Halide insertion regulation for efficient and stable wide-bandgap perovskite photovoltaics

Domain: physics
Published: 2025-12-02
Editorial outcome: major_revision

Abstract
Wide-bandgap (WBG) perovskite solar cells (PSCs) are employed for tandem solar cells. Understanding the crystallization mechanism of mixed-halide WBG perovskite will contribute to achieving the high-performance photovoltaics. Herein, we demonstrate that the asynchronous halide insertion is accompanied by random crystal facets and orientations, restricting the efficient carrier extraction. Guided by density functional theory calculations, we construct a π-conjugated molecular wall structure using o-phenylenediamine (OPD). The molecular wall at the grain boundary induces templated perovskite crystallization through the ortho-diamine group, enabling synchronous [PbBr6]4- and [PbI6]4- halide insertion. The OPD-treated perovskite film exhibits a preferred (100) facet and a highly vertical orientation. Benefited from the improved carrier extraction, the resulting WBG PSC (1.69 eV) achieves a power conversion efficiency of 24.13% (certified 23.43%), representing one of the highest values among WBG PSCs. Meanwhile, the improved perovskite crystal quality ensures the enhanced operational stability of the PSCs.

Introduction
Wide-bandgap (WBG) perovskite materials show advantages for employment as top cells in tandem solar cells (TSCs)1–4. Nevertheless, WBG perovskite solar cells (PSCs) suffer from severe power conversion efficiency (PCE) loss of more than 20%, which is significantly higher than that of common formamidinium lead iodide (FAPbI3)-dominated perovskite systems5,6. WBG perovskites are usually constructed with mixed halides to achieve a tunable optical bandgap7, and bromine (Br) contents above 20 mol% are usually used8. Since Br possesses a smaller ionic radius and lower solubility than iodine (I), Br and I halides exhibit large differences in crystallization kinetics9. The crystallization behavior of mixed-halide anions plays a crucial role in preparing high-quality WBG perovskite films10. The differentiated crystallization properties of halides can induce phase separation, residual lattice strain, random facet orientation, etc.11–14, which restrict efficient carrier extraction and crystal structure stability. Unfortunately, researchers have not yet fully understood the crystallization mechanism of mixed-halide perovskite films.

For conventional solution-processed methods, a large number of perovskite grains crystallize unevenly during their independent nucleation and growth processes, and thus spontaneously self-assemble into various crystal facets and orientations15. The preferential crystallization of Br-based components has been widely demonstrated in WBG perovskite systems10, and the subsequent insertion of I components will restructure the unit cells to form mixed-halide perovskite crystals. The asynchronous halide insertion will exacerbate the randomness of crystal facets and orientations16. The macroscopically disordered crystal arrangement induces defects such as atomic dislocation and ion vacancies, resulting in reduced carrier mobility and shortened carrier diffusion length17. Previous works have reported some methods to control crystal orientation and halide distribution by molecular additives. Jiao et al. and Shi et al. are committed to achieving pure α phase in the FAPbI3 perovskite system18,19. They introduce additives to achieve strong coordination forces with the Pb-I skeleton, thereby inducing oriented crystallization of perovskite films. Yan et al. achieves oriented nucleation of I-based Pb-Sn perovskite by reducing the surface energy of the (100) plane20. Crystal growth control of mixed-halide WBG perovskites is more difficult than that of these pure I halide perovskite systems, due to the natural asynchronous crystallization nucleation of I and Br components. Although Li et al. achieve the synchronous phase transition of I-based and Br-based components through intermediate phase regulation, this phase transition at the annealing stage cannot achieve a homogeneous mixed-halide perovskite phase with preferred crystal facets and orientations11. Therefore, understanding the mixed-halide insertion behaviors and achieving controllable halide insertion is the basis for obtaining the WBG perovskite films with efficient carrier transport.

In-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) characterization is an important technique to reveal the evolution of crystallographic information in perovskite films21. For perovskite films with asynchronous insertion of halide components, experimental results show that each crystal facet exhibits distinguishable structural evolution characteristics. Combined with density functional theory (DFT) analysis, it is found that the post-crystallization I component prefers to be inserted along the (100) facet when entering the perovskite lattice. Unfortunately, this directed insertion of the I component does not improve the diversity of crystal facets and orientations. Inspired by the tendency of the I component to be inserted along the (100) facet, we envision realizing the synchronous halide (I and Br) insertion along the (100) facet. Considering that the strong interaction of functionalized π-conjugated molecules can build a molecular wall structure, the amine groups exposed on the same side of the molecular wall can serve as nucleation sites for perovskite crystallization along the (100) facet. It is expected to achieve synchronous halide insertion, thus obtaining preferred crystal facets and orientations.

Guided by DFT calculations, the π-conjugated ortho-diamine cation, o-phenylenediamine (OPD), is identified as an ideal candidate for building a robust molecular wall and regulating halide insertion. As expected, the ortho-diamine groups of OPD molecules show the strongest interaction with the (100) facet of the perovskite crystal, and almost the same binding energy exists between OPD molecules and [PbX6]4- octahedra ([PbBr6]4- and [PbI6]4-). The templated crystallization induced by the OPD-constructed molecular wall ensures the synchronous insertion of mixed-halide components, forming a preferred (100) facet and an orientation perpendicular to the substrate. The resulting perovskite films exhibit reduced defects and prolonged carrier diffusion length, guaranteeing efficient carrier extraction and suppressed non-radiative recombination. As a result, the OPD-treated WBG PSC (1.69 eV) achieves a PCE of 24.13% (certified 23.43%), representing one of the highest PCEs among WBG PSCs. Based on a semi-transparent (ST) PSC, the resulting four-terminal (4T) perovskite/copper indium gallium selenide (CIGS) tandem solar cell (TSC) achieves a PCE of 29.34%. Benefiting from the highly vertical crystal orientation and the stable perovskite structure, the encapsulated WBG PSC still maintains more than 90% of the initial PCE after maximum power point tracking (MPPT) for 800h under the ISOS-L-1 testing protocol.

Results
Crystallographic evolution mechanism of asynchronous halide insertion
To investigate the crystallographic evolution of WBG perovskite films, we perform in-situ GIWAXS characterization of FA0.8MA0.1Cs0.1Pb(I0.8Br0.2)3 film at the spin-coating stage (Fig. 1a)21. As the antisolvent drips, three common perovskite characteristic crystal facets gradually appear, including (100), (110), and (111) facets. The q-value variation corresponding to each facet is extracted (Fig. 1b, Supplementary Table 1), and all crystal facets exhibit decreased q values. It is noteworthy that a significant q-value decrease (Δq, −0.115 nm−1) from 10.150 nm−1 to 10.035 nm−1 is observed on the (100) facet, compared with that on the (110) facet (−0.038 nm−1) and (111) facet (−0.042 nm−1). According to the Bragg equation, a reduced q value means an increased interplanar spacing (d)22. Moreover, almost at the same time as the q-value decreases, all the crystal facets show completely random orientation (Fig. 1c). It is not until 30 s that the perovskite film gradually self-assembles to form a partial orientation trend (Supplementary Fig. 1). Nevertheless, even though the crystallinity is enhanced after annealing, the control film still exhibits random crystal orientation (Fig. 1d). To exclude the influence of solvent on perovskite nucleation and orientation, we introduce a common solvent, N-methyl-2-pyrrolidone (NMP), into the perovskite precursor solution, resulting a mixed solvent system (25 V% of NMP). As shown in the GIWAXS patterns (Supplementary Fig. 2), the control sample still exhibit random crystal facets and orientations after NMP solvent introduction.

Such lattice evolution is usually accompanied by asynchronous crystallization of halides in perovskite films. Asynchronous crystallization of mixed halides has been reported, and preferential crystallization of Br components has been demonstrated9,10. We thus speculate that the q-value decrease is caused by the post-crystallization I ion insertion. As shown in the in-situ GIWAXS data, the (100) facet exhibits a larger change in q value compared to the other two facets, which may be related to the way I components are inserted into the perovskite lattice. Therefore, we perform DFT calculations to simulate the mechanism of asynchronous halide insertion. For perovskite crystals with a cubic ABX3 structure, the atomic layer arrangement shown on the (100) facet is …AX-BX2-AX-BX2…. The atomic arrangements corresponding to the (110) and (111) facets are …X2-ABX-X2-ABX… and …AX2-B-AX2-B…, respectively23. We attempt to insert I element into the ABBr3 lattice along the (100) facet, and the intervening Br ion layers are replaced by I ion layers. As shown in Fig. 1e, the atomic arrangement after I ion insertion is shown on the AX(100), ABX(110), and AX3(111) terminations, respectively24. Changes in the interplanar spacing (Δd) of the (100), (110), and (111) facets can be obtained, which are 0.19 Å, 0.03 Å, and 0.02 Å, respectively. Theoretical simulation results for the I element insertion along the (100) facet show the same trend as the in-situ GIWAXS results. The (100) facet exhibits a sharp interplanar spacing change compared to the other two crystal facets due to the post-crystallization I ion insertion.

To further confirm whether the specific I ion insertion direction determines the above-mentioned change in interplanar spacing, we also simulate a random I ion insertion model. As shown in Supplementary Fig. 3, 80% of the Br atoms are randomly replaced by I atoms at the X sites of each crystal facets, which results a APb(Br0.2I0.8)3 crystal structure. According to the DFT calculation results, almost the same Δd variation is observed at all three crystal facets, which is inconsistent with the in-situ GIWAXS experiments. Therefore, we conclude that the post-crystallization I ion insertion direction shows a preference for the (100) facet. This asynchronous halide insertion is accompanied by random crystal facets and orientations, which are undoubtedly detrimental to efficient carrier extraction. Considering the crystal facets’ selectivity of halide insertion and the dominance of the (100) facet, we are committed to inducing synchronous halide insertion, obtaining a preferred (100) facet and a perpendicular crystal orientation19.

Crystallographic modulation of synchronous halide insertion
We propose to construct a functionalized π-conjugated molecular wall structure to induce the synchronous mixed-halide insertion (Fig. 2a). It has been demonstrated that large-sized amine cations can effectively anchor the [PbX6]4- octahedron20. We therefore design a series of benzene-based monoamine and diamine cations, namely aniline (AD), o-phenylenediamine (OPD), m-phenylenediamine (MPD), and p-phenylenediamine (PPD). Strong intermolecular π-π stacking is crucial for constructing a stable molecular structure25. We simulate three stacking models of π-conjugated molecules using DFT calculations, including parallel (0°), perpendicular (90°), and antiparallel (180°)26. All four molecules exhibit close intermolecular forces in both the perpendicular and antiparallel models, as well as monoamines and diamines (Fig. 2b). In the parallel stacking model, the intermolecular force of the OPD is 2–20 times that of the other three molecules (Supplementary Fig. 4). Moreover, the parallel stacking model of OPD exhibits a larger binding energy (0.163 eV) between molecules, compared with their perpendicular stacking model (0.081 eV) and antiparallel stacking model (0.073 eV) (Fig. 2c). In contrast, the AD with monoamines exhibits close and weak π-π interaction force in both perpendicular and antiparallel modes, making it difficult to form aligned molecular wall. Therefore, the parallel stacking of OPD should be the most stable structure, and OPD with ortho-diamine exhibits advantages in constructing a stable molecular wall structure.

This parallel stacking allows all ortho-diamine groups to be located on the same side of the molecular wall structure. The OPD also exhibits the largest electrostatic potential (ESP) distribution in the ortho-diamine region compared to the other three molecules, driving the perovskite nucleation (Fig. 2d). Since a large number of ortho-diamine groups are exposed on the same side, the increased nucleation sites and the strong electrostatic potential guarantee the templated crystallization. In general, halide components are present in the form of [PbX6]4- octahedra in the perovskite precursor solution before the perovskite crystals are formed. The binding energy between OPD molecules and [PbX6]4- octahedra is crucial for controlling the crystallization kinetics of perovskites. To evaluate whether the OPD-constructed molecular wall is selective for the crystal facet of perovskite nucleation, we employ DFT calculations to simulate the binding energy between OPD cations and [PbI6]4- octahedra of different perovskite crystal facets (Fig. 2e, Supplementary Figs. 5–7). As shown, the maximum binding energy (1.20 eV) is observed at the (100) face than at the (110) facet (0.94 eV) and (111) facet (1.06 eV). Moreover, the binding energies for OPD with [PbBr6]4- at the (110) and (111) facets are lower than that at the (100) facet. This provides a theoretical basis for the OPD-constructed molecular wall to induce a preferred (100) facet18. More importantly, OPD cation exhibits similar binding energies with both [PbI6]4- and [PbBr6]4- octahedra, suggesting that the synchronous insertion of I and Br halides is possible during the templated crystallization process.

We then monitor the crystallization dynamics of OPD molecular wall-induced mixed-halide WBG perovskite films through in-situ GIWAXS characterization (Fig. 2f, j). All perovskite films transform directly from the solvent phase to the perovskite phase, and no additional transitional phase is observed (Supplementary Fig. 8). As shown in the extracted q-value evolution, the (100) facet of the AD-treated film still exhibits a large q-value decrease from 10.112 nm−1 to 10.058 nm−1 (Fig. 2g). This may be because the monoamine molecules cannot exert strong forces to induce the simultaneous insertion of halides and templated crystallization of the perovskite film. Therefore, the preferred (100) facet and vertical crystal orientation are not fully achieved (Fig. 2h, i). Due to the indiscriminate anchoring of [PbBr6]4- and [PbI6]4- halides by the stable molecular wall structure, the OPD-treated perovskite film exhibits great potential to achieve synchronous halide insertion. The OPD-treated film also exhibits the fastest increase in GIWAXS signal intensity for the (100) facet (Fig. 2k), implying that the nucleation sites provided by the ortho-diamine accelerate the crystallization rate of the perovskite film27. The same conclusion can also be obtained from in-situ laser scanning confocal microscopy (LSCM) images (Supplementary Fig. 9). As expected, the resulting film obtains nearly constant q values (10.088 nm−1) for the (100) facet. Within a very short time (1 s) after the antisolvent is added, the preferred (100) facet and the crystals perpendicular to the substrate are formed (Fig. 2l Supplementary Fig. 10). We also monitor the GIWAXS evolution of the films at the annealing stage (Supplementary Fig. 11). All films exhibit nearly constant q values on all facets, which suggests that the halide insertion-induced perovskite crystal structure is formed at the spin-coating stage.

