completely suppress\n60 2 3\nelectron injection. Nevertheless, Sb O -based single-junction devices achieve high efficiency that is insensitive\n2 3\nto its thickness (Fig. R6), confirming substantial electron extraction and transport. UV-Vis spectroscopy\nindicates a high density of in-gap states within 100 nm Sb O films (Fig. R7). Collectively, these findings point\n2 3\nto a unique defect-mediated conduction mechanism distinct from quantum tunneling.\nFig. R2 Tauc-plot of Sb O film.\n2 3\nFig. R3 UPS spectra of Sb O films from different test institutions.\n2 3\nFig. R4 Energy level scheme of Sb O films from different test institutions.\n2 3\nFig. R5 UPS spectra of C and Sb O films.\n60 2 3\nFig. R6 Statistics of PCE, V , J and FF of the PSCs with different Sb O thicknesses.\nOC SC 2 3\nFig. R7 UV-vis absorption spectra of 100 nm Sb O films under different processing conditions: (i) as-deposited,\n2 3\n(ii) after annealing in N at 350 °C, and (iii) after annealing in air at 350 °C; The difference in absorption\n2\nspectrum (air-annealed minus as-deposited samples).\nWe further performed a series of correlated experiments and calculations to verify our hypothesis. We\nconducted a controlled annealing experiment (Fig. R5): the 100 nm Sb O film was annealed at 350 °C under\n2 3\nN atmosphere, which resulted in negligible change in its sub-bandgap absorption. In contrast, the Sb O film\n2 2 3\nannealed in air dramatically suppressed the sub-bandgap absorption. This distinct response identifies oxygen-\nrelated defects (including interstitial Sb, I ) as the primary source of the sub-gap states. Meanwhile, XPS\nSb\nconfirmed the presence of the Sb0 atoms7 (Fig. R8), which serve as precursors for the formation of I . We\nSb\nfurther calculated the density of states (DOS) for various defect types (Fig. R9-10). DFT calculations further\nidentify I -induced donor (E of 2.90 eV) and acceptor levels (E of 1.06 eV and E of 1.86 eV) within the\nSb D A1 A2\ngap (Fig. R11), with the donor level aligned closely with the C LUMO, enabling efficient defect-assisted\n60\ninjection. In contrast, oxygen vacancy-related states were less favorably positioned, pointing to I as the\nSb\ndominant functional defect.\nTo bridge theory calculation and experiment, we correlate the measured absorption difference spectrum\n(Δα, the difference between the two absorption spectra) with the defect energy levels identified by theoretical\ncalculations (Fig. R5 and R11). The Δα exhibits distinct inflection points at 2.2 and 3.27 eV, which attributed\nto optical transitions from the E and E to the CBM, respectively. The inflection point at 2.74 eV is assigned\nA2 A1\nto transitions from the VBM to the E . The nearly linear evolution of the absorption difference between 2.2 and\nD\n3.27 eV signifies the formation of quasi-continuous defect state around these I . This band effectively bridges\nSb\nthe ~1.2 eV interface energy barrier, enabling efficient electron transport from the LUMO of C via a defect-\n60\nassisted percolation mechanism (Fig. R13). Besides, the discrepancy between the observed quasi-continuous\ndefect band and the calculated discrete levels can be understood by considering the realistic film environment.\nHigh defect density, local micro-environment fluctuations, and defect-defect interactions cause significant\ninhomogeneous broadening and state hybridization, ultimately merging discrete levels into a continuous defect\nband. Sum up, Sb O enables efficient vertical charge transport and extraction via defect-assisted conduction\n2 3\nthrough its nanocrystalline pathways.\nFig. R8 XPS spectrum of Sb 3d of Sb O film.\n3/2 2 3\nFig. R9 Electronic band structures of perfect cubic Sb O and defective systems with various point defects\n2 3\ncalculated by DFT (e.g., Sb interstitials or oxygen vacancies).\nFig. R10 Top views of the Sb O crystal and defect structures (e.g. I and V ).\n2 3 Sb O\nFig. R11 Energy level structure and optical transitions induced by I defects. Schematic diagram of the Sb O\nSb 2 3\nenergy levels upon introduction of I , obtained from DFT calculations. The optical transition energies E and\nSb 1\nE from the acceptor levels E and E to the CBM, and E from the VBM to the donor level E are indicated.\nFig. R12 Schematic energy level alignment and electron transport mechanism at the C /Sb O interface. The\n60 2 3\nenergy level diagram of C and Sb O , based on UPS results, illustrates that electrons can be efficiently\n60 2 3\ntransported from the LUMO of C to the Sb O layer via a quasi-continuous defect band induced by I , despite\n60 2 3 Sb\nthe large conduction band offset (~1.2 eV).\nTo further evaluate the efficacy of this transport mechanism, we conducted comparative TPC and TPV\nmeasurements on Sb O - and SnO -based devices (Fig. R13-14). The TPC results showed comparable\n2 3 X\nphotocurrent decay lifetimes, demonstrating that the defect-assisted transport in Sb O enables efficient electron\n2 3\nextraction. Simultaneously, the TPV measurements revealed similar photovoltage decay lifetimes, indicating\nthat the defect states in Sb O do not introduce severe non-radiative recombination losses. Thus, these findings\n2 3\nconfirm that the defect-assisted transport mechanism achieves high-efficiency charge collection while\nmaintaining high interfacial quality.\nIn conclusion, Sb O enables efficient vertical charge transport and extraction via defect-assisted\n2 3\nconduction through its nanocrystalline pathways. This mechanism successfully overcomes the high energy\nbarrier at the C /Sb O interface, providing a new material strategy for developing high-performance of devices.\n60 2 3\nFig. R13 TPC measurements of SnO - and Sb O -based PSCs.\nX 2 3\nFig. R14 TPV measurements of SnO - and Sb O -based PSCs.\nX 2 3\nReferences\nantimony oxide films by ellipsometry and XPS. Journal of Electroanalytical Chemistry 645, 143-148\n(2010). https://doi.org/10.1016/j.jelechem.2010.04.023\nComment #3. In Figure 2d and 2f, please clarify the voltage scan direction. In Figure 2h, please clarify\nwhat the current densities correspond to.\nResponse: Thank you for the valuable comments and have updated the text and figure accordingly. We clarified\nthat the J-V curves in Fig. 2c and 2e (previous Fig. 2d and 2f) were both measured in reverse scan from 1.3 to\nSC\nPSCs with 1.59, 1.62, 1.64 and 1.68 eV bandgaps matched well with the J values from J-V curves (Fig. 2c\nSC\nand 2e).\nComment #4. Section 5 of Page 10: to examine the homogeneity of Sb O , the authors deposited a 45 nm\n2 3\nSb O layer on 10×10 cm2 glass substrate. Could the authors comment on uniformity of the 15 nm thick\n2 3\nSb O for scaling up cells?\n2 3\nResponse: Thank you for the valuable comments. Following your suggestions, we deposited a 15 nm Sb O\n2 3\nfilm on 100 cm2 substrate. We selected five representative positions on the film and conducted the AFM tests\n(Fig. R15-16), showing the approximate mean step heights (~15 nm) of the five sub-samples. Moreover, the\nsimilar surface potential (~700 mV) of these five sub-samples further confirmed the superior uniformity of the\n15 nm Sb O film (Fig. R17). Besides, we fabricated 5nm C films as electron transport layer in 100 sub-cells\n2 3 60\nwith the device structure illustrated in Fig. R18, showing uniform PCE distribution.\nFig. R15 Photograph of a 15 nm Sb O on a 10×10 cm2 glass substrate and transmittance spectra measured from\n2 3\nfive representative positions.\nFig. R16 AFM images and mean step height of 15 nm Sb O films measured from five positions.\n2 3\nFig. R17 AFM and KPFM images of 15 nm Sb O films measured from five positions.\n2 3\nFig. R18 Statistical distribution of normalized PCE with 100 sub-cells based on Sb\n3\non a 10×10 cm2 substrate.\nComment #5. Page 8: to evaluate the optical benefits of Sb O layer and reduced C thickness, the authors\n2 3 60\nshould compare the average transmittance of C /Sb O and C /SnOx stacked layers.\n60 2 3 60\nResponse: Thank you for the valuable comments. To explicitly illustrate the optical benefits afforded by Sb O ,\n2 3\nwe re-implement UV-vis spectroscopy measurements on both the C -5/Sb O and C -15/SnOx samples,\n60 2 3 60\nrespectively in Fig. R19 (Fig. 3g in Manuscript). Furthermore, the average transmittance (T ) of the C -\navg 60\n5/Sb O (74.85%) and C -15/SnOx (62.68%) were quantified in the wavelength range from 300 to 560 nm and\n2 3 60\npresented in the corresponding Fig. 3g.\nFig. R19 Absorptance and transmittance spectrum of C /Sb O and SnO films.