# In-Situ Constructing Eosin Y Sensitized Cs2PtSnCl6 Perovskites for Enhanced Photocatalytic Hydrogen Evolution

Jin Wang, Siyu He, Meng Zhang, Fa Yang, Qiaowen Zhang, Zhengquan Li, Marc Robert

► To cite this version:

Jin Wang, Siyu He, Meng Zhang, Fa Yang, Qiaowen Zhang, et al. In-Situ Constructing Eosin Y Sensitized Cs2PtSnCl6 Perovskites for Enhanced Photocatalytic Hydrogen Evolution. Advanced Energy Materials, In press, 10.1002/aenm.202406048. [https://doi.org/10.1002/aenm.202406048](https://doi.org/10.1002/aenm.202406048)

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# In-Situ Constructing Eosin Y Sensitized $Cs_2PtSnCl_6$ Perovskites for Enhanced Photocatalytic Hydrogen Evolution

Jin Wang,* Siyu He, Meng Zhang, Fa Yang, Qiaowen Zhang, Zhengquan Li,* and Marc Robert*

Vacancy-ordered $Cs_2SnX_6$ perovskites, with low-toxicity and high stability, have emerged as promising photocatalysts for hydrogen evolution reaction (HER). However, most $Cs_2SnX_6$ and derivatives have low catalytic activity mainly due to their insufficient light utilization efficiency. Herein, a simple in situ method is introduced to sensitize $Cs_2PtSnCl_6$ with Eosin Y (EY), forming EY-$Cs_2PtSnCl_6$ for HER in aqueous solution. Various characterizations indicate that the EY is immobilized onto the $Cs_2PtSnCl_6$ during the synthesis process. The EY-$Cs_2PtSnCl_6$ displayed extended light absorption range and efficient charge transfer from EY to $Cs_2PtSnCl_6$. The resulting EY-$Cs_2PtSnCl_6$ material exhibits high HER rate of 17.6 mmol $g^{-1} h^{-1}$, ≈1760 folds than that of the pristine $Cs_2PtSnCl_6$. This work demonstrates an effective method to construct dye-sensitized perovskites and highlights the importance of interaction between dye and perovskite. It provides useful guidance for the design of new perovskite-based photocatalysts and it will advance the development of perovskites for solar energy conversion into renewable fuels.

## 1. Introduction

Photocatalytic $H_2$ evolution reaction (HER) is an attractive approach for contributing to the development of clean energy vectors.[1-3] Among various semiconductors, lead halide perovskites have attracted considerable attention due to their appropriate properties,[4-16] including tunable bandgaps, defect

tolerance, and long carrier diffusion lengths.[17,18] However, practical application of lead halide perovskites is hindered by the high toxicity of lead (Pb) and their instability in polar solvents, making large-scale application challenging. In recent years, vacancy-ordered $Cs_2SnX_6$ perovskites have garnered significant interest for their potential in optoelectronic applications.[19-21] These materials offer an alternative to Pb-based perovskites since they have high structural stability, low toxicity, and low cost.[22-25] Nevertheless, compared to conventional Pb-based perovskites, $Cs_2SnX_6$ perovskites typically exhibit lower light-harvesting efficiency,[26] which largely limits their use in photocatalytic applications.

Inspired by dye-sensitized solar cells, dye-sensitized photocatalysts (DSPs) integrate the complementary advantages

of semiconductors and molecular dyes. In DSP systems, semiconductors efficiently accumulate and transport multiple charge carriers, while their optical properties can be tailored by incorporating interchangeable molecular dyes. This approach allows precise modulation of the light absorption range through dye selection.[27,28] For instance, dyes such as Erythrosine B (ErB), Rose Bengal (RB), Rhodamine B (RhB), and Eosin Y (EY) have been successfully employed as photosensitizers to extend the light absorption range of semiconductors.[29] Recently, some research groups have developed dye sensitized halide perovskites and studied the possibility of charge or energy transfer between dye molecules and halide perovskites.[30,31] For example, Pérez-Prieto et al. functionalized $CsPbBr_3$ nanocrystals with borondipyromethene (BODIPY) dyes and demonstrated the ability of these dyes to extract hole carriers from $CsPbBr_3$.[30] Kamat et al. employed $CsPbI_3$ nanocrystals as donors and rhodamine dye derivatives as acceptors, revealing that functional groups on the rhodamine-based moieties significantly influence the energy transfer efficiency and rate constants.[32] In another study, Shao et al. showed that N719 dye could extend the light absorption range and accelerate hole extraction from $Cs_2AgBiBr_6$-based solar cells.[31] These early studies highlighted the potential of dye sensitization to enhance the optoelectronic properties of $Cs_2SnX_6$ perovskites.