To further substantiate the synergistic halide insertion, we measure in-situ UV-Vis absorption spectra of perovskite films at the spin-coating stage. As shown in Supplementary Fig. 12, the absorption edge of the control perovskite film gradually red-shifts with the addition of antisolvent, indicating that the Br-rich component is formed preferentially, and the subsequent I insertion narrows the bandgap. Although the AD-treated film accelerates the red shift of the absorption edge, subsequent I halide insertion still exists and synchronous halide insertion cannot be successfully achieved. In contrast, the OPD-treated film exhibits a constant absorption edge almost immediately after the antisolvent is added. This constant bandgap also implies the simultaneous halide insertion, which is consistent with the results of in-situ GIWAXS characterization. As a result, the strong vertical orientation of (100) facet is dominant in the OPD-treated film (Supplementary Fig. 13). After OPD treatment with the optimal concentration of 1.0 mol% (Supplementary Fig. 14), the perovskite film shows the preferred (100) facet and the vertical crystal orientation (Fig. 2m). We extract the GIWAXS signal of the perovskite films on the (100) facet, and perform deconvolution of the GIWAXS peaks (Supplementary Fig. 15). Control and AD-treated samples exhibit additional fitting peak components near the main peak of (100) facet. This may be related to the inhomogeneous WBG perovskite phase. In contrast, a single (100) peak and the smallest full width at half maximum (FWHM) value can be observed in the OPD-treated films. The narrow FWHM of the (100) peak can also rule out contributions from grain size variation (Supplementary Fig. 16), indicating that the synchronized halide insertion leads to a high-quality homogeneous WBG perovskite phase.

We then perform the depth-profiling X-ray photoelectron spectroscopy (XPS), to investigate the halogen element distribution in the resulting perovskite films. As displayed in XPS spectra of I and Br elements (Supplementary Fig. 17), the signal of the Br element in the control film gradually decreases as the etching depth increases, while the signal of the I element gradually increases. The Br-rich component formed first on the surface is distributed on the top of the perovskite film, while the I-rich phase formed later is distributed on the bottom. Due to the accelerated crystallization rate, the inhomogeneous halide distribution in the AD-treated film is alleviated to a certain extent, but it is still not negligible. In contrast, the OPD-treated film exhibited an almost homogeneous halide distribution from top to bottom. The same conclusion can be obtained from EDS spectra of the cross-sectional PSCs (Supplementary Fig. 18). The XPS peak at 291 eV shows that π-conjugated OPD molecules exist in the OPD-treated perovskite film28,29 (Supplementary Fig. 19). The signal gradually disappears with the increase of etching depth (Supplementary Fig. 20), which indicates that the OPD molecules are mainly concentrated in the top region of the perovskite film. The OPD molecular wall located on the top film will induce top-down templated crystallization of the perovskite film (Fig. 2a). The OPD molecular wall can also be demonstrated by the anisotropic GIWAXS pattern of OPD-treated perovskite film (Fig. 2m). The π-π interactions signal is observed at 15.3 nm−1, which corresponds to the distance (4.1 Å) between OPD molecules in the stacked structure (Supplementary Fig. 21). The OPD molecular wall structure at the grain boundary will form a strong anchoring effect with the perovskite precursor, which is confirmed by the Fourier transform infrared (FTIR) spectra and XPS spectra (Supplementary Figs. 22–25). This strong anchoring effect determines synchronous halide insertion and templated crystallization. Therefore, the resulting preferred (100) facet and highly vertical crystal orientation will ensure efficient carrier extraction.

Efficient carrier extraction of perovskite films
According to the atomic force microscopy (AFM) images, we can obtain distinguishable grain boundaries of the perovskite films (Supplementary Fig. 26). Low surface roughness is observed in the OPD-treated films, and the smooth surface morphology may be related to the preferred (100) facet and highly vertical orientation. As shown in Fig. 3a–c, height and the contact potential difference (VCPD) line-scan spectra are extracted from the region marked with horizontal lines in AFM and Kelvin probe force microscopy (KPFM) images. Combined with AFM images, we can detect surface electrical information at the perovskite grain interior (GI). Control film exhibits non-uniform surface potential at GIs, resulting in a large VCPD difference (ΔVCPD,GI) of 101 mV. The ΔVCPD,GI (71 mV) of the AD-treated film is reduced, and the OPD-treated film shows the smallest ΔVCPD,GI (48 mV). Moreover, the lowest average surface potential can also be observed in the OPD-treated film compared to the control and AD-treated samples. The reduced and uniform VCPD at GIs may be attributed to the preferred (100) facets, and similar results have been obtained in previous work30. In general, a low surface potential means a low work function, resulting in a Fermi level closer to the conduction band, which will be more conducive to electron extraction31.

We perform confocal fluorescence microscopy (TCFM) mapping on perovskite films with an electron transport layer (ETL) to evaluate the electron extraction capability (Fig. 3d–f). As expected, the lowest photoluminescence (PL) signal intensity is evenly distributed in the OPD-treated film compared to the control and AD-treated films. The reduced PL intensity can also be observed in the steady-state PL spectrum of OPD-treated film (Supplementary Fig. 27)32. Similarly, for the perovskite films with hole transport layer (HTL), the OPD-treated sample exhibit the lowest PL intensity compared to control and AD-treated samples (Supplementary Fig. 28). Considering that defect-induced carrier recombination in the perovskite film may also lead to the reduced PL intensity, we also measure the TCFM mapping of the bare perovskite film. The strongest PL intensity and longest PL lifetime are exhibited on the OPD-treated film (Supplementary Fig. 29), indicating the lowest defect-induced carrier recombination. The density of defect states (tDOS) of perovskite films can be measured by thermal admittance spectroscopy (TAS)33. The density of defect states (tDOS) of the OPD-treated film is nearly an order of magnitude lower than that of the control film (Fig. 3g). Therefore, we can conclude that the reduced PL intensity in the perovskite/ETL and perovskite/HTL samples should be attributed to the efficient charge extraction, while excluding the defect-induced carrier recombination. Efficient and uniform carrier extraction is benefited from the preferred (100) facet and highly vertical orientation.

We further evaluate the crystalline quality and carrier transport behavior of the perovskite films. The space-charge-limited current (SCLC) model with electron-only device is often used to extract trap density (Nt) and carrier mobility (μ) in perovskite films (Supplementary Fig. 30). As displayed in Fig. 3h, OPD-treated films show the lowest Nt of 2.31×1015 cm−3, compared to control (1.04×1016 cm−3) and AD-treated films (3.02×1015 cm−3). This is consistent with the conclusion obtained from the TAS results. Moreover, an increased μ of 1.77×10−3 cm2 V−1 S−1 is obtained in the OPD-treated sample, which is tens of times higher than that of the control (7.21×10−5 cm2 V−1 S−1) and AD-treated samples (7.48×10−4 cm2 V−1 S−1). Low defects and high carrier mobility should be beneficial to prolonging the carrier diffusion length (LD). An approximation of the LD can be estimated by the following equation34:
LD = sqrt(2 * π * d^2 * τ / τ2,quench) (1)
Where d is the perovskite film thickness, τ and τ2,quench is the bimolecular recombination lifetime of the perovskite film with and without a charge transport layer, respectively. The LD-e and LD-h are the diffusion lengths of electrons and holes, which can be calculated by the time-resolved PL (TRPL) decay (Supplementary Fig. 31)35. As expected, the OPD-treated film exhibits enhanced carrier diffusion capabilities for both electrons and holes, specifically, LD-e increased from 389 nm to 648 nm, and LD-h increased from 299 nm to 687 nm (Fig. 3i). The prolonged carrier diffusion length can facilitate the carrier extraction from the perovskite layer to the charge transport layer. Moreover, LD-e close to LD-h also ensure balanced charge extraction for electrons and holes, which is beneficial for achieving high-performance WBG PSCs.

Improved performances and stability of WBG PSCs
We further analyze the carrier transport characteristics at the device level. According to the Mott-Schottky equation, the built-in potential (Vbi) can be extracted from the capacitance-voltage (C-V) curves of PSCs (Fig. 4a). The OPD-treated device shows a higher Vbi (1.01 V) than the control and AP-treated devices (0.89 V and 0.95 V). The strong built-in electric field will drive the efficient separation of electrons and holes. To evaluate the carrier recombination behavior in the PSCs, we measure the current density-voltage (J-V) curves of PSCs under dark conditions. As shown in Fig. 4b, the OPD-treated device exhibits the lowest reverse saturation current density (J0) (3.30×10−8 mA cm−2). A low J0 means that leakage current caused by carrier recombination is effectively suppressed. The results of electrochemical impedance spectroscopy (EIS) also support the same conclusion (Supplementary Fig. 32), and the charge recombination resistance (Rrec) of the device treated with OPD is increased from 811 Ω to 2526 Ω. The ideality factor (n) is usually used to quantitatively measure the carrier recombination of PSCs. It can be obtained from the light intensity-dependent VOC relationship by fitting the slope (Fig. 4c). The n value (1.53) close to 1 indicates that free-carrier-induced radiative recombination is dominant in the OPD-treated device, and thus defect-induced non-radiative recombination is reduced.

Suppressed non-radiative recombination is generally accompanied by reduced VOC losses in PSCs. When a solar cell is operated as a light-emitting diode, the VOC loss of the device can be calculated using the electroluminescence external quantum efficiency (EQEL). When the injected current density is approximate to the short-circuit current density (JSC) under 1-sun illumination, the corresponding EQEL values can be used to evaluate the VOC loss of PSCs (Fig. 4d). The potential VOC of PSCs can be obtained by the previously reported equation as follows:36
VOC = VOC,rad + kT/e * ln(EQEL) (2)
where VOC,rad, k, T, and e are the radiative limit of VOC, Boltzmann’s constant, thermodynamic temperature, and elementary charge. The second term in the equation represents the VOC loss induced by non-radiative recombination. The OPD-treated device achieves an EQEL of 0.78%, and thus a VOC loss of 0.126 V could be obtained. According to the Shockley-Queisser (S-Q) limit theory37, the perovskite with bandgap of 1.69 eV corresponds to the theoretical radiative limit VOC of 1.400 V. Therefore, a potential VOC of 1.274 V should be obtained in the OPD-treated devices.

Solar cell capacitance simulator (SCAPS-1D) is a professional one-dimensional simulation tool for solar cells38. It is often used to simulate and analyze key physical phenomena within solar cells, such as charge transport and carrier recombination. This can guide optimizing device structure design and improving device performance. Based on the preferred (100) facet and highly vertical orientation, the improved perovskite material properties are employed in SCAPS simulations (Fig. 4e, Supplementary Table 2). As a result, the OPD-treated PSC achieves a high PCE of 24.60%, with a VOC of 1.275 V. Guided by SCAPS simulation, we fabricate 1.69 eV-bandgap PSCs with an inverted device structure of ITO/NiOx/SAM/Perovskite/ PEAI/C60/BCP/Ag. The optimized OPD-treated PSC with negligible hysteresis exhibits an improved PCE from 21.12% to 24.13% (Supplementary Figs. 33, 34), which is accompanied by a high fill factor (FF) of 83.78% and JSC of 22.72 mA cm−2 (Fig. 4f). The resulting PCE of reaches 82.8% of the Shockley-Queisser (S-Q) limit, which represents one of the highest PCEs among all WBG PSCs (Fig. 4g, Supplementary Table 3). The resulting device exhibits reproducibility (Supplementary Fig. 35), demonstrating the reliability of the synchronous halide insertion strategy. The external quantum efficiency (EQE) spectra of PSC are used to evaluate the efficiency of utilizing light of different wavelengths, which is closely related to the transmittance of ITO glass and the reflectance of perovskite films (Supplementary Figs. 36, 37). The JSC extracted from the EQE spectrum is also close to that obtained from the J-V curve (Supplementary Fig. 38). The bandgap of the perovskite can be also determined to be 1.69 eV according to the slope of the EQE absorption edge39 (Supplementary Fig. 39). It is worth noting that a high VOC of 1.274 V is obtained in the OPD-treated PSC, which is close to the EQEL prediction and SCAPS simulation results.

We then measure the champion device at the National Measurement and Test Centre for Photovoltaic Industry (Fujian Institute of Metrology and Science). The OPD-treated PSC achieves a certified PCE of 23.42% under reverse scan conditions (Supplementary Fig. 40). Moreover, the resulting device exhibits power output characteristics under MPPT conditions, achieving a steady-state PCE of 23.80% (certified 23.28%) (Fig. 4h, Supplementary Fig. 41). Furthermore, we increase the Br content of the perovskite film to 30 mol%, obtaining a PSC with bandgap of 1.75 eV. The resulting OPD-treated PSC achieves a PCE of 20.45% (Supplementary Fig. 42). This demonstrates that the use of ODP to direct templated crystallization via a molecular wall is generalizable for mixed-halide WBG PSCs. Benefited from the high-quality perovskite film and the carrier transport properties, the OPD-treated ST WBG PSC (1.69 eV) also achieves a PCE of 22.28%. Integrated with a narrow-bandgap CIGS solar cell, the resulting 4T Perovskite/CIGS TSC achieves a PCE of 29.34% (Fig. 4i, Supplementary Table 4).

