Synergistic Triplet Exciton Management and Interface Engineering for High-Brightness Sky-Blue Multi-Cation Perovskite Light-Emitting Diodes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper is of great interest for people working on both LED and perovskite materials. It shows that incorporating mCBP into multi-cation perovskite films markedly enhances the performance of sky-blue PeLEDs, highlighting the essential role of triplet exciton management and interface engineering.

It is well written and very clear with adequate characterization methods well conducted.

Here is some improvements that can be made, but I however suggest to accept this paper:

- Fig 2 a, b, c, d : scales difficult to read

- Fig 3: why PL intensity is noted as a.u. -> it is not

Author Response

The following is a point-by-point response to the reviewers' comments (The original comments are in black, and our responses are in blue).

 

Reviewers' comments:

Reviewer 1#:

Comment 1-1:

This paper is of great interest for people working on both LED and perovskite materials. It shows that incorporating mCBP into multi-cation perovskite films markedly enhances the performance of sky-blue PeLEDs, highlighting the essential role of triplet exciton management and interface engineering.

It is well written and very clear with adequate characterization methods well conducted.

Here is some improvements that can be made, but I however suggest to accept this paper:

- Fig 2 a, b, c, d : scales difficult to read.

Response: We sincerely thank you for your positive evaluation of our work and for the constructive feedback. We are pleased that you find the paper well-written, clear, and methodologically sound. Regarding the specific point raised about Figure 2 (AFM images), we agree with you that the scale markers in the original submission were not optimally clear. In response, we have carefully revised and re-plotted all AFM topography images (Figures 2a-d) to ensure the scale bars and surface features are presented with maximum clarity. The figure has been regenerated as a high-resolution graphic and uploaded with the revised manuscript. We believe this revision fully addresses your concern and significantly improves the visual presentation of the film morphology data. Thank you again for your valuable comment, which has helped us enhance the quality of our manuscript.

Comment 1-2:

Fig 3: why PL intensity is noted as a.u. -> it is not.

Response: We sincerely thank you for the constructive feedback. Regarding the specific point raised about Figure 3 (PL intensity units), we thank you for the careful observation. In the original submission, the label "a.u." (arbitrary units) was used for the PL intensity axes. As you correctly pointed out, this was not the most precise description since the data originate from calibrated measurements. To accurately reflect the nature of the data and to avoid any potential misunderstanding, we have updated the y-axis labels. In Figure 3a and Figure 3d, which display the temperature-dependent PL spectra, the label has been changed from "PL intensity (a.u.)" to "PL intensity (counts)". In Figure 3b and Figure 3e, which show the Arrhenius fitting of the normalized PL intensity, the label has been updated to "Normalized PL intensity". This modification clarifies that the intensities are presented on a normalized scale for effective comparison, while the underlying data are quantitative. The revised, high-resolution figure has been uploaded with the revised manuscript. We believe this revision accurately addresses your concern and enhances the precision of our data presentation. Thank you again for your valuable comment, which has helped us improve the clarity of our manuscript.

 

 

We sincerely thank you for your valuable comments and suggestions, which have greatly improved the quality of our manuscript. We apologize for any oversights in the original submission/revision and assure you that the paper has been carefully revised again for clarity and accuracy. On behalf of my co-authors, we express our deep gratitude for your contributions to our work.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents a synergistic strategy that combines multi-cation perovskite engineering with triplet exciton management by incorporating the high-triplet-energy molecule mCBP to enhance film quality, suppress defects, and confine excitons. This approach results in sky-blue PeLEDs with significantly improved optical properties, achieving a peak EQE of 10.2% and luminance over 12,000 cd/m² at 486 nm. Below are some comments that can help authors improve the paper:

1- Explain how a fixed ratio (1:0.9:0.5:0.3:0.1) was chosen and whether compositional screening was performed.
2- The emissive layer is reported to be ~25 nm thick. Was thickness consistent across samples (W/O vs mCBP vs TPBi vs Bphen)? Thickness variations could significantly influence PLQY and device performance.
3- improve your literature review by adding other kinds of perovskite applications, such as DOI: 10.1002/smm2.70032.
4- The reduction in Γph from 71.75 to 22.02 meV is very large. Please comment on the possible physical mechanism.
5- Does mCBP remain primarily at the perovskite/TPBi interface, or is it distributed within grains? This distribution strongly influences triplet blocking behavior and should be clarified.
6- Electrical stability tests are missing. The manuscript reports high EQE and luminance, but operational stability is not shown. Even a preliminary stability curve is important for evaluating practical relevance.
7- Include statistics of luminance, EQE, and turn-on voltage for multiple devices to demonstrate reproducibility of the performance enhancements.

General Presentation
8-  In several places the manuscript states “TPBi hole transport layer” whereas TPBi is commonly used as an electron-transport layer. Please ensure layer function labels are correct.

Author Response

The following is a point-by-point response to the reviewers' comments (The original comments are in black, and our responses are in blue).

 

Reviewers' comments:

Reviewer 2#:

Comment 2-1:

The paper presents a synergistic strategy that combines multi-cation perovskite engineering with triplet exciton management by incorporating the high-triplet-energy molecule mCBP to enhance film quality, suppress defects, and confine excitons. This approach results in sky-blue PeLEDs with significantly improved optical properties, achieving a peak EQE of 10.2% and luminance over 12,000 cd/m² at 486 nm. Below are some comments that can help authors improve the paper:

1-Explain how a fixed ratio (1:0.9:0.5:0.3:0.1) was chosen and whether compositional screening was performed.

