High-quality perovskite crystal for efficient and bright pure-blue light-emitting diodes with narrow emission

Domain: biology
Published: 2026-04-01
Editorial outcome: major_revision

Abstract
Metal halide perovskite light-emitting diodes have exhibited great potential for the next-generation
displays. However, the realization of highly efficient and bright pure-blue devices with narrow
emission bandwidth remains a significant challenge. Herein, we propose a controllable crystal
facet growth to diminish random crystal facet-correlated defects and reveal the underlying
mechanism of energy-driven facet-selective crystal growth. This strategy enables high-quality
pure-blue emitters with high crystallinity, low defects, and large exciton binding energy.
Consequently, we achieve highly performing pure-blue devices with a narrow emission bandwidth
of 14 nm, an external quantum efficiency of 14.0% at 1,699 cd m-2, and an impressive peak
brightness of 8,334 cd m-2 at an emission of 473 nm. We verify a good applicability of the strategy
in achieving high-performance sky-blue devices with a narrow emission of 15 nm, a high
efficiency of 23.8%, and a large luminance of 13,230 cd m-2 at 488 nm.

Introduction
Metal halide perovskite light-emitting diodes (PeLEDs) have garnered substantial attention in
next-generation display technologies due to their featured characteristics, including narrow
emission, high luminance, wide color gamut, and low-cost solution-processable fabrication.1-6
Remarkable progress has been made in green, red, and near-infrared PeLEDs,2,7-10 with their
external quantum efficiencies (EQE) comparable to those of quantum dot light-emitting diodes
(QLEDs) and organic light-emitting diodes (OLEDs).11-13 Regrettably, blue PeLEDs, especially
pure-blue devices (<475 nm), merely present moderate performance,14-17 remaining inferior to that
of their green and red counterparts. More critically, broad emission bandwidths exceeding 25 nm
are frequently reported in current blue PeLEDs.14,18-20 These issues restrict the practical application
of PeLEDs in displays.

The popular blue-emissive perovskites consist of CsPbBr Cl colloidal nanocrystals,21,22 quasi-
x 3-x
two-dimensional (quasi-2D) perovskites,14,18,23-25 and three-dimensional (3D) bromide-chloride
mixed perovskites26-29. In the low-dimensional perovskite systems of colloidal nanocrystals and
quasi-2D perovskites, there is a concern of the poor charge transport in the perovskites due to the
presence of massive insulating ligands and/or large organic cations. Meanwhile, the wide phase
distribution in quasi-2D perovskites is extensively observed to induce broad emissions for the
PeLEDs.30-32 Instead, the 3D perovskites with high charge mobility, relatively fixed component,
and high Auger recombination threshold are promising candidates for achieving efficient, bright,
and narrowband blue PeLEDs.26,27 However, pure-blue emissive 3D perovskites usually suffer
from severe halide heterogeneity and high defect density during perovskite film preparation, which
prohibits further improvements in device performance. Encouragingly, the halide heterogeneity in
mixed bromide-chloride perovskites has been well addressed with the effective strategies, such as
vapor-assisted crystallization (VAC) treatment27 and cationic surfactant additives33.

Nevertheless, the performance of the pure-blue PeLEDs is still hindered by the presence of massive
defects (e.g., halogen vacancy defect). To minimize the defect density of 3D perovskites, organic
halide salts have been extensively employed to saturate the vacancy defects by post-treatment of
the crystallized perovskites34,35. Very recently, an all-site alloy method has been reported to
facilitate sequential A-site doping growth for high-quality formamidinium and cesium hybrid
perovskite with less trap density26. However, the fundamentally disordered crystal growth with
random facets during perovskite crystallization has not yet been solved. While the crystal facet has
been demonstrated to strongly correlate with the generation of trap states36. For example, Tao et
al. exhibited that the perovskite (111) facet has the highest defect density, whereas the perovskite
(100) facet has the least defects37. Similarly, Etheridge et al. showed the significantly enhanced
device performance by diminishing the (111) facet defects of perovskites38. Meanwhile, the (100)
facet was reported to have an excellent optical property with efficient carrier radiative
recombination39. As shown above, the crystal facet-correlated defects in the perovskites result in a
strong dependence of the device performance on the crystal facets. Therefore, the manipulation of
perovskite growth with desired crystal facets is essential to achieve high-quality perovskites and
thus high-performance devices.

In this work, we propose an effective approach of bis(3-aminopropyl)polyethylene glycol
(BAPEG)-assisted perovskite crystal oriented growth with preferred (100) and (200) crystal facets.
We reveal the mechanism of this facet-selective crystal growth by clarifying the energy-driven
selective adsorption of BAPEG on specific perovskite facets. The desired crystal facets promote
high-quality pure-blue perovskites by reducing more than 78% of the density of trap states.
Meanwhile, we also demonstrate a large enhancement in exciton binding energy for BAPEG-based
perovskites. Consequently, we report highly performing pure-blue PeLEDs with a narrow emission
bandwidth of merely 14 nm, a remarkable external quantum efficiency (EQE) of 14.0% at 1,699
cd m-2, and an impressive brightness of 8,334 cd m-2 among the best-performing pure-blue PeLEDs
based on 3D perovskites. Moreover, the devices exhibit an excellent lifetime of 45.7 min at 100 cd
m-2 and a consistent EL peak during operation and lifetime tests. In addition, our strategy is
applicable for high-performance sky-blue devices, where a narrow emission of 15 nm, a
remarkable efficiency of 23.8%, and a large luminance of 13,230 cd m-2 have been achieved. The
results manifest an effective approach for achieving efficient and bright pure-blue PeLEDs.
Particularly, the peak EQE is achieved at high brightness, which breaks through the extensively
reported high efficiency at low brightness, suggesting a great potential for practical applications.

Results
Controllable crystal growth strategy. The control pure-blue (Cs/Rb/FA)Pb(Cl/Br) perovskites
with a regular three-dimensional structure were fabricated by spin-coating the perovskite
precursors dissolved in dimethyl sulfoxide (DMSO), followed by a typical vapor-assisted
crystallization treatment for improved compositional homogeneity.27 After that, the perovskites
were annealed at 80 °C for 10 min to promote the crystal growth and remove the residual solvent.
For the target perovskites, the Bis(3-aminopropyl)polyethylene glycol (BAPEG) was employed to
treat the wet perovskites by spin-coating BAPEG solution (dissolved in chlorobenzene) before the
annealing process. Details are shown in the experimental section. As shown in the scanning
electron microscopy (SEM) images (Fig. 1a, b, Supplementary Fig. 1), distinct variations of the
film morphology are observed between the control and target perovskites. The control perovskites
have a typical island-like morphology with random crystal facets, as verified by X-ray diffraction
(XRD) measurements (Fig. 1c), where the characteristic diffraction peaks of (100), (110), (111),
and (200) facets are clearly observed. Differently, the target perovskites exhibit single crystal-like
morphology with regular crystal grains and dominant facets (Fig. 1b). While no variation of the
perovskite morphology after chlorobenzene treatment verifies the important role of BAPEG in
modulating the perovskite growth (Supplementary Fig. 2). The diffraction signals of (110) and
(111) planes are significantly weakened in the target perovskites, being accompanied by the
appearance of the sharp and strong diffraction peaks of (100) and (200) planes with nearly 5.5-fold
higher peak intensity than the control ones (Fig. 1c), which indicates the dominant (100) and (200)
facets in the target perovskites with high crystal quality. Sequentially, the crystal facet orientations
of the control and target perovskites were further detected by grazing-incidence wide-angle X-ray
scattering (GIWAXS) measurement (Supplementary Fig. 3). The control perovskites exhibit a
weak diffraction ring at q = 1.1 Å−1, indicating the random orientations of (100) facet thus the
randomly oriented perovskite crystals (Fig. 1d).40 Conversely, the stronger discrete pattern of (100)
facet along q axis was observed for the target perovskites, showing the enhanced crystallinity with
preferential parallel lattice plane to the substrate (Fig. 1e).

To investigate the underlying mechanism of the distinct variation in crystal facet for the target
perovskites, theoretical simulations based on density functional theory (DFT) calculations were
performed to estimate the adsorption energy (E ) of BAPEG on different perovskite facets. The
ads
molecular structure of BAPEG is shown in Fig. 1f, which consists of the functional groups of ether
bond (C−O) and terminated amino (−NH ) with an average molecular weight (Mn) of ~ 1,500. The
2
degree of polymerization (n) of BAPEG was selected as one to simplify the calculation. The
electrostatic forces between the functional groups of BAPEG and the lead-halide complex of the
perovskites, including coordination and hydrogen bonding interactions, induce the spontaneous
adsorption of BAPEG on the (100), (110), and (111) facets of the perovskites, as verified by the
differential charge density images (Supplementary Fig. 4). The calculated adsorption energies for
BAPEG on the (100), (110), and (111) facets are −0.518, −0.707, and −0.763 eV, respectively (Fig.
1g). The larger E on the (110) and (111) facets than that on (100) facet indicates the
ads
thermodynamically favorable adsorption of BAPEG on the (110) and (111) facets. The large
adsorption energy of BAPEG on (110) and (111) facets derives from the strong coordination
interaction between BAPEG and the perovskites. Since the (110) and (111) facets have smaller
halogen vacancy formation energy than that for (100) facet (Fig. 1h, Supplementary Fig. 5), this
suggests the easier formation of halogen vacancy on (110) and (111) facets. The resultant halogen
vacancy provides massive uncoordinated Pb sites for the favorable adsorption of BAPEG.
Meanwhile, there are rich Pb atoms exposed on the (110) and (111) facets of the perovskites41, as
clearly shown in their top views (Fig. 1i), which further favors the adsorption of BAPEG. The
steric hindrance effect from the long chain of the BAPEG would inhibit the diffusion of the
perovskite precursor ions to the (110) and (111) crystal facets, thus diminishing the crystal growth
of these facets (Supplementary Fig. 6). As a result, more precursor ions easily diffuse and attach
to the (100) crystal facet, thereby promoting the crystal growth along such facet. Encouragingly,
the large defect formation energy for the (100) facet (Fig. 1h) would contribute to a great reduction
of the trap state density for the target perovskites, as discussed later. Consequently, the remarkable
variation in film morphology, dramatic improvement in the perovskite crystallinity, and distinctive
orientation in crystal growth contribute to the uniqueness and effectiveness of our approach to
conventional additive-assisted modulation of perovskite crystallization and film formation. We
also reveal a different crystal growth mechanism of energy-driven facet-selective crystal growth
from the latent heat-induced cool interfacial layer-assisted crystal growth42 by accurately
modulating certain facet growth processes. The morphological changes from irregular and island-
like control perovskites to regular and single crystal-like high-quality target perovskites contribute
to good crystal stability (Supplementary Fig.7), as well as high device performance shown in the
following part.

Photocarrier recombination dynamics. The time-resolved emission spectra (TRES) were first
performed to probe the photocarrier relaxation process in the perovskites. As shown in Fig. 2a, b,
both the control and target perovskites exhibit the strongest emission and longest lifetime at a
centered wavelength of around 473 nm, indicating a dominant band-to-band radiative
recombination within the perovskites43. While the target perovskites show a much longer lifetime
decay process than that of control perovskites (Fig. 2b), this benefits from the suppressed trap
states. We further extracted the time-resolved photoluminescence (TRPL) decay process of the
perovskites to directly present the photocarrier recombination dynamics (Fig. 2c) and fitted the
decay curves by a bi-exponential function. The fast and slow decay components of τ and τ relate
1 2
to the trap-assisted non-radiative recombination and radiative recombination, respectively.44 The
τ and τ values of 0.94 and 8.66 ns for target perovskites are much longer than 0.62 and 5.10 ns
1 2
of control perovskites (Supplementary Table 1). The prolonged lifetime for target perovskites has
been further verified by the TRPL spectra under different excitation intensities (Supplementary
Fig. 8), where the target perovskites show much longer lifetimes than that of control perovskites
at the same excitation power. These results suggest the efficient suppression of trap states for more
radiative recombination in the target perovskites.

The ultrafast transient absorption (TA) spectroscopy was further carried out to reveal the
photogenerated carrier recombination dynamics in the control and target perovskites. The TA
spectra of the perovskites at different timescales are recorded in Fig. 2d, e. Both the control and
target perovskites show a distinctive photobleaching (PB) peak located at around 470 nm, which
is attributed to the ground-state bleaching signal, being consistent with their steady-state
absorption spectra (Supplementary Fig. 9). It is observed that the PB peaks gradually decrease
with prolonging the decay time, indicating the photogenerated carrier recombination process. To
clearly clarify the carrier recombination process, time traces of the PB peaks are extracted in Fig.
2f. The decay curve of the target perovskites exhibits a slower decay rate than that of the control
perovskites. Accordingly, the fitting analysis reveals significantly prolonged decay components
for the target perovskites (Supplementary Table 2), indicating a lower defect density for enhanced
radiative recombination, which is well consistent with the TRPL results. Moreover, the trap state
densities of the perovskites are quantized by the space charge-limited current measurements
(Supplementary Fig. 10), where the trap-filled limit voltage (V ) is proportional to the density of
TFL
trap states (N). The calculated N for the target perovskites is 9.79 × 1016 cm−3, which is reduced
t t
by more than 78% from 4.50 × 1017 cm−3 of the control perovskites.

Besides, the strong carrier radiative recombination for the target perovskites was further verified
by the temperature-dependent PL measurements (Fig. 2g, h). We monitored the perovskite PL
spectra from 80 K to 300 K, and exhibited a declined PL intensity by elevating the temperature,
deriving from the increased electron-phonon interaction and lattice expansion at high
temperatures45. We show more radiative recombination within the target perovskites than control
perovskites by observing a stronger PL peak intensity at the same temperature. We further
extracted the exciton binding energy (E ) of the perovskites from the fitting curves (Fig. 2i) based
b
on the equation of I =I /(1+A exp(−E /(k T)), where I , A, and k represent the integrated PL
T 0 b B 0 E B
intensity at 0 K, a coefficient, and Boltzmann constant, respectively.46 The obtained E for the
b
target perovskites is 55.2 meV, which is larger than 40.7 meV for the control perovskites, thus
favoring the inhibition of exciton dissociation and leading to more radiative recombination.
Consistently, we observe an over 2-fold higher photoluminescence quantum yields (PLQY) from
18.6% to of 41.5% for the target perovskites under different excitation intensities (Supplementary
Fig. 11). The increased E of the target perovskites can be ascribed to the enhanced dielectric
b
confinement by the adsorption of BAPEG on the perovskite surface (Supplementary Fig. 10c).
Consequently, we have exhibited strong radiative recombination of the photocarriers in the target
perovskites, benefiting from the large reduction in trap state density and the significant increase in
exciton binding energy, thereby promoting high emission efficiency in the devices, as will be
discussed later.

Interaction with the perovskites. We further demonstrated a strong interaction between BAPEG
and the perovskites (mainly the lead-halide complex). To directly show the interaction between
BAPEG and the lead-halide complex, the Raman spectra were first performed on BAPEG and
BAPEG-treated Pb(Br/Cl) powder (BAPEG-Pb(Br/Cl) ). As shown in Fig. 3a, a distinct Raman
2 2
peak located at 143.4 cm-1, being attributed to the characteristic signal of Pb−O bond47, is observed
for BAPEG-Pb(Br/Cl) . This signal is absent in the Raman spectra of either BAPEG or Pb(Br/Cl) ,
2 2
indicating an interaction between O in BAPEG and Pb2+ in Pb(Br/Cl) . To further confirm the
2
interaction between BAPEG and the perovskite, X-ray photoelectron spectroscopy (XPS)
measurements were carried out. The Pb 4f signals of the control perovskites in Fig. 3b exhibit two
characteristic peaks centered at 142.5 (Pb 4f ) and 137.6 eV (Pb 4f ), which shift to lower
5/2 7/2
binding energies of 142.3 and 137.4 eV for the target perovskites. The low binding energy indicates
the reduced oxidation state of lead due to the interaction between BAPEG and the perovskite.
We further show the interaction between C−O and the perovskites by the observation of an obvious
shift in the O 1s signal (Fig. 3c). The characteristic O 1s peak located at 532.6 eV in BAPEG shifts
to a higher binding energy of 532.9 eV for the target perovskites, suggesting a declined electron
cloud density of oxygen due to the electron donation to lead ions in the perovskites. Meanwhile,
the Br 3d signals of the perovskites can be deconvoluted into two peaks at 68.0 and 67.0 eV (Fig.
3d), which correspond to the Br 3d and 3d signals. The characteristic peaks shift to higher
3/2 5/2
binding energies of 68.2 and 67.2 eV for the target perovskites, respectively. Similarly, the Cl 2p
signals are also observed with the characteristic peaks shifting to high binding energies after
BAPEG treatment (Fig. 3e), indicating the hydrogen bonding interaction between the halide ions
and BAPEG. The formed hydrogen bond is clarified with Fourier transform infrared spectroscopy
(FT-IR) (Fig. 3f). A distinct shift of the N−H stretching vibration peak from 3,425 cm−1 to 3,451
cm−1 is observed for BAPEG-Pb(Br/Cl) , showing a hydrogen bonding interaction between N−H
2
and the halide ions.48 Besides, a large chemical shift of -NH
2
signal in 1H nuclear magnetic
resonance (1H NMR) for BAPEG-Pb(Br/Cl) also demonstrates the hydrogen bonding interaction
2
(Supplementary Fig. 12). Meanwhile, the FT-IR spectroscopy exhibits an interaction between C–
O and the lead-halide complex by presenting the shift of C–O stretching vibration peak from 1,115
cm−1 to 1,121 cm−1 for BAPEG-Pb(Br/Cl) . In addition, the deformation of the electron
2
distributions in charge density differences due to charge transfer (Supplementary Fig. 4) verifies
the interaction between BAPEG and the perovskites. Consequently, we have demonstrated the
strong interaction between BAPEG and the perovskites, which promotes the adsorption of BAPEG
for the effective regulation of the crystal facet growth.

Device structure and performance. The excellent optoelectronic properties of the target
perovskites encourage us to evaluate their electroluminescence (EL) performances. The pure-blue
PeLEDs were fabricated with a configuration of indium tin oxide (ITO)/ NiO / poly(9-
x
vinylcarbazole) (PVK)/ perovskite emitter/ 1,3,5-benzinetriyl-tris(1-phenyl-1-H-benzimidazole)
(TPBi)/LiF/Al (Fig. 4a). The thicknesses of NiO /PVK transport layer, perovskite, TPBi, and
x
LiF/Al cathode are ~ 20, 47, 38, and 92 nm, respectively, as estimated from the cross-sectional
transmission electron microscopy (TEM) image (Supplementary Fig. 13). The energy levels of the
target perovskite films were determined by ultraviolet photoelectron spectroscopy (UPS,
Supplementary Fig. 14). The flat energy bands between the highest occupied molecular orbital
(HOMO) of PVK and valence band of the target perovskites promote an efficient hole
transportation. The target PeLEDs show an emission peak located at 473 nm with reduced full
width at half-maximum (fwhm) from 17 (control devices) to 14 nm (Fig. 4b, Supplementary Fig.
15), revealing a considerably narrow emission bandwidth among the state-of-the-art pure-blue
PeLEDs reported so far (Supplementary Table 3). The narrow pure-blue emission enables a good
color purity for the devices with a Commission Internationale de L’Eclairage (CIE) chromaticity
coordinates at (0.119, 0.082).