\n60 2 3 X\nReviewer #3 (Remarks to the Author):\nShi et al. introduce an antimony oxide as buffer layer for perovskite based single junction and tandem\nsolar cells. This approach enhances the power conversion efficiency (PCE) and stability of\nperovskite/silicon tandem cells. The optimized tandem device achieves a PCE of 30.1%. These results\nunderscore the strategy’s potential for industrial-scale applications. However, the stability and efficiency\nof the devices in the article is not that impressive to garentee its publicaiton in Nature Communications.\nOverall, this work demonstrates interesting result with good material design. Therefore, I recommend\nthis paper to be reconsidered after revisions and suggest some points for further improvement.\nComment #1. The maximum power point testing should be incorporated in the manuscript with certain\nduration. Additionally, post-aging microstructural analysis using SEM, XRD and TOF-SIMS should be\napplied correspondingly.\nResponse: Thank you for the valuable comments. Combined with Comment #9 and #10, we performed\ncomprehensive aging researches on intrinsic Sb O films, multilayer stacks, and complete devices. It is crucial\n2 3\nto clarify that in the application context of this study, Sb O serves as a buffer layer within an encapsulated\n2 3\ndevice. Since effective encapsulation mitigates the ingress of moisture and oxygen, our investigation targets the\noptical (100 mW/cm2 white LED illumination) and thermal (65°C) stability in a N atmosphere for 40 days.\n2\n(Besides, because it was impossible to extract the encapsulated PSTs for direct measurement, we designed\nPVK/C /SnO or Sb O /IZO stacks to simulate the actual device environment, allowing for post-aging analysis.)\nFirst, the intrinsic stability of Sb O was evaluated through multiple characterization techniques. Both TEM\n2 3\nand XRD results confirmed the crystal structural integrity of the Sb O after aging (Fig. R1-2). XPS spectra\n2 3\nshowed no obvious change of the peak information before and after aging, indicating its remarkable chemical\nstability (Fig. R3).\nFig. R1 TEM images of the pristine, thermal aged and light aged Sb O films. All aging tests were conducted\n2 3\nin a N₂ atmosphere for 40 days. The thermal aging was performed at 65 °C, and the optical aging used a white\nLED source (100 mW/cm2).\nFig. R2 GIXRD patterns (θ =0.3, 1 and 3°) of Glass/C /Sb O films under different aging conditions. (i)\ninc 60 2 3\nPristine film, and films aged after 40 days in N atmosphere under (ii) 65 °C or (iii) a white LED source (100\n2\nmW/cm2).\nFig. R3 XPS spectra of the pristine, thermal aged and light aged Sb O films.\n2 3\nSecond, the Sb₂O₃-based stack architectures demonstrated excellent interfacial stability under aging.\nOptical microscopy confirmed that the C /Sb₂O₃ interface, governed by van der Waals interaction, exhibited no\n60\ncracking, warping, or delamination, indicating effective stress release. (Fig. R4). Moreover, the microstructure\nof the C /Sb O sample was examined by GIXRD in Fig. R2. By tuning the incident angle θ from 0.3° to 3°,\n60 2 3 inc\nthe probe depth was varied from the surface to the deeper regions of the film8, which was confirmed by the\nemergence of a broad diffraction signal from the amorphous glass/C substrate at θ =3°. Notably, XRD peaks\n60 inc\nshowed no shift with depth before and after aging, confirming negligible stress gradient within the Sb O film\n2 3\nand poor residual interfacial stress, attributed to the van der Waals contact at the C /Sb O . Moreover, we\n60 2 3\nevaluated the thermal and optical stability of the PVK/SnO /IZO and PVK/Sb O /IZO stack, respectively. No\nX 2 3\nnoticeable decomposition or morphological degradation was observed by visual inspection or SEM (Fig. R5-\n7). XRD further indicated the aged perovskite nearly maintain intact crystal structure (Fig. R8).\nFig. R4 Optical microscopy images of Glass/C /Sb O samples before and after thermal, light aged tests.\n60 2 3\nFig. R5 Photographs of Glass/Me-4PACz/PVK/C /SnO - or Sb O /patterned IZO stacks under different aging\nconditions. (i) Pristine film, and films aged after different days in N atmosphere under (ii) 65 °C or (iii) a white\ncharacterization.)\nFig. R6 SEM images of PVK/C /SnO or Sb O /IZO samples before and after thermal aging at 65℃ in a N\natmosphere.\nFig. R7 SEM images of PVK/C /SnO or Sb O /IZO samples before and after light aging under a white LED\nlamp illumination at 100 mW/cm2 in a N atmosphere.\nconditions. (i) Pristine film, and films aged after different days in N atmosphere under (ii) 65 °C or (iii) a white\nFinally, we conducted a MPP tracking of encapsulated Sb O -based PST for 500 hours under white LED\n2 3\nlamp illumination at 100 mW/cm2 (Fig. R9). The PCE of the devices was maintained without significant loss.\nBesides, the encapsulated SnO - and Sb O -based PST exhibited robust optical and thermal stability during\nX 2 3\ncontinuous testing exceeding 1,000 hours under a white LED illumination (100 mW/cm²) and thermal aging at\n65°C, respectively, retaining over 90% of their initial PCE (Fig. R10-11).\nFig. R9 Normalized PCE, V , J , FF of encapsulated Sb O -based PST for MPP tracking under a white LED\nOC SC 2 3\nlamp illumination at 100 mW/cm2 in air.\nFig. R10 Normalized PCE, V , J , FF of encapsulated SnO - or Sb O -based tandem devices for thermal\nOC SC X 2 3\naging tests at 65℃ in a N atmosphere.\nOC SC X 2 3\ntests under a white LED lamp illumination at 100 mW/cm2 in a N atmosphere.\nphotovoltage loss. Science 388, 88-95 (2025). https://doi.org/10.1126/science.adt3417\nComment #2. The TEM image in Fig. 1g appears blurred, and the interfaces are difficult to distinguish.\nA low-magnification TEM image should be provided to clearly demonstrate the long-range behavior of\nthe interlayer.\nResponse: Thank you for the valuable comments. To show the long-range behavior of the interlayer, we re-\nprepared the cross-sectional sample with the structure of Si/NiO /Me-4PACz/PVK/C /Sb O /IZO using\nX 60 2 3\nfocused ion beam (FIB) technology and provided its TEM and EDS images at low magnification (Fig. R12-13).\nThe EDS mapping clearly outlines the sandwich structure, in which an inconspicuous amount of indium\nelements was detected in the C and perovskite layers, displaying the qualified sputtering tolerance of the Sb O\n60 2 3\nfilm. Also, the undamaged Sb O nanocrystalline with a cubic structure also further verifies its excellent\n2 3\nsputtering tolerance.\nFig. R12 Cross-sectional TEM image and EDX mapping of PVK/C /Sb O /IZO stack films.\n60 2 3\nFig. R13 Cross-sectional TEM image and EDX mapping of Si/NiO\nX\n/Me-4PACz/PVK/C\n60\n/Sb\n3\n/IZO stack.\nComment #3. The AFM results show that the RMS roughness decreases after Sb O deposition compared\n2 3\nto the reference film. Does this imply that Sb O does not form a uniformly coverage?\n2 3\nResponse: Thank you for the valuable comments. In Fig. R14 (SI in Fig. S2), the reduction in surface roughness\nof the PVK/C sample after Sb O deposition is most likely associated with to the slightly different thickness\n60 2 3\nof thermally evaporated Sb O layers at the valleys and protrusions of the underlying PVK/C substrate. The\n2 3 60\nthermally evaporated Sb O layer is beneficial to filling the valleys and hence slightly thicker at valleys, thereby\n2 3\ncontributing to a smoother surface morphology. However, the thermally evaporated Sb O layer is uniform\n2 3\nenough to cover the rough PVK/C substrate.\n2 3 2 3\nsubstrate. Additionally, we selected five representative positions on this film and conducted thickness\nmeasurements on via AFM and KPFM tests (Fig. R15-17). By comprehensively analyzing the data, we\nconfirmed the coverage uniformity of 15 nm Sb O . Besides, the uniformity of 15 nm Sb O can also be\n2 3 2 3\nintuitively demonstrated in cross-sectional TEM images (Fig. R12) shown in Comments 2.\nFig. R14 AFM images of PVK/C /without and with Sb O .\n60 2 3\nFig. R15 Photograph of a 15 nm Sb O on a 10×10 cm2 glass substrate and transmittance spectra measured from\n2 3\nfive representative positions.\nFig. R16 AFM images and mean step height of 15 nm Sb O films measured measured from five positions.\n2 3\nFig. R17 AFM and KPFM images of 15 nm Sb\n3\nfilms measured measured from five positions.\nComment #4. The explanation of the electron transfer mechanism remains unclear. Additional\ncharacterizations are necessary to elucidate the underlying charge transfer behavior in the Sb O layer.