Perovskite solar cells with enhanced thermal fatigue resistance under extreme temperature cycling

Domain: chemistry
Published: 2026-03-09
Editorial outcome: minor_revision

Abstract
Metal halide perovskite solar cells combine high power density with low-cost manufacturing, but durability under repeated extreme temperature cycling remains insufficiently understood. We investigate thermal fatigue under cycling between −80 °C and +80 °C as an accelerated stress protocol. Mismatched thermal expansion between the perovskite absorber and glass substrate induces biaxial tensile strain, leading to degradation at the substrate–perovskite interface and within grain boundaries. To mitigate these failure modes, we introduce a co-additive molecular strategy based on lipoic acid, dihydrolipoic acid, and a sulfonium-based derivative to enhance interfacial adhesion, while in situ polymerisation during annealing reinforces grain-boundary cohesion. This dual reinforcement improves robustness and performance, achieving stabilised efficiencies of 26% under standard solar illumination. Devices retain 84% of initial efficiency after 16 extreme temperature cycles. Our experiments reveal that thermal exposure duration is more critical than cycle number, with most degradation occurring during initial cycles.

Introduction
Metal halide perovskite solar cells (PSCs) have attracted significant attention due to their high power conversion efficiencies, low fabrication costs, and compatibility with lightweight device architectures.1 These attributes make PSCs attractive for applications in which high specific power and mechanical compliance are required. They present a potential alternative to conventional III–V-based photovoltaic technologies, which are well known for their robustness under extreme operating conditions but are limited by high material and fabrication costs and relatively short operational lifetimes.2 However, the long-term mechanical and structural stability of layered perovskite device stacks under repeated thermomechanical stress remains a key challenge limiting their broader deployment.

Repeated temperature cycling induces volumetric expansion and contraction within the solar cell stack, giving rise to mechanical fatigue that can ultimately lead to delamination, crack formation, or failure at weakly bonded interfaces.2,3 Such effects are particularly pronounced in multilayer thin-film devices due to mismatches in the coefficients of thermal expansion (CTE) between adjacent layers. In perovskite solar cells, large CTE differences between the glass substrate (3.7 × 10-6 K-1)4, the transparent conductive oxide (e.g., ITO, 8.5 × 10-6 K-1)4, and the perovskite absorber (e.g., FAPbI3, ~203 × 10-6 K-1)5 concentrate strain at grain boundaries and heterointerfaces, accelerating mechanical degradation during temperature cycling.

Extreme temperature cycling represents a particularly severe stress condition for thin-film photovoltaic devices and is encountered in several scenarios, including high-altitude platforms, aerospace systems, and accelerated laboratory stress testing. In comparison to standard terrestrial qualification protocols—such as IEC thermal cycling tests typically limited to −40 °C to +85 °C—these conditions involve wider temperature excursions and often faster thermal ramp rates, resulting in rapid stress evolution within the device stack. Environments such as low-Earth orbit (LEO) are frequently cited as representative examples of extreme thermal cycling conditions, where repeated transitions between sunlight and shadow lead to pronounced temperature fluctuations, with cycling frequencies approaching ~6,000 cycles per year and thermal ramp rates on the order of 4–5 °C min-1, resulting in rapid stress evolution within the solar cell stack6-9. Recent systematic studies have also examined perovskite solar cell performance under extreme temperature cycling and in-orbit conditions, further highlighting the importance of understanding thermal fatigue for space deployment.10-12 Understanding thermally induced mechanical fatigue under these conditions is therefore essential for improving the durability of thin-film photovoltaic technologies for extreme temperature conditions.

Previous studies have demonstrated that incorporating functional additives into perovskite precursor solutions can improve film quality, defect tolerance, and mechanical resilience. In particular, polymerizable or cross-linkable additives are introduced into the perovskite precursor, polymerizing during annealing and localizing at grain boundaries to heal defects and improve film quality.13 For example, polymers containing isocyanate groups include poly(oxime-urethanes)14 and polyurea with PDMS blocks,15 polymers with disulfide groups include polyurethane elastomers (PUDS)16, polyurethanes with pendant fullerene units (C60-PU)17, and polyurethanes without fullerene moieties.18 Finally, polymers with carboxylic acid groups include poly(LA)19 and its salt form, poly(TA-NI)20, which is based on a hydrazide-derived ammonium ion. Across all these systems, thermal-triggered healing has resulted in more than 80% recovery of solar cell performance after stress testing11-18, while systems based on poly(LA) and poly(TA-NI) demonstrated recovery rates exceeding 90%17,18. Notably, the behaviour of such materials under thermal cycling tests, particularly their protective effects on PSCs, remains unexplored and represents a significant knowledge gap in this field.

To improve adhesion at the interface between the transparent conductive oxide (TCO) and the perovskite layer, several surface-engineering strategies have been developed. Reported approaches include increasing surface hydroxylation by replacing crystalline TCOs with amorphous ones,21,22 removing terminal hydroxyls and hydrolysis byproducts via combined HF and UV–ozone treatments,23 introducing hetero-chiral linker molecules,24 and employing self-assembled molecules (SAMs) such as iodine-terminated carbazole derivatives or bifunctional thiol–carboxylic acid systems with varying alkyl chain lengths.25 However, most reported studies focus primarily on initial device performance or environmental stability under moisture or light exposure, while systematic investigations of interfacial robustness under repeated extreme temperature cycling remain limited.

In this work, we use 5-(1,2-dithiolan-3-yl)pentanoic acid (α-lipoic acid, LA) and functionalize it further as part of our two-step reinforcement strategy, and the synthetic procedures are provided in Supplementary Figure 1, while the NMR analyses are shown in Supplementary Figures 2–4. To promote inter-grain connectivity, LA is incorporated into the perovskite precursor solution with the expectation that it can undergo in situ polymerization during crystallization (as shown in Fig. 1b). Specifically, we aim to investigate whether, upon heating above 70 °C, the disulfide bonds in LA would initiate thermally driven ring-opening polymerization, and whether, during cooling, the carboxylic acid groups would form stable hydrogen-bonded dimers. Together, we aim for these processes to enhance cross-linking and mechanical cohesion at the grain boundaries. For interfacial reinforcement between the transparent conductive oxide (TCO) and perovskite, we aim to enhance chemical interactions beyond the disulfide bonding provided by LA and synthesize and explore its derivatives. Furthermore, to approximate the mechanical stresses associated with these rapid and extreme temperature shifts, we adopt a custom thermal cycling protocol spanning −80 °C to +80 °C, consistent with practical satellite temperature measurements and recent thermal stress studies on perovskite solar cells,26-28 which necessitates the development of a dedicated test setup. We systematically evaluate the impact of this dual reinforcement approach on the mechanical durability and performance stability of perovskite solar cells.

Results
Crosslinking of LA in the Grain Boundaries
LA molecules polymerize at the grain boundaries (as sketched in Figure 1a-b) within the perovskite bulk during the thermal annealing process, as they are unable to fit the perovskite crystal lattice, due to the large molecular size of both the monomeric and polymeric forms.19,29 X-ray photoelectron spectroscopy (XPS) results indicate that the poly(LA) primarily interacts with the perovskite lattice through the –COOH side group, which does not participate in polymerization, as shown in Supplementary Figure 5a, specifically via hydrogen bonding between the –OH group of poly(LA) and perovskite octahedra, –OH···IPbI5. Additionally, the =O group (a Lewis base) within the same carboxylic acid functional group is shown to coordinate with under-coordinated Pb2+ ions (acting as Lewis acids), as evidenced by the energy shifts (Supplementary Figure 5b-c) observed in the orbitals of the involved lead atoms.19 Indirect evidence of LA polymerization is provided by the FTIR spectra (Supplementary Figure 6a), where the –COOH stretching vibration shifts from 1,690 cm-1 to 1,703 cm-1 under similar thermal conditions, suggesting the occurrence of polymerization.30 To further investigate the possible localization of poly(LA) within the perovskite bulk structure, particularly at the grain boundaries, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and the corresponding energy-dispersive X-ray spectroscopy (EDX) elemental mapping were performed, as shown in Supplementary Figure 6b-c. Furthermore, XRD analysis revealed that the intensity of the excess PbI2 signal observed in the control group (Supplementary Figure 7a) was reduced in the LA-treated films, suggesting a potential chemical interaction between LA and PbI2. This interaction is further supported by ¹H-NMR spectra of LA and its mixture with PbI2 (Supplementary Figure 7b), which show a slight upfield shift of the proton signal corresponding to the carbonyl group of LA (acting as a Lewis base), from 12.00 to 11.99 ppm.31 Finally, GIWAXS measurements performed on the same films, as shown in Supplementary Figure 8, revealed no change in the orientation of the perovskite planes and no additional reflections, indicating the absence of new phases.