The current density−luminance−voltage (J−L−V) curves of control and target perovskite-based
devices are shown in Fig. 4c, where the target PeLEDs show a slightly lower current density than
that of the control devices before the electroluminescence turn-on, indicating the suppressed
leakage current49. This observation is probably due to the isolation of PVK and TPBi transport
layers by the BAPEG blocking layer. While the significant increase in current density for the target
device can be attributed to the improved carrier mobility (Supplementary Fig. 10). Meanwhile, a
very low turn-on voltage of 2.4 V is achieved for the target PeLEDs. More importantly, the target
PeLEDs exhibit a large brightness of 8,334 cd m-2 and a peak efficiency of 14.0% (Fig. 4d, e)
among the best-performing 3D perovskite-based pure-blue PeLEDs26-29,33,50-53 (Fig. 4f,
Supplementary Table 4). Notably, the high efficiency of 14.0% is achieved at a high brightness of
1,699 cd m-2, which breaks the conventional pattern of the peak efficiency generally obtained at
low brightness for blue PeLEDs, indicating promising candidates for the practical application in
displays. As a comparison, the control devices exhibit a moderate performance with a brightness
of 5,273 cd m-2 and a peak efficiency of 6.7%, which are comparable to those of the pristine devices
reported previously26,28,34. The average efficiency extracted from 20 devices for the target PeLEDs
is 11.8% (Fig. 4g), which is much higher than 5.7% of the control devices. Besides, we also
demonstrate a good applicability of our strategy in achieving high-performance sky-blue PeLEDs
with a very narrow emission bandwidth of 15 nm among the state-of-the-art sky-blue devices
(Supplementary Table 5). Meanwhile, great enhancements in efficiency and luminance from 16.7%
and 11,926 cd m-2 to 23.8% and 13,230 cd m-2 are achieved for the sky-blue devices
(Supplementary Fig. 16). Particularly, the devices show a remarkably high efficiency of 11.5% at
the peak luminance of 13,230 cd m-2 and 15.4% at a luminance of ~10,000 cd m-2, which is largely
higher than previously reported ones with efficiencies lower than 10% at peak luminance and/or a
luminance of 10,000 cd m-2. Furthermore, we demonstrate excellent operational and spectral
stability for the target PeLEDs. The lifetime (T , defined as the elapsed time of PeLEDs decaying
50
to 50% of the initial luminance (L )) of the target PeLEDs is 45.7 min at an initial luminance of
0
100 cd m-2 (Fig. 4h, Supplementary Fig. 17), which is over 6-fold longer than 7.2 min of the control
devices. Moreover, the EL peak position and the CIE y coordinate of the target PeLEDs remains
constant during the lifetime test (Fig. 4i, Supplementary Fig. 18), benefiting from the significantly
enlarged ion migration activation energy of the target perovskites (Supplementary Fig. 19).
Besides, we also exhibit constant EL peak under various bias voltages for the target PeLEDs
(Supplementary Fig. 20), verifying the excellent spectral stability during operation. Consequently,
we achieve highly performing pure-blue PeLEDs with a considerably narrow emission bandwidth
of merely 14 nm among the state-of-the-art pure-blue PeLEDs. The remarkable efficiency and
brightness, as well as the excellent operational and spectral stability, enable our devices to be the
best-performing pure-blue 3D perovskite-based devices.

Methods
Materials and chemicals. Cesium bromide (CsBr, 99.999%), lead bromide (PbBr , 99.999%),
2
lead chloride (PbCl , 99.999%), and rubidium bromide (RbBr, 99.99%) were purchased from Alfa
2
Aesar. Formamidinium bromide (FABr, 99.99%) was purchased from Greatcell Solar Materials.
Poly(9-vinylcarbazole) (PVK), 1,3,5-benzinetriyl-tris(1-phenyl-1-H-benzimidazole) (TPBi), and
LiF (99.99%) were purchased from Luminescence Technology Corp. Bis (3-aminopropyl)
polyethylene glycol (BAPEG), 4,7,10-trioxa-1,13-tridecanediamine (TTDDA), anhydrous
dimethyl sulfoxide (DMSO), and N, N-dimethylformamide (DMF) were purchased from Sigma-
Aldrich.

Preparation of perovskite films. The pure-blue perovskite precursor solution was prepared by
dissolving CsBr, RbBr, FABr, PbBr , PbCl , and TTDDA at a molar ratio of 1.1: 0.2: 0.2: 0.275:
2 2
0.725: 0.1 in DMSO, where the concentration of Pb cation was 0.13 M. The above precursors with
a ratio of 1.1: 0.2: 0.2: 0.44: 0.56: 0.1 was prepared for the sky-blue perovskites. The precursor
solution was stirred in a nitrogen-filled glovebox at 80 °C for 12 h, and then filtered through the
polytetrafluoroethylene syringe (0.2 μm) before use. The perovskite films were prepared by spin-
coating the precursor at 3,000 rpm for 60 s, followed by a vapor-assisted crystallization (VAC)
treatment for 1.5 min (i.e., the wet films were placed into a petri-dish (diameter: 60 mm) with 30
μL of DMF dropped before the sample placement). Then, the samples were annealed at 80 °C for
10 min to complete the control perovskite fabrication. For the target perovskite preparation, the
BAPEG solution (0.125 mg mL-1 in chlorobenzene) was spin-coated on the VAC-treated films at
3,000 rpm for 60 s, followed by an annealing process at 80 °C for 10 min.

Fabrication of devices. The indium tin oxide (ITO) substrates were successively washed with
deionized water, ethanol, and isopropanol. Then the substrates were dried with nitrogen and treated
with UV-ozone for 15 min. The NiO solution with a concentration of 20 mg mL-1 was spin-coated
x
on ITO substrates at 2000 rpm for 60 s, followed by an annealing process at 120 °C for 10 min to
obtain dense NiO films. Then the PVK solution (4 mg mL-1 in chlorobenzene) was spin-coated
x
on NiO at 3,000 rpm for 60 s and then annealed at 140 °C for 30 min. Then, the polyvinyl
x
pyrrolidone (PVP) solution (1 mg mL−1 in isopropanol) was spin-coated at 4,000 rpm and annealed
at 120 °C for 10 min to improve the wettability of the perovskite precursor on PVK. After the
substrate cooled down, the perovskite films were prepared by spin-coating the perovskite precursor
solution. Finally, the functional layers of TPBi, LiF, and Al electrode were sequentially evaporated
on the perovskite films to complete the device fabrication process.

Perovskite film and device characterization. The morphology of control and target perovskites
were detected by using the scanning electron microscope (Zeiss 1550). The XPS and UPS
measurements were carried out with a Thermo Fisher Escalab 250Xi instrument equipped with a
monochromatic Al K𝛼 radiation and an unfiltered He I (21.22 eVS) gas-discharge lamp. The XRD
patterns were obtained using an X-ray diffractometer of Bruker D8 Advance (Cu Kα radiation, λ
= 1.54 Å). The FTIR spectra were collected by using a FTIR spectroscopy (Thermo Scientific,
Nicolet iS10) in the range of 4,000 to 400 cm−1. Raman spectra were obtained through a micro-
Raman spectrometer (Horiba XploRA PLUS). The fluence-dependent PLQYs were detected using
an integrating sphere system equipped with an Edinburgh FLS1000 and a 405 nm CW laser. The
HAADF cross-sectional TEM samples were prepared using a dual-beam FIB system (Helios
Nanolab 600i, FEI) and the elemental mapping were captured on a Cs-corrected FEI Titan G2
TEM at 300 kV equipped with an integrated windowless Super-EDX system. GIWAXS
measurements were performed with a Xeuss 2.0 SAXS/WAXS laboratory beamline using a Cu X-
ray source and a Pilatus3R 300K detector. The device performances were recorded by an Ocean
Optics system equipped with a source meter (Keithley 2400), a spectrometer (QE Pro), and an
integrating sphere (FOIS-1). The lifetime of the devices was measured in a nitrogen-filled glove
box with the Ocean Optics system, which was calibrated with a radiometric calibration light source
(HL-3plus-CAL) before use. The devices were driven by a Keithley 2400 source meter, where a
constant current was applied to the devices lying on the top of the integrating sphere. The
brightness variation versus operation time was traced and recorded by a QE Pro spectrometer.

Transient spectroscopy. TRES spectra were acquired using an Edinburgh FLS 1000 fluorescence
spectrophotometer equipped with a picosecond pulse laser (365 nm) with a pulse width of 50 ps.
TA spectroscopy was obtained by using an ExciPro XL Femtosecond Transient Absorption Pump-
Probe Spectrometer (CDP systems). The samples were pumped with a femtosecond laser pulse
(365 nm), which was generated from an optical parametric amplifier. The probe pulses ranging
from 380 to 800 nm were derived from the fundamental 800 nm laser pulses with a small portion
(≈5 μJ) of a 2 mm thick CaF plate.
2