\n2 3\nResponse: Thank you for the valuable comments. Through systematic investigation across structural, electrical,\nand energetic dimensions, we have confirmed the existence of a defect-mediated nanocrystal transport\nmechanism in thermally evaporated Sb O films.\n2 3\nStructurally, TEM and XRD results verify the embedding of α-Sb O nanocrystals within an amorphous\n2 3\nmatrix, establishing the nanocrystal conduction pathways (Fig. R18-19).\nFig. R18 TEM images of Sb O film.\n2 3\nFig. R19 XRD spectrum of Sb O film.\n2 3\nElectrically, longitudinal c-AFM image reveals current localization at nanocrystalline hotspots, indicating\nthe electron transport by the nanocrystals as channel (Fig. R20). Meanwhile, the Sb O -based single-junction\n2 3\ndevices exhibit high-efficiency and stable performance across 15-25 nm Sb O (Fig. R21).\n2 3\nFig. R20 AFM and corresponding c-AFM images of the Sb O film under a bias voltage of 3 V.\n2 3\nFig. R21 Statistics of PCE, V , J and FF of the PSCs with different Sb O thicknesses.\nOC SC 2 3\nEnergetically, as a wide-bandgap material (~4.25 eV), Sb O tends to form high energy barriers at interface\n2 3\n(Fig. R22). The UPS results reveal a substantial interfacial energy barrier of ~1.2 eV at the C /Sb O interface\n60 2 3\n(Fig. R23). Among, the UPS results of Sb O were reproduced and cross-verified at three independent\n2 3\ninstitutions, ensuring its accuracy (Fig. R24-25). But the efficient electron injection persists even through thick\nSb O layers (Fig. R21), inconsistent with quantum tunneling5 or amorphous conduction6. Furthermore, UV-vis\n2 3\nspectra of 100 nm Sb O film shows significant sub-bandgap absorption (Fig. R26), indicating the existence of\n2 3\nabundant gap states. Based on these data, we support a defect-assisted, nanocrystal-mediated percolation\ntransport model.\nFig. R22 Tauc-plot of Sb O film.\n2 3\nFig. R23 UPS spectra of C and Sb O films.\n60 2 3\nFig. R24 UPS spectra of Sb O films from different test institutions.\n2 3\nFig. R25 Energy level scheme of Sb O films from different test institutions.\n2 3\nFig. R26 UV-vis absorption spectra of 100 nm Sb O films under different processing conditions: (i) as-\n2 3\ndeposited, (ii) after annealing in N at 350 °C, and (iii) after annealing in air at 350 °C; The difference in\n2\nabsorption spectrum (air-annealed minus as-deposited samples).\nNext, we systematically verified our hypothesis through correlated experiments and calculations. We\nconducted a controlled annealing experiment (Fig. R26): the 100 nm Sb O film was annealed at 350 °C under\n2 3\nN atmosphere, which resulted in negligible change in its sub-bandgap absorption. In contrast, the Sb O film\n2 2 3\nannealed in air dramatically suppressed the sub-bandgap absorption, indicating oxygen-related defects (e.g.\ninterstitial Sb, I ) as the source. Also, XPS confirmed the presence of the Sb0 atoms (Fig. R27), which serve as\nSb\nprecursors for the formation of I . To further identify the dominant defect species, we systematically\nSb\ninvestigated the band structure of α-Sb O using DFT calculations, with particular focus on the defect energy\n2 3\nlevels introduced by various types of defects (Fig. R28-29). Crucially, we observed that the I defects introduce\nSb\nspecific in-gap states: two acceptor levels (E at 1.06 eV, E at 1.86 eV) and a donor level (E at 2.90 eV).\nA1 A2 D\nThe close alignment of E with the C LUMO enables efficient defect-mediated electron injection. In contrast,\nD 60\noxygen vacancy-related states were less favorably positioned, pointing to I as the dominant functional defect.\nSb\nSystematic correlation of measured absorption difference spectrum (Δα, the difference between the two\nabsorption spectra) with theoretical calculations provides compelling evidence for defect-mediated charge\ntransport (Fig. R26). The Δα reveals inflection points at 2.2, 2.74, and 3.27 eV, corresponding to calculated\nE →CBM (E =2.18 eV), VBM→E (E =2.90 eV), and E →CBM (E =2.98 eV) transitions in whole\nA2 2 D 3 A1 1\nVBM→CBM transition, respectively (Fig. R30). Besides, the nearly linear absorption evolution between 2.2\nand 3.27 eV demonstrates the formation of quasi-continuous defect state around these I levels (Fig. R26). This\nSb\nband architecture enables efficient electron injection across the 1.2 eV C /Sb O interface barrier via defect-\n60 2 3\nassisted percolation (Fig. R30). The transition from discrete theoretical levels to continuous experimental bands\nis rationally explained by collective environmental effects in real material systems, where high defect density\nand local fluctuations induce significant state broadening and hybridization.\nFig. R27 XPS spectrum of Sb 3d of Sb O film.\n3/2 2 3\nFig. R28 Electronic band structures of perfect cubic Sb O and defective systems with various point defects\n2 3\ncalculated by DFT (e.g., Sb interstitials or oxygen vacancies).\nFig. R29 Top views of the Sb O crystal and defect structures (e.g. I and V ).\n2 3 Sb O\nFig. R30 Energy level structure and optical transitions induced by I defects. Schematic diagram of the Sb O\nSb 2 3\nenergy levels upon introduction of I , obtained from DFT calculations. The optical transition energies E and\nSb 1\nE from the acceptor levels E and E to the CBM, and E from the VBM to the donor level E are indicated.\nFig. R31 Schematic energy level alignment and electron transport mechanism at the C /Sb O interface. The\n60 2 3\nenergy level diagram of C and Sb O , based on UPS results, illustrates that electrons can be efficiently\n60 2 3\ntransported from the LUMO of C to the Sb O layer via a quasi-continuous defect band induced by I , despite\n60 2 3 Sb\nthe large conduction band offset (~1.2 eV).\nTo further evaluate the efficacy of this transport mechanism, we conducted TPC and TPV measurements\n(Fig. R32-33). The Sb O -based devices exhibit photocurrent decay lifetimes comparable to their SnO -based\n2 3 X\ncounterparts, demonstrating efficient charge extraction via the unique defect-assisted transport. Furthermore,\nthe similar photovoltage decay lifetimes in TPV measurements confirm that the gap states in Sb O do not\n2 3\nintroduce significant non-radiative recombination. Above-mentioned results confirm the effectiveness of the\ndefect-mediated conduction mechanism.\nIn conclusion, Sb O enables efficient vertical charge transport and extraction via defect-assisted\n2 3\nconduction through its nanocrystalline pathways. This mechanism successfully overcomes the high energy\nbarrier at the C /Sb O interface, providing a new material strategy for developing high-performance of devices.\n60 2 3\nFig. R32 TPC measurements of SnO - and Sb O -based PSCs.\nX 2 3\nFig. R33 TPV measurements of SnO - and Sb O -based PSCs.\nX 2 3\nReferences\nMgFx. Science 377, 302-306 (2022). https://doi.org/10.1126/science.abn8910\n(2024). https://doi.org/10.1038/s41586-023-06892-x\nComment #5. The nature of the Sb O /C interface is not well defined. It should be clarified whether the\n2 3 60\ninterface is governed by simple physical contact or involves specific chemical interactions.\nResponse: Thank you for the valuable comments. Based on XRD results (Fig. R34), the Sb O layer is a cubic-\n2 3\nphase nanocrystal film with an interplanar spacing of d =0.32 Å4,9,10. To investigate their interaction style\nbetween C and Sb O , we prepared a cross-sectional sample containing the C /Sb O films using FIB\n60 2 3 60 2 3\ntechnology. Subsequently, we further characterized the samples by TEM (Fig. R35), and showed the unchanged\nmicrostructure of the Sb O nanocrystal in contact with C . Moreover, we further performed grazing incidence\n2 3 60\nX-ray diffraction (GIXRD) to observe the difference of C /Sb O /IZO sample in vertical microstructure8 (Fig.\n60 2 3\nR36). Furthermore, when the incidence angle θ increased to 3°, a broad peak representing amorphous C\ninc 60\nsubstrate was observed in the XRD results. No peak shift is observed at the interface between the Sb O and C\n2 3 60\nlayers. Therefore, C /Sb O interface involves only a simple physical contact via van der Waals forces.\n60 2 3\nFig. R34 XRD spectrum of Sb O film.\n2 3\nFig. R35 Cross-sectional TEM image of PVK/C /Sb O /IZO films.\n60 2 3\nFig. R36 GIXRD pattern of the Sb O film at different incidence angles (θ =0.3, 1 and 3°).