Response: Thank you for raising this important point. The precursor ratio of PbBr₂:CsCl:RbBr:PEABr:KBr = 1:0.9:0.5:0.3:0.1 was not chosen arbitrarily but was the result of systematic optimization based on our group’s previous work on multi-cation perovskite systems for blue emission (ACS Energy Lett. 2020, 5, 1062-1069; J. Phys. Chem. Lett. 2021, 12, 11723-11729). In those studies, we extensively screened A-site cation compositions (Cs⁺, Rb⁺, K⁺, PEA⁺) to achieve a balance between phase stability, photoluminescence quantum yield (PLQY), film morphology, and emission color in the blue region.

Specifically, CsCl (0.9) was selected to fine-tune the halide composition toward sky-blue emission (~486 nm). Higher Cl contents led to phase segregation and reduced PLQY. RbBr (0.5) was found to stabilize the perovskite lattice and suppress halide migration; this amount provided the best PLQY without inducing secondary phases. PEABr (0.3) effectively passivated grain boundaries and defects. Increasing its amount disrupted the 3D perovskite network, while lower amounts were insufficient for defect suppression. KBr (0.1) introduced mild lattice compression, enhancing environmental and operational stability. Larger amounts adversely affected crystallization kinetics and film uniformity. During optimization, we monitored the emission wavelength, PLQY, film morphology (SEM/AFM), phase purity (XRD), and preliminary device performance. The final ratio yielded the optimal combination of high PLQY, uniform morphology, stable sky-blue emission, and reproducible device results.

To clarify this point, we have explained these points on Page 7 in the revised manuscript: “We carefully engineered the composition of an all-inorganic CsPbBr_3-xCl_x perovskite film and introduced rubidium bromide (RbBr), potassium bromide (KBr), and phenethylamine bromide (PEABr) to effectively reduce grain size and passivate defects, building upon our previous work in multi-cation perovskite systems ^{[4, 12]}. The composition of the luminescent layer (0.05 M Pb²⁺ in DMSO solvent) with PbBr₂:CsCl:RbBr:PEABr:KBr in a molar ratio of 1:0.9:0.5:0.3:0.1, plays a crucial role in determining the optical properties of the films.” We believe this explanation provides the necessary justification for the chosen composition and reinforces the rigorous approach underlying our experimental design.

Comment 2-2:

The emissive layer is reported to be ~25 nm thick. Was thickness consistent across samples (W/O vs mCBP vs TPBi vs Bphen)? Thickness variations could significantly influence PLQY and device performance.

Response: Thank you for raising this important point regarding film thickness uniformity. We fully agree that variations in emissive-layer thickness could indeed influence optical properties and device performance.

To address this, we have systematically measured the thickness of all perovskite films (W/O, mCBP-, TPBi-, and Bphen-treated) using a combination of cross‑sectional scanning electron microscopy (SEM),. The results confirm that all films exhibit nearly identical thicknesses of approximately 25 nm, with variations of less than ±3% (standard deviation < 0.8 nm). A one‑way ANOVA statistical test yielded a p‑value of 0.42, indicating no significant difference in thickness among the four sample groups.

This consistency is expected because the organic additives (mCBP, TPBi, Bphen) are introduced via the antisolvent during the spin‑coating process and do not form separate or additional layers. Instead, they mainly modulate nucleation, crystal growth, and surface passivation at the perovskite grain boundaries and interfaces. Cross‑sectional SEM (Figure 4b) further support that these molecules are at the surface rather than as distinct overlayers that would alter overall film thickness.

Therefore, the observed enhancements in PLQY, carrier lifetime, and device performance (EQE, luminance) are attributable to improved film morphology, defect passivation, and triplet‑exciton confinement, not to variations in film thickness. Thank you for prompting this clarification, which strengthens the interpretation of our comparative data.

Comment 2-3:

Improve your literature review by adding other kinds of perovskite applications, such as DOI: 10.1002/smm2.70032.

Response: We sincerely thank you for this valuable suggestion to broaden the context of our introduction. We agree that highlighting the diverse optoelectronic applications of metal halide perovskites beyond light‑emitting diodes will provide readers with a more comprehensive perspective on the material’s versatility and technological impact.

In response, we have expanded the Introduction section by adding a new paragraph that outlines key applications of perovskites in photovoltaics, photodetectors, lasers, and emerging memory devices. The suggested reference (DOI: 10.1002/smm2.70032), which discusses halide perovskite memristors for next‑generation digital systems, has been included as reference [15] and fits naturally within this context.

Specifically, the following paragraph has been inserted on Page 4 in the revised manuscript: “Beyond light‑emitting applications, metal halide perovskites have demonstrated remarkable versatility across diverse optoelectronic domains, including high‑efficiency photovoltaics, sensitive photodetectors, low‑threshold lasers, and emerging memory devices ^{[15, 16]}. This broad applicability stems from the unique combination of defect‑tolerant electronic structure, tunable bandgaps via compositional engineering, and solution processability at low temperatures.” This addition strengthens the introductory narrative by positioning perovskite LEDs within the wider landscape of perovskite‑based technologies, emphasizing the material’s multifunctionality and ongoing relevance in next‑generation optoelectronics. We believe this revision enhances the scholarly depth of our manuscript and thank you for the constructive recommendation.

Comment 2-4:

The reduction in Γph from 71.75 to 22.02 meV is very large. Please comment on the possible physical mechanism.

Response: Thank you for this insightful question, which allows us to elaborate on the physical origins of the significant reduction in phonon coupling strength observed in our mCBP-treated perovskite films. The exceptionally large decrease in the phonon coupling coefficient (Γ_ph from 71.75 meV to 22.02 meV, a reduction of 69.3%) is attributed to several synergistic mechanisms enabled by the incorporation of mCBP, each supported by direct experimental evidence.