Calculations. The adsorption energy calculations based on density functional theory were
implemented with the Vienna Ab initio Simulation Package (VASP). The generalized gradient
approximation proposed by Perdew-Burke-Ernzerhof (PBE) was selected for the exchange-
correlation potential. The cut-off energy of 480 eV for plane wave was set. The structures were
relaxed until the residual forces on the atoms declined to less than 0.05 eV Å-1 and a vacuum
spacing of 20 Å was applied perpendicular to the slab to avoid interlaminar interactions.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, Chen et al. report Bis(3-aminopropyl)polyethylene glycol (BAPEG)–assisted crystal facet regulation to achieve efficient and bright pure-blue perovskite light-emitting diodes. The authors claim that the selective adsorption of BAPEG leads to preferential (100) and (200) crystal growth, reduced defect density, enhanced exciton binding energy, and consequently narrowband blue emission with high efficiency and stability.\nHowever, compared with the previous work (Nat. Commun. 12, 361, 2021, Adv. Mater. 2021, 33, 2007169), this work appears to lack substantial novelty. The authors mainly reduced the vapour treatment time, which in turn lowered the performance of the control devices. The subsequent improvement achieved by introducing a surface treatment with BAPEG seems to passivate surface and bulk defects rather than demonstrating a fundamentally new mechanism or concept. Also, there are several inconsistencies and logical issues in the manuscript, making it not suitable for publication , the detailed concerns are given below:\n1.There is too much overlap between this work and the previous work from Feng Gao’s group (Nat. Commun. 12, 361, 2021). Both works incorporated Rb+ and used vapour treatment to improve the performance of blue PeLEDs, and the perovskite compositions and device fabrication details are nearly identical. In the previous work, Feng et al. attributed the performance improvement to the vapor treatment, they also observe a more preferential crystal orientation along the (100) and (200) direction and enhancement of crystallinity with VAC-treatment. However, in this manuscript, the authors attribute it to the selective adsorption of BAPEG leads to preferential (100) and (200) crystal growth.\n2.The reported EQE of 14% in this work is significantly lower than that of the best-reported pure blue perovskite LEDs (>20%), such as Sci. Adv. 2024, 10, eado5645; Adv. Mater. 2025, 37(42), e20131; ACS Energy Lett. 2025, 10, 3638; and Nat. Commun. 2024, 15, 10621. Even the highlighted maximum brightness of 8,334 cd m⁻² is not particularly competitive compared with previous reports, for instance 8,136 cd m⁻² (ACS Energy Lett. 2023, 8, 2897-2903) and 29,800 cd m⁻² (ACS Nano 2025, 19, 16850–16858). Overall, both the EQE and brightness achieved in this work are not superior to the state-of-the-art results.\n3.The key claims regarding “defect suppression” lack convincing experimental evidence. The estimated trap-state density differs by less than one order of magnitude in Supplementary Fig. 6 (4.34 × 1017 ~ 1.79 × 1017 cm−3), which does not convincingly support the page 8, lines 209 “the great reduction in trap state density” as claimed.\n4.The authors believe that the PL lifetime is prolonged, suggesting a reduced trap-assisted non-radiative recombination. However, there is no clear difference in table S1 (3~7ns for the averaged lifetime). Also, the authors claim that the extracted decay lifetimes imply reduced defect density in target sample since the PL lifetime reflects the trap-assisted carrier recombination rates. However, carrier recombination rates depend on the inject carrier densities, the PL lifetime comparison between different samples should have been made at constant excitation density, and thus, dependence on laser fluence should be shown. If this is not the case, the inconsistency needs to be discovered critically to understand the photophysics mechanism.\n5.It is a big claim that there is no EL shift during the lifetime measurements. The authors should provide the evolution of the CIE y coordinate as a function of time under a constant current condition. This measurement is essential to evaluate the EL stability of the device during lifetime measurement.\n6.If the authors believe that the exciton binding energies are high, they should also measure the fluence-dependent photoluminescence quantum yield (PLQY) to evaluate the exciton recombination dynamics.\n7.As shown in Fig. 1a and b, the control and target films exhibit markedly different morphologies. The target film displays smaller grain sizes and a higher density of voids. Such morphological differences may strongly influence the PLQY and PL lifetimes through surface-related effects. A discussion on how these morphological changes correlate with crystal and device stability would be valuable.\n8.The authors attribute the observed shift of the Pb 4f binding energy to the coordination between oxygen atoms and Pb²⁺. However, this interpretation requires more rigorous justification. In XPS, a shift in the Pb 4f peak position can also arise from other possible interactions, such as coordination between amino groups (–NH₂) and Pb²⁺, or surface dipole effects. The authors should provide additional supporting evidence.\n9.The authors attribute the positive shift of Br 3d and Cl 2p binding energies to hydrogen bonding interactions between halide ions and the N–H groups of BAPEG. However, this interpretation seems not convincing. A shift in binding energy alone cannot unambiguously confirm hydrogen bonding, as it can also originate from other factors such as changes in the local chemical environment, lattice contraction, compositional variation, or ionic incorporation. Additional evidence, such as FTIR, NMR, or DFT calculations, would be necessary to substantiate the claim of hydrogen bonding interactions.\n10.It seems that the PL peak positions of the control and target samples appear inconsistent in Supplementary Fig. 5, with the control sample showing a redshifted PL emission, while in Supplementary Fig. 9 the EL peak positions of both samples are identical. Please provide a reasonable explanation.\n11.Although the authors report improved device performance after BAPEG modification, it is unclear why the efficiency of their reference device is significantly lower than that reported in previous works (Nat. Commun. 12, 361, 2021) using same compositions and processing conditions. Notably, previous studies have achieved efficiencies of ~6% at 467 nm, and 11% at 477 nm, whereas the present device shows comparable efficiency (~6%) even at 473 nm. The authors are encouraged to clarify this discrepancy and discuss possible causes.\nSome minor technical concerns:\n1.The cross-sectional SEM image presented in Supplementary Fig. 7 lacks sufficient clarity, making it difficult to clearly resolve the device architecture.\n2.Regarding the NIOX/PVK/Perovskite/TPBi/LiF/Al structure mentioned in this manuscript, please provide a reasonable explanation of how an identical perovskite precursor compared with previous related literature can be uniformly formed on the hydrophobic PVK layer surface without any modification.\n3.Please provide references for all the data points in Figure 4g. The author should provide a thorough, up-to-date overview of recent advancements in pure-blue perovskite LEDs.", "reviewer_2": "In this work, the authors propose an interesting and novel approach to achieve facet-selective crystal growth and further reveal the underlying mechanism of energy-driven selective adsorption of BAPEG to specific perovskite facets. The resultant high-quality crystals enable fantastic pure-blue PeLEDs with an extremely narrow emission bandwidth of 14 nm at an emission of 473 nm, a remarkable efficiency of 14.0% at 1699 cd m-2, a high brightness of 8334 cd m-2, and excellent operational and spectral stability. These encouraging results support its publication in this journal after a couple of minor corrections.\n1. The comparisons in emission bandwidth with the reported pure-blue PeLEDs should be further discussed to highlight the considerably narrow emission achieved in this work.\n2. The high-quality perovskites may benefit the suppression of the ion migration process, which is considered as one of the important parameters to determine the device stability. The ion migration activation energy of the perovskites should be compared.\n3. The target perovskites display an increased exciton binding energy (i.e., 55.2 meV vs. 40.7 meV), which benefits the inhibition of exciton dissociation for more radiative recombination. The reason for this enhancement needs to be clarified.\n4. The perovskite emission layer shows a discontinuous crystal distribution on the substrates. Is there any leakage current in the devices by considering the probable direct contact between the electron and hole transport layers?\n5. Illustrations of the perovskite crystal facet orientations are suggested to be included in Fig. 1 to visually show the orientation variations.", "reviewer_3": "The manuscript presents a new strategy for preparing high-quality perovskite crystals by the manipulation of crystal facet growth. The mechanism of the facet-selective crystal growth has been partially clarified with both theoretical and experimental results. Moreover, pure-blue device performances with a narrow emission and high efficiency and stability have been demonstrated. Therefore, this manuscript might be considered for future publication after addressing all the following concerns.\n1. Given the remarkable efficiency advances in pure-blue nanocrystals and quasi-2D PeLEDs, the manuscript should more clearly highlight the distinct advantages of 3D perovskites. Specifically, the issue of poor charge transport should be addressed with comparative mobility data, and the link between narrow emission spectra and 3D perovskites requires stronger justification, particularly compared with nanocrystal systems.\n2. The morphological differences between control and target perovskite in Figures 1a and 1b are notable. While the facet-growth mechanism is proposed, it remains unclear whether the grain corner change stems from enhanced (111) facet growth or an alternative mechanism. A discussion of how adjacent facets interact and form corners during grain formation would be helpful.\n3. The schematic illustration in Figure 1g looks a little weird. It looks as if the BAPEG molecules are randomly placed on the (1 1 0) and (1 1 1) surface without significant orientation and binding to perovskite surface. Are there any more reasonable absorption configurations? The author might need to check the electron density changes of BAPEG molecules to perovskite surface absorption and find out the exact interactions.\n4. The adopted molecule of bis(3-aminopropyl)polyethylene glycol was dissolved in chlorobenzene. The potential impact of this solvent on perovskite morphology should be evaluated, with comparisons to alternative polar and non-polar solvents.\n5. It is noted that the BAPEG treatment is applied to the perovskite films before the annealing. Is there any difference in the perovskite morphology of the BAPEG treatment after the annealing process?\n6. The carrier mobility of the target perovskite films should be measured to verify the high-quality perovskite crystals after BAPEG treatment.\n7. The energy levels of the target perovskite films are shown in the manuscript, while corresponding data for the control films should be included for comprehensive comparison.\n8. The operational stability tests in Figure 4h should include concurrent voltage changes to better correlate performance decay with electrical behavior.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Point-by-point response to reviewers\nWe have revised our manuscript carefully based on the reviewers’ comments. Follows\nare our replies (R) to reviewers’ comments (C):\nResponses to the 1st reviewer's comments\nReviewer #1: In this manuscript, Chen et al. report Bis(3-aminopropyl)polyethylene glycol\n(BAPEG)–assisted crystal facet regulation to achieve efficient and bright pure-blue perovskite\nlight-emitting diodes. The authors claim that the selective adsorption of BAPEG leads to\npreferential (100) and (200) crystal growth, reduced defect density, enhanced exciton binding\nenergy, and consequently narrowband blue emission with high efficiency and stability.\nHowever, compared with the previous work (Nat. Commun. 12, 361, 2021, Adv. Mater. 2021,\n33, 2007169), this work appears to lack substantial novelty. The authors mainly reduced the\nvapour treatment time, which in turn lowered the performance of the control devices. The\nsubsequent improvement achieved by introducing a surface treatment with BAPEG seems to\npassivate surface and bulk defects rather than demonstrating a fundamentally new mechanism\nor concept. Also, there are several inconsistencies and logical issues in the manuscript, making\nit not suitable for publication, the detailed concerns are given below:.\nR: Thank the reviewer for the concerns, and sorry for the misunderstanding. In our\nwork, we propose a novel approach of bis(3-aminopropyl)polyethylene glycol\n(BAPEG)-mediated perovskite crystal oriented growth with preferred (100) and (200)\ncrystal facets. This crystal growth regulation strategy solves the crucial issue of random\ncrystal facet-correlated defects of the 3D perovskites and yields high-quality pure-blue\nemitters. We further reveal the new mechanism of this facet-selective crystal growth by\nclarifying the energy-driven selective adsorption of BAPEG on specific perovskite\nfacets to thoroughly understand the crystal facet evolution.\nThe previous work in Nat. Commun. 12, 361 (2021) mainly addresses the halide\nheterogeneity in mixed bromide-chloride perovskites by vapor-assisted crystallization\n(VAC) treatment. However, the enhancements in crystal orientation and crystallinity\nwith VAC-treatment were limited, where the authors said “slight enhancement of\ncrystallinity with VAC-treatment” (on page 2 of the work Nat. Commun. 12, 361,\n(2021), shown in Fig. R1 below). Meanwhile, the limitation in crystal orientation and\ncrystallinity with VAC-treatment was further verified by extensively reported works,\nsuch as Nat. Commun. 16, 3254 (2025); Matter 7, 1054 (2024); Small Methods 8,\n2300572 (2024); Adv. Mater. 37, 2414788 (2024), details shown in our following reply\nto the comment (C1). Differently, our work reports the precise modulation of 3D blue\nperovskites for regular and single crystal-like morphology with high crystallinity\n(shown in Fig. 1 below), which is rarely reported in previous works, stressing the\nuniqueness of our work for high-quality 3D blue perovskites.\nFig. R1 a) The words on page 2 of the work Nat. Commun. 12, 361, (2021), and the\ncorresponding b) GIWAXS and c) XRD measurements.\nFig. 1 a, b) SEM images and c) XRD measurements of control and BAPEG-treated\n(target) perovskites.\nIn the work of Adv. Mater. 33, 2007169 (2021), the authors focus on the defect\npassivation of quasi-2D perovskite (PEA PbBr (CsPbBr ) ) by the additive of\n2 4 3 4\nethoxylated trimethylolpropane triacrylate, which did not involve the crystal growth\nregulation. Differently, our work aims to solve the crucial issue of random crystal facet-\ncorrelated defects of the 3D perovskites by proposing the novel approach of BAPEG-\nassisted perovskite crystal growth. We reveal the new mechanism of energy-driven\nselective adsorption of BAPEG for oriented crystal facet growth to thoroughly\nunderstand the crystal facet evolution. Both the strategy and mechanism are very\ninstructive to the field in precisely modulating the crystal facet.\nBased on the high-quality pure-blue emitters, we achieve highly performing pure-blue\nPeLEDs with the narrowest emission bandwidth of merely 14 nm among the state-of-\nthe-art pure-blue PeLEDs (Fig. R2a and Supplementary Table 3 of the revised\nSupplementary Information), along with a remarkable efficiency of 14.0% at 1699 cd\nm-2 and an impressive peak brightness of 8334 cd m-2 at an emission of 473 nm. The\ndevice performance is greatly higher than the very recently published results of 668 cd\nm-2 and 11.9% for the pure-blue PeLEDs in Nat. Commun. 16, 3254 (2025),\nrepresenting the brightest and most efficient pure-blue PeLEDs among the 3D\nperovskite-based pure-blue devices (Fig. R2b and Supplementary Table 4 of the\nrevised Supplementary Information).\nFig. R2 Comparisons of pure-blue PeLEDs: a) device emission bandwidth between our\nwork and previous devices, and b) device efficiency and brightness of the 3D\nperovskite-based pure-blue devices. Detailed comparisons are listed in Supplementary\nTable 3. Refs: [1] Nat. Commun. 16, 3254 (2025); [2] ACS Photonics 11, 5380 (2024);\n[3] Adv. Opt. Mater. 13, 2500544 (2025); [4] J. Phys. Chem. Lett. 15, 12435 (2024); [5]\nAdv. Mater. 37, 2414788 (2025); [6] Nat. Commun. 12, 361 (2021); [7] Adv. Mater. 35,\n2207111 (2023); [8] Nano Energy 79, 105486 (2021); [9] Research 2020, 9017871\n(2020).\nMore importantly, in the revised manuscript, we have verified the good applicability of\nour strategy in achieving high-performance sky-blue PeLEDs with the narrowest\nemission bandwidth of 15 nm among the state-of-the-art sky-blue PeLEDs (Fig. R3a\nand Supplementary Table 5 of the revised Supplementary Information). Meanwhile,\nthe sky-blue PeLEDs exhibit a high efficiency of 23.8% and a large luminance of 13230\ncd m-2 at 488 nm. Particularly, the devices show a remarkably high efficiency of 11.5%\nat the peak luminance of 13230 cd m-2 and 15.4% at a luminance of ~10000 cd m-2,\nwhich is largely higher than previously reported ones with efficiencies lower than 10%\nat peak luminance and/or a luminance of 10000 cd m-2, shown in Fig. R3b and\nSupplementary Table 5), overcoming the typical efficiency-brightness trade-off. This\nsuggests a great potential of our approach for practical display applications.\nFig. R3 Comparisons of sky-blue PeLEDs: a) device emission bandwidth between our\nwork and previous devices and b) device efficiency at peak luminance and/or at 10000\ncd m-2 for the sky-blue devices. Detailed comparisons are listed in Supplementary Table\n5. Refs: [1] Adv. Mater. 37, 2506970 (2025); [2] ACS Nano 19, 16850 (2025); [3] Adv.\nMater. 37, 2409718 (2025); [4] Nat Commun 16, 9590 (2025); [5] Nature 612, 679\n(2022); [6] ACS Nano 18, 6513 (2024); [7] Angew. Chem. Int. Ed. 64, 202419746\n(2025); [8] Nat. Commun. 15, 10621 (2024); [9] Adv. Optical Mater. 11, 202528 (2023);\n[10] ACS Energy Lett. 10, 1183 (2025); [11] Adv. Optical Mater. 13, 500544 (2025).\nConsequently, we propose a novel and unique crystal growth regulation strategy to\nachieve regular crystal orientation with single crystal-like morphology. This strategy\neffectively diminishes random crystal facet-correlated defects for high-quality pure-\nblue emitters. We further reveal a new mechanism of energy-driven selective\nadsorption of BAPEG for oriented crystal facet growth to thoroughly understand the\ncrystal facet evolution. Furthermore, we demonstrate good applicability of our strategy\nin achieving high-performance pure-blue and sky-blue PeLEDs with the narrowest\nemission bandwidth among the state-of-the-art blue PeLEDs. Therefore, we strongly\nbelieve that the work makes a solid contribution to the blue PeLED community and\nthus is very suitable for publication in Nature Communications.\nC1: There is too much overlap between this work and the previous work from Feng Gao’s\ngroup (Nat. Commun. 12, 361, 2021). Both works incorporated Rb+ and used vapour treatment\nto improve the performance of blue PeLEDs, and the perovskite compositions and device\nfabrication details are nearly identical. In the previous work, Feng et al. attributed the\nperformance improvement to the vapor treatment, they also observe a more preferential crystal\norientation along the (100) and (200) direction and enhancement of crystallinity with VAC-\ntreatment. However, in this manuscript, the authors attribute it to the selective adsorption of\nBAPEG leads to preferential (100) and (200) crystal growth.\nR: Sorry for the confusion. The previous work (Nat. Commun. 12, 361, (2021)) served\nas an important work to inspire the fabrication of blue PeLEDs. They demonstrated that\nthe halide heterogeneity in mixed bromide-chloride perovskites can be well addressed\nby vapor-assisted crystallization (VAC) treatment (shown in Fig. R4a below). Based\non this inspiring strategy, excellent works have been done to promote rapid\ndevelopment for the 3D perovskite-based blue PeLEDs, such as Nat. Commun. 16, 3254\n(2025); Matter 7, 1054 (2024); Adv. Mater. 37, 2414788 (2024); Small Methods 8,\n2300572 (2024); Small Struct. 4, 2200393 (2023); Nano Energy 97, 107181 (2022), etc.\nHowever, the enhancements in crystal orientation and crystallinity with VAC-treatment\nwere limited. The diffraction rings of (200) and (110) facets for VAC-treated\nperovskites were observed (Fig. R4c, d), showing the existing randomly oriented\nperovskite crystals, as verified by the irregular morphology (Fig. R4b). Meanwhile, the\ncomparable peak intensity after VAC-treatment suggests the limited enhancement of\ncrystallinity (Fig. R4d, e). Therefore, the authors in Nat. Commun. 