\n2 3 inc\nReferences\nNature Electronics 4, 906-913 (2021). https://doi.org/10.1038/s41928-021-00683-w\nphotovoltage loss. Science 388, 88-95 (2025). https://doi.org/10.1126/science.adt3417\nhttps://doi.org/10.1038/s41467-019-12569-9\nfilms. Journal of Optoelectronics and Advanced Materials 5, 907-912 (2003).\nComment #6. It should be specified whether the XPS and UPS measurements were conducted on the\nSb O film alone or on the C /Sb O stack, considering the limited detection depth of these techniques.\n2 3 60 2 3\nAny potential band bending effects at the interface should also be discussed.\nResponse: Thank you for the valuable comments. We fully acknowledge the importance of considering\ninterfacial band bending. Based on UPS results (Fig. R23 and R31), we have obtained the energy level structures\nof individual C and Sb O layers. It is noteworthy that both C and Sb O , being n-type semiconductors,\n60 2 3 60 2 3\nexhibit nearly identical Fermi level positions (C : -4.39 eV, Sb O : -4.29 eV). This energy level alignment\n60 2 3\nsignificantly reduces the driving force for built-in electric field formation at the C /Sb O interface,\n60 2 3\nmaking band bending effects negligible.\nFig. R23 UPS spectra of C and Sb O films.\n60 2 3\nFig. R31 Schematic energy level alignment and electron transport mechanism at the C /Sb O interface. The\n60 2 3\nenergy level diagram of C and Sb O , based on UPS results, illustrates that electrons can be efficiently\n60 2 3\ntransported from the LUMO of C to the Sb O layer via a quasi-continuous defect band induced by I , despite\n60 2 3 Sb\nthe large conduction band offset (~1.2 eV).\nComment #7. Although the IZO layer thickness is claimed to exceed 50 nm, it is not clearly visible in the\nSEM image of the perovskite/IZO film. TOF-SIMS measurements may provide more insightful\ninformation to correlate potential IZO damage with changes in the perovskite morphology.\nResponse: Thank you for the valuable comments, which prompted us to conduct a more thorough and repeated\ninvestigation of this specific phenomenon. We would like to clarify that we intentionally adopted thin (~10 nm)\nIZO layer in SEM images of PVK/IZO samples, whereas IZO thickness in the actual device is 40–50 nm.\nMoreover, we repeatedly measured the SEM of PVK/IZO and PVK/Sb O /IZO samples to investigate the\n2 3\nsputtering damage (Fig. R37). In newly fabricated PVK/IZO samples, we indeed observed no obvious pinholes,\nwhich is inconsistent with the previous SEM results (Fig. R38). We conclude that the pinhole structures shown\nin the original manuscript were not representative but likely resulted from occasional factors during sample\npreparation. However, it should be noted that the absence of morphological damage does not rule out\nelectrical damage caused by sputter. Consistent with extensive literature11-15, the PST without a buffer layer\nexhibited significantly reduced PCE and FF, confirming the necessity of a protective interlayer (Fig. R39). In\naddition, the critical role of a buffer with sputtering tolerance is highlighted by the poor performance of BCP-\nbased PST14,15, despite its high PCE (>22%) in single-junction configurations (Fig. R40). Consequently, the\nhigh performance of Sb O -based tandem devices intuitively demonstrates its superior sputtering tolerance.\n2 3\nFig. R37 Previous measured SEM images of PVK/C /IZO and PVK/C /Sb O /IZO samples.\n60 60 2 3\nFig. R38 SEM images of PVK/C /IZO and PVK/C /Sb O /IZO samples.\n60 60 2 3\nFig. R39 The J-V curves of champion PST without buffer layer and with BCP, BCP: Ag.\nFig. R40 The J-V curve of champion PSC based on BCP buffer layer.\nReferences\nsemitransparent perovskite solar cells. Journal of Materials Chemistry A 12, 14816-14827 (2024).\nhttps://doi.org/10.1039/d3ta06654a\nwith reversed diode model. The Journal of Physical Chemistry C 120, 28441-28447 (2016).\nhttps://doi.org/10.1021/acs.jpcc.6b09219\ntransparent front-electrode for monolithic perovskite/silicon tandem solar cells. Solar Energy Materials\nand Solar Cells 252, 112180 (2023). https://doi.org/10.1016/j.solmat.2023.112180\ncells. Journal of Materials Chemistry A 10, 1343-1349 (2022). https://doi.org/10.1039/d1ta09143c\nperovskite/silicon tandem solar cells. ACS Applied Materials & Interfaces 17, 17599-17610 (2025).\nhttps://doi.org/10.1021/acsami.5c00090\nComment #8. The reference device employing a SnO buffer layer shows a PCE of only ~28%, which is\n2\nnoticeably lower than previously reported values from the same research group. The reason for this\nperformance decline should be clarified.\nResponse: Thank you for the valuable comments regarding the performance of our SnO₂-based reference device.\nCompared to perovskite films prepared by the one-step solution method16-18, those fabricated via the vacuum-\nsolution hybrid (VSH) method exhibit inferior crystallinity, which consequently lead to a relatively lower PCE\nin tandem devices based on the VSH-processed absorber19-24.\nMoreover, the reason for the relatively lower PCE (~28%) compared to our previous reports is primarily\nattributed to a strategic shift in our device architecture, specifically the change from a large-textured silicon\nsubstrate to a small-textured one21-24. While the large-textured PSTs offered marginally superior light-trapping\nand a higher potential J , it posed a significant barrier to the uniform deposition of the self-assembled\nSC\nmonolayer (SAM)25-27, which is crucial for high-performance and reproducible tandem devices. The results led\nto inconsistent device performance and hindered scalable-PSTs fabrication28. Therefore, we temporarily adopted\nthe small-textured substrate to prioritize SAM uniformity and process reliability. This modification led to an\nimprovement in V , but it also caused a slight reduction in J 25. In future work, we will further focus on the\nOC SC\napplication of high-efficiency large-textured devices by addressing the issues derived from large-textured\nsubstrates.\nReferences\n912-919 (2025). https://doi.org/10.1038/s41586-025-09333-z\n603 (2024). https://doi.org/10.1038/s41586-024-07997-7\nphotovoltaics. Science 387, eadv4551 (2025). https://doi.org/10.1126/science.adv4551\nScience 381, 59-62 (2023). https://doi.org/10.1126/science.adg0091\ntextured silicon. Science, eadx1745 (2025). https://doi.org/10.1126/science.adx1745\nEnergy 122, 109285 (2024). https://doi.org/10.1016/j.nanoen.2024.109285\ncommercially textured silicon. Advanced Energy Materials 12, 2202404 (2022).\nhttps://doi.org/10.1002/aenm.202202404\nof hybrid sequential deposited perovskite. Advanced Materials 36, 2308692 (2024).\nhttps://doi.org/10.1002/adma.202308692\n4-fluorobenzylamine hydroiodide. Nano-Micro Letters 16, 189 (2024). https://doi.org/10.1007/s40820-\n024-01406-4\non textured silicon substrates. PRX Energy 1, 023005 (2022).\nhttps://doi.org/10.1103/PRXEnergy.1.023005\ninverted perovskite solar cells and modules. Energy & Environmental Science 18, 468-477 (2025).\nhttps://doi.org/10.1039/d4ee01960a\n624, 289-294 (2023). https://doi.org/10.1038/s41586-023-06745-7\nof perovskite solar cells. Nature Energy 8, 462-472 (2023). https://doi.org/10.1038/s41560-023-01227-\n2 3\nimpact on the long-term stability (under thermal treatment, light illumination, and moisture) of the\nunderlying perovskite film remains unclear and should be addressed.\nResponse: Thank you for the valuable comments. We fully agree with the importance of the intrinsic stability\nof Sb O film and its potential impact on the stability of perovskite. As detailed in our response to Comment\n2 3\n#1, we have demonstrated that intrinsic Sb O exhibits excellent optical and thermal stability. After aging tests,\n2 3\nno significant changes were observed in either its physical structure or chemical state (Fig. R1-3). Besides, the\nC /Sb O interface, via weak van der Waals interactions, demonstrates excellent stress release capability under\n60 2 3\nthermal and optical aging (Fig. R4). This conclusion directly addresses the present question as well. Please refer\nto our response to Comment #1 for supporting experimental data and a more comprehensive discussion.\nComment #10. Related to 9, the device stability under various stresses should also be addressed. At least,\nfor the single junction devices.\nResponse: Thank you for the valuable comments. As detailed in our response to Comment #1, we performed\nseparate light (under a 100 mW/cm2 white LED) and thermal aging (at 65 °C) tests for encapsulated SnO and\nX\nSb O -based PSTs, respectively. Both PSTs retained over 90% of their initial PCE after 1,000 hours of\n2 3\ncontinuous aging. This conclusion directly addresses the present question as well. Please refer to our response\nto Comment #1 for supporting experimental data and a more comprehensive discussion.