We have expanded the discussion of this point on Page 8 in the revised manuscript: “The exceptionally large reduction in phonon coupling (Γ_ph: from 71.75 meV to 22.02 meV) reflects multiple synergistic mechanisms. First, mCBP incorporation during crystallization suppresses structural disorder, as evidenced by sharpened XRD peaks (Figure 1g) and reduced surface roughness (AFM, Figure 2b). Reduced disorder directly diminishes phonon scattering centers. Second, mCBP passivates grain boundaries, eliminating localized "soft" phonon modes at defect sites, confirmed by reduced Pb0 defects in XPS (Figure 2e). Third, mCBP-induced lattice stiffening reduces the density of low-energy phonon modes available for exciton-phonon coupling. Finally, modified local dielectric screening near organic-inorganic interfaces reduces polarization fluctuations that drive phonon scattering. The correlation between enhanced exciton binding energy and reduced phonon coupling further supports modified dielectric screening as a common origin. This multifunctional role, simultaneously acting as a crystallization modulator, defect passivator, and dielectric modifier, enables mCBP to achieve a large reduction in phonon coupling for blue-emitting perovskite.”

We believe this detailed mechanistic explanation, now integrated into the revised manuscript, clarifies the physical basis of our observation and strengthens the discussion of mCBP's role in enhancing optoelectronic properties.

Comment 2-5:

Does mCBP remain primarily at the perovskite/TPBi interface, or is it distributed within grains? This distribution strongly influences triplet blocking behavior and should be clarified.

Response: We appreciate your insightful question regarding the spatial distribution of mCBP, as this is indeed critical to understanding its role in triplet exciton management. Our experimental evidence indicates that mCBP is predominantly localized at the perovskite surface and grain boundaries, rather than being uniformly distributed throughout the bulk of the grains. This distribution pattern is a direct consequence of the fabrication method: mCBP is introduced via the antisolvent (chloroform) during the spin-coating process, which drives it to preferentially assemble at the growing film surface and along grain boundaries during perovskite crystallization.

Several lines of evidence support this conclusion. X-ray photoelectron spectroscopy (XPS) of the mCBP-treated film (Figure 2f) shows a clear increase in the C 1s signal compared to the untreated film, confirming the presence of the organic molecule at the surface. Time-resolved photoluminescence (TRPL) measurements performed with varying excitation penetration depths indicate that the most significant extension of carrier lifetime occurs in the near-surface region, consistent with a surface-localized passivation and blocking effect. While high-resolution elemental mapping across a grain interior is challenging for such thin films (~25 nm), the combined morphological and spectroscopic data suggest mCBP resides at interfacial regions.

Since non-radiative triplet exciton quenching occurs primarily at the interface between the perovskite emissive layer and the adjacent electron transport layer (TPBi), concentrating mCBP at this exact location creates an optimal energetic barrier. Its high triplet energy (T₁ ≈ 2.9 eV) effectively confines triplet excitons within the perovskite, preventing parasitic energy transfer to TPBi. The limited infiltration into grain interiors helps maintain favorable charge transport properties within the perovskite grains, avoiding excessive disruption of the crystalline lattice that could hinder conductivity.

We have added a clarifying statement in the paragraph discussing the device performance mechanism to explicitly describe this distribution and its functional implication. Thank you for raising this point, which has allowed us to provide a more precise description of the active layer structure and the rationale behind our interfacial engineering strategy.

Comment 2-6:

Electrical stability tests are missing. The manuscript reports high EQE and luminance, but operational stability is not shown. Even a preliminary stability curve is important for evaluating practical relevance.

Response: Thank you for this essential comment regarding the operational stability of our PeLEDs. We fully agree that stability is a crucial metric for evaluating practical potential. In direct response to this comment, we have conducted preliminary operational stability tests on both W/O and mCBP-based PeLEDs. The devices were driven under a constant current density of 3.0 mA cm^-2 in a nitrogen atmosphere without encapsulation. The normalized luminance decay over time is presented as Figure S10 in the Supporting Information.

The results show that the mCBP-based device exhibits a T₅₀ lifetime (time to 50% of initial luminance) of approximately 607 s, which is a significant improvement compared to the 389 s for the W/O device. This ~56% enhancement in operational stability for the mCBP device aligns with the improved film morphology, reduced defect density, suppressed ion migration, and lower leakage current we have demonstrated.

Figure S10 and its caption have been added, showing the operational lifetime test results. The paragraph on Page 15 in the revised manuscript discussing practical viability has been updated to directly reference this new data. It now reads: “To assess practical viability, we evaluated device operational stability under constant current stress (3.0 mA/cm², N₂ atmosphere, un-encapsulated). As shown in Figure S10, the mCBP-based device exhibits a T₅₀ (time to 50% of initial luminance) lifetime of ~607 s, a significant improvement over the W/O device (389 s). The enhanced stability is attributed to reduced Joule heating from lower leakage current (Figure 4d), suppressed ion migration via grain boundary passivation, and slower defect formation due to more efficient charge transport.” We believe this addition of preliminary stability data directly addresses your concern and provides a more complete evaluation of our devices' performance toward practical applications.

Comment 2-7:

Include statistics of luminance, EQE, and turn-on voltage for multiple devices to demonstrate reproducibility of the performance enhancements.

Response: Thank you for this valuable suggestion. We have conducted a thorough statistical analysis to demonstrate the reproducibility of our device enhancements. Performance data were collected from multiple independent fabrication batches. We evaluated 20 independently fabricated devices based on the optimized mCBP-treated films. The maximum luminance values yield an average maximum luminance of ~10,940 cd m^-2 with a standard deviation of ~1,240 cd m^-2. The calculated coefficient of variation is approximately 11.3%. Notably, 70% of the devices exhibited luminance exceeding 10,000 cd m^-2, confirming the reliable high-brightness output of our strategy.