12, 361, (2021)\nmerely said “slight enhancement of crystallinity with VAC-treatment” (on page 2 of\nthe work Nat. Commun. 12, 361, (2021) shown in Fig. R1 above). In addition, the\nlimited crystallinity and crystal orientation of the 3D blue perovskites with VAC\ntreatment were also verified by the extensively reported works shown in Fig. R5 below\n(e.g., Nat. Commun. 16, 3254 (2025); Matter 7, 1054 (2024); Small Methods 8, 2300572\n(2024); Adv. Mater. 37, 2414788 (2024)), where all irregular perovskite crystal\nmorphologies and moderate crystallinity were clearly presented.\nFig. R4 The previous work in Nat. Commun. 12, 361, (2021): a) the vapor-assisted\ncrystallization (VAC) treatment, b) the SEM image and c) GIWAXS pattern for VAC-\ntreated perovskites, d) the plot extracted by integrating over all angles in GIWAXS,\nand e) XRD patterns of the control and VAC-treated perovskites.\n[FIGURE REDACTED]\nFig. R5 The 3D blue perovskites with VAC treatment in the works of a) Nat. Commun.\n16, 3254 (2025), b) Matter 7, 1054 (2024), c) Small Methods 8, 2300572 (2024), and\nd) Adv. Mater. 37, 2414788 (2024). All the fabricated perovskites exhibit irregular\ncrystal morphologies and moderate crystallinity.\nVery differently, our work reports the precise modulation of 3D blue perovskites for\nregular and single crystal-like morphology with high crystallinity (shown in Fig. 1\nbelow) by proposing a novel approach of BAPEG-assisted perovskite crystal-oriented\ngrowth. This strategy is rarely reported in previous works. Moreover, we reveal the new\nmechanism of the high facet-selective crystal growth by clarifying the energy-driven\nselective adsorption of BAPEG on specific perovskite facets to thoroughly understand\nthe crystal facet evolution. In all, our work concentrates on the crystal facet regulation\nand the underlying mechanism of crystal facet evolution to solve the crucial issue of\nrandom crystal facet growth and the correlated defects of the 3D perovskites, which is\ndifferent from previous works, contributing to a very instructive strategy to precisely\nmodulate the crystal facet for high-quality 3D pure-blue perovskites in the field.\nFig. 1 a, b) SEM images and c) XRD measurements of control and BAPEG-treated\n(target) perovskites.\nC2: The reported EQE of 14% in this work is significantly lower than that of the best-reported\npure blue perovskite LEDs (>20%), such as Sci. Adv. 2024, 10, eado5645; Adv. Mater. 2025,\n37(42), e20131; ACS Energy Lett. 2025, 10, 3638; and Nat. Commun. 2024, 15, 10621. Even\nthe highlighted maximum brightness of 8,334 cd m⁻² is not particularly competitive compared\nwith previous reports, for instance 8,136 cd m⁻² (ACS Energy Lett. 2023, 8, 2897-2903) and\n29,800 cd m⁻² (ACS Nano 2025, 19, 16850–16858). Overall, both the EQE and brightness\nachieved in this work are not superior to the state-of-the-art results.\nR: Thanks for the concern. The references mentioned above involve blue PeLEDs based\non perovskite quantum dots (QDs) (Sci. Adv. 10, eado5645 (2024); Adv. Mater. 37(42),\ne20131 (2025)), quasi-2D perovskites (ACS Energy Lett. 10, 3638 (2025); Nat.\nCommun. 15, 10621 (2024)), and 3D perovskites (ACS Energy Lett. 8, 2897−2903\n(2023); ACS Nano 19, 16850−16858 (2025)). We have performed the device\nperformance comparison with the state-of-the-art blue PeLEDs (shown in Table R1\nbelow), where our pure-blue devices exhibit the narrowest emission bandwidth of\nmerely 14 nm among all the mentioned works with typical broad emission bandwidths\nfrom 17 to 25 nm. Besides, we also show the narrowest emission bandwidth of 14 nm\namong the pure-blue PeLEDs (Table R2 below)\nMoreover, we have further verified the good applicability of our strategy in achieving\nhigh-performance sky-blue PeLEDs with the narrowest emission bandwidth of 15 nm\namong the state-of-the-art sky-blue PeLEDs (shown in Supplementary Fig. 16 and\nSupplementary Table 5 below). Meanwhile, the sky-blue PeLEDs exhibit a high\nefficiency of 23.8% and a large luminance of 13230 cd m-2 at 488 nm among the best-\nperforming sky-blue devices. In particular, the devices show a remarkably high\nefficiency of 11.5% at the peak luminance of 13230 cd m-2 and 15.4% at a luminance\nof ~10000 cd m-2, which is largely higher than the previously reported ones with\nefficiencies lower than 10% at peak luminance and/or a luminance of10000 cd m-2\n(Supplementary Table 5 below), overcoming the typical efficiency-brightness trade-\noff.\nFor the device efficiency and brightness, we achieve a breakthrough in 3D perovskite-\nbased pure-blue PeLEDs. The device performance with a large brightness of 8334 cd\nm-2 and a peak efficiency of 14.0% is greatly higher than the very recently published\nresult of 668 cd m-2 and 11.9% in Nat. Commun. 16, 3254 (2025), representing the\nbrightest and most efficient pure-blue PeLEDs among the 3D perovskite-based pure-\nblue PeLEDs (shown in Supplementary Table 4 below). In addition, we report the\npeak efficiency at a high brightness of 1699 cd cm-2, which is greatly higher than 5 cd\ncm-2 (Sci. Adv. 10, eado5645 (2024)), ~ 10 cd cm-2 (Nat. Commun. 15, 10621 (2024)),\n~ 100 cd cm-2 (ACS Energy Lett. 10, 3638 (2025), ACS Nano 19, 16850−16858 (2025)),\nand 400 cd cm-2 (ACS Energy Lett. 8, 2897−2903 (2023)) in the mentioned works\n(Table R1), and is comparable to ~2000 cd cm-2 in Adv. Mater. 37, e20131 (2025).\nConsequently, we demonstrate an effective and applicable strategy for high-\nperformance blue PeLEDs with the narrowest emission bandwidth among the state-of-\nthe-art pure-blue and sky-blue PeLEDs. We report the brightest and most efficient pure-\nblue PeLEDs among the 3D perovskite-based pure-blue PeLEDs. Furthermore, our blue\ndevices overcome the typical efficiency-brightness trade-off, where a considerably\nhigher brightness at the peak efficiency than most of the reported ones is achieved.\nIn particular, the sky-blue PeLEDs show a remarkably high efficiency of 11.5% at the\npeak luminance of 13230 cd m-2 and 15.4% at a luminance of ~10000 cd m-2, which is\nlargely higher than the previously reported ones with efficiencies lower than 10% at\npeak luminance and/or a luminance of 10000 cd m-2, suggesting a great potential for\npractical applications.\nTable R1Comparison of the EL performance of the reviewer-mentioned works.\nEL L\npeak\nEQE L FWHM\nmax\nType Perovskites peak (cd Published journals\nEQE\n(%) (cd m-2) (nm)\n(nm) m-2)\nSci. Adv.\nQDs CsPb(Cl/Br) 470 21.3 5 635 17 10, eado5645\n3\n(2024)\nAdv. Mater. 37,\nQDs CsPbBr 469 20.3 ~2000 31407 25\n3 e20131 (2025)\nACS Energy Lett.\nQuasi-2D (Cs/PEA)Pb(Cl/Br) 468 17.4 ~100 2346 22\n3\n10, 3638 (2025)\n(Cs/FA/p- Nat. Commun.\nQuasi-2D 478 20.9 ~10 200 ~22\nPEA/K)Pb(Cl/Br) 15, 10621 (2024).\n3D (Cs/Rb/FA)Pb(Cl/Br) 478 10.3 400 8136 18\n3\n8, 2897 (2023)\nACS Nano 19,\n3D (Cs/Rb/FA)Pb(Cl/Br) 478 10.0 100 29800 18\n3\n16850 (2025)\n3D (Cs/Rb/FA)Pb(Cl/Br) 473 14.0 1699 8334 14 Our work\nEL peak FWHM\nType Perovskite Published journal\n(nm) (nm)\nCsPbBr 469 21 ACS Energy Lett. 8, 731 (2023)\nAngew. Chem. Int. Ed. 63,\nQDs CsPb(Cl/Br)3 467 ~20\ne202408726 (2024)\nCsPb(Cl/Br)3 470 ~17 Sci. Adv. 10, eado5645 (2024)\nCsPbBr 469 25 Adv. Mater. 37, e20131 (2025)\n3\n(Cs/pFPEA)Pb(Br/Cl) 468 ~21 Adv. Mater. 35, 2302161 (2023)\n3\n(Cs/pFPEA)/PPN)Pb(Cl/Br) 474 ~21 Nat. Photonics 18, 425 (2024).\n3\n(Cs/FA/pFPEA)Pb(Cl/Br) 468 ~22 Nat Commun. 15, 10621 (2024).\n3\n(Cs/pFPEA)Pb(Br/Cl) 469 22 Adv. Mater. 37, 2412041 (2024)\nQuasi-2D 3\n(Cs/PEA)Pb(Cl/Br)3 468 22 ACS Energy Lett. 10, 3638 (2025).\nPPA/PEA/Li-CsPb(Br/Cl) 467 23 Adv. Mater. 37, 2409718 (2025)\n(Cs/pFPEA)Pb(Br/Cl)3 468 ~27\ne202513617 (2025)\n(Cs/Rb/FA)Pb(Cl/Br) 467 18 Nat Commun. 12, 361 (2021).\n3\n3D CsPb(Cl/Br) 468 15 Adv. Mater. 35, 2207111 (2023)\n3\n(Cs/Rb/FA)Pb(Cl/Br) 473 17 ACS Photonics 11, 5380 (2024)\n3\n(Cs/Rb/FA)Pb(Cl/Br)3 466 ~16 Adv. Mater. 26, 2414788 (2024)\nAdv. Optical Mater. 13, 2500544\n(Cs/Rb/FA)Pb(Cl/Br)3 466 ~19\n(2025)\n(FA/Cs/Rb)(Pb/Sr)(Br/Cl)3 468 ~17 Nat Commun. 16, 3254 (2025)\n(Cs/Rb/FA)Pb(Cl/Br) 473 14 Our work\ncurrent density (EQE-J), and c) EL spectra for control and target sky-blue PeLEDs at\n488 nm. The target devices show great enhancements in efficiency and luminance from\n16.7% and 11926 cd m-2 (control) to 23.8% and 13230 cd m-2, as well as a reduced\nemission bandwidth from 19 nm (control) to 15 nm for the target devices.\nSupplementary Table 5 Comparison of the EL performance of sky-blue (475 − 490\nnm) PeLEDs\nL peak EQE peak\nEL\nEQE EQE luminance L max FWHM Published\nType Perovskites peak\n(%) (cd m- (%) (cd m-2) (nm) journals\n(nm)\n2)\nNature 612, 679\nCsPbBr3 480 13.8 ~30 ~5 2751 21\n(2022)\nAdv. Mater. 36,\nCsPb(Br/Cl)3 490 23.5 / / 2843 /\n2402325 (2024)\nQDs\nSci. Adv. 10,\nCsPb(Br/Cl)3 480 26.4 ~5 / 1601 17\neado5645 (2024)\nACS Nano 19,\nCsPbBr3 480 23.5 ~1 / 1030 21\n42455 (2025)\nACS Nano 18,\nQuasi-\n(Cs/pFPEA)Pb(Cl/Br)3 485 16.3 / ~4 5740 ~25\n6513 (2024)\n2D Nat. Commun.\n(Cs/pFPEA)Pb(Cl/Br)3 488 23.6 <10 ~2 831 ~22\n15, 10621 (2024).\nAngew. Chem.\n(Cs/PEA)Pb(Cl/Br)3 490 22.88 ~15 ~3 2011 ~25 Int. Ed. 64,\n202419746 (2025)\nAdv. Mater. 37,\n(Cs/PEA/PPA)Pb(Cl/Br)3 485 24.03 113 ~7 3472 23\n2409718 (2025)\nAdv. Mater. 37,\n(Cs/PEA)PbBr3 485 26.2 ~200 ~8 4506 ~20\n2506970 (2025)\nNat Commun 16,\nPEACsxEA1-xPbBr3 489 22.5 ~20 ~6 ~1000 20.8\n9590 (2025)\nACS Energy Lett.\n(Cs/PEA)PbBr3 485 22.66 ~60 ~1 2357 ~22\n10, 1183 (2025)\nAdv. Optical\n(Cs/Rb/FA)Pb(Cl/Br)3 486 6.3 ~15 ~1.5 1926 18 Mater. 11, 202528\n(2023)\nACS Energy Lett.\n(Cs/Rb/FA)Pb(Cl/Br)3 487 13.6 ~1000 / 18748 18\n8, 2897 (2023)\nAdv. Mater. 26,\n(Cs/Rb/FA)Pb(Cl/Br)3 482 19.28 / / 1457 /\n2414788 (2024)\nAdv. Optical\n3D (Cs/Rb/FA)Pb(Cl/Br)3 483 16.2 20 ~1 ~3000 / Mater. 13, 500544\n(2025)\n8% at 10000 ACS Nano 19,\n(Cs/Rb/FA)Pb(Cl/Br)3 478 10.0 100\ncd m-2\n29800 18\n16850 (2025)\nNat Commun 16,\n(Cs/Rb/FA)(Pb/Sr)(Cl/Br)3 487 23.3 ~7 / 5700 /\n3254 (2025).\n15.4% at ~\n(Cs/Rb/FA)Pb(Cl/Br)3 488 23.8 1632 13230 15 Our work\n10000 cd m-2\nSupplementary Table 4 Comparison of detailed performances for 3D perovskite-\nbased pure-blue (<475 nm) devices.\nEL peak EQE L L V T\npeak EQE max turn- 50\nPerovskites Published journals\n(nm) (%) (cd m-2) (cd m-2) (V) (min)\non\nResearch. 2020,\nCsPb(Cl/Br) 469 1.00 ~500 1363 3.1 /\n3\n9017871 (2020)\nNano Energy 79,\nFAPbBr Cl 474 3.1 <1 2810 3.9 /\n3-x x\n105486 (2021)\nNat Commun\n(Cs/Rb/FA)Pb(Cl/Br) 467 5.5 ~1 330 2.9 /\n3\n12, 361 (2021).\nAdv. Mater. 35,\nCsPb(Cl/Br) 468 4.6 ~50 1680 2.8 3.67\n3\n2207111 (2023)\nJ. Phys. Chem. Lett.\nCsPb(Cl/Br) 465 6.8 13 90 3.1 /\n3\n15, 12435 (2024)\nACS Photonics 11,\n(Cs/Rb/FA)Pb(Cl/Br) 473 9.15 / 5550 2.4 4.97\n3\n5380 (2024)\nAdv. Mater. 26,\n(Cs/Rb/FA)Pb(Cl/Br) 466 7.28 ~5 ~850 2.6 /\n3\n2414788 (2024)\nAdv. Optical Mater.\n(Cs/Rb/FA)Pb(Cl/Br) 466 7.6 ~10 ~300 ~2.8 /\n3\n13, 2500544 (2025)\nNat Commun\n(FA/Cs/Rb)(Pb/Sr)(Br/Cl) 468 11.9 ~40 668 2.7 /\n3\n16, 3254 (2025).\n(Cs/Rb/FA)Pb(Cl/Br) 473 14.0 1699 8334 2.4 45.7 Our work\npages S11 and S18 of the revised Supplementary Information, respectively. Meanwhile,\nwe have added the new results in the manuscript (lines 13-21, page 11) as follows:\nBesides, we also demonstrate a good applicability of our strategy in achieving high-\nperformance sky-blue PeLEDs with the narrowest emission bandwidth of 15 nm among\nthe state-of-the-art sky-blue devices (Supplementary Table 5). Meanwhile, great\nenhancements in efficiency and luminance from 16.7% and 11926 cd m-2 to 23.8% and\n13230 cd m-2 are achieved for the sky-blue devices (Supplementary Fig. 16).\nParticularly, the devices show a remarkably high efficiency of 11.5% at the peak\nluminance of 13230 cd m-2 and 15.4% at a luminance of ~10000 cd m-2, which is largely\nhigher than previously reported ones with efficiencies lower than 10% at peak\nluminance and/or a luminance of 10000 cd m-2.\nC3: The key claims regarding “defect suppression” lack convincing experimental evidence.\nThe estimated trap-state density differs by less than one order of magnitude in Supplementary\nFig. 6 (4.34 × 1017 ~ 1.79 × 1017 cm−3), which does not convincingly support the page 8,\nlines 209 “the great reduction in trap state density” as claimed.\nR: Sorry for the confusion. We performed the space charge limited current (SCLC)\nmeasurement once on the control and target perovskite films to determine the trap state\ndensity variations (shown in Supplementary Fig. 10 below). The result is consistent\nwith previous observation of the reduction in trap state density for the target perovskites.\nIn detail, the trap-filled limit voltages (V ) for the control and target perovskites are\nTFL\n0.84 V and 0.32 V, corresponding to the trap state densities of 4.50 × 1017 cm−3 and\n9.79 × 1016 cm−3, respectively. The trap state density for the target perovskites is\nreduced by over 78%. This decline percentage is significantly larger than previously\nreported blue-emissive perovskites (shown in Table R3 below), indicating a large\nreduction in trap state density.\nSupplementary Fig. 10 Space charge limited current (SCLC) measurements of a)\ncontrol and b) target perovskite devices and c) the capacitance–frequency (C–f) curves.\nTable R3 Comparison of the decline percentage of trap state densities for control and\ntarget perovskites with blue emission.\nDecline\nControl Target\nPerovskite percentage Published journals\n(cm-3) (cm-3)\n(%)\nACS Energy Lett. 10, 3638\n(Cs/PEA)Pb(Cl/Br) 2.28 × 1017 1.93 × 1017 15.4\n3\n(2025)\nACS Nano 18, 4570,\nCsPb(Cl/Br) 3.02 × 1018 2.51 × 1018 16.8\n3\n(2024)\n(Cs/FA/p- Nat. Commun.\n3.99 × 1018 2.88 × 1018 27.8\nPEA/K)Pb(Cl/Br) 15, 10621 (2024)\n(Cs/FA/pFPEA)Pb(Cl/Br) 4.21 × 1018 2.92 × 1018 30.6\n3\ne202319730 (2024).\nAdv. Mater. 35, 2302161\n(Cs/GA/pFPEA)Pb(Cl/Br) 2.81 × 1018 1.02 × 1018 63.7\n3\n(2023)\n(Cs/Rb/FA)Pb(Cl/Br) 4.50 × 1017 9.79 × 1016 78.2 Our work\nSupplementary Information (page S8). Meanwhile, to avoid confusion, the expression\nof “benefiting from the great reduction in trap state density” has been revised as\n“benefiting from the large reduction in trap state density” (line 29, page 8).\nC4: The authors believe that the PL lifetime is prolonged, suggesting a reduced trap-assisted\nnon-radiative recombination. However, there is no clear difference in table S1 (3~7ns for the\naveraged lifetime). Also, the authors claim that the extracted decay lifetimes imply reduced\ndefect density in target sample since the PL lifetime reflects the trap-assisted carrier\nrecombination rates. However, carrier recombination rates depend on the inject carrier\ndensities, the PL lifetime comparison between different samples should have been made at\nconstant excitation density, and thus, dependence on laser fluence should be shown. If this is\nnot the case, the inconsistency needs to be discovered critically to understand the photophysics\nmechanism.\nR: Thanks for the very kind suggestion. To further verify the prolonged PL lifetime for\nthe target perovskites, time-resolved PL (TRPL) spectra under different excitation\nintensities have been performed. As shown in Supplementary Fig. 8 below, the decay\ncurves can be well-fitted by a bi-exponential function, where the fast decay component\n(τ ) relates to the trap-assisted non-radiative recombination and the slow decay\n1\ncomponent (τ ) associates with the radiative recombination (Science 350, 1222 (2015);\ntarget perovskites under different excitation intensities are shown in Supplementary\nFig. 8c below. It is revealed that all the lifetimes for the target perovskites are much\nlonger than those of control perovskites across the whole detection range with different\nexcitation intensities, i.e., the target perovskites show much larger lifetimes than those\nof control perovskites at the same excitation intensity. The results are in good\nagreement with the prolonged lifetime in Supplementary Table 1, verifying the\nprolonged PL lifetime with more radiative recombination for the target perovskites.\nSupplementary Fig. 8 Time-resolved PL spectra under different excitation intensities\nof a) control and b) target perovskites and c) the extracted average lifetimes by fitting\nthe decay curves under various excitation light powers.\nAccordingly, Supplementary Fig. 8 has been added to the revised Supplementary\nInformation (page S5). Meanwhile, the following discussion has been added to the\nrevised manuscript (lines 19-22, page 7).\nThe prolonged lifetime for target perovskites has been further verified by the TRPL\nspectra under different excitation intensities (Supplementary Fig. 8), where the target\nperovskites show much longer lifetimes than that of control perovskites at the same\nexcitation power.\nC5: It is a big claim that there is no EL shift during the lifetime measurements. The authors\nshould provide the evolution of the CIE y coordinate as a function of time under a constant\ncurrent condition. This measurement is essential to evaluate the EL stability of the device\nduring lifetime measurement.\nR: Thanks for the suggestion. The evolution of the CIE y coordinate during the lifetime\nmeasurements was monitored and shown in Supplementary Fig. 18 below. It is\nrevealed that the control devices show a distinct increase in the CIE y coordinate value\nby prolonging the measurement time. However, the target PeLEDs show a constant CIE\ny value throughout the lifetime measurements. This observation is well consistent with\nthe unchanged EL peak position for the target devices, verifying the excellent spectral\nstability during operation.\nSupplementary Fig. 18 The evolution of the CIE y coordinate during the lifetime\nmeasurements of control and target devices.\nAccordingly, Supplementary Fig. 18 has been added to the revised Supplementary\nInformation (page S12). Meanwhile, the following discussion has been added to the\nrevised manuscript (lines 26 and 27, page 11).\nMoreover, the EL peak position and the CIE y coordinate of the target PeLEDs remain\nconstant during the lifetime test (Fig. 4i, Supplementary Fig. 18).\nC6: If the authors believe that the exciton binding energies are high, they should also measure\nthe fluence-dependent photoluminescence quantum yield (PLQY) to evaluate the exciton\nrecombination dynamics.\nR: Thanks for the suggestion. To further verify the increased exciton binding energy of\nthe target perovskite for more radiative recombination, the fluence-dependent\nphotoluminescence quantum yields (PLQY) for the control and target perovskites were\nmeasured. As shown in Supplementary Fig. 11 below, we observe a distinct\nenhancement in PLQYs for the target perovskites under different excitation intensities.\nThe target perovskites exhibit a peak PLQY of 41.5%, which is much larger than 18.6%\nof the control perovskites, indicating strengthened radiative recombination in target\nperovskites.\nSupplementary Fig. 11 Fluence-dependent PLQYs for control and target perovskites.\nAccordingly, Supplementary Fig. 11 has been added to the revised Supplementary\nInformation (page S9). Meanwhile, we have added the following discussion to the\nrevised manuscript (lines 23-25, page 8).\nConsistently, we observe a distinct enhancement in photoluminescence quantum yields\n(PLQY) for the target perovskites under different excitation intensities (Supplementary\nFig. 11).\nC7: As shown in Fig. 1a and b, the control and target films exhibit markedly different\nmorphologies. The target film displays smaller grain sizes and a higher density of voids. Such\nmorphological differences may strongly influence the PLQY and PL lifetimes through surface-\nrelated effects. A discussion on how these morphological changes correlate with crystal and\ndevice stability would be valuable.\nR: Thanks for the suggestion. In the manuscript (Fig. 1a and b), distinct variations of\nthe film morphology are observed for the control and target perovskites. The control\nperovskites have a typical island-like morphology, while the target perovskites exhibit\nsingle crystal-like morphology with regular crystal grains. The grain size distributions\nof control and target perovskites are shown in Supplementary Fig. 1 below, where the\naverage grain sizes of control and target perovskites are ~ 162 and 176 nm, respectively.\nAs a result, the void area fraction increases from 52.0% (control perovskites) to 54.8%\nfor target perovskites due to the grain fusion from small sizes to the large ones.\nSupplementary Fig. 1 The grain size distributions of a) control and b) target\nperovskites and c) the void area fraction. The average grain sizes of control and target\nperovskites are ~ 162 and 176 nm, respectively. The void area increases from 52.0% to\n54.8% for target perovskites due to the grain fusion from small sizes to the large ones.\nBesides, the morphological differences also influence the PLQY and PL lifetimes of\nthe perovskites. The fluence-dependent PLQYs for the control and target perovskites\nwere measured (shown in Supplementary Fig. 11 below). We observe a distinct\nenhancement in PLQYs for the target perovskites under different excitation intensities.\nThe peak PLQY of 41.5% for target perovskites is much larger than 18.6% of the\ncontrol perovskites, indicating strengthened radiative recombination in target\nperovskites. In addition, the excitation intensity-dependent PL lifetimes for the control\nand target perovskites were measured (shown in Supplementary Fig. 8 below). The\nextracted average PL lifetimes for the target perovskites are much longer than those of\ncontrol perovskites at the same excitation intensity, showing the prolonged PL lifetimes\nfor the target perovskites.