Nanoscale atomic force microscopy (AFM) analysis with the quantitative nanomechanical characterization technique revealed that compared to the control group, the perovskite films, which have LA and its derivatives in combination with SAM (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid, 4PADCB) at the substrate interface — with a fixed amount of LA incorporated into the bulk — exhibited enhanced adhesion at grain boundaries. Notably, DHLA resulted in an increase of over 50% in average adhesion at grain boundaries, while DMSLA led to an increase of approximately 40%; in contrast, the LA form did not cause a significant change. Note that any overestimation of adhesion forces due to increased surface contact at grain boundaries is minimal, since the depth and width of the grain boundaries at the perovskite/SAM interface are larger than the tip apex curvature. (Figure 1c). Hence, the enhanced adhesion can be primarily attributed to the polymer, which preferentially localizes at the grain boundaries and plays a significant role in improving adhesion in these critical regions.

Young’s modulus values derived from the same imaging dataset (Supplementary Figure 9), along with adhesion and modulus measurements from the top surfaces of control and LA-containing perovskite films, are presented in the Supporting Information (Supplementary Figure 10). Additionally, an increase in inter-grain adhesion was observed, which may arise from two contributing factors: (1) enhanced adhesion at the grain boundaries due to polymer cross-linking, and (2) a potential overestimation of mechanical properties resulting from an increased contact area at the grain boundaries (Figure 1c, bottom line). Given that the control sample exhibits lower adhesion at the grain boundaries despite having a similar boundary depth, the observed adhesion enhancement can be attributed to the cross-linked polymer network. In contrast, we observe no change in the Young’s modulus of the grains (excluding regions with exposed polymer), while a decrease in modulus at the interface is evident, likely due to the inherently lower stiffness of the polymer.

Linker Molecules at the HTL Perovskite Interface
We engineered the ITO/perovskite interface by co-functionalizing the surface with lipoic acid derivatives together with the standard SAM molecule, 4PADCB, to strengthen interfacial adhesion. All molecules featured carboxylic acid (–COOH) anchoring groups for binding to the TCO electrode. To diversify binding interactions, we introduced sulfur-containing head groups: the disulfide ring in LA, the free thiol (–SH) groups in dihydrolipoic acid (DHLA, 6,8-dimercaptooctanoic acid), and the sulfonium cation in 7-carboxy-3-(methylthio)heptyl dimethylsulfonium (DMSLA). The molecular structures of the linker molecules are shown in Figure 2a.

We examined the adhesion strength of SAM-linker contacts at the ITO/perovskite interface through pull-off testing. Indeed, as such systems are known to have intrinsically a very low toughness, it is important to inhibit any initiation of delamination between the layers. Consequently, the strength of adhesion is the right quantity to quantify the performance of such systems towards mechanical integrity. For this, a stack consisting of glass/ITO/4PADCB-linkers/perovskite/PMMA was prepared, and a dolly was attached to the top surface using an adhesive. PMMA served as an interlayer to protect the underlying layers from the damage of epoxy glue and improve the adhesion strength between the glue and the specimen surface, as shown in Figure 2b. From the resulting load–displacement graphs, we extracted the interfacial adhesion strength, which increased from 3.61 MPa for the control sample to 4.89 MPa for the DMSLA-treated samples (Figure 2c). Pull-off tests showed a wide distribution of adhesion strength across all samples, likely arising from small preparation imperfections such as slight misalignment angles or adhesive layer thickness differences, yet DMSLA-based samples consistently showed the highest average strength. The resulting stress distributions follow the same trend, indicating that DMSLA-treated interfaces require greater force to induce interfacial failure (Figure 2d).

Beyond macroscopic mechanical analysis, we performed XPS at the substrate/perovskite interface, analysing each side independently after mechanical peeling. Example samples included LA in the SAM precursor, noting that perovskite also incorporates LA. On the glass–ITO side, the –COO signal was 2.01%, corresponding to the –COOH anchoring groups of the linker molecules. On the perovskite side, the –COO signal was 6.45% for samples without LA in the SAM precursor (Supplementary Figure 11). In contrast, with LA in the SAM precursor, the –COO signal decreased to 0.96% on the glass–ITO side but increased to 7.09% on the perovskite side. These results indicate a strong interaction between LA in the perovskite layer and LA in the SAM.

Further, we performed Density Functional Theory (DFT) analyses of the bare SAM (4PADCB), LA, and its derivatives—both individually and in mixtures—on the ITO surface and in contact with the adjacent perovskite layer. Among the investigated molecules, DMSLA exhibits the strongest interaction with the perovskite surface, as evidenced by its high interfacial interaction energy, as shown in Figure 2e-f. In the planar-averaged charge density difference (CDD) plot (Supplementary Figure 12), DMSLA displays the broadest and most pronounced peak at the interface region, suggesting a significantly enhanced interfacial charge transfer. Furthermore, the isosurface representation of the CDD indicates extensive charge accumulation and depletion regions spanning both the molecular layer and the perovskite substrate, further confirming the superior electronic coupling. In addition, the co-attachment of LA and its derivatives with 4PADCB on the ITO surface, as well as the interactions between the SAM and LA-derived molecules anchored to the ITO surface and the perovskite at the top contact, were investigated using DFT calculations. All related data are provided in the Supporting Information, Supplementary Figure 13-14. This trend is consistent with our pull-off test results (Figure 2c-d), which show that the sulfonium cation head group establishes the strongest and most favourable chemical bonding with the perovskite layer. Accordingly, the observed macroscopic improvement in adhesion strength can be attributed to the cumulative effect of these strong and chemically effective interfacial interactions.

We validated the binding of SAM–linker mixtures to the ITO surface using XPS, through the detection of characteristic –COOH-related signals around 289 eV, as shown in Supplementary Figure 15. To quantify the surface coverage factor of SAMs, we employed cyclic voltammetry (CV) measurements using glass/TCO/SAM-linker stacks.32 The coating density was calculated through the integration of the redox peak corresponding to the electroactive moiety anchored via the SAM. This method allows an indirect estimation of the surface coverage by correlating the charge passed during the redox process to the number of active molecules present on the surface. The coating density of the SAM molecules—both in their pure forms (controls) and in mixtures with linkers—was calculated using Eq. (1).

iₚ = n²F² / 4RTNA * AΓ*ν (1)

Here, iₚ is the oxidative peak current (A), v is the scan rate (V s-1), n is the number of electrons transferred, F is the Faraday constant (96,485 C mol-1), R is the universal gas constant (8.3144 J K-1 mol-1), T is the temperature (K), N is Avogadro’s number (6.022 × 1023 mol-1), A is the electrode surface area (1.5 cm2), and Γ* (molecules cm-2) is the surface coverage, which can be determined from the slope of the iₚ versus v plot. SAM forms coated on the ITO surface in mixtures with linkers exhibited higher surface coverage compared to the pure SAM, with coating densities reaching the highest value with DMSLA, with 3.75 × 1013 molecules cm-2, while only 4PADCB is 2.84 × 1013.33 Details for the analysis are provided in Supplementary Figure 16.

Ultraviolet photoelectron spectroscopy (UPS) was used to analyse energy-level alignment between different contact stacks and the crystallized perovskite bulk (with LA) (Supplementary Figure 17). The smallest energy gap between the ITO work function—modified by the SAM mixture—and the perovskite valence band, critical for efficient charge transfer, was observed for the DMSLA-blended 4PADCB (Supplementary Table 1). This notable downshift in the ITO work function can be attributed to the large dipole moment of DMSLA (31.9 D, see results in Supplementary Figure 18), which induces an interfacial dipole layer and modifies the surface vacuum level. The reduced energy difference between the levels involved in hole transfer is known to facilitate hole extraction at the modified interface.

Scanning electron microscopy (SEM) was performed to investigate the effects of LA and its derivatives, applied with the SAM layer on ITO substrates, on the perovskite/ITO interface and bulk perovskite morphology. SEM micrographs revealed that the incorporation of LA and its derivatives, both within the bulk and at the SAM–perovskite interface, led to increased grain sizes in the perovskite films. As shown in Supplementary Figure 19 and supported by the XRD data in Supplementary Figure 7a, this structural change is accompanied by an improvement in the crystallinity of the perovskite layer. In contrast to the control films, which show visible pinholes, particularly in cross-sectional images, the blended films display a more compact and pinhole-free morphology (Supplementary Figures 19-21). These findings suggest that the additives influence the number and size of perovskite crystal grains formed during crystallization, thereby affecting grain size distribution and the prevalence of multi-domain structures.29 This indicates improved film uniformity and domain connectivity at the interface.25

Solar Cell Performances
We fabricated solar cells with the structure of ITO/4PADCB-linkers/Cs0.05MA0.10FA0.85PbI3 (w/o LA)/C60/BCP/Ag, as shown in Figure 3a. Detailed device fabrication for all devices is provided in the Methods section. From J-V analysis, we found that the target devices —featuring DMSLA at the HTL interface and LA in the perovskite bulk—exhibited the highest performance, as shown in Figure 3b. This device achieved a PCE of 25.21%, with a Voc of 1.16 V, a Jsc of 26.06 mA cm-2, and a FF of 0.83. We further verified the proposal molecules by transferring our linker approach to colleagues in Tianjin University, and their independent molecule synthesis and device fabrication results showed a close match to those measured in our laboratory, LMU Munich: PCE of 25.98%, with Voc of 1.16 V, Jsc of 26.35 mA cm-2, and FF of 0.85 (steady-state PCE: 25.51%, in the Figure 3c). The slight variation in device performances is due to the different perovskite processing recipes and conditions as given in the Methods section.