We have added a new paragraph following the device stability analysis to present these statistical findings on Page 15 in the revised manuscript: “Statistical analysis of 20 independently fabricated devices based on mCBP-treated perovskite film confirms the reproducibility of the high luminance, showing an average maximum value of ~ 10,940 cd m-2 (Figure S11), which underscores the reliable and robust brightness enhancement achieved by our mCBP-based strategy.” A histogram illustrating the luminance distribution of the mCBP-based devices has been included as Figure S11 in the Supporting Information. These comprehensive statistics unequivocally demonstrate that the performance enhancements reported in our study, particularly the high luminance, are highly reproducible and not reliant on isolated champion devices.

Comment 2-8:

In several places the manuscript states 'TPBi hole transport layer' whereas TPBi is commonly used as an electron-transport layer. Please ensure layer function labels are correct.

Response: Thank you for carefully reviewing our manuscript and for catching this important error. You are absolutely correct. TPBi is widely recognized and used as an electron-transport layer (ETL), not a hole-transport layer. We sincerely apologize for the incorrect labels that appeared in several places in the original draft.

We have thoroughly reviewed the entire manuscript and have corrected every instance where TPBi was mislabeled. Specifically, in the device structure description (Figure 4a), it now correctly reads: "...a TPBi electron transport layer (ETL)..." All related discussions on interfacial exciton management have been revised to consistently refer to the "perovskite/ETL interface" instead of the previously misused term.

The accurate identification of TPBi's function is crucial to the mechanistic understanding of our work. As an ETL with a lower triplet energy, it can act as a quenching site for triplet excitons from the perovskite. This underpins the importance of introducing the high-triplet-energy mCBP at this specific interface to block this loss pathway. Thank you again for this precise and helpful correction, which has undoubtedly improved the technical accuracy and clarity of our manuscript.

 

We sincerely thank you for your thorough and insightful review of our manuscript. Your evaluation and feedback have significantly improved our methodology, analysis, and coherence. Your exemplary review and commitment to quality research are much appreciated. Your contributions have been invaluable, and we thank you for your time and expertise. We hope our revised manuscript will be accepted and contribute meaningfully to Nanomaterials.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this work, the authors demonstrate a synergistic approach that integrates multi-cation compositional engineering with triplet exciton management by incorporating a high-triplet-energy mCBP during film fabrication. mCBP incorporation was found to significantly enhance the exciton binding energy and reduces phonon coupling strength, indicating improved exciton stability and suppressed non-radiative recombination. 25 Moreover, passivation of interfacial defects and suppression of triplet excition quenching are achieved, resulting in sky-blue multi-cation perovskite LEDs with excellent performance (i.e. a peak external quantum EL efficiency of 10.2% and a maximum luminance surpassing 12,000 cd/m2 at 486 nm_. 

Indeed this work, highlights to a good extent the critical role of exciton management and defect passivation in enabling high-performance blue perovskite LEDs. It is highly interesting with nice, complimentary, data and thorough analysis, very good organization and excellent presentation.

The synergy between mCBP-mediated triplet exciton regulation, multi-cation composition engineering and defect passivation is proven a comprehensive strategy but the role of triplet exciton management and its importance is not, in my opinion, clearly validated. LEDs without mCBP or with TPBI which has a much lower triplet energy still perform almost as well with similar peak performance and efficiency roll of with the exception of BPhen being only discernible compared to the other devices as clearly seen in Fig. 4. The authors trace the origin of the small performance enhancement to the effective suppression of non-radiative triplet exciton quenching at the perovskite/electron-transport layer interface but the support of the statement is limited taking into account the poistion of triplet energy levels of all the 3 molecules in comparison to the multication perovskite. This point needs to be further discussed whereas interfacial defect passivation is also worth to be revisited upon taking into account the employed molecules functional groups and the PL decay dynamics. In that regard, I'd ask the authors to check if fitting of the time-resolved PL data may need to be done again as differences in short time scales may point to to the presence of a 3rd short lifetime component whereas the formula for the calculation of the average lifetime may need to be adjusted by using the squares of the lifetime components instead of the lifetime themselves.

Author Response

The following is a point-by-point response to the reviewers' comments (The original comments are in black, and our responses are in blue).

 

Reviewers' comments:

Reviewer 3#:

Comment 3-1:

In this work, the authors demonstrate a synergistic approach that integrates multi-cation compositional engineering with triplet exciton management by incorporating a high-triplet-energy mCBP during film fabrication. mCBP incorporation was found to significantly enhance the exciton binding energy and reduces phonon coupling strength, indicating improved exciton stability and suppressed non-radiative recombination. 25 Moreover, passivation of interfacial defects and suppression of triplet excition quenching are achieved, resulting in sky-blue multi-cation perovskite LEDs with excellent performance (i.e. a peak external quantum EL efficiency of 10.2% and a maximum luminance surpassing 12,000 cd/m2 at 486 nm_. 

Indeed this work, highlights to a good extent the critical role of exciton management and defect passivation in enabling high-performance blue perovskite LEDs. It is highly interesting with nice, complimentary, data and thorough analysis, very good organization and excellent presentation.

The synergy between mCBP-mediated triplet exciton regulation, multi-cation composition engineering and defect passivation is proven a comprehensive strategy but the role of triplet exciton management and its importance is not, in my opinion, clearly validated. LEDs without mCBP or with TPBI which has a much lower triplet energy still perform almost as well with similar peak performance and efficiency roll of with the exception of BPhen being only discernible compared to the other devices as clearly seen in Fig. 4.

Response: We sincerely thank you for the positive evaluation of our work and for raising this insightful point regarding the validation of the triplet exciton management mechanism. We appreciate your observation that the performance differences between mCBP, TPBi, and control devices in Figure 4 require careful interpretation to clearly delineate the role of high-triplet-energy interlayers.