The crystal structure stability of perovskite films is crucial to achieving robust operational stability of photovoltaics40. We perform accelerated aging experiments on perovskite films at 65 °C and 45% relative humidity (RH), investigating the crystallographic evolution by in-situ GIWAXS characterization. As shown in Fig. 5a, a recognizable lead iodide (PbI2) signal quickly appears in the control film, indicating the decomposition of the perovskite film. AD treatment can suppress the decomposition of the perovskite film to a certain extent, but the PbI2 signal still appears in the film after 25 h. In contrast, the OPD-treated film exhibits a constant perovskite phase with negligible decomposition even after 100 h. The decomposition of the perovskite film is also reflected in the crystal orientation evolution as displayed in Fig. 5b. The crystal orientation of the control sample and AD-treated films is destroyed at 25 h and 60 h, respectively. The OPD-treated film still maintains well-defined orientation on the preferred (100) facet.

We evaluate the light stability of perovskite films under continuous 1-sun illumination by in-situ PL measurements (Fig. 5c). Rapidly decreasing PL signals occur in the control and AD-treated films, while the OPD-treated film exhibits a constant PL intensity after 400 h. We also monitor the stability of the perovskite films under electric fields by EL spectra at various bias conditions (Fig. 5d). Control and AD-treated films exhibit a split EL peak at a bias of ~3.5 V, implying that the ion migration-induced phase separation is amplified under a strong electric field. In contrast, the OPD-treated film still maintains a stable perovskite crystal structure, and its EL peak remains constant even under a bias of 5 V. Based on the preferred facet and the vertical orientation, the stability of the perovskite films and the resulting PSCs is significantly improved. The OPD-treated PSC exhibits improved long-term stability under continuous 1-sun illumination conditions (Fig. 5e). According to the ISOS-L-1 test standard, we monitor the PCE evolution of the encapsulated devices under MPPT conditions41. The OPD-treated device still maintains 90% of the initial PCE (T90) for more than 800 h, while the control and AD-treated devices quickly decay to 40% and 66% of their initial PCE in a very short time. Meanwhile, we monitor the PCE evolution of the encapsulated PSCs under the conditions of damp heat at 85 °C and 45% RH according to ISOS-D-2 protocol (Supplementary Fig. 43). The OPD-treated device still maintains 90% of its initial PCE after 800 h, while the control device and the AD-treated device only maintains 50% and 75% of their initial PCE. We further strictly implement the stability test conditions of PSCs at 85 °C and 85% RH according to ISOS-D-3 protocol. The OPD-treated device still maintains 88% of its initial PCE after 600 h, and the improved device stability is attributed to the enhanced perovskite crystal quality due to the OPD treatment.

Methods
Materials
Indium tin oxide (ITO) glass, [(3,6-dimethoxy-9H-carbazol-9-yl)ethyl] phosphonic acid (MeO-2PACz, 98.0%), [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz, 99.0%), PbI2 (99.9%), lead bromide (PbBr2, 99.9%), formamidinium iodide (FAI, 99.5%), methylammonium bromide (MABr, 99.5%), cesium iodide (CsI, 99.99%), 2-phenylethylamine hydroiodide (PEAI, 99.5%), fullerene-C60 (C60, 99%), tin oxide (SnO2, 99.5%), aniline hydrochloride (ADCl, 99.4%), o-phenylenediamine hydrochloride (OPDCl, 99%), m-phenylenediamine hydrochloride (MPDCl, 99%), and p-phenylenediamine hydrochloride (PPDCl, 99%) were purchased from Advanced Election Technology Co. Bathocuproine (BCP, 99%) was obtained from Xi’an Yuri Solar Co. N,N-dimethylformamide (DMF, 99.9%), dimethyl sulfoxide anhydrous (DMSO, 99.9%), N-methyl-2-pyrrolidone (NMP, 99.9%), ethyl alcohol (EtOH, 99.5%), and chlorobenzene (CB, 99.5%) were supplied by Sigma-Aldrich. Nickel oxide (NiOx, 99.999%) was from Xi‘an E-light New Material Co. All materials and solvents used in this work have not been purified again and are used directly after purchasing from the manufacturer.

Fabrication of single-junction WBG PSCs
The ITO glass was first cleaned and then treated using a plasma machine for 90 s. NiOx solution was deposited on the ITO substrate by spin-coating at 3000 rpm for 30 s, and the NiOx film was annealed at 100 °C for 15 min. Next, a mixed SAM materials of MeO-2PACz and Me-4PACz were dissolved in EtOH. SAM layer was deposited by spin-coating at 3000 rpm for 30 s, and then annealed at 100 °C for 10 min. For FA0.8MA0.1Cs0.1Pb(I0.8Br0.2)3 and FA0.8MA0.1Cs0.1Pb(I0.7Br0.3)3 (1.68 eV and 1.75 eV) perovskite precursor solution, OPD, MABr, CsI, PbBr2, PbI2, and FAI were dissolved by DMF:DMSO (4:1) or DMF:NMP (4:1). The precursor solution was spin-coated at 5000 rpm for 40 s, and CB (100 ul) was added at 6 s. Perovskite film was then annealed in a nitrogen glove box at 100 °C for 50 min. After cooling, the PEAI (3 mg ml−1, dissolved in IPA) solution was dynamically spin-coated on the perovskite film at 3000 rpm for 30 s, and then annealed at 100 °C for 10 min. Finally, C60 (30 nm), BCP (8 nm), and Ag (100 nm) were deposited by thermal evaporation.

Fabrication of ST WBG PSC
Preparation of ITO/NiOx/SAM/Perovskite/PEAI/C60 films as shown above. Then, SnO2 (20 nm) was deposited by atomic layer deposition (ALD), and IZO (100 nm) was subsequently deposited by sputtering to form the transparent electrode.

Fabrication of CIGS solar cells
The preparation of CIGS solar cells adopts the following standard process. Firstly, a molybdenum layer (1 μm) was deposited on soda-lime glass by sputtering as the back electrode. Subsequently, a three-stage co-evaporation process was adopted to deposit copper, indium, gallium, and selenium, forming a CIGS light-absorbing layer (2.3 μm). Subsequently, a CdS buffer layer (50 nm) was deposited by chemical bath deposition, while an i-ZnO layer (50 nm) and an Al-doped ZnO window layer (300 nm) were deposited by radio frequency sputtering. To enhance electron collection, a Ni/Al/Ni metal mesh was deposited by electron beam evaporation.

Device characterization
J-V curves characterization was carried out under standard AM 1.5G spectral (100 mW cm-²) illumination, using a calibrated solar simulator and a standard silicon reference cell to ensure light intensity accuracy. Tests were performed in forward (−0.1 V to 1.3 V) and reverse (1.3 V to −0.1 V) voltage scanning modes with the scan rate controlled at 100 mV s−1. The devices were connected with four probes to eliminate the effect of wire resistance. A shading mask (0.0867 cm−2) was used to ensure that the effective light area. PSCs were encapsulated with cover glass and butyl rubber for MPPT stability testing. EQE spectra were obtained by using a QE system (EnliTech).