Furthermore, the efficiency of electron transfer (ET) plays a crucial role in improving the photocatalytic performance of DSP systems. Typically, ET from photosensitizers to semiconductors

J. Wang, S. He, M. Zhang, F. Yang, Q. Zhang, Z. Li
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials
Zhejiang Normal University
Jinhua, Zhejiang 321004, P. R. China
E-mail: wangjin@zjnu.edu.cn; zqli@zjnu.edu.cn

M. Robert
Sorbonne Université
CNRS
Institut Parisien de Chimie Moléculaire
Institut Universitaire de France (IUF)
Paris F-75005, France
E-mail: marc.robert@sorbonne-universite.fr

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aenm.202406048

© 2025 The Author(s). Advanced Energy Materials published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

DOI: 10.1002/aenm.202406048
<figure><img src="image_3.png" /><figcaption>**Figure 1.** a) Schematic illustration of EY-Cs₂PtSnCl₆ preparation. b) Proposed structure of EY-Cs₂PtSnCl₆. c) High-resolution XPS of Br 3d for EY and EY-Cs₂PtSnCl₆. d) SEM image and e-i) EDS elemental mapping of Cs, Pt, Sn, Cl, and Br for the EY-Cs₂PtSnCl₆ material.</figcaption></figure>

is achieved by simply mixing them in solution.[33] However, it is inherently limited by mass transfer.[34] A better approach is to link the dyes to the semiconductors through covalent bonds or surface interactions.[33] This increases the local concentration of dyes on the semiconductor surface and promotes orbital overlap, which enhances electronic communication and boosts ET efficiency. Despite this, establishing strong communication between dyes and perovskites for real photocatalytic reactions remains a challenge. The difficulty lies in the high chemical sensitivity of the perovskite surface.[7] During the photocatalytic process, dyes tend to detach from the perovskite surface, weakening their interaction. To address this issue, more robust strategy is needed to strengthen the interaction between the dyes and perovskites and ensure efficient electron transfer.

Herein, Eosin Y-sensitized Cs₂PtSnCl₆ (EY-Cs₂PtSnCl₆) was synthesized via a solvothermal method and used for visible-light-driven photocatalytic HER. As a prototype, Cs₂PtSnCl₆ represents a vacancy-ordered perovskite, known for its low toxicity and high stability.[26,35] EY is a non-precious metal dye with strong visible light absorption,[36] and its halogen terminal groups can facilitate attachment onto the surface of halide perovskites. Experimental results revealed that EY can be in situ immobilized on Cs₂PtSnCl₆ during the formation of Cs₂PtSnCl₆, leading to an expanded light absorption range for the hybrid EY-Cs₂PtSnCl₆. The EY-Cs₂PtSnCl₆ material showed an impressive HER rate of 17.6 mmol g⁻¹ h⁻¹ in aqueous solution, which is 1760 times higher than pristine Cs₂PtSnCl₆ and 2.6 times greater than the physically mixed EY and Cs₂PtSnCl₆ (noted EY/Cs₂PtSnCl₆).

Furthermore, the HER yield of EY-Cs₂PtSnCl₆ also surpasses most reported halide perovskite-based photocatalysts. The photocatalytic performance is primarily attributed to efficient charge transfer from EY to Cs₂PtSnCl₆, which largely improves charge density on Cs₂PtSnCl₆ for photocatalytic HER.