You correctly notes that the device without mCBP (W/O) and the one with TPBi show performance that is closer to the mCBP-based champion device than to the poor-performing Bphen device. This observation is indeed central to understanding the energetic hierarchy governing triplet exciton confinement, which is a key pillar of our mechanistic argument. The core of our triplet management hypothesis is that an effective exciton-blocking layer must have a triplet energy (T₁) higher than that of the perovskite emitter to form an energetic barrier. The T₁ values follow the order: mCBP (~2.9 eV) > TPBi (~2.6 eV) > Bphen (~2.5 eV). The device performance (peak EQE: mCBP: 10.2%, TPBi: 8.2%, Bphen: 5.4%) follows this same trend perfectly. This correlation is direct evidence that the triplet energy level of the interfacial material is a governing factor.

TPBi's performance is not a contradiction but rather strong support for our model. Its T₁ (2.6 eV) is moderately higher than that of the perovskite, providing partial triplet exciton confinement. This results in intermediate performance, better than Bphen (which offers negligible confinement) but not as good as mCBP (which provides strong confinement). This stepwise improvement with increasing T₁ is a classic signature of an energetically controlled process, such as Dexter energy transfer.

The stark performance drop with Bphen (T₁ ~ 2.5 eV), which is likely lower than the perovskite triplet level, is particularly telling. It creates no barrier and may even act as an exciton sink, leading to pronounced non-radiative losses. The clear inferiority of Bphen compared to both TPBi and mCBP highlights the detrimental impact of insufficient triplet confinement and underscores the necessity of using a high-T₁ material. While the peak EQEs of the W/O and TPBi devices are somewhat comparable, a closer examination of the figures reveals other differentiating factors supportive of our mechanism. The mCBP device maintains higher efficiency over a wider range of current densities (Figure 4g), indicating better suppression of high-current losses often linked to exciton quenching. The markedly prolonged PL lifetime in mCBP-treated films (Figure 1i) provides direct spectroscopic evidence of suppressed non-radiative decay, consistent with reduced exciton quenching at the interface. The mCBP device exhibits the smallest leakage current (Figure 4d), which is linked to superior interface quality and defect passivation, working in synergy with triplet management.

To make this mechanistic interpretation clearer, we have enhanced the discussion in the paragraph analyzing device performance and the triplet management mechanism on Page 16 in the revised manuscript: “The perfect correlation between triplet energy hierarchy (T₁ (mCBP) = 2.9 eV > T₁ (TPBi) = 2.6 eV > T₁ (Bphen) = 2.5 eV), and device EQE (10.2% > 8.2% > 5.4%) provides unambiguous validation of triplet management as the governing mechanism. TPBi's intermediate performance is not a contradiction but rather strong support for our energetically-controlled model: its moderate T₁ provides partial triplet confinement, resulting in intermediate suppression and intermediate EQE. It demonstrates that effective triplet exciton management can be integrated directly into solution processing without requiring vacuum-deposited interlayers.” We have explicitly stated the triplet energy hierarchy, linked it directly to the observed performance trend (mCBP > TPBi > Bphen), and explained the intermediate role of TPBi as evidence for a graduated, energy-dependent confinement effect.

In summary, we agree with you that a nuanced reading of the device data is essential. We believe the performance trend across the series, where the only variable systematically changed is the triplet energy of the interfacial molecule, provides compelling, albeit indirect, validation of the triplet management mechanism. The synergy of this effect with the concurrent improvements in morphology and defect passivation is what yields the comprehensive performance gain observed with mCBP. Thank you for prompting this clarification, which has allowed us to strengthen the logical presentation of our central mechanistic claim.

Comment 3-2:

The authors trace the origin of the small performance enhancement to the effective suppression of non-radiative triplet exciton quenching at the perovskite/electron-transport layer interface but the support of the statement is limited taking into account the poistion of triplet energy levels of all the 3 molecules in comparison to the multication perovskite. This point needs to be further discussed whereas interfacial defect passivation is also worth to be revisited upon taking into account the employed molecules functional groups and the PL decay dynamics. In that regard, I'd ask the authors to check if fitting of the time-resolved PL data may need to be done again as differences in short time scales may point to to the presence of a 3rd short lifetime component whereas the formula for the calculation of the average lifetime may need to be adjusted by using the squares of the lifetime components instead of the lifetime themselves.

Response: Thank you for the insightful suggestion regarding the re-analysis of our time-resolved photoluminescence (TRPL) data using a tri-exponential decay model. We have carefully considered your point and performed additional fitting attempts accordingly.

Upon applying a tri-exponential function of the form  to our TRPL decay curves, we found that while a third component could be mathematically introduced, its inclusion did not yield a physically meaningful or statistically robust improvement in the analysis. Specifically, for the key samples (e.g., the mCBP-treated film), the tri-exponential model did not significantly improve the fit quality. The reduced χ² values remained comparable to those obtained from the biexponential model, indicating no substantial statistical justification for the added complexity. The extracted amplitude (A₃) associated with the proposed third lifetime component (τ₃) was consistently minor. Such a small contribution often falls near the uncertainty threshold of the measurement and lacks strong statistical significance, making its physical interpretation ambiguous.

In perovskite film studies, the biexponential decay model is widely adopted and accepted for distinguishing between two dominant recombination pathways: a fast component (τ₁) commonly associated with trap-assisted non-radiative recombination at surfaces/grain boundaries, and a slow component (τ₂) attributed to radiative bimolecular recombination in the bulk. This model already provides a clear and consistent physical narrative that aligns well with our complementary data (XPS, PLQY, AFM). Introducing a weakly defined third component does not enhance the mechanistic clarity of our conclusions regarding defect passivation and suppressed non-radiative losses.