\nComment #11. The mechanical toughness of the developed interface remains unclear. Additional analysis\nis needed to evaluate its resistance to delamination or mechanical stress, particularly in the context of\nscalable device fabrication and long-term operation.\nResponse: Thank you for the valuable comments. The connection between C and Sb O is supported by weak\n60 2 3\nvan der Waals forces, which possibly results in their low adhesion and mechanical toughness. To further assess\nthe interfacial mechanical toughness of C /Sb O , we deposited Sb O films with thicknesses of 40 nm and 300\n60 2 3 2 3\nnm on flexible polyethylene terephthalate (PET)/C substrates, respectively. After 500 bending cycles, the 300\n60\nnm Sb O film developed severe cracking and delamination in the central bending region, whereas the 40 nm\n2 3\nSb O film remained intact (Fig. R41). Also, the GIXRD measurements of the 40 nm bending sample detected\n2 3\nthe diffraction peak of the PET substrate at a θ =3°8 (Fig. R42). Critically, the XRD peak positions of the\ninc\nC /Sb O showed no shift with varying θ , implying minimal stress residual for the 40 nm Sb O . Thus, the\n60 2 3 inc 2 3\nthinner Sb O is well-suited for future application in large-area and flexible photovoltaic devices.\n2 3\nFig. R41 Photograph and Optical microscopy of the PET/C /40 or 300 nm Sb O samples before and after 500\n60 2 3\ncyclic bending tests.\nFig. R42 GIXRD patterns of PET/C /40 nm Sb O sample after 500 cyclic bending measurement at different\n60 2 3\nincidence angles (θ =0.3, 1 and 3°).\ninc\nReferences\nphotovoltage loss. Science 388, 88-95 (2025). https://doi.org/10.1126/science.adt3417\nComment #12. The manuscript lacks a detailed comparison with other potential buffer layer materials\nthat are frequently used. A discussion on how Sb O performs relative to these commonly used\n2 3\nalternatives would strengthen the manuscript.\nResponse: Thank you for the valuable comments. Despite the prevalence of ALD-SnO with favorable\nX\noptoelectronic properties as a buffer layer in high-performance inverted tandem devices16,18, our work highlights\nthe remarkable competitiveness of thermally evaporated Sb O . As shown in Fig. 2c and Fig. 3d, the single-\n2 3\nand double- junction devices all proved the slightly better performance compared with that of devices based on\nALD-SnO buffer layer. Specifically, Sb O demonstrates comparable electrical characteristics and stability,\nX 2 3\nand even greater advantages in cost-loss and optical performance, establishing it as a compelling alternative.\nBesides, thermally evaporated bathocuproine (BCP) is also commonly employed as a buffer layer in single-\njunction devices27,29. Therefore, we further fabricated single-junction devices based on BCP. We present the J-\nV curve of the champion device, with an excellent PCE above 22% (Fig. R40). However, previous researches\nhave shown that the BCP, an organic material, generally exhibits poor thermal stability6. We also conducted\nthermal stability tests aging at 85℃ for 24 hours, the device based on BCP decomposed macroscopically (Fig.\nR43). Additionally, BCP with poor sputtering resistance cannot be directly used as a buffer layer in tandem\ndevices14. It needs to be combined with ultra-thin metal (such as BCP: Ag) to use30,31. However, we used BCP:\nAg as the buffer layer to prepare tandem solar cells and obtain the champion PCE below 23% (Fig. R39),\npossibly attributed to a narrow process window for the fabrication of ultra-thin metals.\nCompared with BCP, Sb O offers a broader processing window and superior intrinsic stability, making it\n2 3\nmore suitable as buffer layer for fabricating high-performance large-area tandem solar cells.\nFig. R43 Photographs of BCP- and Sb O -based devices under thermal aging at 85℃ in a N atmosphere.\n2 3 2\nReferences\n(2024). https://doi.org/10.1038/s41586-023-06892-x\ncells. Journal of Materials Chemistry A 10, 1343-1349 (2022). https://doi.org/10.1039/d1ta09143c\n912-919 (2025). https://doi.org/10.1038/s41586-025-09333-z\nphotovoltaics. Science 387, eadv4551 (2025). https://doi.org/10.1126/science.adv4551\n624, 289-294 (2023). https://doi.org/10.1038/s41586-023-06745-7\ninverted Perovskite solar cells. Nature Communications 16 (2025). https://doi.org/10.1038/s41467-024-\n55523-0\nperovskite/tunnel oxide passivating contact tandem solar cells. Nature Energy 8, 1250-1261 (2023).\nhttps://doi.org/10.1038/s41560-023-01382-w\nsuppressed stress corrosion. Nature Communications 14, 2166 (2023). https://doi.org/10.1038/s41467-\n023-37877-z\nComment #13. A thorough evaluation, supported by quantitative data, is necessary to assess the economic\nand technical feasibility of implementing the Sb O interlayer in large-scale manufacturing, especially in\n2 3\ncomparison with commonly adopted strategies.\nResponse: Thank you for the valuable comments. SnO is currently the most commonly used buffer layer in\nX\nperovskite/silicon tandem solar cells. Replacing SnO with Sb O results in higher short-circuit current density\nX 2 3\nand power conversion efficiency in tandem solar cells, and the parameters in the main text demonstrate the\ntechnical feasibility of using Sb O as a buffer layer. Taking the highest-efficiency cell in the text as an example,\n2 3\nthe conventional combination is 15 nm C /15 nm SnO , while the innovative combination in this work is 5 nm\nC /15 nm Sb O .\n60 2 3\nCurrently, the techno-economic analysis of tandem cells uses a bottom-up model to predict the levelized\ncost of electricity (LCOE)32-34. The cost of each process step includes materials, equipment, labor, utilities,\nmaintenance, building and facilities costs. However, this analysis method is highly influenced by factors such\nas region, policies, and production line capacity, making the model complex and subject to continuous updates\nas production line designs evolve34. Given that the tandem cell in this study only modified the C and buffer\n60\nlayer, we calculated the material cost, equipment depreciation cost, electricity cost, and sum of them for the\ndifferent combination of C and buffer layer on a 100 cm2 silicon substrate in our laboratory (Table S8). The\n60\ntotal cost of 15 nm C /15 nm SnO is about 3.4 times that of 5 nm C /15 nm Sb O for each experiment,\ndemonstrating the economic feasibility of using Sb O as a buffer layer. (aNote that material utilization factor is\n2 3\nclosely related to factors such as equipment type, geometry, and deposition process. In this statistics, thin films\nwere deposited according to steps in the experimental procedure, and the material loss for each experiment was\ndetermined by weighing the source material before and after deposition using a balance. The average material\nutilization factor was obtained through film quality divided by material loss from three different film thickness\nexperiments. bNote that the unit prices of materials and equipment investments are based on the costs of the\nproducts and equipment used in our laboratory. cNote that the processing duration of evaporated film and ALD-\ndeposited SnO is the minimum total time of evacuating the chamber, source heating, stabilizing evaporation\nX\nrate and depositing film.)\nTable R1 Fabrication cost comparison between C -15/SnO and C -5/Sb O stacks for 100 cm2 PSTs.\nCommon combination Innovation combination\nC SnO C Sb O\nLayer thickness per device (nm) 15 15 5 15\nFilm volume for 100 cm2 (cm3) 0.00015 0.00015 0.00005 0.00015\nFilm density (g/cm3) 1.6535 6.9036 1.65 5.737\nFilm quality (g) 0.0002475 0.001035 0.0000825 0.000855\nAverage material utilization\n0.1 0.04 0.1 0.06\nfactor a\nUsage of precursor (g) 0.002475 0.025875 0.000825 0.01425\nUnit price of material b\n800 100 800 4138\n(CNY/g)\nMaterial Cost (RMB/100 cm2) 1.98 2.5875 0.66 0.58425\nTotal Material Cost\n4.5675 1.24425\n(RMB/100 cm2)\nEquipment investment (CNY)b 394000 360000 394000\nEquipment lifetime (h) 72000 72000 72000\nEquipment depreciation cost\n5.5 5 5.5\n(CNY/h)\nProcessing duration (h) c 1 2.5 1.1\nEquipment depreciation cost\n5.5 12.5 6.05\n(CNY/100 cm2)\nTotal equipment\ndepreciation cost 18 6.05\n(CNY/100 cm2)\nEquipment power (KW) 6 8 6\nProcessing duration (h) 1 2.5 1.1\nAverage electricity price\n0.52 0.52 0.52\n(CNY/KW/h)\nElectricity cost\n3.12 10.4 3.432\n(CNY/100 cm2)\nTotal electricity cost 13.52 3.432\nTotal cost (CNY/100 cm2) 36.09 10.73\nReferences\ntechno-economic analysis of silicon, perovskite and tandem solar cells. IEEE Journal of Photovoltaics\n10, 1632-1641 (2020). https://doi.org/10.1109/jphotov.2020.3024739\nPhotovoltaics: Research and Applications 29, 401-413 (2020). https://doi.org/10.1002/pip.3354\nsolar modules. Joule 9 (2025). https://doi.org/10.1016/j.joule.2024.10.013\n60\nhttps://matweb.com/search/DataSheet.aspx?MatGUID=079e7b90a5914e24bc272fbb0e15fa9b&ckck=\n1 (2025).