## 2. Results and Discussion

The EY-Cs₂PtSnCl₆ was synthesized using a solvothermal method (see Supporting Information for details).[28] This approach offers distinct advantages over conventional composite preparation techniques, particularly in achieving uniform dye incorporation and strong interfacial bonding. Unless otherwise specified, the optimized composition of Cs₂PtSnCl₆ used in this study was Cs₂Pt₀.₀₅Sn₀.₉₅Cl₆ (see Figure S1, Supporting Information). As illustrated in Figure 1a,b, the EY solution is added to the Cs₂PtSnCl₆ precursor solution, leading to the formation of EY-Cs₂PtSnCl₆. The conjugated structure of EY, which contains Br and carboxyl groups, enables multiple modes of interaction with Cs₂PtSnCl₆: 1) Br can interact with Cs₂PtSnCl₆ via halide vacancies;[19] 2) partial substitution of Cl by Br, as indicated by X-ray photoelectron spectroscopy (XPS) data (Figure S2, Supporting Information); 3) direct coordination through carboxyl groups with Sn⁴⁺ or Pt⁴⁺; 4) strong π-π interactions between the EY and Cs₂PtSnCl₆. To further probe the interaction between EY and Cs₂PtSnCl₆, we conducted high-resolution XPS on both EY and EY-Cs₂PtSnCl₆. As shown in Figure 1c, the XPS results revealed significant changes in the binding energies of Br 3d in EY
<figure><img src="image_4.png" /><figcaption>**Figure 2.** a) DRS of the Cs₂PtSnCl₆ and EY-Cs₂PtSnCl₆. b) Diagram of the energy band levels of Cs₂PtSnCl₆ and molecular energy levels of EY. c) Steady- and d) Transient PL spectra of the EY and EY-Cs₂PtSnCl₆ ($\lambda_{ex}$ = 380 nm; $\lambda_{em}$ = 565 nm). e) Time-resolved PL decay of the EY and EY-Cs₂PtSnCl₆, measured at 565 nm.</figcaption></figure>

upon immobilization onto Cs₂PtSnCl₆. Specifically, the binding energies increased by 0.57 eV in the EY-Cs₂PtSnCl₆ compared to the pristine EY, indicating a decrease in electron density around Br. This suggests electron donation from EY toward Cs₂PtSnCl₆, confirming a strong interaction between them.

Powder X-ray diffraction (XRD) analysis confirms that the EY-Cs₂PtSnCl₆ exhibits typical diffraction patterns that index to the cubic space group *Fm$\bar{3}$m,[37,38] indicating high crystallinity and phase purity (Figure S3, Supporting Information). The XRD patterns also suggest that the structure of Cs₂PtSnCl₆ is well-preserved after EY incorporation. Besides, the EY-Cs₂PtSnCl₆ displayed a tangential polyhedra shape with an average grain size of ≈1.7 µm (Figure 1d), which is consistent with the pristine Cs₂PtSnCl₆ (Figure S4, Supporting Information). The EY-Cs₂PtSnCl₆ likely exposes the (111) surface, terminated by Cs–Cl bonds, which has the lowest surface energy and is therefore the most stable.[25] Energy-dispersive X-ray spectroscopy (EDS) elemental mapping (Figure 1e–i) demonstrates uniform distribution of Cs, Pt, Sn, Cl, and Br within the EY-Cs₂PtSnCl₆. Compared to the pristine Cs₂PtSnCl₆ (Figure S4, Supporting Information), the appearance of Br in EY-Cs₂PtSnCl₆ confirms the suc-

cessful immobilization of EY on the Cs₂PtSnCl₆. This conclusion is further supported by XPS data and element analysis (Figures S5, S6, Supporting Information). X-ray fluorescence (XRF) measurements reveal the molar ratio of EY to the Cs₂PtSnCl₆ is ≈ 1.9 (Table S1, Supporting Information). These findings collectively indicate the successful synthesis of the EY-Cs₂PtSnCl₆, with EY immobilized at Cs₂PtSnCl₆.