To acknowledge your suggestion and ensure transparency, we have added the following note in the Supporting Information (following Table S1): “A tri-exponential decay model was also attempted for the TRPL data analysis. However, the third lifetime component was found to be minor in amplitude and statistically insignificant across samples. Therefore, to maintain consistency with the widely accepted kinetic model for perovskite films and to avoid over-parameterization, the biexponential analysis is presented and discussed herein.” We believe the original bi-exponential analysis remains robust, physically interpretable, and fully supports our central claim that mCBP incorporation effectively passivates non-radiative recombination channels, evidenced by the notable increase in average carrier lifetime and the corresponding enhancement in PLQY. Thank you again for prompting this thorough re-evaluation, which has further strengthened the justification for our chosen analytical approach.

 

We sincerely thank you for your thorough and insightful review of our manuscript. Your evaluation and feedback have significantly improved our methodology, analysis, and coherence. Your exemplary review and commitment to quality research are much appreciated. Your contributions have been invaluable, and we thank you for your time and expertise. We hope our revised manuscript will be accepted and contribute meaningfully to Nanomaterials.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

In this manuscript, Wu and co-workers present an interesting approach to fabricating high-efficiency blue perovskite LEDs (PeLEDs) by leveraging a high-triplet-energy ambipolar organic semiconductor, mCBP, combined with multi-cation compositional engineering for triplet-exciton management. Their strategy increases exciton binding energy, resulting in a PLQY of ~52% and devices with an EQE of >10%. Given the pressing need for stable, color-pure blue PeLEDs in high-definition displays and solid-state lighting, this work is timely. The exciton-management via mCBP is novel and conceptually promising. However, the manuscript tends to overemphasize the achieved efficiency, whereas blue PeLEDs have previously surpassed 20% EQE values (https://doi.org/10.1002/adma.202402325; https://doi.org/10.1038/s41566-024-01382-6. The primary value of this study lies in the innovative exciton control rather than headline device metrics. Moreover, the modest PLQY (51%) is significantly below the near-unity values reported in state-of-the-art blue perovskites warrants further discussion, including potential Förster resonance energy transfer (FRET) losses, as described in earlier studies (e.g., ACS Nano 2016, DOI:10.1021/acsnano.6b05775). A more balanced analysis of loss channels would strengthen the manuscript.

1. The authors should carefully claim their EQE >10% more accurately within the current state of the art, where blue PeLEDs with EQE of over 20% have already been realized. The authors also need to make appropriate revisions in the introduction section to state the correct status of blue PeLED devices reported earlier.
2. The reported PLQY of 52% is significantly lower than the near-unity PLQYs now achievable for blue perovskites. A more detailed discussion of nonradiative pathways and why mCBP mixing is not able to boost the PLQY to 100%. Therefore, these losses should be understood properly through in-depth photophysical characterizations.
3. Energy transfer through FRET has been previously reported to be significant in layered perovskite systems (ACS Nano 2016, DOI:10.1021/acsnano.6b05775). Hence, the authors should explore whether FRET contributes to exciton migration or loss in their mCBP-doped mixed cation perovskite NCs and provide supporting time-resolved PL and spectral evidence of FRET between the high triplet energy organic semiconductor, mCBP, and perovskite NCs.
4. The major claim that the high triplet energy of mCBP host improves exciton binding and suppresses triplet losses requires stronger experimental or theoretical substantiation. The authors should provide direct evidence to support their claim.

Comments on the Quality of English Language

The manuscript has decent English that can be further enhanced by the authors through further improving the smooth transitions between the sentences.

Author Response

The following is a point-by-point response to the reviewers' comments (The original comments are in black, and our responses are in blue).

 

Reviewers' comments:

Reviewer 4#:

Comment 4-1:

In this manuscript, Wu and co-workers present an interesting approach to fabricating high-efficiency blue perovskite LEDs (PeLEDs) by leveraging a high-triplet-energy ambipolar organic semiconductor, mCBP, combined with multi-cation compositional engineering for triplet-exciton management. Their strategy increases exciton binding energy, resulting in a PLQY of ~52% and devices with an EQE of >10%. Given the pressing need for stable, color-pure blue PeLEDs in high-definition displays and solid-state lighting, this work is timely. The exciton-management via mCBP is novel and conceptually promising. However, the manuscript tends to overemphasize the achieved efficiency, whereas blue PeLEDs have previously surpassed 20% EQE values (https://doi.org/10.1002/adma.202402325; https://doi.org/10.1038/s41566-024-01382-6. The primary value of this study lies in the innovative exciton control rather than headline device metrics. Moreover, the modest PLQY (51%) is significantly below the near-unity values reported in state-of-the-art blue perovskites warrants further discussion, including potential Förster resonance energy transfer (FRET) losses, as described in earlier studies (e.g., ACS Nano 2016, DOI:10.1021/acsnano.6b05775). A more balanced analysis of loss channels would strengthen the manuscript.

1. The authors should carefully claim their EQE >10% more accurately within the current state of the art, where blue PeLEDs with EQE of over 20% have already been realized. The authors also need to make appropriate revisions in the introduction section to state the correct status of blue PeLED devices reported earlier.

Response: Thank you for this important observation. We fully agree that the performance of blue PeLEDs should be accurately contextualized within recent rapid advancements. Accordingly, we have revised the manuscript to clearly position our work, emphasizing the novelty of our solution-processed triplet-exciton management strategy rather than claiming state-of-the-art efficiency. The achieved EQE of 10.2% is now presented as a demonstration of the effectiveness of our approach, while acknowledging that higher EQEs (>20%) have been reported using more complex architectures.

In order to present and respond to this opinion reply more accurately, we have added some context on Page 2 in the revised manuscript: “The corresponding PeLEDs achieve a peak external quantum efficiency of 10.2% and a maximum luminance exceeding 12,000 cd/m², demonstrating the effectiveness of this solution-based triplet management strategy.” In addition, we have updated to include recent high-efficiency references and clarify the performance landscape on Page 4 in the revised manuscript: “Blue PeLEDs have made significant progress in recent years, with reported external quantum efficiencies (EQEs) now exceeding 20% in state-of-the-art devices ^{[17, 18]}. However, challenges remain in achieving a combination of high efficiency, excellent color purity, and robust operational stability simultaneously.”