As can be seen from the energy level diagram derived from the UPS data presented in Figure 3d—which is critical for charge transfer at the perovskite/SAM interface—the combination of 4PADCB with DMSLA results in the smallest energy offset (0.25 eV) between the valence band maximum (VBM) of the modified ITO and that of the LA-doped perovskite. Furthermore, considering the intrinsic dipole moments calculated for the LA derivatives (Supplementary Figure 18) used in combination with SAM, the significantly large dipole moment of DMSLA and its induced shift in the work function of ITO further support this favourable alignment. Taken together, these findings rationalize the superior Jsc and FF observed for the 4PADCB+DMSLA SAM formulation, shown in Figure 3b-f, compared to the control and other LA derivatives. We assign the enhanced Voc of the devices to the effective passivation of crystal defects at the substrate/perovskite interface by LA and its derivatives, and within the perovskite bulk by LA alone. This dual-passivation approach at both the SAM/perovskite interface and the grain boundaries suppresses trap-assisted recombination throughout the structure, thereby leading to an increase in open-circuit voltage. We investigated the charge carrier recombination dynamics of the samples via steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. The perovskite layers on 4APADCB-linker stacks exhibited slightly higher PL intensity and extended carrier lifetimes according to the TRPL results, compared to the only 4PADCB-based samples (Supplementary Figure 22c-d). PL-based implied open-circuit voltage (iVoc) images34 in Figure 3e, acquired over the full device area (six pixels per device), show spatially uniform voltage distributions that are consistent with the electrical performance trends observed in the corresponding solar cells, indicating that the introduced interlayer does not induce macroscopic inhomogeneity. When evaluated alongside the Voc–FF comparison in Figure 3f, the iVoc values derived from PL are slightly lower than the corresponding Voc values, as expected; nevertheless, both measurements—performed at different institutes and at different times—exhibit consistent trends in Voc enhancement across the device series. The accuracy of the Jsc values was validated through integration of the external quantum efficiency (EQE) spectra (Supplementary Figure 23), yielding consistent results with the measured Jsc, specifically 25.10 mA cm-2. Additional statistical distributions of the device performance parameters from LMU Munich and Tianjin University are provided in the Supporting Information (Supplementary Figures 24-25).

Thermal Fatigue Stability Analysis
We performed the thermal fatigue test using a custom-built close-lid setup, as standard climate chambers could not reach the required –80 °C cryogenic range, which induces the highest stress at the perovskite–substrate interface. The samples—one device per condition, each comprising six pixels—were cycled between –80 °C and +80 °C in a stainless-steel container, with controlled heating and cooling rates of +3.40 and –3.80 °C min-1, respectively, and a total cycle duration of ~90 minutes under dry ambient conditions (Figures 4a, b). The 90-minute cycle duration was chosen to approximate a symmetric heating–cooling sequence (~45 minutes per half-cycle), reflecting characteristic thermal timescales reported for low-Earth-orbit environments35 and ensuring sufficient thermal equilibration of the full device stack. A comparative summary of reported thermal-cycling studies on perovskite solar cells under space-relevant or terrestrial conditions is provided in Supplementary Table 2. Thermal cycling was continued until the performance of the target devices dropped below ~90% of their initial power conversion efficiency. A schematic and further explanation of the experimental setup are provided in Supplementary Figure 26. After 16 thermal cycles under the applied temperature protocol, encapsulated solar cells with DMSLA retained 84% of their initial performance, compared to 79% for the control group. In contrast, the solar cells treated with LA and DHLA showed inferior stability, retaining only 64% and 72% of their initial performance, respectively. Performance degradation was observed across all photovoltaic parameters, with the most pronounced losses occurring in the FF. As shown in Figure 4a, control devices exhibited an FF reduction of ~15–20%, whereas DMSLA-modified devices showed a smaller loss of ~10%. This enhanced stability is likely due to the ability of DMSLA to reinforce mechanical adhesion at the perovskite/SAM interface and suppress structural degradation caused by repeated thermal expansion and contraction. The transient decrease and subsequent recovery in Voc observed for DMSLA-treated devices may arise from interfacial relaxation during repeated thermal cycling, reflecting temporary perturbation of interfacial energetics followed by stabilization upon continued cycling. Further studies would be required to determine the exact mechanism. We note that the adhesion ranking (DMSLA > DHLA > LA > control) does not directly mirror the thermal-cycling results because adhesion represents only one component of thermomechanical stability. Thermal cycling also depends on the chemical robustness of the linker molecules and the ability of the grain boundaries to accommodate strain. DMSLA combines strong and stable interfacial bonding—supported by our DFT, XPS, CV, and UPS data—with higher chemical stability under thermal stress, whereas DHLA’s thiol groups are more reactive and may undergo changes during cycling. This interplay of interfacial adhesion, chemical stability, and grain-boundary reinforcement explains the superior cycling performance of DMSLA. Furthermore, the J-V characteristics of representative devices from each group, measured before and after the thermal fatigue test, are shown in Figure 4b. To further elucidate the origin of performance degradation under thermal cycling, the evolution of all photovoltaic parameters (PCE, FF, Voc, and Jsc) was analysed across different cycling conditions in detail and is summarized in Supplementary Figures 27-29. A consolidated comparison of the parameter changes is provided in Supplementary Figure 30, which shows that the dominant degradation pathway is associated with a loss in fill factor, while variations in Voc and Jsc remain comparatively minor. The contour plot shown in Figure 4c reveal that degradation trends correlate more strongly with the accumulated thermal-exposure time than with the number of cycles alone. Together, these results indicate that thermomechanical fatigue primarily manifests through resistive and interfacial losses rather than bulk recombination or optical absorption losses.

Additional J-V measurements under ~1,360 W m-2 (AM0-approximated) illumination further confirm the robustness of the DMSLA-modified devices under elevated operational stress (Figure 4d). Statistical distribution and additional information are provided in Supplementary Figures 31 and 32. Maximum power point tracking (MPPT) analysis of the encapsulated solar cells—conducted under conditions of 45 ± 5 °C, 70 ± 10% relative humidity, and ~1,000 W m-2 equivalent 1-sun illumination- revealed that DMSLA-based target devices remained almost unchanged, while the control samples lost 33% of their initial efficiency after 500 hours (Figure 4e). The high PCE retention observed during MPPT measurements, compared to the lower retention seen in thermal fatigue tests, indicates that extreme temperature cycling may present a more significant challenge than continuous MPPT operation. Nonetheless, maintaining operational stability at elevated temperatures remains equally important and should not be underestimated. The initial J–V curves and corresponding photovoltaic parameters prior to MPPT testing are provided in Supplementary Figure 33.

Methods
Materials
Cesium iodide (CsI, 99.5%), Lead (II) iodide (PbI2, 99.99%), Lead(II) Chloride (PbCl2, 99.0%), α-lipoic acid (LA), and dihydrolipoic acid (DHLA) were sourced from TCI. N, N-dimethylformamide (DMF, 99.8%), dimethyl sulfoxide (DMSO, 99.8%), Isopropanol (IPA, 99.8%), Chlorobenzene (CB, 99.9%), and ethanol (EtOH, 99.8%) were purchased from Sigma Aldrich. Methylammonium iodide (MAI, 99.5%), Methylammonium bromide (MABr, 99.5%), and formamidinium iodide (FAI, 99.5%) were purchased from GreatCell Solar Materials. Fullerene (C60, 99.5%) and (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (4PADCB) were purchased from Lumtec. Indium tin oxide (ITO, YXKJGI-0006,15 Ω sq-1), and Bathocuproine (BCP) were purchased from Yingkou Advanced Election Technology Co., Ltd. Lithium fluoride (LiF) and Ethanediamine dihydroiodide (EDAI2) were purchased from Xi’an Polymer Light Technology, China. All chemicals were used as it is without further purification.

Synthesis of DMSLA
DMSLA was synthesized via a two-step methylation procedure (Supplementary Figure 1). In the first step, the dithiol carboxylic acid precursor was reacted in a biphasic toluene/water system in the presence of aqueous NaOH and tetrabutylammonium iodide as a phase-transfer catalyst. Iodomethane was added dropwise, and the reaction mixture was stirred at room temperature for 12 h. The reaction was then acidified to pH 1 using 2 M HCl, followed by the addition of brine. The product was extracted with dichloromethane, and the combined organic layers were dried over anhydrous MgSO₄. Solvent removal under reduced pressure afforded the methylthio-functionalized intermediate as a yellow solid without further purification.