Other characterizations
GIWAXS patterns of perovskites were measured at BL17B1 beamline of the Shanghai Synchrotron Radiation Facility (SSRF). Incident-angle-dependent measurements were achieved by X-ray with a wavelength of 1.238 Å. GIWAXS data were collected every 2 s for in-situ GIWAXS patterns. TCFM images were acquired using a customized scanning confocal microscope equipped with TCSPC (PicoHarp 300) functionality. The microscope was based on a Nikon TE-2000 inverted microscope and is fitted with an infinity-corrected ×50 dry objective lens (Nikon L Plan, NA 0.7, CC 0-1.2). Excitation was performed using a 470 nm pulsed diode laser (PDL-800 LDH-P-C-470B, pulse width 350 ps), with a repetition rate of 1 MHz for time-resolved fluorescence spectroscopy measurements and 40 MHz for fluorescence image acquisition.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study investigates the crystallization process of mixed-halide wide-bandgap perovskite films, highlighting that post-crystallization iodide insertion preferentially occurs along the (100) plane. Asynchronous halide incorporation leads to random crystal orientation, impairing charge transport. Based on DFT guidance, OPD is introduced to form a π-conjugated molecular wall at grain boundaries, templating perovskite crystallization via ortho-diamine interaction and enabling uniform halide distribution. This yields highly oriented perovskite films with dominant (100) orientation and improved vertical alignment, leading to the significant enhancement of the photovoltaic performance of the device. Overall, this work is interesting and is expected to garner broad interest in the field of solar cells. Consequently, I recommend acceptance of this article after revisions, with detailed comments provided below:\n1, In Fig. 1b, the q-value corresponding to the (110) plane does not exhibit a clear monotonic trend but fluctuates within a certain range. Please provide an explanation for this change behavior.\n2, In the crystallization kinetics analysis (Fig. 2k), the evolution of the (001) peak intensity for AD-perovskite differs noticeably from those of the control and OPD-treated samples. Does this suggest additional transitional phases or a divergent crystallization pathway in AD-perovskite? If so, please clarify the underlying mechanism.\n3, The authors attribute the narrow FWHM of the (100) peak to improved phase homogeneity. However, crystallite size can also significantly affect XRD peak broadening. To strengthen this claim, please provide SEM images to rule out contributions from grain size variation.\n4, Fig. 2m indicates that the OPD-perovskite exhibits not only a strong vertical orientation but also a preferential alignment within the azimuthal range of 40–50°. Could the authors explain the origin of this secondary texture? Quantitative integration of the intensity ratio around 0° and 40–50° for both control and OPD samples would help validate the schematic illustration in Fig. 2a.\n5, While the beneficial role of OPD at the perovskite/ETL interface is clearly demonstrated in Fig. 3, its impact on carrier extraction at the perovskite/HTL interface remains unclear. Please provide corresponding data to evaluate possible interfacial effects at the perovskite/ HTL interface.\n6, The use of ODP to direct templated crystallization via a molecular wall is compelling. To evaluate the generalizability of this approach, could the authors extend the study to perovskites with higher Br content and report corresponding device performance? This would strengthen the conclusion regarding the broad applicability of the strategy.", "reviewer_2": "Song et al. developed OPD molecules that regulate the preferential crystallization orientation of perovskite films along the (100) plane through strong interactions with [PbI6]4− and [PbBr6]4− octahedra. The regulatory effect of OPD molecules on perovskite growth orientation was substantiated by in-situ GIWAXS and DFT calculations, which also revealed lattice spacing changes induced by I-ion insertion along the (100) plane during crystallization. This crystallographic orientation control enhanced charge-carrier transport, thereby contributing to high device PCE. Nevertheless, this work lacks experimental evidence supporting synchronous insertion of Br and I ions under OPD modification. The current data do not sufficiently support the authors’ conclusions, and some statements and analyses appear inconsistent or insufficiently clear. Therefore, in its present form, this manuscript is not suitable for publication in Nature Communications. The detailed comments are as follows:\n1. On page 4, paragraph 1, the authors claim that synchronous halide insertion yields preferred crystal facets and orientations. The rationale for this statement is unclear, and the authors are encouraged to provide a more rigorous discussion and convincing evidence to substantiate this central claim.\n2. Fig. 1 suggests that the (100) plane spacing varies during crystallization of OPD-modified samples, with DFT results attributing this to I-ion insertion. This implies that Br ions dominate in the early stage after antisolvent dripping, followed by I-ion insertion that enlarges the lattice spacing. While the in-situ GIWAXS data confirm the I-ion insertion process, they do not provide evidence of synchronous incorporation of Br and I ions. The authors should conduct and report corresponding experiments on Br-ion insertion. Furthermore, color bars are missing in Fig. 1a–1d and should be included.\n3. On page 4, paragraph 2, the DFT results indicate that OPD molecules exhibit similar binding energies with Br and I ions. On page 9, paragraph 1, the DFT results suggest comparable binding energies with [PbI6]4− and [PbBr6]4− octahedra. The authors should clearly specify which binding energy primarily governs the insertion behavior of Br and I ions.\n4. The authors should clarify how the binding energies between OPD molecular walls at perovskite grain boundaries and Br/I ions, or with [PbI6]4− and [PbBr6]4− octahedra, influence the activation energy for Br- and I-ion insertion into the (100) plane. Since the activation energy reflects the ease of ion insertion into the crystal lattice, this analysis is critical.\n5. On page 4, paragraph 2, the authors report a bandgap of 1.69 eV for the perovskite film, but no calculation method is described. It is recommended that the bandgap be derived from EQE data, as suggested in Adv. Energy Mater. 2021, 11, 2100022.\n6. The XPS peak near 291 eV in Supplementary Fig. 4 corresponds to a π–π* satellite signal. This π–π* (HOMO–LUMO) transition is a characteristic shake-up line of aromatic carbon rings excited by photoelectron emission (J. Chem. Phys. 1995, 103, 6333–6342; Phys. Rev. B 1997, 55, 10051). Therefore, it cannot be used as evidence for strong π–π interactions arising from parallel stacking of OPD molecules, as claimed on page 7, paragraph 2.\n7. In Supplementary Fig. 8, the FWHM of the AD sample appears broader than that of the control sample. The authors should verify this observation. In addition, since the GIWAXS peaks seem to comprise multiple components, it is recommended that peak deconvolution be performed and the FWHM values for the (100) plane signal be explicitly reported.\n8. The AFM and SEM images in Supplementary Figs. 14 and 15 show notably different grain morphologies at comparable scales. The authors should clarify the origin of these discrepancies.\n9. It is recommended that the authors provide the corresponding topography images for the KPFM mappings in Figs. 3a–3c, in order to clearly demonstrate the CPD variations within grain interiors of different samples.\n10. In Fig. 4d, EL EQE is plotted as a function of voltage. The authors should explain the basis for selecting the EL EQE values reported in the manuscript.\n11. The authors should provide the explicit calculation process by which a potential Voc of 1.274 V was obtained from a Voc loss of 0.126 V, as stated on page 13, paragraph 2.", "reviewer_3": "The manuscript by Song et al. reports on a halide insertion regulation strategy for wide-bandgap perovskite solar cells. Using in situ GIWAXS and DFT modeling, the authors reveal an asynchronous halide incorporation process that leads to poor orientation and device inefficiencies. They propose an o-phenylenediamine “molecular wall” strategy to achieve synchronous halide insertion, resulting in vertically aligned (100)-oriented films and record WBG-PSC performance (24.13% PCE, certified 23.43%). The work addresses a key bottleneck in WBG perovskite development, combining mechanistic insights with practical device engineering.\nThe study is of clear interest to the wide-bandgap perovskite photovoltaics community. However, additional evidence and clarification are required to fully support the mechanistic claims. I therefore recommend major revision before the manuscript can be considered for publication in Nature Communications.\n1.The crystallization pathway can be divided into nucleation, growth, and regrowth (Ostwald ripening). The current analysis focuses only on the nucleation stage observed during in situ spin-coating GIWAXS, without considering annealing, which governs the growth stage. It is reasonable to expect merging between Br-rich and I-rich nuclei during growth, which could also explain the observed Δq shifts. Please include a detailed analysis of the annealing process to rigorously validate the claim of facet-selective halide insertion.\n2.The stacking energy analysis suggests OPD’s superior π–π interactions, but direct experimental evidence for the proposed “molecular wall” remains absent. The XPS spectra (Supp. Fig. 4) confirm OPD–perovskite interaction but not alignment into wall structures. Supporting data from techniques such as polarized spectroscopy, anisotropic GIWAXS, or cross-sectional TEM would significantly reinforce this claim.\n3.The manuscript does not address the distribution of OPD after film formation. Large aromatic cations typically have poor conductivity, which could become problematic if OPD accumulates at grain boundaries. TOF-SIMS or depth-profiling studies would clarify the spatial position of OPD and strengthen the mechanistic interpretation.\n4.The thermal stability test conditions (65 °C, 45% RH) are non-standard, although the results show an encouraging trend. To make the findings more broadly comparable, stability assessments following ISOS protocols—such as ISOS-D-2 (85 °C thermal stress) or ISOS-L-2 (85 °C MPP tracking under N₂)—should be included.\nOther Minor Comments\n• Define “asynchronous halide insertion” clearly in the Abstract and Introduction for reader clarity.\n• Ensure consistent terminology throughout (e.g., “halogen ion insertion” vs. “halide insertion”).\n• In Fig. 1c, orientation randomness is attributed solely to asynchronous halide insertion, but nucleation and solvent-related effects may also contribute. A more nuanced discussion is warranted.\n• The random insertion model (Supp. Fig. 2) is only briefly described; please expand the methodological details.", "reviewer_4": "The manuscript reports a halide insertion regulation strategy using o-phenylenediamine to construct π-conjugated molecular walls, promoting synchronous halide incorporation in wide-bandgap perovskites. This approach is supported by in-situ GIWAXS, DFT calculations, spectroscopic characterizations, and device performance evaluation, delivering efficient and stable perovskite solar cells (PSCs) with a certified PCE of 23.43% and encouraging stability. This work is interesting and relevant to the perovskite community. However, the novelty relative to recent literature is not sufficiently clarified, the mechanistic validation lacks direct experimental evidence, and some claims are overstated compared with the state-of-the-art. Additional control experiments, clearer benchmarking, and stronger stability demonstrations are required before the manuscript can be considered for publication.\nI therefore recommend major revision.\n1. Although the authors have performed stability measurements under the ISOS-L-1 protocol, considering the application relevance for tandem devices and the high standards of Nature Communications, additional stability results under harsher conditions (e.g., damp heat at 85 °C/85% RH, or at least higher humidity stress tests) are necessary. This would further validate the robustness of OPD incorporation under realistic and more demanding operating environments.\n2. In Figure S22, all EQE spectra show a distinct downturn around ~325 nm. The authors should clarify the origin of this feature. Moreover, at ~650 nm, the AD-modified device exhibits an opposite fluctuation compared with the Control and OPD-modified devices. Reflectance measurements are recommended to disentangle the optical contributions and provide a clearer understanding of the current gain/loss sources.\n3. The central claim that OPD molecular walls facilitate synchronous halide insertion is mainly supported by GIWAXS and DFT. However, these techniques provide only indirect evidence. Direct chemical or spatial characterization, such as TOF-SIMS depth profiling or STEM-EDS elemental mapping, is needed to unambiguously demonstrate the cooperative insertion of Br and I into the perovskite lattice.\n4. In the DFT results, the authors provide binding energies of OPD with three facets of [PbI6]4- octahedra, but only the (100) facet for [PbBr6]4-. For consistency and completeness, binding energies of OPD with additional facets of [PbBr6]4- (analogous to [PbI6]4-) should be included to allow a fair comparison.\n5. The concept of molecular additives regulating crystal orientation and halide distribution is not new. Several recent studies (e.g., Refs. 11, 22, 23, 26) have already reported oriented nucleation and synchronous crystallization strategies. The authors should more clearly differentiate how the OPD-based molecular wall strategy advances beyond prior methods. The Introduction should also highlight the existing limitations of current halide regulation strategies and explicitly position OPD as addressing a unique bottleneck. Such mechanistic distinction is essential for consideration in Nature Communications.\n6. The authors demonstrate their approach using FA0.8MA0.1Cs0.1Pb(I0.8Br0.2)3 as the model perovskite composition. Since the manuscript emphasizes that Br tends to crystallize preferentially in WBG perovskites, validation of the OPD strategy in perovskites with even higher Br content (wider bandgap compositions) would be important to prove the universality of this halide regulation concept.\n7. The authors employ 1 mol% OPD as the optimal concentration, but the optimization process is not described. A systematic study or at least a clear explanation of how this concentration was determined should be provided to justify the choice."}, "author_response": "Response: Thank you very much for your recognition of our work. We have now revised the manuscript in accordance with the comments of all reviewers.\nComment 1. In Fig. 1b, the q-value corresponding to the (110) plane does not exhibit a clear monotonic trend but fluctuates within a certain range. Please provide an explanation for this change behavior.\nResponse: Thank you very much for your valuable comment. We have now provided an explanation for the evolution of q values corresponding to the (110) plane in Fig. 1b. We have also provided each corresponding q value in Supplementary Table S1.\nAt the spin-coating stage, the evolution of the q-value measured by in-situ GIWAXS primarily reflects the transformation of the perovskite film from a liquid precursor wet film to a solid crystalline film. To accurately reflect the q-value evolution of Fig. 1b, we have now provided each corresponding q value in Supplementary Table S1. For the (110) plane, the film shows a large q value of 14.272 nm-1 at the initial stage (8 s and 10 s) of antisolvent drop. A small fluctuation in the q value range of 14.224 nm-1 - 14.254 nm-1 is subsequently observed (12 s - 40 s), resulting an average q value of 14.234 nm-1. Therefore, a slight q-value decrease (Δq, -0.038 nm-1) is calculated throughout the spin-coating stage. Slight q-value fluctuations at the spin-coating stage are common in previously reported works (Nat. Commun. 15, 8899 (2024); Adv. Opt. Mater. 10, 2102722 (2022)). This may be because that the residual solvent evaporation interferes with the in-situ GIWAXS experimental results during the spin coating process. The small fluctuation is almost negligible for obtaining reliable experimental conclusions.\nSupplementary Table S1 | Extracted q-value evolution of (100), (110), and (111) facets of control perovskite film at the spin-coating stage.