Photoelectronic properties of photocatalysts are critical for catalytic activity. To evaluate the light-harvesting capabilities of the material, we first conducted UV-visible diffuse reflectance (DRS) measurements. As illustrated in **Figure 2a**, the pristine Cs₂PtSnCl₆ displays an absorption edge ≈500 nm. In contrast, EY-Cs₂PtSnCl₆ exhibits strong visible light absorption in the range of 400–600 nm, with the absorption extending to ≈750 nm. This notable red-shift for EY-Cs₂PtSnCl₆ can be attributed to the incorporation of EY (Figure S7, Supporting Information), and is accompanied by a color change from gray to red (Figure 2a, inset). To achieve efficient charge separation, it is crucial to have properly aligned band structures. We utilized Tauc plots and ultraviolet photoelectron spectroscopy (UPS) to determine the band structures of Cs₂PtSnCl₆. Based on the Tauc plots
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Photocatalytic HER performance EY-Cs₂PtSnCl₆ in water. Conditions unless otherwise stated: perovskite (5 mg), TEOA/H₂O (1 mL/5 mL), pH = 8, Ar, λ > 400 nm, 100 mW cm⁻¹, 2 h. a) H₂ evolution rate with EY, Cs₂PtSnCl₆, EY/Cs₂PtSnCl₆, and EY-Cs₂PtSnCl₆. b) Comparison of photocatalytic HER performance between reported photocatalytic systems and EY-Cs₂PtSnCl₆. c) Dependence of HER for different molar ratios between EY and Cs₂PtSnCl₆.</figcaption></figure>

(see Figure S8, Supporting Information), the bandgap (E_g) of Cs₂PtSnCl₆ is estimated to be ≈2.78 eV. Furthermore, the UPS was employed to ascertain the valence band maximum (E_VB) and the conduction band minimum (E_CB) of Cs₂PtSnCl₆ (Figure S8, Supporting Information). When calibrating the vacuum level to the normal hydrogen electrode (NHE, pH 7), the E_CB and E_VB are determined to be -0.88 V versus NHE and +1.90 V versus NHE, respectively. Given that the estimated redox potential of EY (-2.00 V vs NHE) is more negative than the E_CB of Cs₂PtSnCl₆ (-0.88 V vs NHE),[39] this energy level difference is sufficient to drive electron transfer from the photogenerated EY to the Cs₂PtSnCl₆.

We then investigated the photoluminescence (PL) spectra to probe the charge recombination within the sample.[40,41] As shown in Figure 2c, the EY exhibits a typical emission peak centered at 565 nm due to its conjugated xanthene structure and efficient recombination of excited charge carriers.[39] For EY-Cs₂PtSnCl₆, a significant PL quenching is observed. Furthermore, time-resolved photoluminescence spectroscopy (TRPL)

was performed to probe charge transfer kinetics. As shown in Figure 2d, the PL lifetime of EY is 3.9 ns (Table S2, Supporting Information), whereas EY-Cs₂PtSnCl₆ shows faster decay with a decreased PL lifetime of 1.5 ns. These results indicate that the singlet excited state lifetime of EY is shortened in EY-Cs₂PtSnCl₆, suggesting electron transfer from EY to Cs₂PtSnCl₆. The electron injection rate ($k_{et}$) is ≈4.1 × 10⁸ s⁻¹, which is ≈4 times faster than that of the physically mixed sample (EY/Cs₂PtSnCl₆, see Figure S9, Supporting Information). These results indicate that the strong interaction between EY and Cs₂PtSnCl₆ facilitates charge transfer in EY-Cs₂PtSnCl₆.

The optoelectronic properties suggest that EY-Cs₂PtSnCl₆ could be an optimal photocatalyst. We then conducted photocatalytic HER using EY, Cs₂PtSnCl₆, EY/Cs₂PtSnCl₆, and EY-Cs₂PtSnCl₆ in water (pH 8) under visible light illumination (λ > 400 nm). As illustrated in Figure 3a, the pristine EY exhibited low HER rate (0.01 mmol g⁻¹ h⁻¹) due to the fast radiative charge recombination, low intrinsic catalytic activity and absorption in the visible range. EY-Cs₂PtSnCl₆ demonstrated
<figure><img src="image_6.png" /><figcaption>**Figure 4.** In situ high-resolution XPS of Pt 4f for a) $Cs_2PtSnCl_6$, b) EY/$Cs_2PtSnCl_6$, and c) EY-$Cs_2PtSnCl_6$. d) Photocurrent density of EY and EY-$Cs_2PtSnCl_6$ under chopped light irradiation at E = -0.4 V versus Ag/AgCl (bias potential, see SI for details).</figcaption></figure>