\nhttps://matweb.com/search/DataSheet.aspx?MatGUID=8161a17bd90f4ec2b2a16fe15db6c056 (2025).\n2 3\nhttps://matweb.com/search/DataSheet.aspx?MatGUID=7fd3759d5bed4c5b9b832ef8faff6dad (2025).\nhttps://www.sigmaaldrich.cn/CN/zh/product/aldrich/379255 (2025).\nComment #14. For the certification of the large-area tandem device, data on hysteresis behavior and\nsteady-state power output are missing. These measurements are essential to validate the reliability and\nperformance consistency of the device.\nResponse: Thank you for the valuable comments. We have provided the forward and reverse J-V scans of the\nencapsulated large-area champion perovskite/silicon tandem solar cell (64.64 cm2) to illustrate its hysteresis\nbehavior in Fig. R44 (Fig. 4d in Manuscript). According to your suggestions, the steady-state power output\n(SPO) of 27.66% was also recorded after 1800 s MPP tracking, as shown in Fig. R45 (Fig. S45 in SI).\nFig. R44 The J-V curves of the encapsulated large-area champion SnO - and Sb O -based PSTs (64.64 cm2).\nX 2 3\nFig. R45 SPO of the 64.64 cm2 champion PST.\nComment #15. The device performance results using different bandgaps perovskites primarily serve to\ndemonstrate generality and would be more appropriate in the Supplementary Information. In contrast,\nthe comparison of electronic properties should be presented in the main manuscript to support the core\nscientific discussion.\nResponse: Thank you for the valuable comments. Following your suggestions, we now focus on the comparison\nof electronic properties between SnO - and Sb O -based devices to support our scientific viewpoints.\nX 2 3\nAs shown in Fig. R46 (Fig. 2g in Manuscript), TPC measurements of SnO - and Sb O -based devices\nX 2 3\nreveal comparable photocurrent decay lifetimes, indicating that Sb O -based devices achieve efficient charge\n2 3\nextraction for the unique defect-assisted transport mode of Sb O . In Fig. R47 (Fig. 2h in Manuscript), the\n2 3\nsimilar photo voltage decay lifetimes observed in TPV measurements confirm that the gap states in Sb O do\n2 3\nnot introduce significant non-radiative recombination. Collectively, these results provide strong evidence for\nthe effectiveness of the defect-mediated conduction mechanism in Sb O .\n2 3\nFig. R46 TPC measurements of SnO - and Sb O -based PSCs.\nX 2 3\nFig. R47 TPV measurements of SnO - and Sb O -based PSCs.\nX 2 3\nComment #16. The light stability results show no significant difference between the SnO - and Sb O -\n2 2 3\nbased tandem devices. If SnO were causing substantial damage to the perovskite surface, a\n2\ncorresponding impact on device stability would be expected. This apparent inconsistency should be\naddressed and clarified.\nResponse: Thank you for the valuable comments. Based on XPS results (Fig. R48), the deposition of ALD-\nSnO triggers an irreversible interfacial reaction with the perovskite. Thus, we agree with that if SnO directly\nX X\ndeposited on the surface of perovskite, a significant impact on stability would be expected. However, the C\n60\nlayer serves to block this detrimental contact while facilitating electron transport. We found that the detrimental\neffects of ALD-SnO are progressively mitigated with thicker C layers, with normal device performance\nX 60\nrecovery achieved beyond 15 nm (Fig. R49). In previous extensive works, the thicker C layers are commonly\n60\nused in tandem devices with SnO to ensure superior performance and stability. Indeed, our ALD-SnO -based\nX X\ndevices with a 15 nm C layer exhibited excellent stability in aging tests.\nX\nSb O .\n2 3\nFig. R49 Statistics of PCE of the PSCs with different C thicknesses based on SnO and Sb O , respectively.\nReferences\nphotovoltaics. Advanced Energy Materials 8, 1800591 (2018). https://doi.org/10.1002/aenm.201800591\nJournal of Alloys and Compounds 604, 106-111 (2014). https://doi.org/10.1016/j.jallcom.2014.03.098\nx\ninterface chemistry, and solar cell performance. ACS Applied Energy Materials 4, 510-522 (2021).\nhttps://doi.org/10.1021/acsaem.0c02405\nElectronics 4, 906-913 (2021). https://doi.org/10.1038/s41928-021-00683-w\nScience 377, 302-306 (2022). https://doi.org/10.1126/science.abn8910\nhttps://doi.org/10.1038/s41586-023-06892-x\nfilms by ellipsometry and XPS. Journal of Electroanalytical Chemistry 645, 143-148 (2010).\nhttps://doi.org/10.1016/j.jelechem.2010.04.023\nScience 388, 88-95 (2025). https://doi.org/10.1126/science.adt3417\nhttps://doi.org/10.1038/s41467-019-12569-9\nJournal of Optoelectronics and Advanced Materials 5, 907-912 (2003).\nperovskite solar cells. Journal of Materials Chemistry A 12, 14816-14827 (2024).\nhttps://doi.org/10.1039/d3ta06654a\nreversed diode model. The Journal of Physical Chemistry C 120, 28441-28447 (2016).\nhttps://doi.org/10.1021/acs.jpcc.6b09219\nfront-electrode for monolithic perovskite/silicon tandem solar cells. Solar Energy Materials and Solar Cells 252,\n112180 (2023). https://doi.org/10.1016/j.solmat.2023.112180\nJournal of Materials Chemistry A 10, 1343-1349 (2022). https://doi.org/10.1039/d1ta09143c\nperovskite/silicon tandem solar cells. ACS Applied Materials & Interfaces 17, 17599-17610 (2025).\nhttps://doi.org/10.1021/acsami.5c00090\n(2025). https://doi.org/10.1038/s41586-025-09333-z\nhttps://doi.org/10.1038/s41586-024-07997-7\n387, eadv4551 (2025). https://doi.org/10.1126/science.adv4551\n62 (2023). https://doi.org/10.1126/science.adg0091\nsilicon. Science, eadx1745 (2025). https://doi.org/10.1126/science.adx1745\n122, 109285 (2024). https://doi.org/10.1016/j.nanoen.2024.109285\ntextured silicon. Advanced Energy Materials 12, 2202404 (2022). https://doi.org/10.1002/aenm.202202404\nsequential deposited perovskite. Advanced Materials 36, 2308692 (2024).\nhttps://doi.org/10.1002/adma.202308692\nfluorobenzylamine hydroiodide. Nano-Micro Letters 16, 189 (2024). https://doi.org/10.1007/s40820-024-01406-\n4\ntextured silicon substrates. PRX Energy 1, 023005 (2022). https://doi.org/10.1103/PRXEnergy.1.023005\nperovskite solar cells and modules. Energy & Environmental Science 18, 468-477 (2025).\nhttps://doi.org/10.1039/d4ee01960a\n294 (2023). https://doi.org/10.1038/s41586-023-06745-7\nperovskite solar cells. Nature Energy 8, 462-472 (2023). https://doi.org/10.1038/s41560-023-01227-6\nPerovskite solar cells. Nature Communications 16 (2025). https://doi.org/10.1038/s41467-024-55523-0\npassivating contact tandem solar cells. Nature Energy 8, 1250-1261 (2023). https://doi.org/10.1038/s41560-023-\n01382-w\nstress corrosion. Nature Communications 14, 2166 (2023). https://doi.org/10.1038/s41467-023-37877-z\neconomic analysis of silicon, perovskite and tandem solar cells. IEEE Journal of Photovoltaics 10, 1632-1641\n(2020). https://doi.org/10.1109/jphotov.2020.3024739\nPhotovoltaics: Research and Applications 29, 401-413 (2020). https://doi.org/10.1002/pip.3354\nmodules. Joule 9 (2025). https://doi.org/10.1016/j.joule.2024.10.013\n60\nhttps://matweb.com/search/DataSheet.aspx?MatGUID=079e7b90a5914e24bc272fbb0e15fa9b&ckck=1 (2025).\nhttps://matweb.com/search/DataSheet.aspx?MatGUID=8161a17bd90f4ec2b2a16fe15db6c056 (2025).\n2 3\nhttps://matweb.com/search/DataSheet.aspx?MatGUID=7fd3759d5bed4c5b9b832ef8faff6dad (2025).\n(2025)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revised manuscript has addressed all the reviewers’concerns, and I'm pleased to accept it for publication.", "reviewer_2": "The authors have addressed the comments and issues raised by the reviewers. I am satisfied with their response and revision. I would recommend acceptance of this manuscript at its current version.", "reviewer_3": "The manuscript has been improved significantly. However, several important issues remain insufficiently addressed, particularly regarding the tandem characterization, e.g., the textured Si bottom cell, and the functional layers in the full stack.