\nSupplementary Fig. 11 Fluence-dependent PLQYs for control and target perovskites.\nSupplementary Fig. 8 Time-resolved PL spectra under different excitation intensities\nof a) control and b) target perovskites and c) the extracted average lifetimes by fitting\nthe decay curves under various excitation light powers.\nThe morphological differences between control and target perovskites are induced by\nBAPEG-assisted crystal-oriented growth, where the (100) and (200) crystal facets are\ngreatly promoted for target perovskites (shown in Fig. 1c below). In detail, the\ndiffraction signals of (110) and (111) planes are significantly weakened in the target\nperovskites, being accompanied by the appearance of the sharp and strong diffraction\npeaks of (100) and (200) planes, indicating the dominant (100) and (200) facets in the\ntarget perovskites with high crystal quality. Since the (100) facet has larger halogen\nvacancy formation energies than those of (110) and (111) facets (shown in Fig. 1h\nbelow), the target perovskites with preferred (100) crystal facet have a lower trap state\ndensity, thus promoting more stable crystal and device stability. As shown in\nSupplementary Fig. 7, the control perovskites with irregular and island-like\nmorphology show poor stability against environmental erosion, where the PL intensity\ndecreases quickly by prolonging the exposure time. In detail, the PL intensity of control\nperovskites largely decays to ~ 13% of the initial intensity after being exposed for 48\nh. Meanwhile, a large red shift of the PL peak from 470 to 478 nm is observed during\nthe stability test. Conversely, the target perovskites with regular and single crystal-like\nmorphology exhibit excellent tolerance to the environment erosion, where the PL\nintensity retains nearly 90% after 48h exposure. Moreover, the PL spectra show a\nreasonable variation (~ 1 nm) after the test, indicating excellent stability against\nenvironmental erosion.\nFig. 1 c) XRD measurements of control and target perovskites.\nFig. 1 h) the formation energies of bromine and chlorine vacancies on (100), (110), and\n(111) facets\nSupplementary Fig. 7 The time-dependent steady-state photoluminescence (PL)\nspectra of a) control and b) target perovskites under exposure to the environment with\na constant temperature of 20 °C and relative humidity of 70%. c) The time-dependent\nPL intensity variations of the perovskites.\nFor the device stability, despite the increase in the void area fraction from 52.0%\n(control perovskites) to 54.8% for target perovskites, the void area-induced\ndiscontinuous perovskite crystal would not cause a strong leakage current due to a high\ncarrier injection barrier at TPBi/PVK surface by considering the large energy level\nmismatch between TPBi and PVK (Nat. Commun. 12, 361 (2021)). Moreover, our\nintroduced BAPEG not only adsorbs on the perovskite surface but also isolates the PVK\nand TPBi transport layers to suppress the leakage current. As shown in Fig. 4c below,\nwe detect a slightly lower current density for the target PeLEDs than that of the control\ndevices before the electroluminescence turn-on, verifying the suppressed leakage\ncurrent in the target PeLEDs. We further monitor the operational lifetime to determine\nthe device stability. As shown in Fig. 4h below, the target PeLEDs show a lifetime of\n45.7 min at an initial luminance of 100 cd m-2, which is over 6-fold longer than 7.2 min\nof the control devices, clarifying the good device stability for the target PeLEDs.\nConsequently, the above results clearly show that the morphological changes from\nirregular and island-like morphology in control perovskites to high-quality perovskites\nwith regular and single crystal-like morphology promote good crystal and device\nstability.\nFig. 4 c) current density-luminance-voltage (J-L-V) of the devices.\nFig. 4 h) the time-dependent lifetime tests for control and target perovskites\nAccordingly, Supplementary Figs. 1, 7, 8, and 11 have been added to the revised\nSupplementary Information on pages S2, S5, and S9, respectively. Meanwhile, we have\nadded the following discussion to the revised manuscript (lines 1-4, page 7).\nThe morphological changes from irregular and island-like control perovskites to\nregular and single crystal-like high-quality target perovskites contribute to good\ncrystal stability (Supplementary Fig. 7), as well as high device performance shown in\nthe following part.\nC8: The authors attribute the observed shift of the Pb 4f binding energy to the coordination\nbetween oxygen atoms and Pb²⁺. However, this interpretation requires more rigorous\njustification. In XPS, a shift in the Pb 4f peak position can also arise from other possible\ninteractions, such as coordination between amino groups (–NH₂) and Pb²⁺, or surface dipole\neffects. The authors should provide additional supporting evidence.\nR: Thanks for the suggestion. In the manuscript, we employed the measurements of\nRaman spectra, X-ray photoelectron spectroscopy (XPS), and Fourier transform\ninfrared spectroscopy (FT-IR) to demonstrate the interaction between BAPEG and the\nperovskites (mainly the lead-halide complex). The BAPEG molecule has the functional\ngroups of ether bond (C−O) and terminated amino (−NH ) with an average molecular\n2\nweight (Mn) of ~ 1500. The Raman spectra (shown in Fig. 3a below) exhibit a\ncharacteristic peak located at 143.4 cm-1, which is assigned to the signal of Pb−O bond\n(Device 2, 100285 (2024)), indicating the interaction between BAPEG (ether bond) and\nthe perovskite (lead-halide complex). Meanwhile, the variations of the O 1s signal in\nXPS (shifts from 532.6 to 532.9 eV shown in Fig. 3c below) and C–O stretching\nvibration signal in FT-IR (shifts from 1115 to 1121 cm−1 shown in Fig. 3f below) further\nconfirm the interaction between BAPEG (ether bond) and the perovskite (lead-halide\ncomplex).\nFig. 3 a) The Raman spectra of BAPEG and BAPEG-Pb(Br/Cl) .\nFig. 3 f) FT-IR spectroscopy of BAPEG and BAPEG-Pb(Br/Cl) .\ncoordination of O in the ether bond with Pb²⁺ (shown in Fig. 3a, c, and f above), as well\nas the coordination of N in the amino group with Pb²⁺. As shown in Fig. R6 below,\nthe C–N stretching vibration signal in FT-IR spectra shows a slight shift from 1244\n(BAPEG) to 1246 cm-1 for BAPEG-Pb(Br/Cl) (i.e., BAPEG-treated Pb(Br/Cl) ).\n2 2\nMeanwhile, the XPS N 1s signal for the BAPEG (399.2 eV) shifts to a slightly higher\nbinding energy of 399.3 eV for BAPEG-Pb(Br/Cl) . However, the variation ranges in\n2\nbinding energy and wavenumber for the N 1s signal (0.1 eV) and C-N stretching\nvibration (2 cm-1) are smaller than those of the O 1s signal (0.3 eV) and C-O stretching\nvibration (6 cm-1), which may be induced by the higher ratio of O atom than N atom in\nBAPEG. Thus, the main coordination between oxygen atoms and Pb²⁺ is considered.\nConsistently, both the coordination interactions of O with Pb²⁺ and N with Pb²⁺\ndemonstrate the interaction between BAPEG and the perovskites.\nFig. R6 a) FT-IR spectroscopy and b) XPS spectra of N 1s signal of BAPEG and\nBAPEG-Pb(Br/Cl) .\ntheory (DFT) calculations to show the interaction between BAPEG and the perovskite\n(shown in Supplementary Fig. 4 below). As demonstrated, the valence electrons are\nmerely gathered and distributed near the separated atoms of BAPEG if there is no\ninteraction between BAPEG and the perovskite. Conversely, the deformation of the\nelectron distributions clearly elucidates the distinct charge transfer processes between\nhydrogen and Br/Cl halide atoms, as well as oxygen and lead atoms for BAPEG-treated\nperovskite. The differential charge density images strongly show the bonding\ninteraction between BAPEG and the perovskite facets.\nSupplementary Fig. 4 The differential charge density images of BAPEG adsorption\non a) (100), b) (110), and c) (111) facets of the perovskites.\nAccordingly, Supplementary Fig. 4 has been added to the revised Supplementary\nInformation (page S3). To avoid the confusion, we have revised the expression of “The\nlow binding energy indicates the reduced oxidation state of lead owing to the\ncoordination with the C−O functional group of BAPEG” to “The low binding energy\nindicates the reduced oxidation state of lead due to the interaction between BAPEG\nand the perovskite” in the revised manuscript (line 13, page 9).\nMeanwhile, the following discussion has been added to the revised manuscript (lines\n4-7, page 10).\nThe interaction between BAPEG and the perovskites is also demonstrated by the charge\ndensity differences (Supplementary Fig. 4), where the deformation of the electron\ndistributions clearly elucidates the distinct charge transfer processes between BAPEG\nand the perovskites.\nC9: The authors attribute the positive shift of Br 3d and Cl 2p binding energies to hydrogen\nbonding interactions between halide ions and the N–H groups of BAPEG. However, this\ninterpretation seems not convincing. A shift in binding energy alone cannot unambiguously\nconfirm hydrogen bonding, as it can also originate from other factors such as changes in the\nlocal chemical environment, lattice contraction, compositional variation, or ionic\nincorporation. Additional evidence, such as FTIR, NMR, or DFT calculations, would be\nnecessary to substantiate the claim of hydrogen bonding interactions.\nR: Sorry for the confusion, and thanks for the suggestion. Besides the shift of Br 3d and\nCl 2p binding energies, the hydrogen bonding interaction between N−H and the halide\nions was further verified by Fourier transform infrared spectroscopy (FT-IR) (shown in\nFig. 3f below). The BAPEG shows a characteristic N−H stretching vibration peak\nlocated at 3425 cm−1, which shifts to a higher wavenumber of 3451 cm−1 for BAPEG-\nPb(Br/Cl) (i.e., BAPEG-treated Pb(Br/Cl) ), indicating a strengthened stretching\n2 2\nvibration deriving from the hydrogen bonding interaction between N−H and the halide\nions (Nat. Photonics. 17, 478 (2023)).\nFig. 3 f)FT-IR spectroscopy of BAPEG and BAPEG-Pb(Br/Cl) .\nresonance (1H NMR) measurements (shown in Supplementary Fig. 12 below). The\nBAPEG shows a characteristic peak at 3.42 ppm, corresponding to the hydrogen of the\namino group. While the signal shifts from 3.42 ppm to a larger chemical shift (low-\nfield) of 3.46 ppm for the BAPEG-Pb(Br/Cl) , suggesting a decreased shielding effect\n2\ninduced by the hydrogen bonding interaction between N−H and the halide ions (Nat.\nCommun. 12, 6856 (2021)).\nSupplementary Fig. 121H NMR spectra of BAPEG and BAPEG-Pb(Br/Cl) dissolved\n2\nin DMSO-d (the right image shows the magnified 1H NMR signal in the dotted box of\n6\nthe left image).\nFurthermore, the charge density differences based on density functional theory (DFT)\ncalculations were performed to show the hydrogen bonding interactions between halide\nions and the N–H groups of BAPEG. As shown in Supplementary Fig. 4 below, the\ndeformation of the electron distributions on the hydrogen and halide ions is clearly\nobserved, showing the distinct charge transfer process between hydrogen and Br/Cl\nhalide atoms due to the formation of hydrogen bonds.\nSupplementary Fig. 4 The differential charge density images of BAPEG adsorption\non a) (100), b) (110), and c) (111) facets of the perovskites.\nAccordingly, Supplementary Figs. 4 and 12 have been added to the revised\nSupplementary Information (pages S3 and S9). Meanwhile, the following discussion\nhas been added to the revised manuscript (lines 31-33, page 9).\nThe hydrogen bonding interaction between N−H and the halide ions is also verified by\n1H nuclear magnetic resonance (1H NMR) measurements (Supplementary Fig. 12),\nwhere the signal of -NH shifts to a large chemical shift (low-field) due to the de-\n2\nshielding effect induced by the formation of hydrogen bond.\nC10: It seems that the PL peak positions of the control and target samples appear inconsistent\nin Supplementary Fig. 5, with the control sample showing a redshifted PL emission, while in\nSupplementary Fig. 9 the EL peak positions of both samples are identical. Please provide a\nreasonable explanation.\nR: Sorry for the confusion. We have carefully checked and compared the emission peak\nposition of control and target perovskites and find that there is no significant difference\nbetween their emission peak positions. The nearly 1-nm difference in PL peak positions\n(Supplementary Fig. 5 of the original manuscript) may originate from the test error.\nWe have corrected the PL spectra of control and target perovskites in Supplementary Fig.\n9b below. While we observe a slight redshift (~3 nm) of the EL peak for the PeLEDs\nwith respect to the PL peak of 470 nm. This phenomenon can be attributed to the electric\nfield-induced Stark effect, as also reported previously (Adv. Mater. 35, 2302161 (2023);\nNano Lett. 24, 15, 4571 (2024); Adv. Optical Mater. 8, 1902092 (2020)).\nSupplementary Fig. 9 b) photoluminescence spectra of the control and target\nperovskites.\nAccordingly, Supplementary Fig. 9b has been updated in the revised Supplementary\nInformation (page S6).\nC11: Although the authors report improved device performance after BAPEG modification,\nit is unclear why the efficiency of their reference device is significantly lower than that reported\nin previous works (Nat. Commun. 12, 361, 2021) using same compositions and processing\nconditions. Notably, previous studies have achieved efficiencies of ~6% at 467 nm, and 11% at\n477 nm, whereas the present device shows comparable efficiency (~6%) even at 473 nm. The\nauthors are encouraged to clarify this discrepancy and discuss possible causes.\nR: Thanks for the kind concern. The device performances are susceptible to various\nconditions, such as preparation conditions (e.g., environment temperature, evaporation\nparameters), material differences (e.g., the purity of perovskite precursors, solvent, and\ntransport materials), etc. We have investigated and listed the device performances of\nthe control perovskites fabricated with similar compositions and processing conditions\nto Nat. Commun. 12, 361 (2021) in Table R4 below. As shown, our fabricated control\ndevices exhibit an efficiency of 6.7% at 473 nm, which is comparable to those reported\npreviously, indicating merely moderate device performance based on the control\nperovskites.\nHowever, we report the BAPEG-modulated crystal growth for high-quality pure-blue\nperovskites, which enables high device performance with an efficiency of 14% and a\nnarrow emission bandwidth of 14 nm at 473 nm. Moreover, we demonstrate a good\napplicability of the strategy in achieving high-performance sky-blue PeLEDs with the\nefficiency greatly increased from 16.7% to 23.8%, as well as a reduced emission\nbandwidth from 19 nm to 15 nm at 488 nm (Supplementary Fig. 16 of the revised\nSupplementary Information). These encouraging results highlight the importance of our\nstrategy for high-performance blue PeLEDs.\nTable R4. Comparison of the control device performance with similar compositions\nand processing conditions to Nat. Commun. 12, 361 (2021).\nEL peak EQE of control device\nReference Perovskite\n(nm) (%)\nNat. Commun. 16, 3254 (2025) (FA/Cs/Rb)Pb(Br/Cl) 464 ~2\n(FA/Cs/Rb)Pb(Br/Cl) 475 4\n3\n2500544 (2025)\nAdv. Mater. 26, 2414788\n(FA/Cs/Rb)Pb(Br/Cl) 466 ~4\n3\n(2024)\nMatter 7, 1054 (2024) (FA/Cs)Pb(Br/Cl) 479 5\n(FA/Cs/Rb)Pb(Br/Cl) 478 ~1.5\n3\n(2023)\nSmall Methods 8, 2300572\n(FA/Cs/Rb)Pb(Br/Cl) 474 4.3\n3\n(2024)\nAdv. Optical Mater. 11,\n(FA/Cs/Rb)Pb(Br/Cl) 486 3\n3\n2202528 (2023)\nNano Energy 97, 107181\n(FA/Cs)Pb(Br/Cl) 475 2.02\n3\n(2022)\nOur work (FA/Cs/Rb)Pb(Br/Cl) 473 6.7\nC1: The cross-sectional SEM image presented in Supplementary Fig. 7 lacks sufficient clarity,\nmaking it difficult to clearly resolve the device architecture.\nR: To sufficiently show the device architecture, the high-angle annular dark-field\n(HAADF) cross-sectional TEM image with EDS mapping was performed on the\ndevices. As shown in Supplementary Fig. 13 below, the functional layers of\nNiO /PVK transport layer, perovskite, TPBi, and LiF/Al cathode can be easily observed\nx\nwith the thickness of ~ 20, 47, 38, and 92 nm, respectively.\nSupplementary Fig. 13 The device structure characterized by high-angle annular dark-\nfield (HAADF) cross-sectional transmission electron microscopy (TEM) with element\nmapping.\nAccordingly, Supplementary Fig. 13 has been added to the revised Supplementary\nInformation (page S10).\nC2: Regarding the NIOX/PVK/Perovskite/TPBi/LiF/Al structure mentioned in this manuscript,\nplease provide a reasonable explanation of how an identical perovskite precursor compared\nwith previous related literature can be uniformly formed on the hydrophobic PVK layer surface\nwithout any modification.\nR: Sorry for the confusion. During the device fabrication process, the surface\nmodification of PVK with polyvinyl pyrrolidone (PVP) was adopted to improve the\nwettability of the perovskite precursor, which was omitted in the original manuscript.\nTo avoid confusion, we have added the following fabrication process of the PVP\ninterfacial layer to the revised manuscript (lines 1-3, page 14).\nThen, the polyvinyl pyrrolidone (PVP) solution (1 mg mL−1 in isopropanol) was spin-\ncoated at 4000 rpm and annealed at 120 °C for 10 min to improve the wettability of the\nperovskite precursor on PVK.\nC3: Please provide references for all the data points in Figure 4g. The author should provide\na thorough, up-to-date overview of recent advancements in pure-blue perovskite LEDs.\nR: Thanks for the valuable suggestion. We have added the references for all the data\npoints in Fig. 4f below. In Fig. 4f, we show that our target pure-blue PeLEDs exhibit a\nlarge brightness of 8334 cd m-2 and a peak efficiency of 14.0%. The performance is\ngreatly higher than the recently published result of 668 cd m-2 and 11.9% in ref. 26 (Nat.\nCommun. 16, 3254 (2025)), representing the brightest and most efficient pure-blue\nPeLEDs among the 3D perovskite-based pure-blue PeLEDs.\nFig. 4 f) Comparison of the efficiency and brightness of the 3D perovskite-based pure-\nblue devices.\nMeanwhile, we have listed the recent advancements in pure-blue PeLEDs based on the\npopular blue-emissive perovskites of colloidal quantum dots (QDs), quasi-two-\ndimensional (quasi-2D) perovskites, and three-dimensional (3D) bromide-chloride\nmixed perovskites. As shown in Supplementary Table 3 below, our pure-blue devices\nexhibit the narrowest emission bandwidth of merely 14 nm among the state-of-the-art\npure-blue PeLEDs. Furthermore, we have verified the good applicability of our strategy\nin achieving high-performance sky-blue PeLEDs with the narrowest emission\nbandwidth of 15 nm among the state-of-the-art sky-blue PeLEDs (shown in\nSupplementary Table 5 below). Meanwhile, the sky-blue PeLEDs exhibit a high\nefficiency of 23.8% and a large luminance of 13230 cd m-2 at 488 nm. In particular, the\ndevices show a remarkably high efficiency of 11.5% at the peak luminance of 13230\ncd m-2 and 15.4% at a luminance of ~10000 cd m-2, which is largely higher than the\npreviously reported ones with efficiencies lower than 10% at peak luminance and/or a\nluminance of 10000 cd m-2, overcoming the typical efficiency-brightness trade-off.\nThis suggests a great potential of our approach for practical display applications.\nSupplementary Table 3 Comparison of the EL performance of pure-blue (<475 nm)\nPeLEDs.\nEL EQE\npeak\nEQE L L FWHM\npeak EQE max\nType Perovskite peak Published journal\nluminance\n(%) (cd m-2) (cd m-2) (nm)\n(nm) (%)\nACS Energy Lett. 8,\nCsPbBr 469 10.3 ~1400 ~4 12060 21\n3\n731 (2023)\nACS Energy Lett. 9,\nCsPb(Cl/Br)3 467 7.45 ~160 ~6 ~1400 ~20\n3261 (2024)\nAngew. Chem. Int.\nQDs CsPb(Cl/Br)3 467 9.1 ~300 / 2000 ~20 Ed. 63, e202408726\n(2024)\nSci. Adv. 10,\nCsPb(Cl/Br)3 470 21.3 ~5 ~2 635 ~17\neado5645 (2024)\nAdv. Mater. 37,\nCsPbBr 469 20.3 ~2000 ~9 31407 25\n3\ne20131 (2025)\nAdv. Mater. 35,\n(Cs/pFPEA)Pb(Br/Cl) 468 11.87 ~80 ~2 710 ~21\n3\n2302161 (2023)\n(Cs/pFPEA)/PPN)Pb(Cl/ Nat. Photonics 18,\n474 13.2 2 ~1 700 ~21\nBr) 425 (2024).\n3\n(Cs/FA/pFPEA)Pb(Cl/Br Nat. Commun. 15,\n468 15 ~10 ~2 ~100 ~22\n) 10621 (2024).\nQuasi- (Cs/pFPEA)Pb(Br/Cl) 469 10.4 ~300 ~5 2428 22\n3\n2412041 (2024)\n2D\nACS Energy Lett. 10,\n(Cs/PEA)Pb(Cl/Br)3 468 17.4 ~100 2 2346 22\n3638 (2025).\nPPA/PEA/Li- Adv. Mater. 37,\n467 8.55 30 ~2 336 23\nCsPb(Br/Cl) 2409718 (2025)\n(Cs/pFPEA)Pb(Br/Cl)3 468 16.3 <1 ~1 282 ~27 Ed. 64, e202513617\n(2025)\nNat. Commun. 12,\n(Cs/Rb/FA)Pb(Cl/Br) 467 5.5 ~1 ~1 330 18\n3\n361 (2021).\nAdv. Mater. 35,\nCsPb(Cl/Br) 468 4.6 ~50 / 1680 15\n3\n2207111 (2023)\nACS Photonics\n(Cs/Rb/FA)Pb(Cl/Br) 473 9.15 / / 5550 17\n3\n11,5380 (2024)\n3D Adv. Mater. 26,\n(Cs/Rb/FA)Pb(Cl/Br)3 466 7.28 ~5 <1 ~850 ~16\n2414788 (2024)\nAdv. Optical Mater.\n(Cs/Rb/FA)Pb(Cl/Br)3 466 7.6 ~10 ~0.5 ~300 ~19\n13, 2500544 (2025)\n(FA/Cs/Rb)(Pb/Sr)(Br/Cl) Nat. Commun. 16,\n468 11.9 ~40 / 668 ~17\n)3 3254 (2025)\n(Cs/Rb/FA)Pb(Cl/Br) 473 14.0 1699 4.5 8334 14 Our work\nnm) PeLEDs\nL peak EQE peak\nEL\nEQE EQE luminance L max FWHM Published\nType Perovskites peak\n(%) (cd m- (%) (cd m-2) (nm) journals\n(nm)\n2)\nNature 612, 679\nCsPbBr3 480 13.8 ~30 ~5 2751 21\n(2022)\nAdv. Mater. 