In the second step, the methylthio-functionalized intermediate was dissolved in ethanol, and iodomethane was added dropwise at room temperature. The reaction mixture was stirred for 24 h, after which the solvent was removed under reduced pressure. Addition of diethyl ether induced precipitation of a yellow solid, which was collected by filtration and washed three times with diethyl ether to yield the final product, 1,3-bis(dimethylsulfonio)heptane-7-carboxylic acid diiodide (DMSLA).

Full synthetic schemes and spectroscopic characterization (^1H and ^13C NMR) are provided in the Supplementary Information (Supplementary Figures 1–4).

Single junction device fabrication LMU Munich
ITO-coated glass substrates were sequentially cleaned with acetone and isopropyl alcohol (IPA) in an ultrasonic bath for 15 minutes each, then dried under a stream of nitrogen gas. They were subsequently treated with oxygen plasma for 15 minutes before the coating process. Following this, the substrates were transferred into a nitrogen-filled glove box. A solution of 4PADCB (0.5 mg mL-1), prepared in methanol and blended solutions containing LA, DHLA, or DMSLA (in a 4:1 weight ratio), was spin-coated onto the ITO surface at 3,000 rpm for 30 seconds. The films were then annealed on a hot plate at 100 °C for 10 minutes. The perovskite precursor solution was prepared in 1 mL of a DMF/DMSO (4:1, v/v) mixture, containing 1.7 M Cs0.05MA0.10FA0.85PbI3 and doped with LA (0.2 mg mL-1). This solution was deposited onto the modified ITO substrates by spin coating at 5,000 rpm for 45 seconds. Anisole (250 µL) was used as an antisolvent, dropped onto the spinning substrate at the 15th second. The resulting films were immediately annealed at 100 °C for 30 minutes. Notably, no surface passivation has been applied to perovskite layers. Subsequently, C60 (28 nm), BCP (7 nm) (or 20 nm SnO2 by ALD followed by 70 nm IZO by sputtering for thermal-shock test), and finally a metallic silver electrode (120 nm) was thermally evaporated in an MBraun thermal evaporator with 1 Å s-1 deposition rate through a shadow mask.

Single junction device fabrication Tianjin University
The 1.6 M perovskite precursor solution with the composition of FA0.8MA0.15Cs0.05PbI3 (bandgap: 1.55 eV) was prepared by fully dissolving CsI: 20.8 mg, MABr: 7.6 mg, MAI: 38.1 mg, FAI: 234 mg, PbI2: 738 mg, PbCl2:18 mg in a mixed solvent of DMF: 800 μL, DMSO:200 μL. The 4PADCB solution with a concentration of 0.5 mg mL-1 was prepared by dissolving it in EtOH. The EDAI2 solution with a concentration of 0.5 mg mL-1 was prepared by dissolving it in IPA. Inverted device architecture was ITO/SAMs/PIVK/LiF/C60/BCP/Ag. The ITO was washed with detergent, deionized water, acetone, and ethanol in sequence for 30 minutes. After that, the cleaned ITO substrate was dried by N2 gas and then treated with plasma for 15 minutes. The 100 μL 4PADCB (0.5 mg mL-1) dissolved in ethanol, as a hole transport material, was spin-coated on ITO for 30 s at 3,000 rpm and then annealed at 100 °C for 10 minutes. Subsequently, 60 μL perovskite precursor was deposited on the 4PADCB layer. The perovskite solution was spin-coated at 1,000 rpm for 10 s, and 5,000 rpm for 30 s. At 16 seconds before the end of the procedure, 200 μL of CB as the antisolvent was dripped into the precast film surface. After that, the substrates were quickly transferred to a hot plate at 100 °C for 50 min annealing. For post-treatment, the 55 ml EDAI2 dissolved in IPA was spin-coated on the perovskite surface at 5,000 rpm for 30 s and then annealed at 100 °C for 10 minutes. The spin-coating processes were all conducted at room temperature (about 25 ℃) in a N2-filled glovebox. Finally, 1 nm LiF at a rate of 0.1 Å s-1, 25 nm C60 at a rate of 0.1 Å s-1, 6 nm BCP at a rate of 0.1 Å s-1, and 100 nm silver electrode at a rate of 1.0 Å s-1 were thermally evaporated, respectively, under high vacuum (< 4 × 10−4 Torr).

Solar cell device encapsulation
The device is covered with two barrier films (polyethylene terephthalate), using Polyolefin Elastomer (POE) as the top and bottom encapsulation material and butyl rubber as the edge sealant. Under a temperature of 110°C and a pressure of 1,000 mbar, the assembly is pressed for 20 minutes to soften the edge sealant and cure the encapsulation material.

Solar cell performance analysis
Current density–voltage (J–V) measurements were performed using a Newport Oriel Sol 2A solar simulator, coupled with a Keithley 2401 source meter. Devices were illuminated through a shadow mask, defining an active area of 0.1 cm². J–V curves were recorded under standard AM 1.5G illumination from a Xenon arc lamp, with the light intensity calibrated to 100 mW cm-2 using a Fraunhofer ISE-certified silicon reference cell, with a stabilization time of 5 s and a voltage step size of 0.02 V, and the measurements were performed in ambient atmosphere at room temperature. Additionally, at LMU, a spectrophotometer was used to measure the spectrum of the solar simulator, and the illumination intensity was directly calibrated to minimize spectral mismatch by using the provided EQE data together with the NREL AM 1.5G reference spectrum. EQE curves were acquired using a solar cell spectral response measurement system (QE-R, Enli Technology Co. Ltd).

NMR
¹H NMR and ¹³C NMR spectra were recorded using a Bruker AVANCE III HD XXX 400 MHz spectrometer. Chemical shifts were calibrated using the solvent signal DMSO-d6 as an internal reference.

CV measurements
CV measurements were performed using a CHI660 electrochemical workstation (CH Instruments). An Ag/AgCl (3 M NaCl) reference electrode and a Pt-wire counter electrode were used. The CV experiments were performed in a solution containing 1,2-dichlorobenzene (o-DCB) with 0.1 M tetrabutylammonium hexafluorophosphate (TBA+PF6–). The geometric area of the ITO electrode exposed to the solution for electrochemical measurement was 1.245 cm2, and the CV data were measured at scan rates of 100 mV s-1, 200 mV s-1, 300 mV s-1, and 400 mV s-1. Samples for the C-V measurements were prepared by depositing 4PADCB or a mixture of 4PADCB:LA/DHLA/DMSLA (in a molar ratio of 2:1) in ethanol solution was uniformly spread on ITO and allowed to rest for 10 s, followed by spinning of the films at 3,000 rpm for 30 s. The films were then annealed at 100 °C for 10 min.

UPS and XPS analysis
X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Scientific K-Alpha with an Al-Kα X-ray source. Ultraviolet photoemission spectroscopy (UPS) was performed using a Kratos Analytical ESCALAB-250Xi photoelectron spectrometer, with He(I) excitation at 21.22 eV.

UV Vis absorption spectroscopy
UV–Vis optical measurements were carried out using a PerkinElmer Lambda 1050 spectrometer equipped with an integrating sphere. Both transmittance (T) and reflectance (R) spectra were recorded on thin-film samples deposited on glass substrates. The absorptance (A) of the films was then calculated according to the relation A = 1 – T – R, which inherently corrects for baseline offsets by accounting for substrate transmission and surface reflection losses. The resulting spectra were used to construct Tauc plots for bandgap estimation, as shown in Supplementary Figure 22a–b. All films exhibited similar absorption characteristics with no major spectral shifts, although a slight red shift was observed for the DMSLA-treated sample. The estimated optical bandgaps for all conditions were approximately 1.55 eV, confirming negligible variation among the samples (Supplementary Figure 22-b).

Time resolved PL spectroscopy
Time-resolved photoluminescence (PL) spectra of the perovskite films fabricated on different SAM-modified ITO substrates were studied using a Picoquant FluoTime 300 spectrofluorometer with an excitation wavelength of 375 nm.

Scanning electron microscopy
The morphology of perovskite films on textured Si with different self-assembled monolayers (SAMs) was analysed using an in-house FEI Helios Nanolab G3 UC DualBeam scanning electron microscope (SEM). Cross-sectional and top-view images were acquired at 2 kV and 3 kV, respectively, to minimise beam-induced damage to the perovskite film while ensuring adequate resolution and contrast, using the TLD detector. Samples, prepared from the active area, were mounted on silver paste, and no additional conductive coating was applied.

GIWAXS and XRD
GIWAXS measurements were carried out on an Anton-Paar SAXSpoint 2.0 with a Primux 100 microfocus source with Cu-Kα1 radiation (λ = 1.5406 Å) and a Dectris Eiger R 1M 2D Detector.XRD.