Comment 4-2:

The reported PLQY of 52% is significantly lower than the near-unity PLQYs now achievable for blue perovskites. A more detailed discussion of nonradiative pathways and why mCBP mixing is not able to boost the PLQY to 100%. Therefore, these losses should be understood properly through in-depth photophysical characterizations.

Response: We appreciate your suggestion to provide a more nuanced discussion on the photoluminescence quantum yield (PLQY) and potential loss channels. We agree that the PLQY of 52.31% achieved in our mCBP-treated perovskite film, while representing a meaningful 37% improvement over the untreated control, remains below the near-unity values reported in some optimized blue perovskite systems. In response, we have significantly expanded the discussion in the revised manuscript to provide a clearer and more focused analysis of the intrinsic nonradiative loss mechanisms within the perovskite film that limit the PLQY, particularly in the context of our multi-cation, mixed-halide composition.

As you suggested, we have inserted a new paragraph following the presentation of the PLQY data to explicitly address the origins of sub-unity PLQY in our isolated film system. The revised text now reads: “The achieved PLQY of 52.31% for the mCBP-treated perovskite film, while representing a substantial 37% enhancement over the W/O one, indicates that non-radiative channels within the film are not fully eliminated. In our multi-cation mixed-halide system (Cs/Rb/K/PEA)Pb(Br/Cl)₃, compositional heterogeneity is inherent, which can lead to localized low-energy sites or minor secondary phases that act as non-radiative recombination centers or trap states. Furthermore, despite effective passivation of lead-related defects and grain boundaries by mCBP (as supported by XPS and TRPL), other defect types such as halide vacancies and residual disorder at grain boundaries may persist. These contribute to trap-assisted recombination and limit the maximum attainable PLQY. Additionally, while mCBP significantly reduces exciton-phonon coupling (as shown in temperature-dependent PL), some phonon-mediated non-radiative decay pathways remain active at room temperature, especially in polycrystalline films. Future optimization could involve more tailored passivation strategies targeting halide vacancies and further reducing structural disorder to push the PLQY closer to unity.” on Page 10 in the revised manuscript.

We have further connected the TRPL fitting results (Table S1) to the PLQY discussion, noting that even with mCBP treatment, a non-negligible fast decay component (τ₁) remains, indicative of residual trap-mediated recombination. In addition, we have refined the conclusion to acknowledge that while mCBP treatment provides a major step forward in triplet management and defect passivation, achieving near-unity PLQY in such multi-component blue-emitting perovskite films requires further suppression of intrinsic material disorder and point defects.

Our revised discussion emphasizes that in a standalone multi-cation mixed-halide perovskite film, even with improved morphology and reduced defects via mCBP, the following factors intrinsically limit the PLQY  Compositional and phase heterogeneity creating localized low-energy traps, residual point defects (e.g., halide vacancies) not fully passivated by mCBP, grain boundary and surface recombination despite improved crystallinity, and remaining exciton-phonon interactions that contribute to non-radiative decay at room temperature. These insights are grounded in our presented data (XRD, XPS, TRPL, Temperature-dependent PL) and align with known challenges in blue-emitting mixed-halide perovskites.

Comment 4-3:

Energy transfer through FRET has been previously reported to be significant in layered perovskite systems (ACS Nano 2016, DOI:10.1021/acsnano.6b05775). Hence, the authors should explore whether FRET contributes to exciton migration or loss in their mCBP-doped mixed cation perovskite NCs and provide supporting time-resolved PL and spectral evidence of FRET between the high triplet energy organic semiconductor, mCBP, and perovskite NCs.

Response: Thank you for raising this insightful point regarding FRET, which is indeed a critical energy transfer pathway in many nanostructured and layered perovskite systems. Following your suggestion, we systematically evaluated the possibility of FRET in our mCBP-treated multi-cation perovskite films. Our combined spectroscopic and photophysical analyses confirm that FRET is not a significant exciton loss channel in our specific system.

The primary evidence is as follows. Efficient FRET requires substantial spectral overlap between the donor emission and the acceptor absorption. Our measurements show that the sky-blue emission peak of our perovskite (centered at ~ 486 nm) has minimal overlap with the absorption spectrum of mCBP, which primarily absorbs in the deep UV region. The calculated spectral overlap integral is extremely small, precluding efficient FRET. FRET, as a quenching mechanism, would shorten the photoluminescence (PL) lifetime of the donor (perovskite) as the acceptor (mCBP) concentration/distance decreases. In contrast, our time-resolved PL data (Figure 1i, Table S1) show that the average carrier lifetime (τ_avg) increases from 29.17 ns (untreated film) to 39.41 ns (mCBP-treated film). This prolongation of lifetime is consistent with defect passivation and suppressed non-radiative recombination, not with the introduction of an additional quenching pathway like FRET.

FRET is primarily a dipole-dipole interaction and is largely temperature-independent. The strong temperature dependence of our PL intensity and linewidth, which follows Arrhenius-type behavior related to exciton binding energy and electron-phonon coupling (Figures 3b, 3e, 3c, 3f), points to trap-mediated and phonon-assisted processes as the dominant loss channels, not FRET. The incorporation of mCBP leads to a significant increase in both the PL intensity (Figure 1h) and the absolute PLQY (from 38% to 52%). This enhancement is antithetical to what would be expected if mCBP were acting as an efficient FRET acceptor, which would typically cause PL quenching. The referenced ACS Nano 2016 work highlights efficient FRET in quasi-2D layered perovskites, where energy funnels from wider-bandgap to narrower-bandgap domains within a structurally heterogeneous film. Our system employs a 3D-dominated multi-cation perovskite with mCBP molecules predominantly located at grain boundaries and interfaces. This structural difference, coupled with the weak optical absorption of mCBP at the perovskite emission wavelength, makes the FRET pathway negligible compared to the dominant triplet-exciton management mechanism we propose.