36,\nCsPb(Br/Cl)3 490 23.5 / / 2843 /\n2402325 (2024)\nQDs\nSci. Adv. 10,\nCsPb(Br/Cl)3 480 26.4 ~5 / 1601 17\neado5645 (2024)\nACS Nano 19,\nCsPbBr3 480 23.5 ~1 / 1030 21\n42455 (2025)\nACS Nano 18,\n(Cs/pFPEA)Pb(Cl/Br)3 485 16.3 / ~4 5740 ~25\n6513 (2024)\nNat. Commun.\n(Cs/pFPEA)Pb(Cl/Br)3 488 23.6 <10 ~2 831 ~22\n15, 10621 (2024).\nAngew. Chem.\n(Cs/PEA)Pb(Cl/Br)3 490 22.88 ~15 ~3 2011 ~25 Int. Ed. 64,\n202419746 (2025)\nQuasi-\nAdv. Mater. 37,\n2D (Cs/PEA/PPA)Pb(Cl/Br)3 485 24.03 113 ~7 3472 23\n2409718 (2025)\nAdv. Mater. 37,\n(Cs/PEA)PbBr3 485 26.2 ~200 ~8 4506 ~20\n2506970 (2025)\nNat Commun 16,\nPEACsxEA1-xPbBr3 489 22.5 ~20 ~6 ~1000 20.8\n9590 (2025)\nACS Energy Lett.\n(Cs/PEA)PbBr3 485 22.66 ~60 ~1 2357 ~22\n10, 1183 (2025)\nAdv. Optical\n(Cs/Rb/FA)Pb(Cl/Br)3 486 6.3 ~15 ~1.5 1926 18 Mater. 11, 202528\n(2023)\nACS Energy Lett.\n(Cs/Rb/FA)Pb(Cl/Br)3 487 13.6 ~1000 / 18748 18\n8, 2897 (2023)\nAdv. Mater. 26,\n(Cs/Rb/FA)Pb(Cl/Br)3 482 19.28 / / 1457 /\n2414788 (2024)\nAdv. Optical\n3D (Cs/Rb/FA)Pb(Cl/Br)3 483 16.2 20 ~1 ~3000 / Mater. 13, 500544\n(2025)\n8% at 10000 ACS Nano 19,\n(Cs/Rb/FA)Pb(Cl/Br)3 478 10.0 100\ncd m-2\n29800 18\n16850 (2025)\nNat Commun 16,\n(Cs/Rb/FA)(Pb/Sr)(Cl/Br)3 487 23.3 ~7 / 5700 /\n3254 (2025).\n15.4% at ~\n(Cs/Rb/FA)Pb(Cl/Br)3 488 23.8 1632 13230 15 Our work\n10000 cd m-2\nAccordingly, we have updated Fig. 4f in the revised manuscript (page 24) and added\nSupplementary Tables 3 and 5 to pages S16 and S18 of the revised Supplementary\nInformation, respectively. Meanwhile, we have added the new results in the manuscript\n(lines 13-21, page 11) as follows:\nBesides, we also demonstrate a good applicability of our strategy in achieving high-\nperformance sky-blue PeLEDs with the narrowest emission bandwidth of 15 nm among\nthe state-of-the-art sky-blue devices (Supplementary Table 5). Meanwhile, great\nenhancements in efficiency and luminance from 16.7% and 11926 cd m-2 to 23.8% and\n13230 cd m-2 are achieved for the sky-blue devices (Supplementary Fig. 16).\nParticularly, the devices show a remarkably high efficiency of 11.5% at the peak\nluminance of 13230 cd m-2 and 15.4% at a luminance of ~10000 cd m-2, which is largely\nhigher than previously reported ones with efficiencies lower than 10% at peak\nluminance and/or a luminance of 10000 cd m-2.\nResponses to the 2nd reviewer's comments\nReviewer #2: In this work, the authors propose an interesting and novel approach to achieve\nfacet-selective crystal growth and further reveal the underlying mechanism of energy-driven\nselective adsorption of BAPEG to specific perovskite facets. The resultant high-quality crystals\nenable fantastic pure-blue PeLEDs with an extremely narrow emission bandwidth of 14 nm at\nan emission of 473 nm, a remarkable efficiency of 14.0% at 1699 cd m-2, a high brightness of\n8334 cd m-2, and excellent operational and spectral stability. These encouraging results\nsupport its publication in this journal after a couple of minor corrections.\nR: Thank the reviewer for confirming the novelty and importance of our work and the\nhighly encouraging comments.\nC1: The comparisons in emission bandwidth with the reported pure-blue PeLEDs should be\nfurther discussed to highlight the considerably narrow emission achieved in this work.\nR: Thanks for the suggestion. The comparisons of the EL emission bandwidth of pure-\nblue (<475 nm) PeLEDs are shown in Table R2 below, where we achieve the narrowest\nemission bandwidth of merely 14 nm among the state-of-the-art pure-blue PeLEDs.\nGenerally, the broad emission bandwidths exceeding 20 nm are reported for the pure-\nblue PeLEDs based on low-dimensional perovskite systems of colloidal QDs and quasi-\n2D perovskites. In quasi-2D perovskites, the wide phase distribution is extensively\nobserved, which induces broad emissions for the PeLEDs. For the QDs pure-blue\nemitters, it is a big challenge to obtain a very uniform size distribution. The non-\nuniform size of the pure-blue QDs causes a broad emission for the PeLEDs. For\nexample, the large size distribution range of over 3 nm were frequently observed for\nthe small-sized CsPbBr nanocrystals with average sizes of ~ 3 − 10 nm, resulting in a\n3\nbroad blue emission of over 20 nm (ACS Energy Lett. 8, 731 (2023); Small 20, 2400885\n(2024); Adv. Mater. 37, e20131 (2025)). While we report high-quality 3D pure-blue\nperovskite emitters with single crystal-like morphology and reduced trap state density,\nachieving the narrowest emission for the pure-blue PeLEDs. Thus, our work serves as\nan instructive approach to realize pure emission for the blue PeLEDs, which could\nsignificantly impact the field of PeLEDs.\nTable R2Comparison of the EL emission bandwidth of pure-blue (<475 nm) PeLEDs.\nEL peak FWHM\nType Perovskite Published journal\n(nm) (nm)\nCsPbBr 469 21 ACS Energy Lett. 8, 731 (2023)\nAngew. Chem. Int. Ed. 63,\nQDs CsPb(Cl/Br)3 467 ~20\ne202408726 (2024)\nCsPb(Cl/Br)3 470 ~17 Sci. Adv. 10, eado5645 (2024)\nCsPbBr 469 25 Adv. Mater. 37, e20131 (2025)\n3\n(Cs/pFPEA)Pb(Br/Cl) 468 ~21 Adv. Mater. 35, 2302161 (2023)\n3\n(Cs/pFPEA)/PPN)Pb(Cl/Br) 474 ~21 Nat. Photonics 18, 425 (2024).\n3\n(Cs/FA/pFPEA)Pb(Cl/Br) 468 ~22 Nat Commun. 15, 10621 (2024).\n3\n(Cs/pFPEA)Pb(Br/Cl) 469 22 Adv. Mater. 37, 2412041 (2024)\nQuasi-2D 3\n(Cs/PEA)Pb(Cl/Br)3 468 22 ACS Energy Lett. 10, 3638 (2025).\nPPA/PEA/Li-CsPb(Br/Cl) 467 23 Adv. Mater. 37, 2409718 (2025)\n(Cs/pFPEA)Pb(Br/Cl)3 468 ~27\ne202513617 (2025)\n(Cs/Rb/FA)Pb(Cl/Br) 467 18 Nat Commun. 12, 361 (2021).\n3\n(Cs/Rb/FA)Pb(Cl/Br) 473 17 ACS Photonics 11, 5380 (2024)\n3\n(Cs/Rb/FA)Pb(Cl/Br)3 466 ~16 Adv. Mater. 26, 2414788 (2024)\n3D\nAdv. Optical Mater. 13, 2500544\n(Cs/Rb/FA)Pb(Cl/Br)3 466 ~19\n(2025)\n(FA/Cs/Rb)(Pb/Sr)(Br/Cl)3 468 ~17 Nat Commun. 16, 3254 (2025)\n(Cs/Rb/FA)Pb(Cl/Br) 473 14 Our work\nSupplementary Information (page S16).\nC2: The high-quality perovskites may benefit the suppression of the ion migration process,\nwhich is considered as one of the important parameters to determine the device stability. The\nion migration activation energy of the perovskites should be compared.\nR: Thanks for the suggestion. The ion migration activation energy (E ) of the control\na\nand target perovskites was measured by using the Arrhenius equation of (T) = A\nexp(−E /(k T)), where (T) represents the conductivity, A is a constant, and k is\na B 𝜎 B\nBoltzmann’s constant (Nat. Energy 6, 624 (2021)). The E value can be obtained from\n𝜎 a\nthe slope of the ln( ) − 1/(k T) relation. The obtained E for the target perovskites is\nB a\n0.51 eV (shown in Supplementary Fig. 19 below), which is over 2-fold larger than\n𝜎\n0.24 eV for the control perovskites. The result indicates that the high-quality target\nperovskites can effectively suppress the ion migration process, thus benefiting good\ndevice stability.\nSupplementary Fig. 19 The measurements of ion migration activation energy in the\ncontrol and target perovskites.\nAccordingly, Supplementary Fig. 19 has been added to the revised Supplementary\nInformation (page S13). Meanwhile, the following discussion has been added to the\nrevised manuscript (lines 28 and 29, page 11).\nMoreover, the EL peak position of the target PeLEDs remains constant without any\nchange during the lifetime test (Fig. 4i), benefiting from the significantly enlarged ion\nmigration activation energy of the target perovskites (Supplementary Fig. 19).\nC3: The target perovskites display an increased exciton binding energy (i.e., 55.2 meV vs. 40.7\nmeV), which benefits the inhibition of exciton dissociation for more radiative recombination.\nThe reason for this enhancement needs to be clarified.\nR: As reported, the exciton binding energy (E ) value of the perovskites closely relates\nb\nto the dielectric mismatch between the lead halide framework and the surface organic\nligand (i.e., the dielectric confinement effect on the perovskites (Chem. Rev. 119,\n3140−3192 (2019)). The larger exciton binding energy of the target perovskites than\nthat of the control perovskites can be ascribed to the increased dielectric confinement\nby the adsorption of bis(3-aminopropyl)polyethylene glycol (BAPEG) on the\nperovskite surface.\nAs shown in Supplementary Fig. 10c below, the target perovskites show smaller\ncapacitance than that of control perovskite at the same frequency, indicating a lower\ndielectric constant (ε) for the target perovskites, as determined from the equation ε =\n(CL)/(ε S), where L is the thickness of the perovskite film, S is the device area, C is the\n0\ngeometrical capacitance, and ε is the absolute dielectric permittivity. Since the lower ε\n0\nis induced by the adsorption of BAPEG on the target perovskite surface, it can be\nspeculated that there is a larger dielectric mismatch between BAPEG and the lead halide\nframework. In other words, the smaller dielectric constant (ε) of BAPEG than the lead\nhalide framework causes a larger dielectric mismatch for a higher exciton binding\nenergy.\nSupplementary Fig. 10 c) the capacitance–frequency (C–f) curves of the control and\ntarget perovskite-based devices.\nAccordingly, Supplementary Fig. 10c has been added to the revised Supplementary\nInformation (page S8). Meanwhile, the following discussion has been added to the\nrevised manuscript (lines 25-27, page 8).\nThe increased E of the target perovskites can be ascribed to the enhanced dielectric\nb\nconfinement by the adsorption of BAPEG on the perovskite surface (Supplementary Fig.\n10c)\nC4: The perovskite emission layer shows a discontinuous crystal distribution on the substrates.\nIs there any leakage current in the devices by considering the probable direct contact between\nthe electron and hole transport layers?\nR: Thanks for the concern. The discontinuous crystal distribution on the substrates\nallows direct contact between the electron and hole transport layers. While the\ndiscontinuous perovskite crystal may not result in a strong leakage current due to a high\ncarrier injection barrier at TPBi/PVK surface by considering the large energy level\nmismatch between TPBi and PVK (Nat. Commun. 12, 361 (2021)). In addition, our\nintroduced BAPEG not only adsorbs on the perovskite surface but also isolates the PVK\nand TPBi transport layers to suppress the leakage current. As shown in Fig. 4c below,\nwe detect a slightly lower current density for the target PeLEDs than that of the control\ndevices before the electroluminescence turn-on, verifying the suppressed leakage\ncurrent in the target PeLEDs.\nFig. 4 c) current density-luminance-voltage (J-L-V) of the devices.\nC5: Illustrations of the perovskite crystal facet orientations are suggested to be included in Fig.\n1 to visually show the orientation variations.\nR: Thanks for the suggestion. The crystal facet orientations of the control and target\nperovskites were detected by grazing-incidence wide-angle X-ray scattering (GIWAXS)\nmeasurement (shown in Supplementary Fig. 3 below). The control perovskites exhibit\na weak diffraction ring at q = 1.1 Å−1, indicating the random orientations of the (100)\nfacet, thus the randomly oriented perovskite crystals (shown in Fig. 1d below).\nConversely, the stronger discrete pattern of (100) facet along the q axis was observed\nz\nfor the target perovskites, showing the enhanced crystallinity with a preferential parallel\nlattice plane to the substrate (illustrated in Fig. 1e and Supplementary Fig. 1c).\nSupplementary Fig. 3 GIWAXS patterns of a) control and b) target perovskite films.\nIllustrations of the facet orientations extracted from the target perovskite films: c) the\n(100) facet along the q axis (q = 1.1 Å−1) and d) the inclined angle of 45° with respect\nz\nto the substrate for (110) facet (q = 1.5 Å−1). Both c) and d) show the preferential\nparallel (100) lattice plane of target perovskites to the substrate.\nFig. 1 d, e) Illustrations of the perovskite crystal facet orientations of control and target\nperovskites.\nAccordingly, the illustrations of the control and target perovskite crystal facet\norientations have been added to Figs. 1d and e of the revised manuscript (page 21).\nResponses to the 3rd reviewer's comments\nReviewer #3: The manuscript presents a new strategy for preparing high-quality perovskite\ncrystals by the manipulation of crystal facet growth. The mechanism of the facet-selective\ncrystal growth has been partially clarified with both theoretical and experimental results.\nMoreover, pure-blue device performances with a narrow emission and high efficiency and\nstability have been demonstrated. Therefore, this manuscript might be considered for future\npublication after addressing all the following concerns.\nR: Thank the reviewer for confirming the novelty of our work and the helpful comments.\nC1: Given the remarkable efficiency advances in pure-blue nanocrystals and quasi-2D PeLEDs,\nthe manuscript should more clearly highlight the distinct advantages of 3D perovskites.\nSpecifically, the issue of poor charge transport should be addressed with comparative mobility\ndata, and the link between narrow emission spectra and 3D perovskites requires stronger\njustification, particularly compared with nanocrystal systems.\nR: Thanks for the valuable suggestion. The nanocrystals and quasi-2D perovskites are\nvery popular blue emitters for pure-blue PeLEDs, and significantly important works\nhave been done based on pure-blue nanocrystals (e.g., Adv. Mater. 37, e20131 (2025);\nSci. Adv. 10, eado5645 (2024)) and quasi-2D perovskites (e.g., Angew. Chem. Int. Ed.\n64, e202513617 (2025); Adv. Mater. 37, 2409718 (2025)). These works greatly\npromote the development of the pure-blue PeLEDs. However, compared with the low-\ndimensional perovskite systems, the 3D perovskites have the advantages of high charge\nmobility, relatively fixed component, and high Auger recombination threshold (Nat.\nCommun. 16, 3254 (2025); Nat. Commun. 12, 361 (2021)), thus serving as very\npromising candidates for achieving efficient, bright, and narrowband blue PeLEDs.\nHowever, the issue of poor charge transport in the low-dimensional perovskite systems\nhas raised our concern due to the presence of massive insulating ligands and/or large\norganic cations around the nanocrystals and quasi-2D perovskites. The extensively\nreported carrier mobilities for blue emissive quasi-2D perovskites and nanocrystals are\n~ 10-6 − 10-5 cm2 V-1 s-1 (e.g., quasi-2D perovskites: 3.4 × 10-6 cm2 V-1 s-1, ACS Nano\n19, 39181 (2025); 7.5 × 10-5 cm2 V-1 s-1, Nat. Commun. 10, 1027 (2019) and\nnanocrystals: 6.24 × 10-6 cm2 V-1 s-1, Light Sci. Appl. 11, 346 (2022); 1.09× 10-5 cm2 V-\n1 s-1, Inorg. Chem. 62, 11665 (2023); 3.4 × 10-5 cm2 V-1 s-1, ACS Energy Lett. 10, 4518\n(2025)). Instead, the 3D perovskites usually have relatively higher carrier mobilities of\n~ 10-4 cm2 V-1 s-1 (e.g., 2.93 × 10-4 cm2 V-1 s-1 in this work).\nIn addition, the broad emission bandwidths exceeding 20 nm were frequently reported\nfor the quasi-2D perovskites and nanocrystal-based pure-blue PeLEDs (shown in Table\nR2 below). In quasi-2D perovskites, the wide phase distribution is typically observed,\nwhich accounts for broad emissions for the pure-blue PeLEDs. For the pure-blue\nnanocrystal systems, it is a big challenge to obtain a very uniform size distribution. The\nnon-uniform size of the pure-blue QDs induces a broad emission for the devices. For\nexample, the large size distribution range of over 3 nm were extensively observed for\nthe small-sized CsPbBr nanocrystals with average sizes of ~ 3 − 10 nm, resulting in a\n3\nbroad blue emission of over 20 nm (ACS Energy Lett. 8, 731 (2023); Small 20, 2400885\n(2024); Adv. Mater. 37, e20131 (2025)). In addition, the emission bandwidth was\nreported to further increase from 25 to 53 nm with enlarging the nanocrystal size\ndistribution range from ~ 5 to 20 nm (shown in Fig. R7 below).\nFor the 3D pure-blue perovskite emitters, the emission bandwidth is greatly influenced\nby the halide homogeneity and the defect density. The halide heterogeneity in mixed\nbromide-chloride perovskites has been well addressed by the effective strategies, such\nas vapor-assisted crystallization (VAC) treatment, where the full-width at half-\nmaximum (FWHM) of ~18 nm could be achieved (Nat. Commun. 12, 361 (2021)). Very\nencouragingly, we report high-quality 3D pure-blue perovskite emitters with single\ncrystal-like morphology for reduced trap state density. Subsequently, we further narrow\nthe emission bandwidth to merely 14 nm, representing the narrowest emission\nbandwidth among the state-of-the-art pure-blue PeLEDs (Table R2 below). The result\nshows an instructive approach of our work to achieve narrow emissive pure-blue\nPeLEDs.\nTable R2Comparison of the EL emission bandwidth of pure-blue (<475 nm) PeLEDs.\nEL peak FWHM\nType Perovskite Published journal\n(nm) (nm)\nCsPbBr 469 21 ACS Energy Lett. 8, 731 (2023)\nQDs\nAngew. Chem. Int. Ed. 63,\nCsPb(Cl/Br)3 467 ~20\ne202408726 (2024)\nCsPb(Cl/Br)3 470 ~17 Sci. Adv. 10, eado5645 (2024)\nCsPbBr 469 25 Adv. Mater. 37, e20131 (2025)\n3\n(Cs/pFPEA)Pb(Br/Cl) 468 ~21 Adv. Mater. 35, 2302161 (2023)\n3\n(Cs/pFPEA)/PPN)Pb(Cl/Br) 474 ~21 Nat. Photonics 18, 425 (2024).\n3\n(Cs/FA/pFPEA)Pb(Cl/Br) 468 ~22 Nat Commun. 15, 10621 (2024).\n3\n(Cs/pFPEA)Pb(Br/Cl) 469 22 Adv. Mater. 37, 2412041 (2024)\nQuasi-2D 3\n(Cs/PEA)Pb(Cl/Br)3 468 22 ACS Energy Lett. 10, 3638 (2025).\nPPA/PEA/Li-CsPb(Br/Cl) 467 23 Adv. Mater. 37, 2409718 (2025)\n(Cs/pFPEA)Pb(Br/Cl)3 468 ~27\ne202513617 (2025)\n(Cs/Rb/FA)Pb(Cl/Br) 467 18 Nat Commun. 12, 361 (2021).\n3\n(Cs/Rb/FA)Pb(Cl/Br) 473 17 ACS Photonics 11, 5380 (2024)\n3\n(Cs/Rb/FA)Pb(Cl/Br)3 466 ~16 Adv. Mater. 26, 2414788 (2024)\n3D\nAdv. Optical Mater. 13, 2500544\n(Cs/Rb/FA)Pb(Cl/Br)3 466 ~19\n(2025)\n(FA/Cs/Rb)(Pb/Sr)(Br/Cl)3 468 ~17 Nat Commun. 16, 3254 (2025)\n(Cs/Rb/FA)Pb(Cl/Br) 473 14 Our work\n3\n[FIGURE REDACTED]\nFig. R7 The synthesized CsPbBr nanocrystals in the work of Small 20, 2400885 (2024),\n3\nwhich includes the variations in nanocrystal morphology, size distribution, and\nemission spectra.\nAccordingly, Table R2 has been included in Supplementary Table 3 of the revised\nSupplementary Information (page S16)\nC2: The morphological differences between control and target perovskite in Figures 1a and 1b\nare notable. While the facet-growth mechanism is proposed, it remains unclear whether the\ngrain corner change stems from enhanced (111) facet growth or an alternative mechanism. A\ndiscussion of how adjacent facets interact and form corners during grain formation would be\nhelpful.\nR: Thanks for the suggestion. For the perovskites with cubic phase, the grain corner is\ninvolved in different facets, such as (100) and (111) facets (Joule 6, 2626 (2022)). In\nour proposed target perovskites, the grain corner change is also contributed from the\ngrowth of (100) and (111) facets, i.e., the (100) and (111) facet growths promote the\ngrain corner growth. However, we demonstrate that the crystal growth along the (100)\nfacet is dominant in the target perovskites, as verified by the sharp and strong diffraction\npeaks of the (100) plane (shown in Fig. R8a below). Consistently, the diffraction peak\nintensity ratio of the (100)/(111) crystal facets increases from 1.5 (control) to 27.1 for\nthe target perovskites. The results indicate that the (100) facet growth contributes\ndominantly to both grain corner and lattice plane growths (illustrated in Fig. R9 below),\nwhich prompt the single crystal-like morphology with regular crystal grains (shown in\nFig. 1b below). The (100) facet growth-assisted fabrication of MAPbBr single crystal\n3\nwas also demonstrated in previous works (J Mater Sci 52, 7907–7916 (2017), Fig.\nR10a below). Meanwhile, the modulation of one certain facet growth for single-\ncrystalline morphology has also been reported for the Sn-based perovskite system very\nrecently (Adv. Mater. DOI: 10.1002/adma.202512927, Fig. R10b below). These results\nfirmly support our strategy for high-quality perovskite crystals.\nFig. R8 a) The XRD measurements and b) the diffraction peak intensity ratio of the\n(100)/(111) crystal facets of control and target perovskites.\nFig. R9 Illustrations of the plane growth and the corner growth along the (100) facet.\nFig. 1 Characteristics of perovskite morphology and facet. SEM images of a) control\nand b) target perovskites.\n[FIGURE REDACTED]\nFig. R10 a) The (100) facet growth-assisted fabrication of MAPbBr perovskite single\n3\ncrystal in the work of J Mater Sci 52, 7907–7916 (2017) and b) the (001) facet growth\nin CsSnI films for single-crystalline morphology (Adv. Mater. DOI:\n3\n10.1002/adma.202512927).\nC3: The schematic illustration in Figure 1g looks a little weird. It looks as if the BAPEG\nmolecules are randomly placed on the (1 1 0) and (1 1 1) surface without significant orientation\nand binding to perovskite surface. Are there any more reasonable absorption configurations?\nThe author might need to check the electron density changes of BAPEG molecules to perovskite\nsurface absorption and find out the exact interactions.\nR: Sorry for the confusion, and thanks for the suggestion. The interaction between\nBAPEG and the perovskite (i.e., the coordination and hydrogen bonding interactions\nbetween BAPEG and the lead-halide complex) induces the adsorption of BAPEG on\nthe perovskite facets. The bonding interaction between BAPEG and the perovskite\nfacets was usually omitted as exhibited in previous works (e.g., Nano-Micro Lett. 15,\n138 (2023); Joule 8, 3169 (2024); Nature 620, 323 (2023); Adv. Mater. 