\nTime (s) (100) facet (nm-1) (110) facet (nm-1) (111) facet (nm-1)\n8 10.148 14.272 17.438\n10 10.154 14.272 17.432\n12 10.148 14.242 17.426\n14 10.130 14.230 17.426\n16 10.130 14.224 17.420\n18 10.094 14.224 17.403\n20 10.058 14.224 17.408\n22 10.052 14.230 17.408\n24 10.046 14.236 17.402\n26 10.035 14.242 17.385\n28 10.035 14.224 17.385\n30 10.035 14.224 17.391\n32 10.035 14.248 17.385\n34 10.035 14.230 17.385\n36 10.035 14.230 17.391\n38 10.035 14.254 17.385\n40 10.035 14.248 17.385\nFigure 1 | b Extracted q-value evolution of (100), (110), and (111) facets.\nAction: Each corresponding q value of Fig. 1b has been provided in revised Supporting Information (Supplementary Table S1).\nComment 2. In the crystallization kinetics analysis (Fig. 2k), the evolution of the (001) peak intensity for AD-perovskite differs noticeably from those of the control and OPD-treated samples. Does this suggest additional transitional phases or a divergent crystallization pathway in AD-perovskite? If so, please clarify the underlying mechanism.\nResponse: Thank you very much for your comment. We have now provided in-situ GIWAXS patterns (2.5 - 9.5 nm-1) of perovskite films to explore the crystallization pathway (Supplementary Fig. 8), and we have also clarified the crystallization mechanism.\nAs shown in in-situ GIWAXS patterns (Supplementary Fig. 8), the control, AD-treated, and OPD-treated perovskite films all transform directly from the solvent phase to the perovskite phase, and no additional transitional phase is found on three samples (Fig. 1a, 2f, and 2g).\nAs mentioned by the reviewer, the crystallization kinetics analysis (Fig. 2k) shows that the evolution of the (001) peak intensity for AD-treated perovskite film differs noticeably from those of the control and OPD-treated samples. The AD-treated film shows an increase rate of q-value signal intensity between the control and OPD-treated films. This difference in crystallization rate could be further confirmed by in-situ laser scanning confocal microscopy (LSCM) images. The difference in crystallization rate among the three samples is related to the number of amine groups in the bulky cations. AD monoamine cations can accelerate perovskite crystallization compared with the control sample. In contrast, molecular wall structure at the grain boundary forms a strong interaction with the perovskite precursor through the ortho-diamine group on the same side, which further accelerates the formation of the perovskite phase. As a result, the OPD-treated perovskite film achieved the fastest crystallization rate.\nSupplementary Fig. 8 | In-situ GIWAXS patterns (2.5 - 9.5 nm-1) of (a) Control, (b) AD-treated, and (c) OPD-treated perovskite films at the spin-coating stage.\nFigure 1 | a In-situ GIWAXS patterns of control perovskite film at the spin-coating stage.\nFigure 2 | In-situ GIWAXS patterns of (f)AD-treated and (j) OPD-treated perovskite films at the spin-coating stage. k Extracted signal intensity of (100) facet for control, AD-treated, and OPD-treated perovskite films.\nAction: In-situ GIWAXS patterns (2.5 - 9.5 nm-1) of perovskite films (Supplementary Fig. 8) have been provided, and the relevant crystallization mechanism has also clarified in the revised manuscript.\nComment 3. The authors attribute the narrow FWHM of the (100) peak to improved phase homogeneity. However, crystallite size can also significantly affect XRD peak broadening. To strengthen this claim, please provide SEM images to rule out contributions from grain size variation.\nResponse: Thank you very much for your valuable suggestion. We have now supplemented the SEM images of control, AD-treated, and OPD-treated perovskite films (Supplementary Fig. 16) to rule out contributions from grain size variation.\nAs shown in SEM images for control, AD-treated, and OPD-treated perovskite films (Supplementary Fig. 16), almost the same grain size (approximately 320 nm) can be observed in all regions of the three films. This excludes that grain size of perovskite affects FWHM of the XRD peak. Therefore, the narrow FWHM of (100) signal is attributed to a homogeneous perovskite phase of OPD-treated film.\nSupplementary Fig. 16 | SEM images and grain size statistics for (a) control, (b) AD-treated, and (c) OPD-treated of perovskite films.\nAction: The SEM images and grain size statistics of perovskite films (Supplementary Fig. 16) have been supplemented in the revised manuscript.\nComment 4. Fig. 2m indicates that the OPD-perovskite exhibits not only a strong vertical orientation but also a preferential alignment within the azimuthal range of 40° - 50°. Could the authors explain the origin of this secondary texture? Quantitative integration of the intensity ratio around 0° and 40 - 50° for both control and OPD samples would help validate the schematic illustration in Fig. 2a.\nResponse: Thank you very much for your suggestion. We have now extracted quantitative integration of the GIWAXS signal intensity within the azimuthal range of -55° to 55° (Supplementary Fig. 13) for control and OPD-treated films (Fig. 1d and 2m), to validate the schematic illustration in Fig. 2a that the strong vertical orientation is dominant in the OPD-treated film. We have also explained the origin of this secondary texture within the azimuthal range of 40° - 50°.\nAs the reviewer suggested, we extract the GIWAXS signal intensity within the azimuthal range of -55° to 55° (Supplementary Fig. 13) for control and OPD-treated films (Fig. 1d and 2m). The control sample exhibits very close signal intensities at 0° and ±42°, indicating low perovskite crystal orientation. In contrast, the signal intensity at 0° for the OPD-treated sample is more than three times that at ±42°, indicating that the strong vertical orientation of (100) facet is dominant (Fig. 2a). Moreover, the weak signal intensity at 45° is close to the signals at other azimuthal angles, which means that a small number of small-sized crystals show random orientation. Nevertheless, the dominant vertical (100) orientation induced by the OPD molecular wall still ensures efficient carrier transport.\nSupplementary Fig. 13 | Extracted the GIWAXS signal intensity of (a) control and (b) OPD-treated perovskite films.\nFigure 1 | d GIWAXS pattern of the control perovskite film after annealing.\nFigure 2 | m GIWAXS pattern of the OPD-treated perovskite film after annealing.\nFigure 2 | a Schematic diagram of the OPD molecular wall-induced synchronous halide insertion and templated crystallization of perovskite film.\nAction: Extracted the GIWAXS signal intensity of control and OPD-treated perovskite films (Supplementary Fig. 13) and the relevant explanation has also clarified in the revised manuscript.\nComment 5. While the beneficial role of OPD at the perovskite/ETL interface is clearly demonstrated in Fig. 3, its impact on carrier extraction at the perovskite/HTL interface remains unclear. Please provide corresponding data to evaluate possible interfacial effects at the perovskite/ HTL interface.\nResponse: Thank you very much for your valuable comment. We have now provided confocal fluorescence microscopy (TCFM) mapping of perovskite films with HTL (Supplementary Fig. 28), to evaluate interfacial effects at the perovskite/HTL interface.\nAs shown in TCFM mapping of perovskite films with HTL (Supplementary Fig. 28), the OPD-treated sample exhibited the lowest PL signal intensity compared to control and AD-treated samples. We have excluded the defect-induced carrier recombination by tDOS. Therefore, we can conclude that the reduced PL intensity in the perovskite/HTL sample should be attributed to the efficient charge extraction. Efficient and uniform carrier extraction is benefited from the preferred (100) facet and highly vertical orientation.\nSupplementary Fig. 28 | PL intensity mapping of (a) control, (b) AD-treated, and (c) OPD-treated of perovskite films with HTL.\nAction: TCFM mapping of perovskite films with HTL (Supplementary Fig. 28) have been supplemented in the revised manuscript.\nComment 6. The use of ODP to direct templated crystallization via a molecular wall is compelling. To evaluate the generalizability of this approach, could the authors extend the study to perovskites with higher Br content and report corresponding device performance? This would strengthen the conclusion regarding the broad applicability of the strategy.\nResponse: Thank you very much for your valuable suggestion. We have now provided the photovoltaic performance of PSCs with a higher bromine content (Supplementary. Fig 42), to evaluate the generalizability of this approach.\nAs suggested by the reviewer, we increased the Br content of the perovskite film (FA0.8MA0.1Cs0.1Pb(I0.7Br0.3)3) to 30 mol%. As shown in Supplementary. Fig 42, the optical bandgap of the perovskite film was determined to be 1.75 eV according to absorption and EQE spectra. The resulting PSC with OPD treatment achieves a PCE of 20.45%, with a Voc of 1.316 V, an FF of 80.40%, and a Jsc of 19.43 mA cm-2, which is higher than that (18.54%) of the control device. This demonstrates that the use of ODP to direct templated crystallization via a molecular wall is generalizable for mixed-halide WBG PSCs.\nSupplementary Fig. 42 | a J-V curves and b EQE spectrum of PSC with Br content of 30 mol%. c Absorption spectrum of corresponding perovskite films.\nAction: J-V curves, EQE spectrum, and absorption spectrum of perovskite with Br content of 30 mol% (Supplementary Fig. 42) have been supplemented in the revised manuscript.\nReviewer #2:\nSong et al. developed OPD molecules that regulate the preferential crystallization orientation of perovskite films along the (100) plane through strong interactions with [PbI6]4− and [PbBr6]4− octahedra. The regulatory effect of OPD molecules on perovskite growth orientation was substantiated by in-situ GIWAXS and DFT calculations, which also revealed lattice spacing changes induced by I-ion insertion along the (100) plane during crystallization. This crystallographic orientation control enhanced charge-carrier transport, thereby contributing to high device PCE. Nevertheless, this work lacks experimental evidence supporting synchronous insertion of Br and I ions under OPD modification. The current data do not sufficiently support the authors’ conclusions, and some statements and analyses appear inconsistent or insufficiently clear. Therefore, in its present form, this manuscript is not suitable for publication in Nature Communications. The detailed comments are as follows:\nResponse: Thank you very much for your valuable comments and suggestions. We have now supplemented some new experiments including in-situ UV-vis absorption spectra, depth-profiling XPS spectra, etc., to support synchronous insertion of [PbBr6]4- and [PbI6]4- ions under OPD modification. We have also further elaborated on the relevant physical mechanisms and revised some inappropriate expressions. The manuscript has been thoroughly revised based on the comments of all the reviewers, and we hope that the revised manuscript will meet your high standards.\nComment 1. On page 4, paragraph 1, the authors claim that synchronous halide insertion yields preferred crystal facets and orientations. The rationale for this statement is unclear, and the authors are encouraged to provide a more rigorous discussion and convincing evidence to substantiate this central claim.\nResponse: Thank you very much for your valuable suggestion. We have now comprehensively analyzed the crystallization dynamics of perovskite films at the spin-coating stage by combining DFT simulations (Fig. 2e, Supplementary Fig. 7), in-situ UV-Vis absorption spectra (Supplementary Fig. 12), and in-situ GIWAXS patterns (Fig. 2j and Supplementary Fig. 8), to further elucidate the relationship between synchronous halide insertion and preferred crystal facets and orientations.\nAccording to the DFT calculation results (Fig. 2e, Supplementary Fig. 7), OPD shows the largest binding energy with the (100) facet compared with the (110) and (111) facets. This provides a theoretical basis for the OPD-constructed molecular wall to induce the preferred (100) facet. Moreover, the binding energy between OPD and [PbBr6]4- octahedron is very close to that between OPD and [PbI6]4- octahedron. This provides a theoretical basis for the OPD-constructed molecular wall to induce the synchronous halide insertion.\nSynchronous halide insertion has been demonstrated by in-situ UV-Vis absorption spectra and in-situ GIWAXS patterns. The stable crystal structure (constant q values) (Fig. 2g) and constant bandgap (constant absorption edge) (Supplementary Fig. 12) indicate that a homogeneous mixed-halide perovskite structure is formed at the moment of antisolvent droplet addition at the spin-coating stage, without the presence of an intermediate phase or other impurities (Supplementary Fig. 8).\nMeanwhile, it was noticed that the preferred (100) facet (Fig. 2j) and the vertical crystal orientation (Fig. 2l) were detected almost immediately after the antisolvent was dropped. Since the strongest interaction force exists between the OPD molecules and the (100) facet, OPD molecules with ortho-diamine group will preferentially anchor the [PbBr6]4- and [PbI6]4- octahedron and preferentially nucleate and crystallize along the (100) facet of the perovskite crystal.\nThe OPD-constructed molecular wall structure at the grain boundary forms a strong interaction with the perovskite precursor through the ortho-diamine group on the same side (Fig. 2a). Benefiting from the templated crystallization induced by the molecular wall, the OPD-treated perovskite film achieves the preferred (100) facet and highly vertical crystal orientation.\nFigure 2 | Crystallographic modulation of synchronous halide insertion. a Schematic diagram of the OPD molecular wall-induced synchronous halide insertion and templated crystallization of perovskite film. b Binding energies of OPD, MPD, PPD, and AD with different stacking models by DFT simulations. c Binding energy of OPD with parallel, perpendicular, and antiparallel models. d ESP distribution of four molecules. e Binding energy between OPD and different crystal facets of perovskite by DFT simulation. In-situ GIWAXS patterns of (f) AD-treated and (j) OPD-treated perovskite films at the spin-coating stage. g Extracted q-value evolution of (100), (110), and (111) facets for AD-treated and OPD-treated perovskite films. k Extracted signal intensity of (100) facet for control, AD-treated, and OPD-treated perovskite films. Extracted crystal orientation evolution of (110) facet for (h) AD-treated and (l) OPD-treated perovskite films. GIWAXS patterns of (i) AD-treated and (m) OPD-treated perovskite films after annealing.\nSupplementary Fig. 7 | The binding energy and longitudinal integral curves of differential charge density between OPD and the [PbBr6]4- at (a) (110) and (b) (111) facets.\nSupplementary Fig. 12 | In-situ UV-Vis absorption spectra of (a) control, (b) AD-treated, and (c) OPD-treated perovskite films at the spin-coating stage.\nSupplementary Fig. 8 | In-situ GIWAXS patterns (2.5 - 9.5 nm-1) of (a) Control, (b) AD-treated, and (c) OPD-treated perovskite films at the spin-coating stage.\nAction: DFT simulations (Supplementary Fig. 7), in-situ UV-Vis absorption spectra (Supplementary Fig. 12), and in-situ GIWAXS patterns (Supplementary Fig. 8) have been provided, and the relationship between synchronous halide insertion and preferred crystal facets and orientations is also elucidated in the revised manuscript.\nComment 2. Fig. 1 suggests that the (100) plane spacing varies during crystallization of OPD-modified samples, with DFT results attributing this to I-ion insertion. This implies that Br ions dominate in the early stage after antisolvent dripping, followed by I-ion insertion that enlarges the lattice spacing. While the in-situ GIWAXS data confirm the I-ion insertion process, they do not provide evidence of synchronous incorporation of Br and I ions. The authors should conduct and report corresponding experiments on Br-ion insertion. Furthermore, color bars are missing in Fig. 1a-1d and should be included.\nResponse: Thank you very much for your valuable and insightful comments. We have now provided in-situ UV-Vis absorption spectra of perovskite films at the spin-coating stage (Supplementary Fig. 12), to unambiguously demonstrate the synchronous incorporation of [PbBr6]4- and [PbI6]4- halides in the OPD-treated perovskite lattice. We have also provided the corresponding color bars in Figs. 1a, 1c, 2f, 2h, 2j, and 2l.