\n1. In this work, long-term stability and MPP tracking are performed under a 100 mW cm-2 white LED source, for single-junction and especially for tandem devices. While this is experimentally convenient, it raises serious concerns for monolithic perovskite/Si tandems, which is not acceptable.\nSimply, the spectral distribution of a “white LED” typically differs from AM 1.5G, particularly in the blue and near-IR regions that are critical for current matching between the perovskite top and Si bottom cells, and bias subcells to affect its efficiency decay dynamics. I therefore recommend that the authors to Demonstrate stability under AM 1.5G. Without such analysis, the reported “negligible efficiency loss” under LED illumination cannot be directly interpreted as stability under realistic PV operating conditions.\n2. The tandem devices are based on double-textured SHJ bottom cells with “sub-micron-pyramid-structured” surfaces. However, the manuscript does not provide quantitative information on this texture, e.g., pyramid height, base width, pitch, or RMS roughness. Moreover, the etching process (e.g., alkaline vs acidic texturing, etch time, orientation dependence) is not described in enough detail to allow reproducibility.\n3. Most of the detailed structural and electronic characterization of Sb2O3 (AFM, TEM, GIXRD, c-AFM, UPS, defect-state analysis) is performed on planar substrates or planar stacks. In contrast, the actual tandem devices use Sb₂O₃ deposited on a NiOx/ITO-coated, pyramid-textured SHJ surface, followed by sputtered IZO and Ag or screen-printed contacts. I suggest the authors providing detailed characterizations on the actual textured tandem stack along and across pyramids, showing continuity and thickness of Sb2O3 over the entire facet and its crystallinity (nanocrystalline as claimed in the manuscript).\n4. Regarding Large-area uniformity, the PCE distribution of sufficient numbmers of small cells on a 10×10 cm2 substrate, are used to support scalability. Please also comment on the yield and variability among large-area devices fabricated under nominally identical conditions.\n5.The authors attribute the inferior long-term stability of Sb2O3-based PSTs to poorer compactness and facilitated ion migration through the molecular-crystal Sb2O3. Please provide direct evidence to support the claim.\n6. Please ensure that all acronyms (TE, PST, PVK, etc.) are defined at first use."}, "author_response": "Reviewer #3 (Remarks to the Author):\nThe manuscript has been improved significantly. However, several important issues\nremain insufficiently addressed, particularly regarding the tandem characterization, e.g.,\nthe textured Si bottom cell, and the functional layers in the full stack.\n1. In this work, long-term stability and MPP tracking are performed under a 100 mW cm-\n2 white LED source, for single-junction and especially for tandem devices. While this is\nexperimentally convenient, it raises serious concerns for monolithic perovskite/Si tandems,\nwhich is not acceptable.\nSimply, the spectral distribution of a “white LED” typically differs from AM 1.5G,\nparticularly in the blue and near-IR regions that are critical for current matching between\nthe perovskite top and Si bottom cells, and bias subcells to affect its efficiency decay\ndynamics. I therefore recommend that the authors to Demonstrate stability under AM\n1.5G. Without such analysis, the reported “negligible efficiency loss” under LED\nillumination cannot be directly interpreted as stability under realistic PV operating\nconditions.\nResponse: Thank you for the valuable comments. We fully understand and acknowledge the\nconcern that the spectral mismatch between a white LED and AM 1.5G could influence the\nprecise assessment of the current-matching and the degradation dynamics in perovskite/Si\ntandem devices.\nHowever, we pioneered a novel functional material in this study. For an initial stability\nbenchmark, we used a white LED as a relative proof-of-concept, following the precedent of\nrecent high-quality literature 1-4.\nReferences\nNature Communications 15 (2024). https://doi.org/10.1038/s41467-024-52309-2\nphotovoltaics. Science, eadv4551 (2025).\nefficiency. Nature Communications 16 (2025). https://doi.org/10.1038/s41467-025-61081-w\ntextured silicon for efficient tandem solar cells. Nature Communications 16 (2025).\nhttps://doi.org/10.1038/s41467-025-64546-0\nNevertheless, the results of device stability observed under LED illumination cannot be\ndirectly interpreted as stability under realistic PV operating conditions. Therefore, regarding all\nthe description of device stability, we have all specified the LED lighting condition and made\ncorresponding modifications in the text.\nA full investigation under standard AM 1.5G conditions can be considered to furtherly\nadvance this pioneering work in the future.\n2. The tandem devices are based on double-textured SHJ bottom cells with “sub-micron-pyramid-structured” surfaces. However, the manuscript does not provide quantitative\ninformation on this texture, e.g., pyramid height, base width, pitch, or RMS roughness.\nMoreover, the etching process (e.g., alkaline vs acidic texturing, etch time, orientation\ndependence) is not described in enough detail to allow reproducibility.\nResponse: Thank you for the valuable comments. The double-textured silicon heterojunction\nbottom cells used in this study are commercial products provided by LONGi Green Energy\nTechnology Co., Ltd. Both sides of the substrate were mildly textured using a relatively low-\nconcentration alkaline solution to form small-sized pyramid structures. This process is\nconsistent in principle with the front-side process described in LONGi’s published literature5.\nThe fabrication process of silicon bottom cells has been added into support information in detail\nand marked with color.\nWe also have performed direct characterization on the substrates used in this work via\nSEM (Fig. R1), which shows that the front-side and rear-side pyramid size is about 300-500\nnm.\nFig. R1 Cross-sectional SEM images of the double-textured SHJ bottom cell.\n596-603 (2024). https://doi.org/10.1038/s41586-024-07997-7\n3. Most of the detailed structural and electronic characterization of Sb O (AFM, TEM,\n2 3\nGIXRD, c-AFM, UPS, defect-state analysis) is performed on planar substrates or planar\nstacks. In contrast, the actual tandem devices use Sb O deposited on a NiOx/ITO-coated,\n2 3\npyramid-textured SHJ surface, followed by sputtered IZO and Ag or screen-printed\ncontacts. I suggest the authors providing detailed characterizations on the actual textured\ntandem stack along and across pyramids, showing continuity and thickness of Sb O over\n2 3\nthe entire facet and its crystallinity (nanocrystalline as claimed in the manuscript).\nResponse: Thank you for the valuable comments. First, it is important to clarify that one of the\nprimary objectives of this study is to investigate the intrinsic material properties of evaporated\nSb O as a novel buffer layer, such as its micro structure, electronic properties, and defect states.\n2 3\nTherefore, conducting systematic physical characterizations on planar substrates or planar\nstacks is a universal and effective methodology in materials science. This approach allows us\nto clearly elucidate its core physical mechanisms under controlled conditions, free from\ninterference by complex morphologies.\nMore importantly, thanks to the submicron-sized pyramids on our substrate, the process\nensures that the resulting perovskite layer filled up the underlying pyramid, resulting in a quasi-\nplanar top surface for the perovskite layer. The critical morphological transformation is\nunambiguously confirmed by cross-sectional TEM and SEM images of the complete tandem\ndevice or films (Fig. R2-3).\nConsequently, the subsequent layers, including the Sb O buffer layer, the IZO, and the\n2 3\nmetal contacts, are deposited on the like-planar perovskite surface. Therefore, the detailed\nstructural and electronic characterizations of Sb O that we performed on planar stacks are\n2 3\nalmost representative of its state in the actual working tandem device.\nFig. R2 Cross-sectional TEM image and EDX mappings of Si/NiO /Me-\nX\n4PACz/PVK/C /Sb O /IZO stack.\n60 2 3\nFig. R3 Cross-sectional SEM images of TE-PbI , PVK and PVK/C /Sb O /IZO stack films\n2 60 2 3\ndeposited on the micro-textured silicon bottom cell.\n4. Regarding large-area uniformity, the PCE distribution of sufficient numbmers of small\ncells on a 10×10 cm2 substrate, are used to support scalability. Please also comment on the\nyield and variability among large-area devices fabricated under nominally identical\nconditions.