36, 2313524\n(2024), shown in Fig. R11 below). To clearly show the interaction between BAPEG\nand the perovskite, the charge density differences based on density functional theory\n(DFT) calculations were analyzed (shown in Supplementary Fig. 4 below).\nSpecifically, the valence electrons are merely gathered and distributed near the\nseparated atoms of BAPEG if there is no interaction between BAPEG and the\nperovskite. Conversely, the deformation of the electron distributions clearly elucidates\nthe distinct charge transfer processes between hydrogen and Br/Cl halide atoms, as\nwell as oxygen and lead atoms for BAPEG-treated perovskite. The differential charge\ndensity images strongly show the bonding interaction between BAPEG and the\nperovskite facets. As for the orientation of BAPEG, it may be difficult to determine\ncertain adsorption sites of BAPEG on the perovskite facet by considering the average\nmolecular weight (Mn) of ~ 1500 for BAPEG. While the horizontal adsorption of\nBAPEG on (100), (110), and (111) facets through the coordination and hydrogen\nbonding interactions is demonstrated, as schematically illustrated in the manuscript (Fig.\n1i).\n[FIGURE REDACTED]\nFig. R11 Illustrations of the molecular adsorptions on the perovskite surface in previous\nworks, where the bonding interactions were usually omitted in the configurations.\nSupplementary Fig. 4 The differential charge density images of BAPEG adsorption\non a) (100), b) (110), and c) (111) facets of the perovskites.\nAccordingly, Supplementary Fig. 4 has been added to the revised Supplementary\nInformation (page S3). Meanwhile, the following discussion has been added to the\nrevised manuscript (line 12, page 6).\nThe electrostatic forces between the functional groups of BAPEG and the lead-halide\ncomplex of the perovskites, including coordination and hydrogen bonding interactions,\ninduce the spontaneous adsorption of BAPEG on the (100), (110), and (111) facets of\nthe perovskites, as verified by the differential charge density images (Supplementary\nFig. 4).\nC4: The adopted molecule of bis(3-aminopropyl)polyethylene glycol was dissolved in\nchlorobenzene. The potential impact of this solvent on perovskite morphology should be\nevaluated, with comparisons to alternative polar and non-polar solvents.\nR: Thanks for the kind suggestion. To investigate the effect of the solvent on the\nperovskite morphology, the chlorobenzene (CB) solvent was solely employed to treat\nthe perovskites. As shown in Supplementary Fig. 2 below, the perovskite morphology\nafter chlorobenzene treatment is very similar to that of the control perovskites,\nindicating no significant effect of the chlorobenzene solvent on the perovskite\nmorphology. Besides, the polar solvent of isopropanol (IPA) was also adopted to treat\nthe perovskites (shown in Fig. R12 below), where there is also no significant variation\nof the perovskite morphology. These observations show that the polar and non-polar\nsolvents, e.g., chlorobenzene and isopropanol, have no significant effect on the\nperovskite morphology, which further verifies the important role of the proposed\nBAPEG in modulating the perovskite morphology.\nSupplementary Fig. 2 SEM images of a) control and b) chlorobenzene (CB)-treated\nperovskites.\nFig. R12 SEM image of isopropanol (IPA)-treated perovskites.\nAccordingly, Supplementary Fig. 2 has been added to the revised Supplementary\nInformation (page S2). Meanwhile, the following discussion has been added to the\nrevised manuscript (lines 20-22, page 5).\nWhile no variation of the perovskite morphology after chlorobenzene treatment verifies\nthe important role of BAPEG in modulating the perovskite growth (Supplementary Fig.\n2).\nC5: It is noted that the BAPEG treatment is applied to the perovskite films before the annealing.\nIs there any difference in the perovskite morphology of the BAPEG treatment after the\nannealing process?\nR: In the manuscript, the BAPEG treatment is applied to the perovskite films before\nthe annealing (i.e., before Ostwald ripening of the perovskite crystals). When the\nBAPEG treatment is applied after the crystal ripening with the annealing process, there\nis no significant role of BAPEG in modulating the perovskite morphology (shown in\nFig. R13 below) due to the completed crystal growth after the annealing process.\nFig. R13 SEM image of the annealed perovskites, followed by treatment with BAPEG.\nC6: The carrier mobility of the target perovskite films should be measured to verify the high-\nquality perovskite crystals after BAPEG treatment.\nR: Thanks for the suggestion. The carrier mobility of the perovskite films can be\nestimated from the space charge limited current (SCLC) measurement with a device\nstructure of ITO/ NiO /PVK/perovskite/MoO /Au. In the space-charge-limited current\nx 3\nregion, the J-V behavior of the perovskite devices can be expressed by the function of\nJ = (9ε εμV2)/(8L3). The carrier mobility can be obtained from the slope of the fitted\n0 r\nJ1/2 -V curves (shown in Supplementary Fig. 10d below). The obtained carrier mobility\nfor the target perovskites is 2.93 × 10-4 cm2 V-1 s-1, which is larger than 9.95 × 10-5 of\nthe control perovskites, verifying the high-quality perovskite crystals after BAPEG\ntreatment for enhanced carrier mobility.\nSupplementary Fig. 10d) J1/2 -V curves of the control and target perovskite devices.\nAccordingly, Supplementary Fig. 10d has been added to the revised Supplementary\nInformation (page S8) with the following discussion (lines 17-19, page S7).\nMeanwhile, the carrier mobility can be obtained from the slope of the fitted J1/2 -V\ncurves, which is estimated as 9.95 × 10-5 and 2.93 × 10-4 cm2 V-1 s-1for the control and\ntarget perovskites, respectively.\nC7: The energy levels of the target perovskite films are shown in the manuscript, while\ncorresponding data for the control films should be included for comprehensive comparison.\nR: Thanks for the suggestion. The energy levels of the control perovskite films were\ndetermined by ultraviolet photoelectron spectroscopy (shown in Supplementary Fig.\n14 below). As observed, the energy levels of the target perovskite films are comparable\nto those of the control perovskite films, indicating no significant effect of BAPEG\ntreatment on the perovskite energy bands. Both the control and target perovskite films\nexhibit flat energy bands to the highest occupied molecular orbital (HOMO) of PVK,\nthus promoting efficient hole transportation.\nSupplementary Fig. 14 UPS measurements and the energy levels of the a-c) control\nand d-f) target perovskite films.\nAccordingly, Supplementary Figs. 14 have been updated in the revised Supplementary\nInformation (page S10).\nC8: The operational stability tests in Figure 4h should include concurrent voltage changes to\nbetter correlate performance decay with electrical behavior.\nR: Thanks for the suggestion. The operational stability tests of the devices were\nperformed under a constant current with an initial luminance of ~ 100 cd m-2. The\nvoltage variations during the operational stability tests were also traced to correlate well\nwith performance decay in electrical behavior. As shown in Supplementary Fig. 17\nbelow, the voltages increase along with the operation time, showing the increased\ndevice resistance during operation.\nSupplementary Fig. 17 The variations of bias voltage traced during the lifetime test\nfor the control and target devices.\nAccordingly, Supplementary Fig. 17 has been added to the revised Supplementary\nInformation (page S12).\nResponses to the 4th reviewer's comments\nReviewer #4: I co-reviewed this manuscript with one of the reviewers who provided the listed\nreports. This is part of the Nature Communications initiative to facilitate training in peer review\nand to provide appropriate recognition for Early Career Researchers who co-review\nmanuscripts.\nR: We thank the reviewer for the valuable suggestions to further improve the quality of\nour manuscript.\nPoint-by-point response to reviewers\nWe have revised our manuscript carefully based on the reviewers’ comments. Follows\nare our replies (R) to reviewers’ comments (C):\nResponses to the 1st reviewer's comments\nReviewer #1(Remarks to the Author):\nChen et al. report a high-performance perovskite LED by incorporating an additive molecule\nthat is claimed to regulate crystal growth. However, the central premise—molecule/additive-\nassisted modulation of perovskite crystallization and film formation—has been extensively\nexplored in the perovskite optoelectronics literature. As presented, the strategy appears\nincremental and lacks clear significance for the field. In particular, the proposed approach\ndoes not demonstrate sufficient novelty in light of prior reports (e.g.,\ndoi.org/10.1002/aenm.202506630; doi.org/10.1002/adom.202403012;\ndoi.org/10.1002/aenm.202403965; Nano Lett. 2024, 24(35), 10972–10979; among others).\nR: Sorry for the misunderstanding. The mentioned reports\n(doi.org/10.1002/aenm.202506630 (Adv. Energy Mater. 2026, 0:e06630);\ndoi.org/10.1002/adom.202403012 (Adv. Optical Mater. 2025, 13, 2403012);\ndoi.org/10.1002/aenm.202403965 (Adv. Energy Mater. 2025, 15, 2403965); Nano Lett.\n2024, 24(35), 10972–10979) concentrate on the additive-assisted modulation of\nperovskite crystallization and film formation, where different additives were directly\nadded into the perovskite precursor solution. However, this strategy was limited in\neffectively modulating the perovskite crystallization and film formation, where there is\nno significant improvement in either the perovskite crystallinity or the film orientation,\nas verified by the XRD and SEM characterizations in the mentioned reports (shown in\nFig. R1 and R2 below). As verified, the authors said merely double peak intensity\ncompared to the control film in the report (Adv. Optical Mater. 2025, 13, 2403012).\nVery differently, we propose a unique crystal growth regulation strategy mediated by\nbis(3-aminopropyl)polyethylene glycol (BAPEG) with the post-treatment approach\ninstead of the additive-assisted strategy, which dramatically improves the perovskite\ncrystallinity with nearly 5.5-fold higher diffraction peak intensity than the control ones.\nMore importantly, the distinct variations of the film morphology from island-like\nmorphology with random crystal facets to single crystal-like morphology with regular\ncrystal grains are demonstrated in our approach (shown in Fig. 1a-c below).\nFurthermore, we demonstrate distinctively oriented crystal growth along the (100) facet\nby suppressing the (110) and (111) planes, where the diffraction peak intensity ratio of\nthe (100)/(111) crystal facets greatly increases from 1.5 (control) to 27.1 for the target\nperovskites (shown in Fig. R3 below). These differences and functions firmly reveal\nthe uniqueness of our approach to previous reports, which contributes to a novel and\neffective strategy in dramatically modulating the perovskite crystallization and film\nformation.\n[FIGURE REDACTED]\nFig. R1 The XRD signals of the perovskite films with the strategy of additive-assisted\nmodulation of perovskite crystallization and film formation in the mentioned reports of\nAdv. Energy Mater. 2026, 0:e06630 (doi.org/10.1002/aenm.202506630), b Adv.\nOptical Mater. 2025, 13, 2403012 (doi.org/10.1002/adom.202403012), c Adv. Energy\nMater. 2025, 15, 2403965 (doi.org/10.1002/aenm.202403965), and d Nano Lett. 2024,\n24(35), 10972–10979.\n[FIGURE REDACTED]\nFig. R2 The SEM images of the perovskite films with the strategy of additive-assisted\nmodulation of perovskite crystallization and film formation in the mentioned reports.\nFig. 1 a, b) SEM images and c) XRD measurements of control and BAPEG-treated\n(target) perovskites.\nFig. R3 a) The XRD measurements and b) the diffraction peak intensity ratio of the\n(100)/(111) crystal facets of control and target perovskites.\nAccordingly, we have extended the discussion in the manuscript (lines 31-33, page 6)\nas follows:\nConsequently, the remarkable variation in film morphology, dramatic improvement in\nthe perovskite crystallinity, and distinctive orientation in crystal growth contribute to\nthe uniqueness and effectiveness of our approach to conventional additive-assisted\nmodulation of perovskite crystallization and film formation.\nMoreover, the mechanistic basis for facet orientation during perovskite crystal growth has\nalready been clearly established (e.g., Nature Synthesis 4, 1088–1094 (2025)). The manuscript\ndoes not convincingly differentiate its mechanistic insights from this existing understanding. At\nthe molecular-design level, the selected additive also appears closely related to molecules\nreported previously (e.g., NH2-PEG5-NH2, ACS Nano 2025, 19(17), 16850–16858), further\nweakening the novelty claim.\nR: Sorry for the misunderstanding. In the mentioned work (Nature Synthesis 4, 1088–\n1094 (2025)), the authors propose the interfacial particle redissolution and monomer\nattachment between the crystal and precursor solution to explain the perovskite crystal\ngrowth. This crystal growth process was driven by a latent heat-induced cool interfacial\nlayer, which did not involve the specific crystal facet modulation.\nVery differently, we propose a mechanism of energy-driven facet-selective crystal\ngrowth to accurately modulate the certain facet formation by promoting (100) and\nsuppressing (110) and (111) facet growth. The specific crystal facet growth modulation\nis driven by thermodynamically favorable selective adsorption of BAPEG on the crystal\nfacet with variable diffusions of the perovskite precursor ions.\nIn addition, in the mentioned report (ACS Nano 2025, 19(17), 16850–16858), the\nmolecule of 3,6,9,12,15-pentaoxaheptadecane-1,17-bis-amine (NH -PEG -NH ) was\n2 5 2\nused as an additive to passivate ionic defects and slow down the crystallization of\nperovskites. However, both the molecular structure and functions of our bis(3-\naminopropyl)polyethylene glycol (with an average molecular weight of ~ 1500) are\ndifferent from those of the reported molecule. Our proposed molecule was employed\nas a post-treatment agent, where the important role of selective adsorption on perovskite\n(100), (110), and (111) facets was adopted to accurately modulate the specific facet\ngrowth process.\nAccordingly, we have extended the discussion in the manuscript (lines 1-4, page 7) as\nfollows:\nWe also reveal a different crystal growth mechanism of energy-driven facet-selective\ncrystal growth from the latent heat-induced cool interfacial layer-assisted crystal\ngrowth42 by accurately modulating certain facet growth processes.\nFinally, the authors do not provide a rigorous, quantitative causal link between the claimed\nimprovements in “crystal quality” and the enhanced EL efficiency. This point is important\nbecause high luminescence efficiency does not necessarily require highly crystalline or highly\nordered films (for example, many high-performance OLEDs employ amorphous emitting\nlayers). Without a clearer structure–property relationship and stronger evidence of distinct\nmechanistic contribution, I do not find the current work suitable for publication in Nature\nCommunications and therefore cannot recommend acceptance.\nR: Sorry for the misunderstanding. Different from the mentioned amorphous emitting\nlayers for high-performance OLEDs, considerable reports have demonstrated the\nessential importance of high-crystallinity perovskite films in achieving high-\nperformance perovskite devices (Nature 628, 299–305 (2024); Nature 536, 312–316\n(2016); Nature 517, 476–480 (2015)).\nIn our work, we clearly show the great improvement in perovskite crystallinity (i.e.,\n5.5-fold higher diffraction peak intensity than the control ones), effective suppression\nof the unfavorable crystal facet-correlated defects (i.e., reduced by more than 78% of\nthe density of trap states), and enhanced carrier radiative recombination (i.e., improved\nexciton binding energy from 40.7 to 55.2 meV) by our approach. As a result, the\nemission efficiency of the perovskite films is largely improved with a peak\nphotoluminescence quantum yield (PLQY) increasing to over 2-fold higher from 18.6%\nto of 41.5%. The perovskite structure-featured emission efficiency improvement\ncontributes to high-performance PeLEDs, as shown in the manuscript.\nAccordingly, we have added the quantitative values of “with nearly 5.5-fold higher\npeak intensity than the control ones” and “an over 2-fold higher photoluminescence\nquantum yields (PLQY) from 18.6% to of 41.5%” in the manuscript (line 24, page 5 and\nlines 26 and 27, page 8)\nReviewer #2’s further comments\nI have carefully checked the response letter and revised manuscript again. The proposed\nmechanisms about the facet orientation during crystallization in this manuscript should be\nclearly manifested about the differences from that reported in Nature Synthesis 4, 1088-1094\n(2025). The authors are suggested to conduct a comprehensive and in-depth study of the\nstructure-property relationship. It lacks scientific logic and rigor that simply attributing the\nimprovement in performance of blue PeLEDs to the reduction of defects. Following are some\ncomments, which may help the authors further improve the quality of the manuscript.\n1. What is the experimental evidence for the claim that perovskite (111) facet and (110) facet\nhave the higher defect density than (100) facet?\nR: The metal halide perovskite crystal facet strongly correlates with the generation of\ntrap states, where the lower defect density of the (100) facet than the (111) and (110)\nfacets has been extensively demonstrated with substantial experimental evidence in\nprevious works (e.g., Nat. Energy 5, 131–140 (2020); Nat. Energy 6, 624 (2021);\nScience 379, 173–178 (2023); Joule 6, 240–257 (2022); Joule 6, 2626–2643 (2022);\nAdv. Mater. 34, 2204342 (2022); Energy Environ. Sci., 18, 9865–9876 (2025); Adv.\nFunct. Mater. 35, 2422783 (2025); Adv. Funct. Mater. 32, 2206838 (2022); Adv. Sci.\n11, 2401184 (2024); Cryst. Growth Des. 18, 6652 (2018)).\nAdditionally, we show the easier formation of halogen vacancy on (110) and (111)\nfacets than on the (100) facet due to their smaller halogen vacancy formation energy\nthan that of the (100) facet. In detail, the chloride vacancy formation energies are 2.98\nand 2.47 eV for the (110) and (111) facets. While the chloride vacancy formation\nenergy is 3.30 eV for the (100) facet, which is much larger than that of the (110) and\n(111) facets. Consistently, the bromide vacancy formation energy of 3.19 eV for the\n(100) facet is also significantly larger than 2.86 and 2.40 eV for (110) and (111) facets,\nrespectively. The result indicates more difficulty in the formation of the trap states on\nthe (100) facet than on the (110) and (111) facets.\nTherefore, our work mainly focuses on specific crystal facet growth modulation to\nachieve high-quality perovskites. We propose a distinctive mechanism of energy-driven\nfacet-selective crystal growth to accurately modulate the certain facet formation, in\nwhich the favorable (100) facet growth is greatly promoted, while the (110) and (111)\nfacet growths are significantly suppressed. As a result, single crystal-like perovskites\nare achieved with high crystallinity, low trap state density, large exciton binding energy,\nand regular crystal morphology, thus contributing to high device performances.\n2. The author claimed that it is the massive defects hinder the performance of pure-blue\nPeLEDs, however, it is inconvincible that the reduction in trap density of only 78% can make\nthe significant performance improvement. The trap density in target film is still at a high level\nof closed to 10^17 cm-3, while the reported state-of-art blue perovskite shows a low trap density\nof only 10^15 cm-3 (e.g. 10.1038/s41586-022-05486-3). The underlying reasons and factors\nshould be further explored.\nR: In space charge-limited current (SCLC) measurements, in addition to the trap-filled\nlimit voltage, the trap density is also closely dependent on the perovskite thickness and\ndielectric constant. In other words, it is inappropriate to directly evaluate the trap\ndensity situations of the perovskites with different thicknesses and compositions.\nHowever, when comparing the trap density of the blue-emissive perovskites with\nsimilar thickness and composition, we observe nearly one order of magnitude decrease\nin the trap density of our target perovskites (Table R1 below).\nBesides, we also exhibit a distinct enhancement in exciton binding energy from 40.7 to\n55.2 meV for the target perovskites in the manuscript (Fig. 2i of the manuscript) due to\nthe increased dielectric confinement by the adsorption of BAPEG on the perovskite\nsurface (Supplementary Fig. 10c of the Supplementary Information). Both the low trap\nstate density and high exciton binding energy promote a largely improved emission\nefficiency of the perovskite films for high-performance devices.\nTable R1 Comparison of the trap state densities of the blue-emissive perovskites with\nsimilar thickness and composition.