a significantly enhanced photocatalytic activity for HER. The $H_2$ evolution rate of EY-$Cs_2PtSnCl_6$ reached 17.6 mmol g$^{-1}$ h$^{-1}$, ≈1760 times higher than that of pristine $Cs_2PtSnCl_6$. This optimized performance is one of the highest HER rates reported so far for perovskites in the absence of HX (Figure 3b; Table S3, Supporting Information).[42–53] Additionally, $H_2$ evolution rate of EY-$Cs_2PtSnCl_6$ is ≈2.5 times higher than that of EY/$Cs_2PtSnCl_6$. This enhancement can be attributed to efficient charge transfer and suppressed radiative charge recombination of EY, as supported by Figure S9 (Supporting Information). The enhancement in photocatalytic properties primarily arises from two main factors: 1) the immobilization of EY onto $Cs_2PtSnCl_6$ extends the light absorption range, leading to enhanced visible light harvesting, and 2) the in situ growth approach endows EY-$Cs_2PtSnCl_6$ with strong interfacial interactions between EY and $Cs_2PtSnCl_6$, resulting in good charge separation and transport. Furthermore, under 520 nm monochromatic light irradiation, the apparent quantum yield (AQY) of EY-$Cs_2PtSnCl_6$ for HER reached 17.5%.

As the mass ratio of EY to $Cs_2PtSnCl_6$ was increased from 0.5:1 to 2:1, the photocatalytic activity of EY-$Cs_2PtSnCl_6$ improved from 7.7 to 17.6 mmol g$^{-1}$ h$^{-1}$ (Figure 3c). However,

further raising the EY content led to a decrease in HER activity. This could be attributed to the detachment of excess EY from EY-$Cs_2PtSnCl_6$ (see Figures S10,S11, Supporting Information), causing free EY to compete with EY-$Cs_2PtSnCl_6$ for light absorption. It is known that $Cs_2PtSnCl_6$ has dense atomic packing and enhanced covalent bonding, which contribute to its good stability in water.[7] As expected, the EY-$Cs_2PtSnCl_6$ showed excellent photocatalytic durability, maintaining its performance over four 2-h cycles without significant degradation (Figure S12, Supporting Information). Furthermore, the morphology and structure of EY-$Cs_2PtSnCl_6$, along with the oxidation state of $Pt^{4+}$ remained unchanged after 2-h photocatalysis (Figures S13,S14, Supporting Information), illustrating the good stability of EY-$Cs_2PtSnCl_6$. Control experiments revealed that the introduction of EY (a photosensitizer) and TEOA (sacrificial agent) are necessary for HER to occur with $Cs_2PtSnCl_6$ (Figures S15–S17, Supporting Information). Notably, Pt in $Cs_2PtSnCl_6$ plays a multifaceted role: it acts as electron traps, facilitating efficient charge separation. It offers active sites for HER (Figure S18, Supporting Information) and it enhances the covalent nature of $Cs_2PtSnCl_6$, thereby improving its stability in polar solvents.[7]
<figure><img src="image_7.png" /><figcaption>**Figure 5.** AFM images of a,c) $Cs_2PtSnCl_6$ and f,h) EY-$Cs_2PtSnCl_6$ under dark condition and light illumination. KPFM images and the corresponding surface potential profile along the white line under dark condition and light illumination for b,d) $Cs_2PtSnCl_6$ and g,i) EY-$Cs_2PtSnCl_6$. Line profiles of the SPV difference for e) $Cs_2PtSnCl_6$ and j) EY-$Cs_2PtSnCl_6$.</figcaption></figure>

These synergistic effects collectively contribute to the enhanced photocatalytic performance and stability observed in our system.

Furthermore, we investigated the photogenerated electron migration and the electronic states of Pt in different samples using in situ high-resolution XPS (Figure 4a–c). Notably, our XPS results revealed significant shifts in the binding energies of Pt 4f before and after light illumination. As shown in Figure 4, all samples exhibited a noticeable decrease in the binding energy of Pt 4f upon irradiation, indicating an increase in electron density at the Pt sites. Interestingly, the most pronounced shift (0.38 eV) in binding energy was observed in EY-$Cs_2PtSnCl_6$,

suggesting the highest electron density accumulation. This finding provides strong evidence that EY injects electrons into the neighboring Pt sites of EY-$Cs_2PtSnCl_6$ under light illumination, thereby facilitating the photocatalytic HER. Moreover, this result indicates that compared to conventional physical mixing of EY/$Cs_2PtSnCl_6$, the EY-$Cs_2PtSnCl_6$ composite enables better electron transfer efficiency from EY to the Pt sites. We further examined the charge separation and transfer efficiency of the samples using photocurrent and electrochemical impedance spectroscopy (EIS) spectra. As shown in Figure 4d, EY-$Cs_2PtSnCl_6$ exhibits a higher photocurrent response compared to pristine $Cs_2PtSnCl_6$, indicating better charge separation and transfer