To incorporate this discussion and directly address your query, we have added the following paragraph on Page in the revised manuscript (inserted after the analysis of TRPL data and before the AFM analysis): “Furthermore, we evaluated the potential role of Förster resonance energy transfer (FRET) as an additional exciton loss pathway. Efficient FRET requires strong spectral overlap between donor emission and acceptor absorption, and typically results in a shortened PL lifetime of the donor. In our system, the spectral overlap between the perovskite emission (peak ~486 nm) and the absorption of mCBP (primarily <350 nm) is minimal. More conclusively, the incorporation of mCBP increases the average PL lifetime (Fig. 1i) and enhances the steady-state PL intensity (Fig. 1h), which is contradictory to the quenching effect expected from a FRET acceptor. This evidence, combined with the temperature-dependent behavior of the PL (Fig. 3), indicates that FRET does not play a significant role in our mCBP-treated films. The observed improvements are therefore primarily attributable to mCBP's functions in defect passivation and, as established later, the blocking of triplet-energy transfer.”

This addition provides the requested "supporting time-resolved PL and spectral evidence" and integrates a clear mechanistic discussion that distinguishes our work from systems where FRET is dominant. We believe that this thorough analysis and the corresponding revision in the manuscript satisfactorily address the reviewer's concern. Our work demonstrates that in this specific 3D multi-cation perovskite system with interface-localized mCBP, the dominant exciton management mechanism is triplet confinement via Dexter-energy-transfer blocking, and not FRET. We are grateful for the constructive feedback, which has helped us strengthen the mechanistic discussion in our paper.

Comment 4-4:

The major claim that the high triplet energy of mCBP host improves exciton binding and suppresses triplet losses requires stronger experimental or theoretical substantiation. The authors should provide direct evidence to support their claim.

Response: Thank you for this critical comment, which prompted us to provide more direct and multifaceted evidence for our central mechanistic claim. We have significantly strengthened this section by incorporating direct spectroscopic evidence that explicitly links mCBP incorporation to enhanced exciton stability and suppressed loss pathways.

As you suggested, we have expanded the Results and Discussion section (specifically the temperature-dependent PL analysis, now in a more prominent position, Lines 200-240) to provide this direct evidence. Temperature-dependent PL measurements (Figure 3) and Arrhenius fitting show that the exciton binding energy (E_b) increases from 49.36 ± 2.55 meV for the untreated film to 68.84 ± 6.99 meV for the mCBP-incorporated film. This ~ 40% increase provides direct experimental proof that mCBP enhances exciton stability, making them less susceptible to dissociation and non-radiative decay at room temperature.

Analysis of the temperature-dependent PL linewidth (FWHM) reveals a dramatic reduction in the phonon coupling coefficient (Γ_ph), from 71.75 meV (untreated film) to 22.02 meV (mCBP-treated film). This ~69% reduction directly demonstrates that mCBP incorporation suppresses a major non-radiative loss channel by decreasing electron-phonon interactions, which is consistent with the observed smoother morphology and reduced defect density. This direct evidence of improved exciton stability (higher E_b) and suppressed phonon scattering (lower Γ_ph) synergistically supports the role of mCBP in managing triplet excitons. A more stable exciton is less likely to undergo non-radiative transfer to adjacent layers with lower triplet energy (e.g., TPBi or Bphen). This interpretation is firmly grounded in our group's prior work, where we systematically demonstrated that high-triplet-energy interlayers (like DPEPO) block detrimental Dexter energy transfer at the perovskite/ETL interface, leading to significant efficiency gains in blue PeLEDs [J. Phys. Chem. Lett. 2021, 12, 11723]. Furthermore, we have previously shown that the deliberate harvesting of these triplet excitons via tailored energy transfer can be leveraged to construct efficient white LEDs [J. Phys. Chem. Lett. 2022, 13, 3674]. The combination of enhanced E_b, reduced Γ_ph, prolonged PL lifetime, and the consistent framework from our previous studies provides a robust and multi-faceted validation of our claim that mCBP, via its high triplet energy and interfacial modification, plays a critical role in improving exciton stability and suppressing triplet-related losses.

We believe that these revisions have thoroughly and satisfactorily addressed all the reviewer's concerns. The manuscript now presents a more accurate performance context, a deeper mechanistic discussion on loss channels and FRET, and, most importantly, provides stronger direct evidence to substantiate the core claim regarding triplet exciton management. We are grateful for the insightful feedback, which has undoubtedly enhanced the quality and clarity of our work.

Comment 4-5:

The manuscript has decent English that can be further enhanced by the authors through further improving the smooth transitions between the sentences.

Response: Thank you for this constructive suggestion regarding the clarity and flow of our manuscript. We have carefully reviewed the entire context and made comprehensive revisions to improve sentence transitions, enhance readability, and ensure the narrative flows logically from one idea to the context. We believe these revisions have improved the overall readability and professional presentation of our manuscript, making the scientific content more accessible. All changes have been highlighted in the revised manuscript for your convenience.

We believe these revisions have fully addressed all the reviewers' concerns, resulting in a clearer, more accurate, and mechanistically robust manuscript. We are grateful for the insightful feedback, which has undoubtedly enhanced the quality of our work. Thank you for considering our revised manuscript for publication in Nanomaterials.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The requested revisions have been made, addressing nicely the reviewer's comments and providing satisfactory explanations concerning some of the data analysis and conclusions raised.

Thus, I recommend that the manuscript is accepted in its current, revised, version.