XRD measurements were carried out on a Bruker D8 Discover diffractometer in Bragg–Brentano geometry, using Ni-filtered Cu-Kα1 radiation (λ = 1.5406 Å) and an apposition-sensitive LynxEye detector.

AFM
AFM measurements were performed using a Bruker Dimension Icon in PeakForce Tapping mode, which enables the simultaneous capture of mechanical properties and topography. The used cantilevers (RTESPA-300) were initially characterized on calibration samples (PFQNM-SMPKIT-12M) and by a thermal tune to determine the deflection sensitivity, spring constant, and tip radius. All scans were performed in a nitrogen atmosphere to reduce the degradation of the perovskite. For the scans, we used a scan rate of 0.8 Hz, 512 samples/line, and a peak force of 20 nN for the top side and 5 nN for the peeled bottom side of the perovskite. Data analysis was performed with the open-source software Gwyddion.

Pull off tests
In this procedure, the sample was prepared following the same steps as in the device fabrication process up to the deposition of the perovskite layer. The perovskite surface was first coated with a thin layer of PMMA to protect the underlying perovskite layer from moisture and to prevent direct contact with the epoxy adhesive used in subsequent preparation steps. A 10 wt% PMMA solution in chlorobenzene was spin-coated onto the prepared perovskite film surfaces at 2000 rpm for 30 seconds, followed by drying at room temperature for 24 hours. A 10 mm-diameter circular steel dolly was then bonded onto the PMMA-coated surface using epoxy adhesive (Huntsman Araldite 420). The assembly was cured at room temperature for 1 hour, followed by an additional curing step at 60 °C for 4 hours to ensure full polymerization of the adhesive. To ensure consistency across all tests, the volume of epoxy applied was carefully controlled so that the bondline area remained consistent. After curing, a steel wire was used to connect the dolly to the upper grip of the universal testing machine. All tests were performed using an Instron 5944 Single Column Electro-Mechanical Testing Machine equipped with a 2 kN load cell, under a constant displacement rate of 0.1 mm/min(quasi-static). The interfacial tensile strength was calculated by dividing the maximum measured pull-off force by the bonded area.

Thermal cycling tests
Thermal cycling experiments were performed using a custom-built closed-lid setup designed to achieve reproducible and well-controlled temperature cycling between –80 °C and +80 °C. To prevent frost formation and maintain dry ambient conditions, dry air was circulated within the sealed chamber, and cycling was initiated only after the integrated DHT22 temperature–humidity sensor indicated 0% relative humidity. The sample temperature was monitored directly from the device surface using a K-type thermocouple placed in contact with the substrate to accurately capture the thermal load experienced by the cells. A schematic representation of the thermal fatigue experimental setup is provided in Supplementary Figure 26.