<figure><img src="image_8.png" /><figcaption>**Figure 6.** Proposed photocatalytic mechanism of the EY-$Cs_2PtSnCl_6$ photocatalysts. The energy band levels of $Cs_2PtSnCl_6$ and molecular energy levels of EY (in V vs NHE, pH 7).</figcaption></figure>
efficiency in EY-Cs₂PtSnCl₆. The EIS spectra show that EY-Cs₂PtSnCl₆ has a smaller charge transfer resistance than pristine Cs₂PtSnCl₆ (Figure S19, Supporting Information). These results confirmed that the interaction between EY and Cs₂PtSnCl₆ in EY-Cs₂PtSnCl₆ significantly suppresses charge recombination and accelerates charge transfer.

To further support the charge transfer process in Cs₂PtSnCl₆ and EY-Cs₂PtSnCl₆, Kelvin Probe Force Microscopy (KPFM) was employed to observe the spatial charge distribution. AFM height mapping images (Figure 5a,c,f,h) show similar morphologies for both materials. The KPFM images and corresponding surface photovoltage (SPV) line profiles (Figure 5b,d,e,g,i,j) reveal no significant SPV signals for the Cs₂PtSnCl₆, indicating rapid charge carrier recombination. In contrast, a distinct negative SPV is observed in EY-Cs₂PtSnCl₆, with more negative signals corresponding to electron accumulation on the surface of EY-Cs₂PtSnCl₆ after illumination. The potential difference between the positive and negative regions in EY-Cs₂PtSnCl₆ is 34.1 mV, higher than the 21.8 mV for Cs₂PtSnCl₆. This difference in SPV signals confirms charge accumulation and depletion at the interfaces in EY-Cs₂PtSnCl₆.

Based on all of these results we propose (Figure 6) that EY is excited under light illumination, absorbing visible light and generating charge carriers upon electron transfer to the perovskite. The proper energy levels alignment and interaction between EY and Cs₂PtSnCl₆ facilitate the transfer of photogenerated electrons from EY to the CB of Cs₂PtSnCl₆. Photogenerated electrons then accumulate at the surface Pt sites, where they reduce H₂O to H₂ while the holes (radical cation of EY) are consumed by the sacrificial agent (TEOA). The in situ assembled EY-Cs₂PtSnCl₆ improves the charge transfer efficiency between EY and Cs₂PtSnCl₆, and further promotes the HER on EY-Cs₂PtSnCl₆.

### 3. Conclusion

In summary, we have developed a facile in situ method to construct EY-Cs₂PtSnCl₆ material for photocatalytic HER. The strong interaction between EY and Cs₂PtSnCl₆ leads to efficient visible light absorption range and charge separation. The resultant EY-Cs₂PtSnCl₆ exhibited a remarkable photocatalytic HER rate of 17.6 mmol g⁻¹ h⁻¹ in aqueous solution. Our spectroscopic and mechanistic studies revealed that the charge transfer rate in immobilized EY on Cs₂PtSnCl₆ is more efficient than in freely diffusing EY with Cs₂PtSnCl₆ through random collisions. This work presents an effective dye-sensitization strategy for tailoring the photocatalytic properties of halide perovskites. It highlights the critical role of building strong interactions between dyes and halide perovskites, providing useful guidance for the design and exploration of new halide perovskite photocatalysts.

### Supporting Information

Supporting Information is available from the Wiley Online Library or from the author.

### Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (21701143, 21975223), the Natural Science Foundation of

Zhejiang Province (LZ22B030002), and the Industrial Key Projects of Jinhua City (2021-1-063). Partial financial support to M.R. from the Institut Universitaire de France (IUF) is acknowledged.

### Conflict of Interest

The authors declare no conflict of interest.

### Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

### Keywords

dye sensitization, H₂ evolution, in situ synthesis, photocatalysis, vacancy-ordered perovskites

Received: December 23, 2024

Revised: February 16, 2025

Published online:

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