\nTo further substantiate the synergistic insertion of [PbBr6]4- and [PbI6]4-, we measured in-situ UV-Vis absorption spectra of perovskite films at the spin-coating stage. As shown in Supplementary Fig. 12, the absorption edge of the control perovskite film gradually red-shifts with the addition of antisolvent, indicating that the Br-rich component is formed preferentially, and the subsequent I insertion narrows the bandgap. Although the AD-treated film accelerates the red shift of the absorption edge, subsequent I insertion still exists and synchronous halide insertion cannot be successfully achieved. In contrast, the OPD-treated film exhibits a constant absorption edge almost immediately after the antisolvent is added. This constant bandgap also implies the simultaneous insertion of I and Br halides, which is consistent with the results of in-situ GIWAXS characterization.\nAs shown in Fig. 1 and Fig. 2, we have also provided the corresponding color bars in Figs. 1a, 1c, 2f, 2h, 2j, and 2l.\nSupplementary Fig. 12 | In-situ UV-Vis absorption spectra of (a) control, (b) AD-treated, and (c) OPD-treated perovskite films at the spin-coating stage.\nFigure 2 | In-situ GIWAXS patterns of (f) AD-treated and (j) OPD-treated perovskite films at the spin-coating stage. Extracted crystal orientation evolution of (110) facet for (h) AD-treated and (l) OPD-treated perovskite films.\nFigure 1 | a In-situ GIWAXS patterns of control perovskite film at the spin-coating stage. c Extracted crystal orientation evolution of (100) facet.\nAction: In-situ UV-Vis absorption spectra (Supplementary Fig. 12) have been provided, and the Figs. 1a, 1c, 2f, 2h, 2j, and 2l have also been updated in the revised manuscript.\nComment 3. On page 4, paragraph 2, the DFT results indicate that OPD molecules exhibit similar binding energies with Br and I ions. On page 9, paragraph 1, the DFT results suggest comparable binding energies with [PbI6]4- and [PbBr6]4- octahedra. The authors should clearly specify which binding energy primarily governs the insertion behavior of Br and I ions.\nResponse: Thank you very much for your valuable comments and reminders. We have now corrected the related statement on page 4, paragraph 2, and we have now clarified that the binding energy between OPD molecule and [PbX6]4- octahedra governs the synchronous insertion of [PbBr6]4- and [PbI6]4- halides.\nIn general, halide ions are present in the form of [PbX6]4- octahedra halides in the perovskite precursor solution before the perovskite crystals are formed. The binding energy between OPD molecules and [PbX6]4- octahedra is crucial for controlling the crystallization kinetics of perovskites. We have revised ‘halogen ion insertion’ to ‘halide insertion’ in the revised manuscript.\nTherefore, the related statement on page 4, paragraph 2 has been revised as follows:\n‘As expected, the ortho-diamine groups of OPD molecules show the strongest interaction with the (100) facet of the perovskite crystal, and almost the same binding energy exists between OPD molecules and [PbX6]4- octahedra ([PbBr6]4- and [PbI6]4-). The templated crystallization induced by the OPD molecular wall ensures the synchronous insertion of mixed-halide component, forming a preferred (100) facet and an orientation perpendicular to the substrate.’\nAction: The related statement on page 4, paragraph 2 has been clarified in the revised manuscript.\nComment 4. The authors should clarify how the binding energies between OPD molecular walls at perovskite grain boundaries and Br/I ions, or with [PbI6]4- and [PbBr6]4- octahedra, influence the activation energy for Br- and I- ion insertion into the (100) plane. Since the activation energy reflects the ease of ion insertion into the crystal lattice, this analysis is critical.\nResponse: Thank you very much for your valuable comments. We have now further analyzed the important role that the binding energy between OPD molecular walls at perovskite grain boundaries and [PbX6]4- octahedron in the crystallization dynamics of perovskites, and we have also elucidated the relationship between this binding energy and the halide insertion of (100) facet.\nWe strongly agree with the reviewer's comments that the activation energy reflects the ease of ion insertion into the crystal lattice. Based on a comprehensive analysis of in-situ crystallization kinetics and DFT simulations, we believe that the control perovskite film exhibits asynchronous halide insertion behavior. The subsequently crystallized I component preferentially inserts into the perovskite lattice along the (100) facet of the perovskite crystal. Although we did not calculate whether the subsequent I component insertion into the perovskite lattice along the (100) facet is easy by simulating the activation energy of I ions, this directional halide insertion behavior along a specific crystal plane gives us inspiration to control the crystallization of perovskite films. Therefore, we propose to construct OPD molecular wall structures to induce preferred (100) facet and vertical orientation by templated crystallization.\nIn general, halide ions are present in the form of [PbX6]4- octahedra halides in the perovskite precursor solution before the perovskite crystals are formed. The binding energy between OPD molecules and [PbX6]4- octahedra is crucial for controlling the crystallization kinetics of perovskites. As shown in Fig. 2e, OPD cation exhibits the strongest and similar binding energies with both [PbI6]4- and [PbBr6]4- octahedra on (100) facet, suggesting that the synchronous insertion of I and Br halides is possible during the templated crystallization process. The synchronized halide incorporation into the perovskite lattice has been confirmed by in-situ GIWAXS patterns and in-situ UV-Vis absorption spectra of perovskite films at the spin-coating stage.\nThe binding energy between OPD molecular and [PbX6]4- octahedron is crucial for the OPD molecular wall at the grain boundary to anchor the perovskite precursor and from homogeneous halide perovskite nucleus. The subsequent templated crystallization mainly relies on the self-assembly crystallization of perovskite precursors induced by the resulting crystal nucleus, thus achieving preferred (100) facet and vertical orientation.\nFigure 2 | e Binding energy between OPD and different crystal facets of perovskite by DFT simulation.\nAction: The relationship between the binding energy and the halide insertion of (100) facet has been clarified in the revised manuscript.\nComment 5. On page 4, paragraph 2, the authors report a bandgap of 1.69 eV for the perovskite film, but no calculation method is described. It is recommended that the bandgap be derived from EQE data, as suggested in Adv. Energy Mater. 2021, 11, 2100022.\nResponse: Thank you very much for your suggestion. We have now provided a calculation method for determining the perovskite bandgap from EQE data (Supplementary Fig. 39), as reported in the literature (Adv. Energy Mater. 2021, 11, 2100022).\nAs reported in Ref. 39 (Adv. Energy Mater. 2021, 11, 2100022), the bandgap of perovskite is closely related to the slope of the EQE absorption edge (Supplementary Fig. 38). As shown in the bandgap diagram of the PSC derived from EQE data (Supplementary Fig. 39), the bandgap of the perovskite can be determined to be 1.69 eV.\nSupplementary Fig. 38 | The EQE spectra of control, AD-treated, and OPD-treated PSCs.\nSupplementary Fig. 39 | Bandgap diagram of the device derived from EQE data.\nAction: Bandgap diagram of the device derived from EQE data (Supplementary Fig. 39 and Ref. 39) has been provided in the revised manuscript.\nComment 6. The XPS peak near 291 eV in Supplementary Fig. 4 corresponds to a π-π satellite signal. This π-π (HOMO-LUMO) transition is a characteristic shake-up line of aromatic carbon rings excited by photoelectron emission (J. Chem. Phys. 1995, 103, 6333-6342; Phys. Rev. B 1997, 55, 10051). Therefore, it cannot be used as evidence for strong π-π interactions arising from parallel stacking of OPD molecules, as claimed on page 7, paragraph 2.\nResponse: Thank you very much for your valuable comments. We have now provided the anisotropic GIWAXS pattern of OPD-treated perovskite film (Supplementary Fig. 21), to demonstrate the strong π-π interactions arising from parallel stacking of OPD molecules.\nAs the reviewer commented, the π-π (HOMO-LUMO) transition is a characteristic shake-up line of aromatic carbon rings excited by photoelectron emission (J. Chem. Phys. 1995, 103, 6333-6342; Phys. Rev. B 1997, 55, 10051). The XPS peak near 291 eV in Supplementary Fig. 19 shows that π-conjugated OPD molecules exist in the OPD-treated perovskite film. We therefore measure the anisotropic GIWAXS pattern of OPD-treated perovskite film, to demonstrate the strong π-π interactions arising from parallel stacking of OPD molecules.\nAccording to the DFT calculation results, the parallel stacking of OPD should be the most stable structure. Due to the intermolecular π-π interactions, the distance (d) between OPD molecules in this stacked structure can be obtained to be 4.1 Å. The corresponding q value can be calculated as 15.3 nm-1 according to the equation,\nq = 2π/d (1)\nAs displayed in Supplementary Fig. 21, the π-π interactions signal is observed at 15.3 nm-1 in the anisotropic GIWAXS pattern of OPD-treated perovskite film (Fig. 2m). The oriented OPD molecular arrangement will ensure the construction of the OPD molecular wall.\nFig. 2 | m GIWAXS pattern of OPD-treated perovskite film after annealing.\nSupplementary Fig. 21 | a Integration of angle and intensity in the anisotropic GIWAXS pattern. b Interplanar spacing of OPD molecules with parallel stacking by DFT simulation calculations.\nAction: The anisotropic GIWAXS pattern of OPD-treated perovskite film (Supplementary Fig. 21) have been provided in the revised manuscript.\nComment 7. In Supplementary Fig. 8, the FWHM of the AD sample appears broader than that of the control sample. The authors should verify this observation. In addition, since the GIWAXS peaks seem to comprise multiple components, it is recommended that peak deconvolution be performed and the FWHM values for the (100) plane signal be explicitly reported.\nResponse: Thank you very much for your valuable suggestions. We have now provided the deconvolution of the GIWAXS peak and determined the FWHM values of the (100) facet (Supplementary Fig. 15, Pristine Supplementary Fig. 8), to explain the broad FWHM observed in the AD-treated samples.\nFollowing the reviewer’s suggestion, we performed deconvolution of the GIWAXS peak on (100) facet. As shown in Supplementary Fig. 15, Pristine Supplementary Fig. 8, the GIWAXS peaks of the AD-treated samples have multiple fitting peak components, and there is also fitting peaks near the main peak of (100) facet. This may be related to the inhomogeneous WBG perovskite phase. In contrast, a single (100) peak can be found in the OPD-treated films. Moreover, we further calculate the FWHM values of the three films to fit the main peak of (100) facet. The OPD-treated film exhibits the smallest FWHM value (0.037) compared to the control (0.044) and AD-treated films (0.042), indicating that the synchronized halide insertion leads to a high-quality uniform WBG perovskite phase.\nSupplementary Fig. 15 | FWHM values of (100) facet extracted from GIWAXS patterns for (a) control, (b) AD-treated, and (c) OPD-treated perovskite films.\nAction: FWHM values of (100) facet extracted from GIWAXS patterns (Supplementary Fig. 15, Pristine Supplementary Fig. 8) have been updated in the revised manuscript.\nComment 8. The AFM and SEM images in Supplementary Figs. 14 and 15 show notably different grain morphologies at comparable scales. The authors should clarify the origin of these discrepancies.\nResponse: Thank you very much for your valuable comments. We have now measured the SEM images of different areas of the perovskite films and statistically analyzed their grain distribution (Supplementary Fig. 16, Pristine Supplementary Fig. 15), to evaluate the grain difference between SEM and AFM images.\nAs shown in SEM images and statistical grain distribution for control, AD-treated, and OPD-treated perovskite films (Supplementary Fig. 16, Pristine Supplementary Fig. 15), almost the same grain size (approximately 320 nm) can be observed in all regions of the three films. Meanwhile, large grain size differences exist in the range of hundreds of nanometers, especially in control and AD-treated films. This may be the main reason why the grain sizes in the AFM images ((Supplementary Fig. 26, Pristine Supplementary Fig. 14) do not seem to be completely consistent.\nSupplementary Fig. 16 | SEM images and grain size statistics for (a) control, (b) AD-treated, and (c) OPD-treated of perovskite films.\nSupplementary Fig. 26 | KPFM topography images for (a) control, (b) AD-treated and (c) OPD-treated of perovskite films.\nAction: The SEM images and grain size statistics of perovskite films (Supplementary Fig. 16, Pristine Supplementary Fig. 15) have been provided in the revised manuscript.\nComment 9. It is recommended that the authors provide the corresponding topography images for the KPFM mappings in Figs. 3a-3c, in order to clearly demonstrate the CPD variations within grain interiors of different samples.\nResponse: Thank you very much for your valuable suggestions. We have now provided the corresponding topography images (Supplementary Fig. 26) of KPFM mappings in Figs. 3a-3c, to clearly observe the internal changes within the grains of different samples.\nAs shown in Supplementary Fig. 26, we have supplemented the corresponding AFM topography maps for KPFM mappings in Figs. 3a-3c. Height and V line-scan CPD spectra are extracted from the region marked with horizontal lines in AFM and KPFM images. According to the AFM images, we can obtain distinguishable grain boundaries of the perovskite films, and detect surface electrical information at the perovskite grain interior (GI). As shown, the OPD-treated film shows the smallest ΔVCPD, GI (48 mV) compared to the control (101 mV) and AD-treated samples (71 mV).\nSupplementary Fig. 26 | KPFM topography images for (a) control, (b) AD-treated and (c) OPD-treated of perovskite films.\nFigure 3 | The spatial V maps and extracted V line-scan spectra of (a) control, (b) AD-treated, and (c) OPD-treated perovskite films.\nAction: The corresponding topography images of KPFM mappings (Supplementary Fig. 26) have been provided in the revised manuscript.\nComment 10. In Fig. 4d, EQE is plotted as a function of voltage. The authors should explain the basis for selecting the EQE values reported in the manuscript.\nResponse: Thank you very much for your valuable comments. We have now provided EQE plotted as a function of injected current density (Fig. 4d), to more intuitively reflect the basis for selecting the EQE values.\nAccording to previous report (Energy Environ. Sci. 15, 7680-7694 (2025)), EQE plotted as a function of injected current density can intuitively reflect the basis for selecting the EQE values. When the injected current density is approximate to the Jsc under 1-sun illumination, the corresponding EQE values can be used to evaluate the Voc loss of PSCs (Fig. 4d). As shown in the experimental J-V curves of PSCs (Fig. 4f), the Jsc of the control, AD-treated, and OPD-treated PSCs are 21.94 mA cm-2, 22.37 mA cm-2, and 22.72 mA cm-2, respectively. Therefore, the corresponding EQE values can be extracted from the EQE spectrum as 0.06%, 0.24%, and 0.78%, respectively.\nFigure 4 | d EQE spectra of PSCs. Inset: EL image of OPD-treated devices.\nFigure 4 | f experimental J-V curves of PSCs.\nAction: EQE spectra of PSCs (Fig. 4d) have been updated in the revised manuscript.\nComment 11. The authors should provide the explicit calculation process by which a potential Voc of 1.274 V was obtained from a 1.274 V loss of 0.126 V, as stated on page 13, paragraph 2.\nResponse: Thank you very much for your valuable and constructive suggestions. We have now provided a detailed calculation process for the potential Voc of 1.274V.\nWhen a solar cell is operated as a light-emitting diode, the Voc loss of the device can be calculated using the EQE. The potential Voc of PSCs can be obtained by the previously reported equation (Phys. Rev. B 76, 085303 (2007)) as follows:\nVoc ≈ Voc,rad + (kT/e) * ln(EQE) (1)\nwhere Voc,rad, k, T and e are the radiative limit of, Boltzmann’s constant, thermodynamic temperature and elementary charge. The second term in the equation represents the Voc loss induced by non-radiative recombination. The OPD-treated device achieved an EQE of 0.78%, and thus a Voc loss of -0.126 V could be obtained. According to the Shockley-Queisser (S-Q) limit theory (IEEE J. Photovolt. 2, 303-311 (2012)), the perovskite with bandgap of 1.69 eV corresponds to theoretical radiative limit Voc of 1.400 V. Therefore, a potential Voc of 1.274 V was obtained in the OPD-treated devices.\nAction: The detailed calculation process for the potential Voc of 1.274V has been provided in the revised manuscript.