Computational methodology
We carried out first-principles calculations based on Density Functional Theory (DFT) using a plane-wave basis set in conjunction with the projector augmented-wave (PAW) method. To describe exchange–correlation interactions, we employed the PBEsol functional, a revised version of the generalised gradient approximation developed by Perdew, Burke, and Ernzerhof. 36 Long-range dispersion interactions were accounted for using the DFT-D3 correction proposed by Grimme.37 Initial structures were constructed using experimentally reported lattice parameters of ITO and FAPbI3. All self-consistent field and structural optimization calculations were performed using a plane-wave energy cutoff of 400 eV and a k-point mesh with a spacing of 0.03 × 2π/Å. Both atomic positions and lattice parameters were relaxed using the conjugate gradient algorithm until the maximum residual force on each atom was less than 0.02 eV/Å. Unless otherwise specified, all simulations were conducted using the VASP software package 38,39 following this protocol.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors present a thorough investigation on the impact of a self-assembled monolayer using a lipoic acid and derivatives. There is rich investigation in the SAM and its functions at the grain boundaries of the perovskite - the methodology is sound. There is suitable information for the work to be reproduced. It is a concern of this reviewer that this manuscript makes broad claims of suitability for space with only 1-day low Earth orbit equivalent thermal cycling and no analysis of the devices in any other space relevant environments.\n1. Line 85 sentence beginning “Across all these systems…” should cite where these claims come from, I believe they are from ref 17 and 18 but would be good to re-cite.\n2. The claims of this SAM being suitable for implementation in space are over inflated. These devices show moderate enhancement to only one stressor at 24 hrs. Authors should temper these claims by mentioning environmental caveats that could prove to be detrimental (vacuum, outgassing, UV degradation, ionizing radiation, etc.) or demonstrating experimentally or computationally that the SAM will exhibit longevity beyond 24 hours and that it can endure other stressors present in the space environment. The authors would likely agree that a material enduring 24 hours does not mean it will exhibit more durability than the control material that undergoes marginally more degradation (~5% absolute enhancement on retained performance. How can the authors demonstrate or suggest that the SAM would continue to outperform the control beyond 24 hours of thermal cycling and considering other relevant space environmental stressors?\n3. JV measurements and MPPT were conducted at AM 1.5, but longevity claims are made for operation in space. Authors should comment on expected observations or variations at AM0 given they’re framing this work for space applications. The solar illumination should be added in the body of the text because readers will assume AM0.\n4. The paragraph beginning at Line 72 with “During thermal cycling…” should site other perovskite investigations into impact of thermal cycling including Krause et al https://doi.org/10.1002/solr.202300468\n5. The claim of the first systematic study of extreme low temperature cycling experiments is invalid and should be edited or removed (conclusion line 377) to acknowledge the similar systematic work published by Chen et al https://doi.org/10.1021/acsenergylett.4c00988 and Li et al https://doi.org/10.1002/aenm.202202887 The first extreme low temperature cycling experiments were probably conducted by Delmas et al who did thermal cycling analysis on the International Space Station https://doi.org/10.1002/aenm.202203920. Authors should read these works and consider citing all the above.\n6. Supplemental information line 227 in “pull-off tests” section second sentence – which surface was first coated with a thin layer of PMMA? Please confirm in text.", "reviewer_2": "While the manuscript presents a detailed technical investigation into the adhesion properties between the perovskite and HTL (SAM) in the presence of LA and its derivatives, as well as the full device performance variation under thermal cycling test, I do not find the novelty sufficiently strong for acceptance in Nature Communications. Poly-LA has already been reported (ref. 17) to serve as a passivating agent that simultaneously optimises interfacial contact, enhances perovskite crystallinity, and maintains robust mechanical properties. In this manuscript, the authors report that LA and its derivatives also form polymers after annealing around the grain boundaries, which is conceptually very similar to the previously published work.\nThe thermal cycling investigation was conducted between –80 °C and +80 °C, and the results show a positive effect after incorporating DMSLA into the HTL. However, the title suggests that the work was carried out under extreme LEO (Low Earth Orbit) conditions, which is somewhat misleading. Thermal vacuum cycling tests should be included if the authors wish to retain the current title. In the conclusion, the authors explicitly mention that thermal vacuum testing will be the next step.\nAdditionally, the manuscript contains numerous vague descriptions, making it difficult to follow. To help the authors improve the clarity and quality of the paper, the following points should be addressed before it can be considered for publication in another journal.\n1. One of the key advantages of perovskite materials for space applications is their high specific power. This should be emphasized in the introduction (lines 48–49).\n2. Line 51: If I understand correctly, the authors state that III–V solar cells exhibit a short operational lifetime. However, III–V solar cells are widely used in current space applications. It would be helpful to clarify which type of commercial solar cells the authors are comparing with—are they referring to Si-based solar cells?\n3. Lines 91–92: There is some confusion regarding the substrate and perovskite description. Does the term “substrate” here refer to TCE without any charge transport layer deposited? In the following sentences (lines 92–94), were all the mentioned methods performed on ITO substrates or on non-TCE substrates? This section should be rewritten for better clarity.\n4. Lines 103–108: The ring-opening of LA is mentioned in the text, but the molecular structure of LA is not shown in this part of the section, making it difficult for readers to follow until reading Fig. 2a. It is suggested to either include the LA structure in the Supporting Information (around Figs. S1–S3) or refer to Fig. 2a directly in the text.\n5. Please add “(DHLA)” after “1H NMR of 6,8-bis(methylthio)octanoic acid” in Fig. S2 caption, consistent with Fig. S3.\n6. It would be helpful to label the atom numbers in the chemical structures and indicate the corresponding numbers in the 1H^ NMR spectra shown in Figs. S1 and S2.\n7. It is suggested to introduce the full chemical name of LA earlier in the text, before its first appearance in Section 2.2 (around line 175).\n8. Please verify the schematic structure of DMSLA in Fig. 2a; it appears incorrect. There seems to be an extra carbon atom attached to one of the sulphur atoms.\n9. Line 192: The meaning of this sentence is unclear. Does the weak adhesion observed for LA and DHLA samples result from imperfections in sample preparation?\n10. In the caption of Fig. S10, please clarify how the authors ensured that LA molecules remained confined within the grain boundaries and were not exposed on the surface.\n11. In Table S1, the data for the perovskite with LA are missing.\n12. Line 297: Please verify whether the energy offset is 0.02 eV rather than 0.04 eV.\n13. How was the bandgap calculated? If it was derived from UV–vis spectra, please provide the corresponding absorption spectra with a proper baseline.\n14. Page 12, line 328: Please explain how the device temperature was maintained at –80 °C when immersed in liquid N₂.\n15. The control devices retained 79% of their initial efficiency after 16 cycles, DMSLA showed 84%, and DHLA showed 72%. These differences appear minor (within ±5% deviation). How many devices were measured to draw this conclusion?\n16. Although the variation is small, why does the VOC curve in Fig. 4a for DMSLA show a decrease after five cycles, followed by a gradual increase after 16 cycles?\n17. In Materials section in SI, BCP and LiF were mentioned twice and also sourced from different suppliers. Please indicate the reason.\n18. Dyesol company no longer exists. Please confirm FA and MA were sourced from GreatCell Solar.\n19. Please provide more details in the caption of Fig. S24. Do the dark blue and light blue boxes correspond to the reverse and forward scans, respectively? The same clarification is suggested for the colours used in Figs. S24 and S25.", "reviewer_3": "Report on NCOMMS-24-15009\nTitle: Perovskite Solar Cells with Enhanced Thermal Fatigue Resistance in Low-Earth Orbit Space Extremes\nby Ali Buyruk et al.\nThe manuscript addresses a crucial aspect for the employment of perovskite solar cells in Low Earth Orbit (LEO): their resilience to thermal fatigue. The authors propose an innovative two-step approach, based on the use of α-lipoic acid and its derivatives, to improve perovskite film cohesion and mitigate delamination. To validate this strategy, they employed several experimental techniques such as XRD, FTIR, AFM, SEM, GIWAXS, which confirmed a significant improvement in both internal grain cohesion and interfacial adhesion. Thermal fatigue tests, performed with a custom-built setup and a thermal cycling protocol ranging from -80°C to +80° C for 16 cycles (equivalent to one day of operation), indicate encouraging stability. The best performing device achieved an efficiency of 26% and retained 84% of its initial performance after the thermal fatigue test.\nThe manuscript is well written, logically structured, and contextualized within the literature. The experimental work is carefully executed, and the short-term data are convincing within the tested scope. The analytical framework is solid, and the interpretation of the available data is careful.\nHowever, while the proposed strategy is novel and the results are encouraging, in our opinion, the current experimental validation does not provide sufficient evidence to substantiate claims of aerospace suitability for the following reasons:\n1) The thermal cycling test (16 cycles) is far too limited to represent orbital conditions, which typically involve hundreds or thousands of cycles.\n2) The working conditions of solar cells in space are extremely harsh, involving not only thermal fluctuations but also high vacuum, atomic oxygen, and high-energy particle radiation (such as protons, electrons, neutrons, γ-rays). Although the authors briefly acknowledge the need for vacuum tests to better simulate the space environment, they do not consider the importance of radiation, leaving a fundamental gap in assessing material’s long-term stability. Without such tests, the applicability of the solar cells for aerospace missions remains speculative.\n3) The proposed additive engineering approach, based on organic additives (lipoic acid and its derivatives), is innovative and could have relevance for improving the durability of perovskite solar cells more broadly. However, the radiation stability of these organic molecules is a fundamental issue that should be addressed, either experimentally or via literature-supported discussion.\nThe lack of comprehensive environmental validation severely limits the impact of the findings for aerospace applications. In its present form, the study is best considered as a proof-of-concept for improved perovskite stability, not as evidence of readiness for space deployment.\nSuggested improvements\n- Increase the number of thermal cycles to a more representative level (hundreds or thousands).\n- Include tests under vacuum condition and radiation exposure (protons, electrons, γ-rays).\n- Provide a discussion of the radiation stability of α-lipoic acid derivatives, supported by prior studies.