\nResponse: Thank you for the valuable comments. Regarding large-area uniformity, we have\nprovided the PCE distribution of 100 sub-cells fabricated on a 10×10 cm2 substrate, which\ndemonstrates good uniformity across the area (Fig. R4). Concerning yield and batch-to-batch\nvariability, our study remains at the lab-scale stage, and thus large-volume production has not\nbeen carried out. While an exact production yield cannot be provided, we have evaluated the\nreproducibility by presenting the performance of four large-area tandem devices fabricated in\nseparate batches under the same conditions.\nThe photovoltaic parameters of these four devices, each representing an independent batch,\nare summarized in Fig. R5 and Table R1. The devices exhibit a high average PCE of 27.82%\nwith an exceptionally low relative standard deviation (RSD) of 1.52% for the PCE. The other\nkey parameters also show remarkably low RSDs, all below 2%. Crucially, this excellent\nconsistency was achieved across four separate batches, which powerfully demonstrates the high\nreproducibility and robustness of our fabrication process. Manuscript and supporting\ninformation have been made corresponding modification and marked with color.\nFig. R4 Statistical distribution of normalized PCE with 100 sub-cells based on Sb O on a\n2 3\n10×10 cm2 substrate.\nFig. R5 J–V curves of four large-area (64.64 cm2) devices from different fabrication batches.\nTable. R1 PV parameters of four large-area (64.64 cm2) devices from different fabrication\nbatches.\nV (V) J (mA/cm2) FF (%) PCE (%)\nOC SC\nDevice 1 1.839 18.93 80.02 27.86\nDevice 2 1.840 18.95 80.42 28.04\nDevice 3 1.862 18.66 78.31 27.21\nDevice 4 1.832 18.96 81.11 28.16\nAverage 1.843 18.88 79.97 27.82\nStd. Dev. 0.0130 0.1439 1.192 0.4233\nRSD 0.71% 0.76% 1.49% 1.52%\n5. The authors attribute the inferior long-term stability of Sb O -based PSTs to poorer\n2 3\ncompactness and facilitated ion migration through the molecular-crystal Sb O . Please\n2 3\nprovide direct evidence to support the claim.\nResponse: Thank you for the valuable comments. To verify our initial speculation regarding\nthe stability difference, we performed XPS analysis on the PVK/C /SnO and PVK/C /Sb O\nstructures before and after photo-thermal aging (Fig. R6-7), which yielded key findings. Firstly,\nregarding ion migration, the iodine signal decreased on the aged SnO surface but increased\nX\nsignificantly on the aged Sb O -based surface. This provides direct evidence for the slightly\n2 3\ninferior halide ion migration suppression capability of the Sb O layer, consistent with its\n2 3\nrelatively poor compactness. Second, the XPS spectra reveal a distinct consumption of metallic\nantimony (Sb0) in the aged Sb O sample. Since conduction mechanism of Sb O buffer layer\n2 3 2 3\nrelies on a quasi-defect band induced by antimony interstitial atoms (I ), the loss of Sb0 implies\nSb\nthe degradation of the crucial electron transport pathway. Therefore, the inferior stability of the\nSb O -based device may arise from its weaker barrier against halide ion migration and the\n2 3\nconsumption of the I .\nSb\nFig. R6 XPS spectra (I 3d) of the pristine and light-thermally aged SnO -based and Sb O -\nX 2 3\nbased samples under white LED (100 mW cm-2) at 65 °C in a N atmosphere.\nX\nand Sb O -based samples under white LED (100 mW cm-2) at 65 °C in a N atmosphere.\n2 3 2\n6. Please ensure that all acronyms (TE, PST, PVK, etc.) are defined at first use.\nResponse: Thank you for the valuable comments. We have revised the manuscript to define all\nacronyms upon their first use. Specifically, \"TE\" is now defined as \"thermally evaporated\",\n\"PST\" as \"perovskite/silicon tandem\", and \"PVK\" as \"perovskite\" in the manuscript. All other\nacronyms have been similarly treated throughout the text.\nReferences\nNature Communications 15 (2024). https://doi.org/10.1038/s41467-024-52309-2\nphotovoltaics. Science, eadv4551 (2025).\nefficiency. Nature Communications 16 (2025). https://doi.org/10.1038/s41467-025-61081-w\ntextured silicon for efficient tandem solar cells. Nature Communications 16 (2025).\nhttps://doi.org/10.1038/s41467-025-64546-0\n596-603 (2024). https://doi.org/10.1038/s41586-024-07997-7"}, {"round": 3, "reviewer_comments": {"reviewer_3": "I appreciate the authors' efforts in addressing the majority of the concerns raised in the previous round, particularly regarding the large-area yield statistics and the structural characterization of the silicon bottom cell.\nHowever, the refusal to validate device stability under standard AM 1.5G conditions remains a critical methodological barrier that prevents publication. For monolithic perovskite/silicon tandems, the spectral mismatch of white LEDs fundamentally alters the current-matching condition, forcing sub-cells into artificial bias states that differ significantly from real-world operation. This renders your degradation analysis unreliable, as the perovskite top-cell may not be under the limiting stress encountered in the field. Labeling the work as \"pioneering\" does not exempt it from basic metrological standards. Without AM 1.5G MPP tracking, I think the claim of device stability is unsubstantiated and the manuscript remains unsuitable for publication."}, "author_response": "Response: Thank you for this important comment. We fully understand your concern regarding\nthe potential impact of spectral mismatch (e.g., under white-LED illumination) on stability\nassessment in monolithic perovskite/silicon tandems, and we agree that stability validation\nunder standard AM 1.5G conditions is an important metrological requirement. To better reflect\nreal-world operation, we followed your suggestion and performed continuous aging tests in air\nunder standard AM 1.5G illumination using a xenon-lamp solar simulator (Model: FG-MN001-\nACA-AM1.5G-100) (Figs. R1–R2). The irradiance was calibrated to 1 sun (100 mW/cm2)\nusing a certified silicon reference cell. The additional AM 1.5G aging test is consistent with our\nearlier LED aging results (Fig. R3), which showed that the Sb O -based devices exhibit partly\n2 3\nlower stability than the SnO -based devices. After 1000 h under LED illumination, the Sb O\nX 2 3\ndevice retained ~90% of its initial PCE, compared with ~97% for SnO In the newly added\nX.\nAM 1.5G test, the corresponding retentions were ~65% (Sb O ) and ~80% (SnO ) after 450 h.\n2 3 X.\nWe suggest that the difference in absolute retention between the two tests may be related to the\ndifferent illumination spectra. The experimental details and corresponding data are provided in\nthe Supplementary Information (Device Characterization, Supplementary Note 5 and Fig.\nS39).\nWe would like to clarify the scope of this work. The primary contribution is the demonstration\nof thermally evaporated Sb O as a new buffer layer offering advantages in light management\n2 3\nover ALD-SnO , which translate into improved device efficiency. The stability data are\nX\npresented as baseline benchmarks to enable objective assessment by the community. As stated\nin the original submission, the stability of Sb O -based devices is not yet on par with the highly\n2 3\nmature ALD-SnO process, which has benefited from extensive optimization over many years.\nX\nThe newly added AM 1.5G aging results are consistent with the initial stability statement and\nprovide clearer references under standard spectra. We sincerely appreciate your rigorous review,\nwhich has improved the scientific rigor of this work.\nFig. R1 Photograph of the stability test for encapsulated SnO - and Sb O -based devices under\nX 2 3\ncontinuous AM 1.5G illumination.\nFig. R2 Light aging tests of encapsulated SnO - or Sb O -based tandem devices under\nX 2 3\ncontinuous AM 1.5G illumination at 100 mW/cm2 in air.\nFig. R3 Light aging tests of encapsulated SnO - or Sb O -based tandem devices under a white\nX 2 3\nLED lamp illumination at 100 mW/cm2 in a N atmosphere.\n2"}, {"round": 4, "reviewer_comments": {"reviewer_1": "I have satified with all the responses.", "reviewer_3": "I appreciate the authors' efforts. I'm satisfied with this revision. The manuscript is ready for publication.", "reviewer_4": "The authors have addressed the comments and issues raised by the reviewers. I am satisfied with their response and revision. I would recommend acceptance of this manuscript at its current version."}, "author_response": ""}]

Decision letter