\nReviewer #3:\nThe manuscript by Song et al. reports on a halide insertion regulation strategy for wide-bandgap perovskite solar cells. Using in-situ GIWAXS and DFT modeling, the authors reveal an asynchronous halide incorporation process that leads to poor orientation and device inefficiencies. They propose an o-phenylenediamine “molecular wall” strategy to achieve synchronous halide insertion, resulting in vertically aligned (100)-oriented films and record WBG-PSC performance (24.13% PCE, certified 23.43%). The work addresses a key bottleneck in WBG perovskite development, combining mechanistic insights with practical device engineering. The study is of clear interest to the wide-bandgap perovskite photovoltaics community. However, additional evidence and clarification are required to fully support the mechanistic claims. I therefore recommend major revision before the manuscript can be considered for publication in Nature Communications.\nResponse: Thank you very much for your interest and recognition of our work. Your suggestions were crucial in helping us improve the quality of the manuscript. We have now added additional evidences and clarifications to fully support the mechanistic claims. The manuscript has also been thoroughly revised based on the comments of all the reviewers, and we hope that the revised manuscript will meet your high standards.\nComment 1. The crystallization pathway can be divided into nucleation, growth, and regrowth (Ostwald ripening). The current analysis focuses only on the nucleation stage observed during in situ spin-coating GIWAXS, without considering annealing, which governs the growth stage. It is reasonable to expect merging between Br-rich and I-rich nuclei during growth, which could also explain the observed Δq shifts. Please include a detailed analysis of the annealing process to rigorously validate the claim of facet-selective halide insertion.\nResponse: Thank you very much for your valuable guidance. We have now provided in-situ GIWAXS patterns and extracted q-value evolution of the control, AD-treated, and OPD-treated films at the annealing growth stage (Supplementary Fig. 11), to rigorously validate the claim of facet-selective halide insertion.\nAs the reviewer commented, the annealing stage is crucial for the growth of perovskite films. We monitored the GIWAXS evolution of the of the control, AD-treated, and OPD-treated films at the annealing stage (Supplementary Fig. 11). All three films exhibited nearly constant q values (Δq is 0) on the (100), (110), and (111) facet. This suggests that the halide insertion-induced perovskite crystal structure is formed at the spin-coating stage, and the residual solvent is evaporated to form a stable perovskite crystal structure at the annealing stage.\nSupplementary Fig. 11 | In-situ GIWAXS patterns and extracted q-value evolution of (a) control, (b) AD-treated, and (c) OPD-treated films at the annealing growth stage.\nAction: In-situ GIWAXS patterns and extracted q-value evolution of perovskite films at the annealing growth stage (Supplementary Fig. 11) have been provided in the revised manuscript.\nComment 2. The stacking energy analysis suggests OPD’s superior π-π interactions, but direct experimental evidence for the proposed “molecular wall” remains absent. The XPS spectra (Supp. Fig. 4) confirm OPD-perovskite interaction but not alignment into wall structures. Supporting data from techniques such as polarized spectroscopy, anisotropic GIWAXS, or cross-sectional TEM would significantly reinforce this claim.\nResponse: Thank you very much for your valuable suggestions. We have now provided the anisotropic GIWAXS pattern of OPD-treated perovskite film (Supplementary Fig. 21), to confirm the existence of the ‘molecular wall’.\nAccording to the DFT calculation results, the parallel stacking of OPD should be the most stable structure. Due to the intermolecular π-π interactions, the distance (d) between OPD molecules in this stacked structure can be obtained to be 4.1 Å. The corresponding q value can be calculated as 15.3 nm-1 according to the equation,\nq = 2π/d (1)\nAs displayed in Supplementary Fig. 21, the π-π interactions signal is observed at 15.3 nm-1 in the anisotropic GIWAXS pattern of OPD-treated perovskite film (Fig. 2m). The oriented OPD molecular arrangement will ensure the construction of the OPD molecular wall.\nFig. 2 | m GIWAXS pattern of OPD-treated perovskite film after annealing.\nSupplementary Fig. 21 | a Integration of angle and intensity in the anisotropic GIWAXS pattern. b Interplanar spacing of OPD molecules with parallel stacking by DFT simulation calculations.\nAction: The anisotropic GIWAXS pattern of OPD-treated perovskite film (Supplementary Fig. 21) have been provided in the revised manuscript.\nComment 3. The manuscript does not address the distribution of OPD after film formation. Large aromatic cations typically have poor conductivity, which could become problematic if OPD accumulates at grain boundaries. TOF-SIMS or depth-profiling studies would clarify the spatial position of OPD and strengthen the mechanistic interpretation.\nResponse: Thank you very much for your valuable comment. We have provided depth-profiling XPS spectra of perovskite films (Supplementary Fig. 20), to determine the spatial distribution of OPD molecules in perovskite films.\nAs the reviewer commented, a large number of aromatic molecules accumulated at the whole grain boundaries of perovskite films will be detrimental to the carrier transport. We therefore investigated the spatial distribution of OPD molecules at different depths in perovskite films by depth-profiling XPS spectra. As shown in C 1s of OPD-treated perovskite film (Supplementary Fig. 20), the π-π interactions signal was observed at 291 eV in the surface region of film. The C 1s signal gradually disappears with the increase of etching depth, which indicates that the OPD molecules are mainly concentrated in the top region (~50 nm) of the grain boundaries of the perovskite film. The OPD molecular wall located on the top film will induce top-down templated crystallization of the perovskite film (Fig. 2a). The small amount of OPD molecular will have little detrimental effect on charge carrier transport.\nSupplementary Fig. 20 | Depth-profiling XPS spectra of C 1s of OPD-treated perovskite film.\nFigure 2 | a Schematic diagram of the OPD molecular wall-induced synchronous halide insertion and templated crystallization of perovskite film.\nAction: Depth-profiling XPS spectra of perovskite films (Supplementary Fig. 20) have been provided, and schematic diagram of the OPD molecular wall-induced synchronous halide insertion and templated crystallization (Fig. 2a) has been updated in the revised manuscript.\nComment 4. The thermal stability test conditions (65 °C, 45% RH) are non-standard, although the results show an encouraging trend. To make the findings more broadly comparable, stability assessments following ISOS protocols—such as ISOS-D-2 (85 °C thermal stress) or ISOS-L-2 (85 °C MPP tracking under N₂)—should be included.\nResponse: Thank you very much for your valuable suggestions. We have now provided the stability testing of PSCs under damp heat conditions at ISOS-D-2 and ISOS-D-3 protocols (Supplementary Fig. 43), to validate the robustness of OPD-treated devices under realistic and more demanding operational environments.\nAs recommended by the reviewer, we monitored the PCE evolution of the encapsulated PSCs under the conditions of damp heat at 85 °C and 45% RH according to ISOS-D-2 protocol. As shown in Supplementary Fig. 43, the OPD-treated device still maintained 90% of its initial PCE after 800 h, while the control device and the AD-treated device only maintained 50% and 75% of their initial PCE. We further strictly implement the stability test conditions of PSCs at 85 °C and 85% RH according to ISOS-D-3 protocol. The OPD-treated device still maintained 88% of its initial PCE after 600 h, and the improved device stability is attributed to the enhanced perovskite crystal quality due to the OPD treatment.\nSupplementary Fig. 43 | Damp-heat stability of PSCs under of (a) ISOS-D-2 and (b) ISOS-D-3 standard protocols.\nAction: The stability testing of PSCs under damp heat conditions at ISOS-D-2 and ISOS-D-3 protocols (Supplementary Fig. 43) have been supplemented in the revised manuscript.\nComment 4. Other Minor Comments\n1) Define “asynchronous halide insertion” clearly in the Abstract and Introduction for reader clarity.\n2) Ensure consistent terminology throughout (e.g., “halogen ion insertion” vs. “halide insertion”).\n3) In Fig. 1c, orientation randomness is attributed solely to asynchronous halide insertion, but nucleation and solvent-related effects may also contribute. A more nuanced discussion is warranted.\n4) The random insertion model (Supp. Fig. 2) is only briefly described; please expand the methodological details.\nResponse: Thank you very much for your valuable suggestions. We have provided a clear definition of ‘asynchronous halide insertion’, and have also ensured consistent terminology in the revised manuscript. We have now provided the GIWAXS patterns of control and OPD-treated perovskite film with other solvent (Supplementary Fig. 2), to exclude nucleation and solvent-related effects. We have now provided a more detailed description of the random insertion model methodology.\n1) The definition of asynchronous halide insertion is as follows: OPD exhibits the strongest and almost equal interactions with [PbBr6]4- and [PbI6]4- octahedra at the (100) facet. Therefore, the OPD molecular wall can anchor [PbBr6]4- and [PbI6]4- octahedra simultaneously, and thus resulted homogeneous halide perovskite phase achieved a preferred (100) crystal facet and a vertical orientation.\nAction: The ‘asynchronous halide insertion’ has been clearly defined in the revised Abstract and Introduction.\n2) We have thoroughly reviewed the manuscript, and all terminology has been standardized. For example, ‘halogen ion insertion’ has been revised to ‘halide insertion’.\nAction: The consistent terminology has been provided in the revised manuscript.\n3) To exclude nucleation and solvent-related effects, we introduced a common solvent, N-methyl-2-pyrrolidone (NMP), into the perovskite precursor solution, resulting a mixed solvent system (25 V% of NMP). Supplementary Fig. 2 showed the GIWAXS patterns of control and OPD-treated perovskite film with NMP. After the introduction of NMP solvent, the control sample still exhibited random crystal facets and orientations, while the OPD-treated sample also achieved a preferred (100) crystal facet and a vertical orientation. Therefore, the introduction of the new solvent did not change the crystal structure of the perovskite film. The templated crystallization induced by the OPD molecular wall determines the crystal facet and orientation of perovskite film.\nSupplementary Fig. 2 | GIWAXS patterns of a control and b OPD-treated perovskite film with NMP solvent (25 V%).\nAction: The GIWAXS patterns of film with other solvent (Supplementary Fig. 2) have been provided in the revised manuscript.\n4) The methodology of the random insertion model is explained in detail as follows:\nAs shown in the Supplementary Fig. 3 (pristine Supplementary Fig. 2), we first construct a ABX3 crystal structure model of pure Br perovskite (APbBr3). The atomic arrangements corresponding to the (100), (110), and (111) facets are …AX-BX2-AX-BX2…, …X2-ABX-X2-ABX…, and …AX2-B-AX2-B…, respectively. For the random insertion model, 80% of the Br atoms are randomly replaced by I atoms at the X sites of each crystal facets, which results a APb(Br0.2I0.8)3 crystal structure. The atomic arrangement after I insertion is shown on the AX(100), ABX(110), and AX2(111) terminations, respectively. According to the DFT calculation results, almost the same Δd variation is observed at all three crystal facets, which is inconsistent with the in-situ GIWAXS experiments. Therefore, we conclude that the post-crystallization I insertion direction shows a preference for the (100) facet.\nSupplementary Fig. 3 | Perovskite crystal models and DFT-calculated interplanar spacings of (100), (110), and (111) facets before and after random I insertion.\nAction: The more detailed description of the random insertion model methodology has been provided in the revised manuscript.\nReviewer #4 :\nThe manuscript reports a halide insertion regulation strategy using o-phenylenediamine to construct π-conjugated molecular walls, promoting synchronous halide incorporation in wide-bandgap perovskites. This approach is supported by in-situ GIWAXS, DFT calculations, spectroscopic characterizations, and device performance evaluation, delivering efficient and stable perovskite solar cells (PSCs) with a certified PCE of 23.43% and encouraging stability. This work is interesting and relevant to the perovskite community. However, the novelty relative to recent literature is not sufficiently clarified, the mechanistic validation lacks direct experimental evidence, and some claims are overstated compared with the state-of-the-art. Additional control experiments, clearer benchmarking, and stronger stability demonstrations are required before the manuscript can be considered for publication. I therefore recommend major revision.\nResponse: Thank you very much for your interest in our work. Your suggestions were crucial in helping us improve the quality of the manuscript. We have now added some necessary experiments to further support our conclusions based on your comments. The manuscript has been thoroughly revised based on the comments of all the reviewers, and we hope that the revised manuscript will meet your high standards.\nComment 1. Although the authors have performed stability measurements under the ISOS-L-1 protocol, considering the application relevance for tandem devices and the high standards of Nature Communications, additional stability results under harsher conditions (e.g., damp heat at 85 °C/85% RH, or at least higher humidity stress tests) are necessary. This would further validate the robustness of OPD incorporation under realistic and more demanding operating environments.\nResponse: Thank you very much for your valuable suggestions. We have now provided the stability testing of PSCs under damp heat conditions at ISOS-D-2 and ISOS-D-3 protocols (Supplementary Fig. 43), to validate the robustness of OPD-treated devices under realistic and more demanding operational environments.\nAs recommended by the reviewer, we monitored the PCE evolution of the encapsulated PSCs under the conditions of damp heat at 85 °C and 45% RH according to ISOS-D-2 protocol. As shown in Supplementary Fig. 43, the OPD-treated device still maintained 90% of its initial PCE after 800 h, while the control device and the AD-treated device only maintained 50% and 75% of their initial PCE. We further strictly implement the stability test conditions of PSCs at 85 °C and 85% RH according to ISOS-D-3 protocol. The OPD-treated device still maintained 88% of its initial PCE after 600 h, and the improved device stability is attributed to the enhanced perovskite crystal quality due to the OPD treatment.\nSupplementary Fig. 43 | Damp-heat stability of PSCs under of (a) ISOS-D-2 and (b) ISOS-D-3 standard protocols.\nAction: The stability testing of PSCs under damp heat conditions at ISOS-D-2 and ISOS-D-3 protocols (Supplementary Fig. 43) have been supplemented in the revised manuscript.\nComment 2. In Figure S22, all EQE spectra show a distinct downturn around ~325 nm. The authors should clarify the origin of this feature. Moreover, at ~650 nm, the AD-modified device exhibits an opposite fluctuation compared with the Control and OPD-modified devices. Reflectance measurements are recommended to disentangle the optical contributions and provide a clearer understanding of the current gain/loss sources.\nResponse: Thank you very much for your valuable comment. We have now provided the transmittance spectrum of ITO glass (Supplementary Fig. 36), to clarify the distinct downturn of EQE spectra around 325 nm. We have also provided the reflectance spectra of perovskite films (Supplementary Fig. 37), to disentangle the optical contributions and current gain/loss sources at ~650 nm.\nAs displayed in Supplementary Fig. 36, a distinct downturn at around 325 nm is observed in the transmittance spectrum of ITO glass. This corresponds to the downturn position of the EQE spectra (Supplementary Fig. 38, pristine Supplementary Fig. 22), and the reduction of incident photons with a wavelength of ~325 nm leads to current loss in perovskite devices.