\nOverall assessment\nThis study introduces a promising approach to improving perovskite solar cell stability and provides convincing short-term laboratory results. However, in its current form, the manuscript does not provide sufficient evidence to demonstrate suitability for aerospace applications. The lack of extended thermal cycling, vacuum testing, and radiation stability assessment constitutes a major gap. Therefore, we do not find the work suitable for publication in Nature Communications at this stage. Substantial additional testing and contextualization would be required before reconsideration.", "reviewer_4": "This manuscript presents an interesting study on the use of additives to enhance the thermal fatigue resistance of perovskite solar cells for space applications. The work is novel and offers valuable insights, especially since thermal fatigue has received comparatively little attention in this field.\nI recommend a revision before the manuscript can be accepted for publication. My detailed comments are as follows:\n1. Since the context is space applications, why was AM0 not used for device measurements? AM0 is more relevant, and its higher UV component could also influence additive stability. Please provide AM0 measurements and comparisons, as this seems necessary.\n2. In the adhesion test, the ranking is DMSLA > DHLA > LA > control. However, this ranking does not align with the thermal cycling results. Does this suggest that adhesion is not the main factor contributing to thermal cycling failure? Please explain and discuss possible alternative failure modes with supporting evidence.\n3. For the thermal cycling tests performed using the in-house equipment, was moisture controlled? The encapsulation method described in the paper may not effectively block moisture, and heating/cooling cycles could allow moisture ingress, which would affect device performance. This condition would not reflect the space environment, so clarification is needed.\n4. The EQE results indicate that the front interface (light-incidence side) does not improve, and there is a noticeable loss at the rear interface when additives are used. Please explain this observation. The evidence for interfacial passivation is not very strong from EQE results.\n5. For the MPPT test, please provide the corresponding IV curves and the initial PCE data.", "reviewer_5": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Response to Reviewers’ Comments on NCOMMS-25-67465\nWe sincerely thank all reviewers for their valuable and constructive comments, which have\ngreatly contributed to improving the quality of our manuscript. Please find our detailed point-\nby-point responses below.\nReviewer #1:\nRemarks to the Author:\nThe authors present a thorough investigation on the impact of a self-assembled monolayer\nusing a lipoic acid and derivatives. There is rich investigation in the SAM and its functions at\nthe grain boundaries of the perovskite – the methodology is sound. There is suitable\ninformation for the work to be reproduced. It is a concern of this reviewer that this\nmanuscript makes broad claims of suitability for space with only 1-day low Earth orbit\nequivalent thermal cycling and no analysis of the devices in any other space relevant\nenvironments.\nResponse:\nWe would like to thank the reviewer for taking the time to review our manuscript and for\nproviding valuable feedback that helped us improve the quality and clarity of our work. Also,\nwe thank the reviewer for giving credit to our work. We now understand that our manuscript\ntitle and some expression in the abstract may have given a misleading impression—although\nthis was not our intention—regarding the thermal cycling experiments and the tests\nperformed under other space-relevant environments. Below, we address these points step by\nstep.\nR1 - Comment 1.\nLine 85 sentence beginning “Across all these systems...” should cite where these claims come\nfrom, I believe they are from ref 17 and 18 but would be good to re-cite.\nR1 - Response 1.\nWe thank the reviewer for this helpful suggestion. In the revised manuscript, we now\nexplicitly re-cite the sources for the performance recovery claims. The sentence in the\nIntroduction has been modified to:\n Lines 91-93 “Across all these systems, thermal-triggered healing has resulted in more\nthan 80% recovery of solar cell performance after stress testing[11-18], while systems\nbased on poly(LA) and poly(TA-NI) demonstrated recovery rates exceeding\n90%[17,18].”\nThe claims of this SAM being suitable for implementation in space are over inflated. These\ndevices show moderate enhancement to only one stressor at 24 hrs. Authors should temper\nthese claims by mentioning environmental caveats that could prove to be detrimental\n(vacuum, outgassing, UV degradation, ionizing radiation, etc.) or demonstrating\nexperimentally or computationally that the SAM will exhibit longevity beyond 24 hours and\nthat it can endure other stressors present in the space environment. The authors would likely\nagree that a material enduring 24 hours does not mean it will exhibit more durability than the\ncontrol material that undergoes marginally more degradation (~5% absolute enhancement on\nretained performance. How can the authors demonstrate or suggest that the SAM would\ncontinue to outperform the control beyond 24 hours of thermal cycling and considering other\nrelevant space environmental stressors?\nR1 - Response 2.\nWe would like to thank the reviewer for the insightful comments regarding the thermal\ncycling tests. From the feedback, we understand that our text may have given the impression\nthat we have fully solved all thermal cycling challenges in space, although this was not our\nintention. We would like to clarify that our tests were designed to approximate realistic stress\nconditions as closely as possible. However, at this stage, it is naturally difficult to perform\nexperiments that include all relevant stressors simultaneously. This situation is similar to\naccelerated testing for terrestrial applications (IEC and ISOS Protocols), where, for example,\nthermal cycling is typically conducted in the dark and within extreme temperature ranges on\nencapsulated cells (i.e., −40 °C to +80 °C), rather than all accelerated tests at the same time,\nsuch as reverse bias, impact hailing, humidity freeze test, PID tests, etc. In principle, for long-\nterm stability predictions, correlating the individual accelerated tests with actual field tests is\nrequired. This situation is the same for space-relevant tests; at some point, performing on-\nground and in-orbit tests and their correlation is required (which is a long-term goal of ours).\nHowever, since the evaluation of perovskite-based solar cells in space-relevant environments\nis still at an early stage, the accelerated test protocols are yet to be fully established. Our\nintention here was not to perform either an accelerated test or a real orbit test. We hope that,\nas a community, we will reach a consensus on these aspects in the future. Instead, our aim\nwas to perform a one-day equivalent test to evaluate device failure mechanisms under\n2\nrealistic temperature ranges observed in low-Earth orbit (LEO), acknowledging that these\nvalues can vary depending on the specific orbit and spacecraft design.\nIn light of the reviewer’s valuable comment, we have revised our manuscript title from\n“Perovskite Solar Cells with Enhanced Thermal Fatigue Resistance in Low-Earth Orbit Space\nExtremes” to “Perovskite Solar Cells with Enhanced Thermal Fatigue Resistance in Low-\nEarth Orbit Relevant Temperature Extremes.”\nFurthermore, we have made the following specific revisions to clarify the scope and ensure\nthat the claims remain consistent with the experimental evidence:\nIn the abstract;\n Line 27: “Previous works have shown that PSCs can exhibit high radiation tolerance;\nhowever, their stability under the extreme thermal cycling conditions of space—a key\nfactor driving degradation in LEO—remains largely unexplored.”\n Line 42: “Dual reinforced devices exhibit 84% performance retention after 16 thermal\ncycles, representing one full day in LEO-relevant temperature extremes.”\n Lines 43–45: “This work highlights the importance of targeted interface engineering\nand thermal fatigue mitigation strategies for advancing PSCs toward space\napplications.”\nIn the introduction;\n Lines 68–71: “Hence, to approximate the mechanical stresses associated with these\nrapid and extreme temperature shifts, we adopted a custom thermal cycling protocol\nranging from -80 °C to +80 °C10, which necessitated the development of a dedicated\ntest setup. We performed a one-day-equivalent experiment with realistic cooling and\nheating rates representative of LEO-relevant temperature extremes under dry-air\nlaboratory conditions.”\n[10] Kim, K., Yang, S., Kim, C. et al. Non-volatile solid-state 4-(N-\ncarbazolyl)pyridine additive for perovskite solar cells with improved thermal and\noperational stability. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01864-z\n Lines 95–96: “However, most studies still lack comprehensive thermal fatigue\nassessments under LEO-relevant temperature conditions, even in laboratory\nenvironments.”\n Lines 344–347: “The high PCE retention observed during MPPT measurements,\ncompared to the lower retention seen in thermal fatigue tests, indicates that LEO-\nrelevant temperature cycling may present a more significant challenge than\ncontinuous MPPT operation.”\nConclusion and Outlook\n Deleted sentence (lines 372–374): “Regarding testing setups, implementing vacuum\nthermal cycling tests could better replicate space-like conditions, highlighting the\nneed for a customized vacuum-compatible tool.”\n Deleted sentences (line 376): “To the best of our knowledge, this is the first report to\nsystematically study extreme low-temperature cycling experiments for PSCs.”\n Added sentences (starting from line 376): “It should also be noted that our\nexperiments were conducted under dry-air and ambient-pressure conditions;\nadditional space-relevant stressors such as vacuum, ultraviolet radiation, atomic\noxygen, outgassing, and ionizing radiation remain important challenges requiring\nfurther investigation. In our future works, we plan to include thermo-vacuum cycling\ntests to extend these findings toward more realistic multi-stressor environments.”\n Revised final sentence: “We believe this work lays the foundation for new research\ndirections and contributes valuable insight into the behavior of perovskite solar cells\nunder simulated LEO-relevant temperature cycling.”\nR1 - Comment 3.\nJV measurements and MPPT were conducted at AM 1.5, but longevity claims are made for\noperation in space. Authors should comment on expected observations or variations at AM0\ngiven they're framing this work for space applications. The solar illumination should be\nadded in the body of the text because readers will assume AM0.\nR1 - Response 3.\nWe appreciate this valuable feedback. Indeed, this is an important point, as it could\npotentially mislead readers. We performed the MPPT tests under equivalent AM1.5G\nillumination conditions, not under AM0 conditions. We note that achieving true AM0\nillumination may remain a challenge for the community in the future as well, since generating\na proper blue/UV spectral component for extended measurement durations is difficult at low\ncost (equipment manufacturer’s feedback).We hope to have these capabilities in the near\nfuture. To avoid any confusion for readers, we explicitly stated in the caption of the stability\ndata that it refers to ~1000 W m⁻² equivalent 1-sun intensity conditions:\n “Figure 4. Thermal fatigue test of perovskite solar cell. a, Temperature variation over\ntime during the thermal cycling process, and the evolution of device parameters over\nsixteen cycles, with measurements taken after every five cycles. b, Schematic\nillustration of the thermal cycling process in LEO. c, J–V curves of solar cell devices\nbefore and after the thermal stress test. d, MPPT results of encapsulated perovskite\nsolar cells under ~1000 W m⁻² equivalent 1-sun intensity, measured at 45 ± 5 °C and\n70 ± 10% relative humidity.”\nIn addition, we added clarification in line 351:\n “Maximum power point tracking (MPPT) analysis of the encapsulated solar cells—\nconducted under conditions of 45 ± 5 °C, 70 ± 10% relative humidity, and ~1000 W\nm⁻² equivalent 1-sun illumination, revealed that DMSLA-based target devices\nremained almost unchanged, while the control samples lost 33% of their initial\nefficiency after 500 hours (Figure 4d).”\nAdditionally, the reviewer raised a valid point regarding reporting device performance under\nAM0 conditions. Using the same solar simulator, we increased the light intensity to 1.36 sun\nto approximate AM0 conditions. We have added IV curves and the statistical distribution of\nthe corresponding devices at 1360 W/m2. The devices obtained higher J and V at AM0\nSC OC\ncompared to those at AM1.5 spectrum.\ndevices at 1360 W/m2 (AM0 approximation).\nSupplementary Figure 29. Statistical distribution of a) V , b) PCE, c) FF, and (d) J\nOC SC\nvalues of the devices at 1360 W/m2. Each condition had 10 devices.\nR1 - Comment 4.\nThe paragraph beginning at Line 72 with \"During thermal cycling...\" should site other\nperovskite investigations into impact of thermal cycling including Krause et al\nhttps://doi.org/10.1002/solr.202300468\nR1 - Response 4\nWe thank the reviewer for this valuable suggestion. Additional works related to thermal\ncycling tests, including the study by Krause et al., have been added to the revised manuscript.\n6\n Lines 78-80: “During thermal cycling, the solar cell stack is exposed to repeated\nvolumetric expansion and contraction, which induces mechanical fatigue, potentially\nleading to delamination or failure at weakly bonded interfaces.11,12”\n[12] Krause, T.S., VanSant, K.T., Lininger, A., Crowley, K., Peshek, T.J. and\nMcMillon-Brown, L. (2023), Thermal Performance of Perovskite-Based\nPhotovoltaics for Operation in Low Earth Orbit. Sol. RRL, 7: 2300468.\nhttps://doi.org/10.1002/solr.202300468\nR1 - Comment 5.\nThe claim of the first systematic study of extreme low temperature cycling experiments is\ninvalid and should be edited or removed (conclusion line 377) to acknowledge the similar\nsystematic work published by Chen et al https://doi.org/10.1021/acsenergylett.4c00988 and\nLi et al https://doi.org/10.1002/aenm.202202887 The first extreme low temperature cycling\nexperiments were probably conducted by Delmas et al who did thermal cycling analysis on\nthe International Space Station https://doi.org/10.1002/aenm.202203920. Authors should read\nthese works and consider citing all the above.\nR1 - Response 5\nWe thank the reviewer for flagging this point. After reviewing these works, the related\ncitations have been revisited and revised accordingly. The corresponding paragraph in the\nmanuscript has been revised, and the claim on the first systematic study of extreme\ntemperature cycling experiments is removed.\n In lines 70-27: “Recent systematic studies have also examined perovskite solar cell\nperformance under extreme low-temperature cycling and in-orbit conditions, further\nhighlighting the importance of understanding thermal fatigue for space deployment.7-\n9”\n[7] Chen, M. et al. Stress Engineering for Mitigating Thermal Cycling Fatigue in\nPerovskite Photovoltaics. ACS Energy Lett. 9, 2582–2589 (2024).\n[8] Delmas, W. et al. Evaluation of Hybrid Perovskite Prototypes After 10‐Month\nSpace Flight on the International Space Station. Advanced Energy Materials 13,\n2203920 (2023).\n7\n[9] Li, G. et al. Structure and Performance Evolution of Perovskite Solar Cells under\nExtreme Temperatures. Advanced Energy Materials 12, 2202887 (2022).\nR1 - Comment 6.\nSupplemental information line 227 in “pull-off tests” section second sentence – which surface\nwas first coated with a thin layer of PMMA? Please confirm in text.\nR1 - Response 6.\nWe thank the reviewer for giving opportunity for further clarification. The perovskite surface\nwas first coated with a thin layer of PMMA before dolly attachment to protect the film from\nmoisture and prevent direct contact with the epoxy adhesive. This information has now been\nexplicitly clarified in the Supplementary Information.\n Lines 230–232: “The perovskite surface was first coated with a thin layer of PMMA\nto protect the underlying perovskite layer from moisture and to prevent direct contact\nwith the epoxy adhesive used in subsequent preparation steps.”\nReviewer #2\nRemarks to the Author:\nWhile the manuscript presents a detailed technical investigation into the adhesion properties\nbetween the perovskite and HTL (SAM) in the presence of LA and its derivatives, as well as\nthe full device performance variation under thermal cycling test, I do not find the novelty\nsufficiently strong for acceptance in Nature Communications. Poly-LA has already been\nreported (ref. 17) to serve as a passivating agent that simultaneously optimises interfacial\ncontact, enhances perovskite crystallinity, and maintains robust mechanical properties. In this\nmanuscript, the authors report that LA and its derivatives also form polymers after annealing\naround the grain boundaries, which is conceptually very similar to the previously published\nwork.\nThe thermal cycling investigation was conducted between –80 °C and +80 °C, and the results\nshow a positive effect after incorporating DMSLA into the HTL. However, the title suggests\nthat the work was carried out under extreme LEO (Low Earth Orbit) conditions, which is\nsomewhat misleading. Thermal vacuum cycling tests should be included if the authors wish\nto retain the current title. In the conclusion, the authors explicitly mention that thermal\nvacuum testing will be the next step.\nWe thank the reviewer for providing valuable feedback on our manuscript and for\nrecognizing the depth of our analysis of the substrate/perovskite interface. We understand the\nreviewer’s concern regarding the novelty of our work, and we appreciate the opportunity to\nelaborate further. The novelty of our study lies in several key aspects: (i) Molecular\ninnovation: It is true that poly-LA has been reported previously, which is not surprising given\nthat during our material screening, we identified it as a promising candidate due to its ability\nto undergo ring-opening reactions and form a polymeric network. However, this was not the\nmain focus of our work. Instead, we prescreened this molecular family, using dihydrolipoic\nacid (DHLA) and synthesizing a sulfonium-based cation (DMSLA) specifically. Our goal\nwas to achieve stronger interactions with the perovskite lattice—one of the weakest interfaces\nin these devices. (ii) Process novelty: Another innovative aspect of our study is the\nincorporation of the linker molecules directly into the SAM solution. This approach\nsimplifies the overall process and enables interface linking in a single step, while\nsimultaneously improving the mechanical adhesion at this critical interface. (iii) Application-\nrelevant thermal cycling: We conducted LEO-relevant thermal cycling experiments,\nfollowing the same heating and cooling rates experienced by actual devices on CubeSats\n(using real heating and cooling rates), using space-compatible encapsulated (DOWSIL 93-\n500) cells.[R1,R2] While previous studies have made important contributions, most do not\nreplicate the heating and cooling rates corresponding to the targeted applications. We have\nsummarized the literature, including our work, doing extreme thermal cycling either in terms\nof range or heating/cooling rate in Table R1. In summary, our work differentiates itself from\nprior studies by combining LEO-relevant thermal cycling with realistic cycle duration (~90\nminutes), space-grade encapsulation, and the unique introduction and synthesis of the\nDMSLA linker at the HTL/perovskite interface.\nRegarding the title, we have revised our manuscript title from “Perovskite Solar Cells with\nEnhanced Thermal Fatigue Resistance in Low-Earth Orbit Space Extremes” to “Perovskite\nSolar Cells with Enhanced Thermal Fatigue Resistance in Low-Earth Orbit Relevant\nTemperature Extremes.”\nWe hope that our explanation addresses the reviewer’s concerns regarding the novelty of our\nwork. However, if needed, we are happy to provide further clarification.\n9\n[R1]Bulut, M. Thermal design, analysis, and testing of the first Turkish 3U communication\nCubeSat in low earth orbit. J. Therm. Anal. Calorim. 143, 4341–4353 (2021).\n[R2] Lamb, D. A., Irvine, S. J. C., Baker, M. A., Underwood, C. I. & Mardhani, S. Thin film\ncadmium telluride solar cells on ultra-thin glass in low earth orbit—3 years of performance\ndata on the AlSat-1N CubeSat mission. Prog. Photovolt. Res. Appl. 29, 1000–1007 (2021).\nR2 - Comment 1.\nOne of the key advantages of perovskite materials for space applications is their high specific\npower. This should be emphasized in the introduction (lines 48–49).\nR2 - Response 1.\nWe thank the reviewer for this valuable suggestion. It has been added into the related part in\nthe introduction.\n Lines 47–49: “Metal halide perovskite solar cells have emerged as a promising option\nfor space photovoltaics, offering a unique combination of high power conversion\nefficiency (PCE), high specific power, low fabrication costs, and inherent radiation\ntolerance.[1]”\nR2 - Comment 2.\nLine 51: If I understand correctly, the authors state that III–V solar cells exhibit a short\noperational lifetime. However, III–V solar cells are widely used in current space applications.\nIt would be helpful to clarify which type of commercial solar cells the authors are comparing\nwith—are they referring to Si-based solar cells?\nR2 - Response 2.\nWe agree that our original phrasing could be interpreted as implying that III–V solar cells have\nshort operational lifetimes, which is not accurate. Our intention was to emphasize their high\ncost and manufacturing complexity, rather than poor reliability.\n Lines 49–51: “They can serve as an alternative to the two main types of commercially\nused solar cells: conventional III–V-based devices, which, despite their widespread\nuse in space applications, suffer from high cost and relatively short operational\n10\nlifetimes,2 and wafer-based crystalline silicon cells, which are relatively heavy and\nexhibit limited radiation tolerance.”\nR2 - Comment 3.\nLines 91–92: There is some confusion regarding the substrate and perovskite description.\nDoes the term \"substrate\" here refer to TCE without any charge transport layer deposited?\nIn the following sentences (lines 92–94), were all the mentioned methods performed on ITO\nsubstrates or on non-TCE substrates? This section should be rewritten for better clarity.\nR2 - Response 3.\nWe thank the reviewer for pointing out this potential ambiguity. In the revised manuscript,\nwe clarified that “substrate” refers to bare ITO-coated glass before any charge transport or\nperovskite layers were deposited. The text was rewritten to eliminate ambiguity.\n Lines 96–102: “To improve adhesion at the interface between the transparent\nconductive oxide (TCO) and the perovskite layer, several surface-engineering\nstrategies have been developed. Reported approaches include increasing surface\nhydroxylation by replacing crystalline TCOs with amorphous ones,[23,24] removing\nterminal hydroxyls and hydrolysis byproducts via combined HF and UV–ozone\ntreatments,[25] introducing hetero-chiral linker molecules,[26] and employing SAMs\nsuch as iodine-terminated carbazole derivatives or bifunctional thiol–carboxylic acid\nsystems with varying alkyl chain lengths.[27]”\nR2 - Comment 4.\nLines 103–108: The ring-opening of LA is mentioned in the text, but the molecular structure\nof LA is not shown in this part of the section, making it difficult for readers to follow until\nreading Fig. 2a. It is suggested to either include the LA structure in the Supporting\nInformation (around Figs. S1–S3) or refer to Fig. 2a directly in the text.\nR2 - Response 4.\nWe thank the reviewer for raising this. In lines 103–108, the lipoic acid (LA) molecule\nmentioned in the context of the ring-opening reaction refers to its molecular structure, which\nis depicted in Fig. 2a. To make it easier for readers to follow the discussion on the ring-\nopening polymerization of LA, we have now added a direct reference to Fig. 2a, where the\nmolecular structure of LA is presented.\n11\n Lines 107–110: “To promote inter-grain connectivity, LA was incorporated into the\nperovskite precursor solution with the expectation that it could undergo in situ\npolymerization during crystallization (the molecular structure of LA is shown in Fig.\n2a).”\nR2 - Comment 5.\nPlease add \"(DHLA)\" after"}]

Decision letter
Several reviewers raised similar questions regarding the inclusion of additional information related to space applications in response to the originally submitted manuscript. Although this was not the authors’ original intention, as explained in their responses to multiple reviewers, the initial manuscript (title) was somewhat misleading. This issue has now been recognised and corrected by the authors. The revised and rewritten abstract, introduction, and conclusion show significant improvement and now clearly focus on the work being addressed.
Based on the through revision, it is recommended to be accepted for publish in this journal.