\nAs recommended by the reviewer, we measured the reflectance spectra of the AD-treated and OPD-treated perovskite films. As shown in Supplementary Fig. 37, an opposite fluctuation is also observed in 1-reflectance (1-R) spectra at ~650 nm for the AD-treated and OPD-treated films, which exhibits the same trend as the EQE spectra. This means that the AD-treated films exhibit stronger photon absorption at ~650 nm, which may be related to the composition of the perovskite films. As we discussed previously, the introduction of AD molecules cannot achieve complete templated crystallization. However, its introduction may form new components that made certain contributions to the absorption of the photons with a wavelength of ~650 nm. Nevertheless, compared with AD-treated films, the OPD-treated perovskite film still exhibits higher crystal quality and higher photocurrent gain the wavelength range of 300 - 800 nm, which ensures efficient photovoltaic devices.\nSupplementary Fig. 36 | Transmittance spectrum of glass/ITO.\nSupplementary Fig. 37 | The 1-R spectra processed of AD -treated and OPD -treated.\nSupplementary Fig. 38 | The EQE spectra of control, AD-treated, and OPD-treated devices.\nAction: The transmittance spectrum of ITO glass (Supplementary Fig. 36) and the reflectance spectra of perovskite films (Supplementary Fig. 37) have been provided in the revised manuscript.\nComment 3. The central claim that OPD molecular walls facilitate synchronous halide insertion is mainly supported by GIWAXS and DFT. However, these techniques provide only indirect evidence. Direct chemical or spatial characterization, such as TOF-SIMS depth profiling or STEM-EDS elemental mapping, is needed to unambiguously demonstrate the cooperative insertion of Br and I into the perovskite lattice.\nResponse: Thank you very much for your valuable suggestions. We have now provided in-situ UV-Vis absorption spectra of perovskite films at the spin-coating stage (Supplementary Fig. 12), depth-profiling XPS spectra of perovskite films (Supplementary Fig. 17), and halogen element distribution statistics extracted from cross-sectional EDS spectra of PSCs. (Supplementary Fig. 18), to unambiguously demonstrate the cooperative insertion of [PbBr6]4- and [PbI6]4- into the OPD-treated perovskite lattice.\nTo further substantiate the synergistic insertion of [PbBr6]4- and [PbI6]4-, we measured in-situ UV-Vis absorption spectra of perovskite films at the spin-coating stage. As shown in Supplementary Fig. 12, the absorption edge of the controlled perovskite film gradually red-shifts with the addition of antisolvent, indicating that the Br-rich component is formed preferentially, and the subsequent I insertion narrows the bandgap. Although the AD-treated film accelerates the red shift of the absorption edge, subsequent I insertion still exists and synchronous halide insertion cannot be successfully achieved. In contrast, the OPD-treated film exhibits a constant absorption edge almost immediately after the antisolvent is added. This stable bandgap also implies the simultaneous insertion of I and Br, which is consistent with the results of in-situ GIWAXS characterization.\nTo further investigate the effect of halide insertion regulation on the halide distribution in perovskite films, we performed the depth-profiling XPS spectra of the resulting perovskite films. As played in XPS spectra of I and Br elements (Supplementary Fig. 17), the signal of the Br element in the control film gradually decreases as the etching depth increases, while the signal of the I element gradually increases. The Br-rich component formed first on the surface is distributed on the top of the perovskite film, while the I-rich phase formed later is distributed on the bottom. Due to the accelerated crystallization rate, the inhomogeneous distribution of halides in the AD-treated film is alleviated to a certain extent, but it is still not negligible. In contrast, the OPD-treated film exhibited an almost homogeneous halide distribution from top to bottom.\nWe then measured the cross-sectional EDS spectra the resulting PSCs, and quantitatively analyzed the distribution of halogen elements in different regions (Supplementary Fig. 18). Strikingly, the OPD-treated sample exhibits almost same bromine content (20%) in different regions of the perovskite film, which is consistent with the depth-profiling XPS results. The homogeneous halide distribution is attributed to the synchronous halide insertion induced by OPD molecular walls.\nSupplementary Fig. 17 | Depth-profiling XPS spectra of Br and I elements of (a) control, (b) AD-treated, and (c) OPD-treated perovskite films.\nSupplementary Fig. 12 | In-situ UV-Vis absorption spectra of (a) control, (b) AD-treated, and (c) OPD-treated perovskite films at the spin-coating stage.\nSupplementary Fig. 18 | Halogen element distribution statistics extracted from cross-sectional EDS spectra at different depths of (a) control, (b) AD-treated, and (c) OPD-treated samples.\nAction: In-situ UV-Vis absorption spectra (Supplementary Fig. 12), depth-profiling XPS spectra (Supplementary Fig. 17), and halogen element distribution statistics extracted from cross-sectional EDS spectra (Supplementary Fig. 18) have been provided in the revised manuscript.\nComment 4. In the DFT results, the authors provide binding energies of OPD with three facets of [PbI6]4- octahedra, but only the (100) facet for [PbBr6]4-. For consistency and completeness, binding energies of OPD with additional facets of [PbBr6]4- (analogous to [PbI6]4-) should be included to allow a fair comparison.\nResponse: Thank you very much for your constructive comments. We have now supplemented the binding energies for OPD with [PbBr6]4- at the (110) and (111) facets (Supplementary Fig. 7), to ensure consistency and completeness.\nAccording to DFT simulations shown in Supplementary Fig. 7, the binding energies for OPD with [PbBr6]4- at the (110) and (111) facets is 0.95 eV and 1.07 eV, separately. This is close to that of OPD with [PbI6]4- at the (110) and (111) facets (Fig. 2e), but it is lower than that OPD with [PbBr6]4-/[PbI6]4- at the (100) facet (1.25 eV and 1.20 eV). A stronger and closer force between OPD and [PbX6]4- will provide a theoretical basis for the OPD-constructed molecular wall to induce the generation of a preferred (100) facet.\nSupplementary Fig. 7 | The binding energy and longitudinal integral curves of differential charge density between OPD and the [PbBr6]4- at a (110) and b (111) facets.\nAction: The binding energy and longitudinal integral curves of differential charge density between OPD and the [PbBr6]4- at (110) and (111) facets (Supplementary Fig.7) have been provided in the revised manuscript.\nComment 5. The concept of molecular additives regulating crystal orientation and halide distribution is not new. Several recent studies (e.g., Refs. 11, 18, 19, 20) have already reported oriented nucleation and synchronous crystallization strategies. The authors should more clearly differentiate how the OPD-based molecular wall strategy advances beyond prior methods. The Introduction should also highlight the existing limitations of current halide regulation strategies and explicitly position OPD as addressing a unique bottleneck. Such mechanistic distinction is essential for consideration in Nature Communications.\nResponse: Thank you very much for your insightful and valuable suggestions. We have now comprehensively summarized the relevant studies (Refs. 11, 18, 19, and 20, pristine Refs. 11, 22, 23, and 26) on orientation regulation and oriented nucleation and synchronous crystallization strategies. We have now further analyzed the advantages of the OPD-based molecular wall strategy, and we have also supplemented the existing limitations of current halide regulation strategies and explicitly position OPD as addressing a unique bottleneck in the revised Introduction.\nJiao et al. (Ref. 18, pristine Ref. 26, Adv. Mater. 36, 2313673 (2024)) added Hydantoin into the FAPbI3 perovskite system to regulate the crystallization of perovskite films. The –C=O and –NH groups of Hydantoin coordinate with Pb2+ and I- ions, which enhances the crystallization of the Pb-I framework. Thus, the resulting α-phase perovskite achieved an out-of-plane orientation. Moreover, Hydantoin distributes across the surface and grain boundaries of films, passivating defects and stabilizing the surface electronic structure. As a result, a small-area PSC achieved a PCE of 25.66%.\nSimilarly, Shi et al. (Ref. 19, pristine Ref. 22, Nature 620, 323-327 (2023)) incorporated pentanamidine hydrochloride (PAD) in the precursor of the organic cations to regulate the FAPbI3 crystallization of perovskite films. The positively charged amidinium head of PAD anchored into the octahedral cavity of the α-phase perovskite by electrostatic and hydrogen-bonding interactions. The reduced surface energy of a specific crystallographic plane suppressed the intermediate phase and avoided the δ-phase FAPbI3. As a result, the resulting α-phase PSC achieved a PCE of 25.4%.\nYan et al. (Refs. 20, pristine Ref. 23, Adv. Funct. Mater. 32, 2201384 (2022)) introduced propanediamine (PDA) cations into narrow-bandgap (NBG) lead-tin (Pb-Sn) perovskite system to regulate the crystallization of perovskite films. The diamine cations anchored onto the surface of the crystals at the nucleation stage, reducing the surface energy of the (100) plane, making it energetically favorable during crystal growth compared with the other planes. As a result, the champion PSC achieved a PCE of 20.03%.\nLi et al. (Refs. 11, Adv. Mater. 37, e05694 (2025)) introduced 1,3-Dimethyl-2-imidazolidinone (DMI) into the WBG perovskite precursor solution to regulate the halide distribution. Due to the strong binding energy between DMI and lead halide (PbX2), the homogeneous DMI-PbX2 adducted intermediate phase is stable in precursor solution and at spin-coating stage. And it then synchronously transforms into a homogeneous halide-phase perovskite film at the annealing stage. As a result, resulting WBG PSC achieved a PCE of 21.42%.\nAs the reviewer commented, these works reported the methods of oriented nucleation or synchronous crystallization strategies. However, we also note that OPD-based molecular wall strategy we proposed possesses unique advantages compared with the above work.\nJiao et al. and Shi et al. are committed to achieving pure α phase in the FAPbI3 perovskite system. They introduce additives to achieve strong coordination forces with the Pb-I skeleton, thereby inducing oriented crystallization of perovskite films. Yan et al. achieves oriented nucleation of I-based Pb-Sn perovskite by reducing the surface energy of the (100) plane. Crystal growth control of mixed-halide WBG perovskites is more difficult than that of these pure iodine halide perovskite systems, due to the natural asynchronous crystallization nucleation of I and Br. Although Li et al. achieved the synchronous phase transition of I-based and Br-based components through intermediate phase regulation, this phase transition at the annealing stage cannot did not have the opportunity to enable templated growth of perovskite films. And it therefore cannot achieve a homogeneous mixed-halide perovskite phase with preferred crystal facets and orientations.\nIn summary, it is very challenging to achieve synchronous crystallization of I-based and Br-based components in mixed-halide WBG perovskite films while maintaining preferred crystal facets and orientations. Based on a comprehensive analysis of in-situ GIWAXS monitoring and DFT calculations, we understand that the physical mechanism of asynchronous crystallization of I-based and Br-based components. Inspired by the tendency of I component to be inserted along the (100) facet, we envision realizing the synchronous insertion of I component and Br component along the (100) facet. Guided by DFT calculations, the ortho-diamine groups of OPD molecules show the strongest interaction with the (100) facet of perovskite crystal, and almost the same binding energy exists between OPD and halides ([PbBr6]4- and [PbI6]4-). Moreover, the templated crystallization induced by the molecular wall ensures the synchronous mixed-halide insertion, forming a preferred (100) facet and a highly vertical orientation. As a result, the OPD-treated PSC achieves an excellent PCE of 24.13% (certified 23.43%), representing one of the highest values among WBG PSCs. Therefore, our proposed the OPD-based molecular wall is unique and crucial for the mixed-halide WBG perovskite system.\nAction: Relevant studies (Refs. 11, 18, 19, and 20) have now been summarized, and the unique advantages of the OPD-based molecular wall strategy have been supplemented in the revised Introduction.\nComment 6. The authors demonstrate their approach using FA0.8MA0.1Cs0.1Pb(I0.8Br0.2)3 as the model perovskite composition. Since the manuscript emphasizes that Br tends to crystallize preferentially in WBG perovskites, validation of the OPD strategy in perovskites with even higher Br content (wider bandgap compositions) would be important to prove the universality of this halide regulation concept.\nResponse: Thank you very much for your valuable suggestion. We have now provided the photovoltaic performance of PSCs with a higher Br content (Supplementary. Fig 42), to evaluate the generalizability of this approach.\nAs suggested by the reviewer, we increased the Br content of the perovskite film (FA0.8MA0.1Cs0.1Pb(I0.7Br0.3)3) to 30 mol%. As shown in Supplementary. Fig 42, the optical bandgap of the perovskite film was determined to be 1.75 eV according to absorption and EQE spectra. The resulting PSC with OPD treatment achieves a PCE of 20.45%, with a Voc of 1.316 V, an FF of 80.40%, and a Jsc of 19.43 mA cm-2, which is higher than that (18.54%) of the control device. This demonstrates that the use of ODP to direct templated crystallization via a molecular wall is generalizable for mixed-halide WBG PSCs.\nSupplementary Fig. 42 | a J-V curves and b EQE spectrum of PSC with Br content of 30 mol%. c Absorption spectrum of corresponding perovskite films.\nAction: J-V curves, EQE spectrum, and absorption spectrum of perovskite with Br content of 30 mol% (Supplementary Fig. 42) have been provided in the revised manuscript.\nComment 7. The authors employ 1 mol% OPD as the optimal concentration, but the optimization process is not described. A systematic study or at least a clear explanation of how this concentration was determined should be provided to justify the choice.\nResponse: Thank you very much for your constructive comments. We have now provided GIWAXS patterns of perovskite films (Supplementary Fig. 14) and J-V curves (Supplementary Fig. 33) of PSCs at different OPD concentrations, to determine the optimal OPD concentration.\nWe introduced different OPD concentrations (0.5 mol%, 1.0 mol%, and 1.5 mol%) into the perovskite film. As shown in Supplementary Fig. 14, when 0.5 mol% OPD was introduced, the perovskite film did not exhibit a preferred (100) plane and vertical crystal orientation. Both 1.0 mol% and 1.5 mol% OPD helped the perovskite film achieve a preferred (100) plane and vertical crystal orientation, but the stronger GIWAXS signal proved that the former possessed higher crystalline quality than the latter. Therefore, PSCs with 1.0 mol% OPD are considered to have the greatest potential to achieve the best photovoltaic performance. As expected, the PSC 1.0 mol% OPD achieves the highest PCE of 24.13%, compared with those with 1.0 mol% (21.32%) and 1.5 mol% OPD (22.19%).\nSupplementary Fig. 14 | GIWAXS patterns of perovskite films with (a) 0.5 mol%, (b) 1 mol%, and (c) 1.5 mol% OPD.\nSupplementary Fig. 33 | J-V curves of PSCs at different OPD concentrations.\nAction: GIWAXS patterns of perovskite films (Supplementary Fig. 14) and J-V curves (Supplementary Fig. 33) of PSCs at different OPD concentrations have been provided in the revised manuscript.\nReviewer #1:\nThe authors have addressed all the questions, and the manuscript is suitable for acceptance.\nResponse: Thank you very much for your recognition of our work.\nReviewer #2：\nThe authors have provided new experimental results and an expanded discussion addressing my previous comments. All of my concerns have been satisfactorily resolved, and I recommend that this work be published in Nature Communications.\nResponse: Thank you very much for your guidance and recognition of our work.\nReviewer #3:\nThe revision has addressed my concerns. I am pleased with the author's response and endorse the publication of their work in its current form.\nResponse: Thank you very much for your recognition of our work.\nReviewer #4:\nThe revised manuscript shows significantly improved quality, and I support the publication of this paper as is.\nResponse: Thank you very much for your guidance and recognition of our work."}]

Decision letter