\nControl Target\nPerovskite Published journals\n(cm-3) (cm-3)\n(Cs/PEA)Pb(Cl/Br) 2.28 × 1017 1.93 × 1017 ACS Energy Lett. 10, 3638 (2025)\n(Cs/FA/pFPEA)Pb(Cl/Br) 4.21 × 1018 2.92 × 1018\n3\n(2024).\n(Cs/GA/pFPEA)Pb(Cl/Br) 2.81 × 1018 1.02 × 1018 Adv. Mater. 35, 2302161 (2023)\n(Cs/FA/K/PEA)Pb(Cl/Br) 2.80 × 1018 1.70 × 1018\n3\ndoi.org/10.1002/adma.202521547 (2026)\n(Cs/GA/4F- ACS Energy Lett. 10, 11, 5405–5413\n3.90 × 1018 3.25 × 1018\nPEA/PEA)Pb(Cl/Br) (2025)\n3\n(Cs/FA/p-\n3.99 × 1018 2.88 × 1018 Nat. Commun.15, 10621 (2024)\nPEA/K)Pb(Cl/Br)\n3\n(Cs/Rb/FA)Pb(Cl/Br) 4.50 × 1017 9.79 × 1016 Our work\n3\n3. The control sample shows a consistent curve trend with the target one in power density-\ndependent PLQYs, absent of the apparent trap-filled region, which is contradicted with the\nassertion of the massive trap in the control film.\nR: Sorry for the confusion. The seemingly consistent curve trend of the power density-\ndependent PLQYs for the control perovskites is induced by the large range of the PLQY\nvalues in y-axis. When we narrow the y-axis range (shown in Supplementary Fig. 11\nbelow), a trap saturation process at low excitation intensity is observed for the control\nperovskites. Whereas the target perovskites show nearly a consistent curve trend,\nshowing fewer trap states in the perovskite films.\nSupplementary Fig. 11 Fluence-dependent PLQYs for control and target perovskites.\nAccordingly, we have updated the y-axis range in Supplementary Fig. 11 of the\nSupplementary Information (page S9)\n4. What is the reason for the significant increase in current density for the target device?\nWill the additive affect the electrical properties of the perovskite film? As different facets may\nshow distinct carrier mobilities, more related analyses are needed to fully uncover the\nmechanism of the device performance.\nR: The significant increase in current density for the target device can be attributed to\nthe increased carrier mobility. The carrier mobility of the perovskite films was\nmeasured in Supplementary Fig. 10 of the Supplementary Information, where the\nobtained carrier mobility for the target perovskites is 2.93 × 10-4 cm2 V-1 s-1, which is\nlarger than 9.95 × 10-5 of the control perovskites, indicating the preferred (100) facet\nfor enhanced carrier mobility. The improved carrier mobility also benefits the high\ndevice performance.\nAccordingly, we have extended the following discussion in the manuscript (lines 5 and\n6, page 11).\nWhile the significant increase in current density for the target device can be attributed\nto the improved carrier mobility (Supplementary Fig. 10).\n5. Generally, the stretching vibration signals from groups such as C-O or NH2 on the additive\nwill shift to lower wavenumbers after interacting with the perovskite. But they shift to a higher\nwavenumbers in the BAPEG-Pb(Br/Cl)2 complex. Please clarify this apparent discrepancy.\nR: Besides the coordination interaction between BAPEG and the lead-halide complex,\nwe also demonstrated the hydrogen bonding interaction between BAPEG and the halide\nions, which shifts the stretching vibration of N-H to a high wavenumber due to the\nstrengthened stretching vibration by accepting the electron from the halide ions. This\ntrend has been widely observed in previous works (e.g., Angew. Chem. Int. Ed. 2024,\n63, e202411361; Adv. Mater. 2024, 36, 2400658; Nano Energy 2022, 95, 107000; Adv.\nMater. 2019, 31, 1904319, shown in Fig. R4a, b below)\nBesides, the characteristic shifts to higher wavenumbers after the interaction with the\nperovskite for C-O bond were also extensively demonstrated previously due to the\nincreased bond order of the C-O bond by coordination with the perovskite (e.g., Adv.\nFunct. Mater. 2024, 34, 2311527; Device 2024, 2, 100285; J. Am. Chem. Soc. 2020,\n142, 47, 19980–19991; Nat. Commun. 2021, 12, 3383, shown in Fig. R4c, d below).\n[FIGURE REDACTED]\nFig. R4 FT-IR signals of a, b) -NH and c, d) C-O groups before and after interaction\n2\nwith the perovskites in previous works."}, {"round": 2, "reviewer_comments": {"reviewer_1": "Chen et al. report a high-performance perovskite LED by incorporating an additive molecule that is claimed to regulate crystal growth. However, the central premise—molecule/additive-assisted modulation of perovskite crystallization and film formation—has been extensively explored in the perovskite optoelectronics literature. As presented, the strategy appears incremental and lacks clear significance for the field. In particular, the proposed approach does not demonstrate sufficient novelty in light of prior reports (e.g., doi.org/10.1002/aenm.202506630; doi.org/10.1002/adom.202403012; doi.org/10.1002/aenm.202403965; Nano Lett. 2024, 24(35), 10972–10979; among others).\nMoreover, the mechanistic basis for facet orientation during perovskite crystal growth has already been clearly established (e.g., Nature Synthesis 4, 1088–1094 (2025)). The manuscript does not convincingly differentiate its mechanistic insights from this existing understanding. At the molecular-design level, the selected additive also appears closely related to molecules reported previously (e.g., NH2-PEG5-NH2, ACS Nano 2025, 19(17), 16850–16858), further weakening the novelty claim.\nFinally, the authors do not provide a rigorous, quantitative causal link between the claimed improvements in “crystal quality” and the enhanced EL efficiency. This point is important because high luminescence efficiency does not necessarily require highly crystalline or highly ordered films (for example, many high-performance OLEDs employ amorphous emitting layers). Without a clearer structure–property relationship and stronger evidence of distinct mechanistic contribution, I do not find the current work suitable for publication in Nature Communications and therefore cannot recommend acceptance.", "reviewer_2": "In the revised manuscript, the authors have well addressed all the reviewers' concerns and further improved the manuscript quality. The work is of great interest to the PeLED community, representing a significant advance in the field of perovskite based optoelectronic devices.. Therefore, I strongly recommend the publication of this work in Nature Communications.\n*******\nI have carefully checked the response letter and revised manuscript again. The proposed mechanisms about the facet orientation during crystallization in this manuscript should be clearly manifested about the differences from that reported in Nature Synthesis 4, 1088-1094 (2025). The authors are suggested to conduct a comprehensive and in-depth study of the structure-property relationship. It lacks scientific logic and rigor that simply attributing the improvement in performance of blue PeLEDs to the reduction of defects. Following are some comments, which may help the authors further improve the quality of the manuscript.\n1. What is the experimental evidence for the claim that perovskite (111) facet and (110) facet have the higher defect density than (100) facet?\n2. The author claimed that it is the massive defects hinder the performance of pure-blue PeLEDs, however, it is inconvincible that the reduction in trap density of only 78% can make the significant performance improvement. The trap density in target film is still at a high level of closed to 10^17 cm-3, while the reported state-of-art blue perovskite shows a low trap density of only 10^15 cm-3 (e.g. 10.1038/s41586-022-05486-3). The underlying reasons and factors should be further explored.\n3. The control sample shows a consistent curve trend with the target one in power density-dependent PLQYs, absent of the apparent trap-filled region, which is contradicted with the assertion of the massive trap in the control film.\n4. What is the reason for the significant increase in current density for the target device? Will the additive affect the electrical properties of the perovskite film? As different facets may show distinct carrier mobilities, more related analyses are needed to fully uncover the mechanism of the device performance.\n5. Generally, the stretching vibration signals from groups such as C-O or NH2 on the additive will shift to lower wavenumbers after interacting with the perovskite. But they shift to a higher wavenumbers in the BAPEG-Pb(Br/Cl)2 complex. Please clarify this apparent discrepancy.", "reviewer_3": "In this version, the authors have provided robust and comprehensive data, and have addressed almost all of my previous concerns. I therefore recommend accepting the manuscript.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Point-by-point response to reviewers\nWe have revised our manuscript carefully based on the reviewers’ comments. Follows\nare our replies (R) to reviewers’ comments (C):\nResponses to the 1st reviewer's comments\nReviewer #1(Remarks to the Author):\nChen et al. report a high-performance perovskite LED by incorporating an additive molecule\nthat is claimed to regulate crystal growth. However, the central premise—molecule/additive-\nassisted modulation of perovskite crystallization and film formation—has been extensively\nexplored in the perovskite optoelectronics literature. As presented, the strategy appears\nincremental and lacks clear significance for the field. In particular, the proposed approach\ndoes not demonstrate sufficient novelty in light of prior reports (e.g.,\ndoi.org/10.1002/aenm.202506630; doi.org/10.1002/adom.202403012;\ndoi.org/10.1002/aenm.202403965; Nano Lett. 2024, 24(35), 10972–10979; among others).\nR: Sorry for the misunderstanding. The mentioned reports\n(doi.org/10.1002/aenm.202506630 (Adv. Energy Mater. 2026, 0:e06630);\ndoi.org/10.1002/adom.202403012 (Adv. Optical Mater. 2025, 13, 2403012);\ndoi.org/10.1002/aenm.202403965 (Adv. Energy Mater. 2025, 15, 2403965); Nano Lett.\n2024, 24(35), 10972–10979) concentrate on the additive-assisted modulation of\nperovskite crystallization and film formation, where different additives were directly\nadded into the perovskite precursor solution. However, this strategy was limited in\neffectively modulating the perovskite crystallization and film formation, where there is\nno significant improvement in either the perovskite crystallinity or the film orientation,\nas verified by the XRD and SEM characterizations in the mentioned reports (shown in\nFig. R1 and R2 below). As verified, the authors said merely double peak intensity\ncompared to the control film in the report (Adv. Optical Mater. 2025, 13, 2403012).\nVery differently, we propose a unique crystal growth regulation strategy mediated by\nbis(3-aminopropyl)polyethylene glycol (BAPEG) with the post-treatment approach\ninstead of the additive-assisted strategy, which dramatically improves the perovskite\ncrystallinity with nearly 5.5-fold higher diffraction peak intensity than the control ones.\nMore importantly, the distinct variations of the film morphology from island-like\nmorphology with random crystal facets to single crystal-like morphology with regular\ncrystal grains are demonstrated in our approach (shown in Fig. 1a-c below).\nFurthermore, we demonstrate distinctively oriented crystal growth along the (100) facet\nby suppressing the (110) and (111) planes, where the diffraction peak intensity ratio of\nthe (100)/(111) crystal facets greatly increases from 1.5 (control) to 27.1 for the target\nperovskites (shown in Fig. R3 below). These differences and functions firmly reveal\nthe uniqueness of our approach to previous reports, which contributes to a novel and\neffective strategy in dramatically modulating the perovskite crystallization and film\nformation.\n[FIGURE REDACTED]\nFig. R1 The XRD signals of the perovskite films with the strategy of additive-assisted\nmodulation of perovskite crystallization and film formation in the mentioned reports of\nAdv. Energy Mater. 2026, 0:e06630 (doi.org/10.1002/aenm.202506630), b Adv.\nOptical Mater. 2025, 13, 2403012 (doi.org/10.1002/adom.202403012), c Adv. Energy\nMater. 2025, 15, 2403965 (doi.org/10.1002/aenm.202403965), and d Nano Lett. 2024,\n24(35), 10972–10979.\n[FIGURE REDACTED]\nFig. R2 The SEM images of the perovskite films with the strategy of additive-assisted\nmodulation of perovskite crystallization and film formation in the mentioned reports.\nFig. 1 a, b) SEM images and c) XRD measurements of control and BAPEG-treated\n(target) perovskites.\nFig. R3 a) The XRD measurements and b) the diffraction peak intensity ratio of the\n(100)/(111) crystal facets of control and target perovskites.\nAccordingly, we have extended the discussion in the manuscript (lines 31-33, page 6)\nas follows:\nConsequently, the remarkable variation in film morphology, dramatic improvement in\nthe perovskite crystallinity, and distinctive orientation in crystal growth contribute to\nthe uniqueness and effectiveness of our approach to conventional additive-assisted\nmodulation of perovskite crystallization and film formation.\nMoreover, the mechanistic basis for facet orientation during perovskite crystal growth has\nalready been clearly established (e.g., Nature Synthesis 4, 1088–1094 (2025)). The manuscript\ndoes not convincingly differentiate its mechanistic insights from this existing understanding. At\nthe molecular-design level, the selected additive also appears closely related to molecules\nreported previously (e.g., NH2-PEG5-NH2, ACS Nano 2025, 19(17), 16850–16858), further\nweakening the novelty claim.\nR: Sorry for the misunderstanding. In the mentioned work (Nature Synthesis 4, 1088–\n1094 (2025)), the authors propose the interfacial particle redissolution and monomer\nattachment between the crystal and precursor solution to explain the perovskite crystal\ngrowth. This crystal growth process was driven by a latent heat-induced cool interfacial\nlayer, which did not involve the specific crystal facet modulation.\nVery differently, we propose a mechanism of energy-driven facet-selective crystal\ngrowth to accurately modulate the certain facet formation by promoting (100) and\nsuppressing (110) and (111) facet growth. The specific crystal facet growth modulation\nis driven by thermodynamically favorable selective adsorption of BAPEG on the crystal\nfacet with variable diffusions of the perovskite precursor ions.\nIn addition, in the mentioned report (ACS Nano 2025, 19(17), 16850–16858), the\nmolecule of 3,6,9,12,15-pentaoxaheptadecane-1,17-bis-amine (NH -PEG -NH ) was\n2 5 2\nused as an additive to passivate ionic defects and slow down the crystallization of\nperovskites. However, both the molecular structure and functions of our bis(3-\naminopropyl)polyethylene glycol (with an average molecular weight of ~ 1500) are\ndifferent from those of the reported molecule. Our proposed molecule was employed\nas a post-treatment agent, where the important role of selective adsorption on perovskite\n(100), (110), and (111) facets was adopted to accurately modulate the specific facet\ngrowth process.\nAccordingly, we have extended the discussion in the manuscript (lines 1-4, page 7) as\nfollows:\nWe also reveal a different crystal growth mechanism of energy-driven facet-selective\ncrystal growth from the latent heat-induced cool interfacial layer-assisted crystal\ngrowth42 by accurately modulating certain facet growth processes.\nFinally, the authors do not provide a rigorous, quantitative causal link between the claimed\nimprovements in “crystal quality” and the enhanced EL efficiency. This point is important\nbecause high luminescence efficiency does not necessarily require highly crystalline or highly\nordered films (for example, many high-performance OLEDs employ amorphous emitting\nlayers). Without a clearer structure–property relationship and stronger evidence of distinct\nmechanistic contribution, I do not find the current work suitable for publication in Nature\nCommunications and therefore cannot recommend acceptance.\nR: Sorry for the misunderstanding. Different from the mentioned amorphous emitting\nlayers for high-performance OLEDs, considerable reports have demonstrated the\nessential importance of high-crystallinity perovskite films in achieving high-\nperformance perovskite devices (Nature 628, 299–305 (2024); Nature 536, 312–316\n(2016); Nature 517, 476–480 (2015)).\nIn our work, we clearly show the great improvement in perovskite crystallinity (i.e.,\n5.5-fold higher diffraction peak intensity than the control ones), effective suppression\nof the unfavorable crystal facet-correlated defects (i.e., reduced by more than 78% of\nthe density of trap states), and enhanced carrier radiative recombination (i.e., improved\nexciton binding energy from 40.7 to 55.2 meV) by our approach. As a result, the\nemission efficiency of the perovskite films is largely improved with a peak\nphotoluminescence quantum yield (PLQY) increasing to over 2-fold higher from 18.6%\nto of 41.5%. The perovskite structure-featured emission efficiency improvement\ncontributes to high-performance PeLEDs, as shown in the manuscript.\nAccordingly, we have added the quantitative values of “with nearly 5.5-fold higher\npeak intensity than the control ones” and “an over 2-fold higher photoluminescence\nquantum yields (PLQY) from 18.6% to of 41.5%” in the manuscript (line 24, page 5 and\nlines 26 and 27, page 8)\nReviewer #2’s further comments\nI have carefully checked the response letter and revised manuscript again. The proposed\nmechanisms about the facet orientation during crystallization in this manuscript should be\nclearly manifested about the differences from that reported in Nature Synthesis 4, 1088-1094\n(2025). The authors are suggested to conduct a comprehensive and in-depth study of the\nstructure-property relationship. It lacks scientific logic and rigor that simply attributing the\nimprovement in performance of blue PeLEDs to the reduction of defects. Following are some\ncomments, which may help the authors further improve the quality of the manuscript.\n1. What is the experimental evidence for the claim that perovskite (111) facet and (110) facet\nhave the higher defect density than (100) facet?\nR: The metal halide perovskite crystal facet strongly correlates with the generation of\ntrap states, where the lower defect density of the (100) facet than the (111) and (110)\nfacets has been extensively demonstrated with substantial experimental evidence in\nprevious works (e.g., Nat. Energy 5, 131–140 (2020); Nat. Energy 6, 624 (2021);\nScience 379, 173–178 (2023); Joule 6, 240–257 (2022); Joule 6, 2626–2643 (2022);\nAdv. Mater. 34, 2204342 (2022); Energy Environ. Sci., 18, 9865–9876 (2025); Adv.\nFunct. Mater. 35, 2422783 (2025); Adv. Funct. Mater. 32, 2206838 (2022); Adv. Sci.\n11, 2401184 (2024); Cryst. Growth Des. 18, 6652 (2018)).\nAdditionally, we show the easier formation of halogen vacancy on (110) and (111)\nfacets than on the (100) facet due to their smaller halogen vacancy formation energy\nthan that of the (100) facet. In detail, the chloride vacancy formation energies are 2.98\nand 2.47 eV for the (110) and (111) facets. While the chloride vacancy formation\nenergy is 3.30 eV for the (100) facet, which is much larger than that of the (110) and\n(111) facets. Consistently, the bromide vacancy formation energy of 3.19 eV for the\n(100) facet is also significantly larger than 2.86 and 2.40 eV for (110) and (111) facets,\nrespectively. The result indicates more difficulty in the formation of the trap states on\nthe (100) facet than on the (110) and (111) facets.\nTherefore, our work mainly focuses on specific crystal facet growth modulation to\nachieve high-quality perovskites. We propose a distinctive mechanism of energy-driven\nfacet-selective crystal growth to accurately modulate the certain facet formation, in\nwhich the favorable (100) facet growth is greatly promoted, while the (110) and (111)\nfacet growths are significantly suppressed. As a result, single crystal-like perovskites\nare achieved with high crystallinity, low trap state density, large exciton binding energy,\nand regular crystal morphology, thus contributing to high device performances.\n2. The author claimed that it is the massive defects hinder the performance of pure-blue\nPeLEDs, however, it is inconvincible that the reduction in trap density of only 78% can make\nthe significant performance improvement. The trap density in target film is still at a high level\nof closed to 10^17 cm-3, while the reported state-of-art blue perovskite shows a low trap density\nof only 10^15 cm-3 (e.g. 10.1038/s41586-022-05486-3). The underlying reasons and factors\nshould be further explored.\nR: In space charge-limited current (SCLC) measurements, in addition to the trap-filled\nlimit voltage, the trap density is also closely dependent on the perovskite thickness and\ndielectric constant. In other words, it is inappropriate to directly evaluate the trap\ndensity situations of the perovskites with different thicknesses and compositions.\nHowever, when comparing the trap density of the blue-emissive perovskites with\nsimilar thickness and composition, we observe nearly one order of magnitude decrease\nin the trap density of our target perovskites (Table R1 below).\nBesides, we also exhibit a distinct enhancement in exciton binding energy from 40.7 to\n55.2 meV for the target perovskites in the manuscript (Fig. 2i of the manuscript) due to\nthe increased dielectric confinement by the adsorption of BAPEG on the perovskite\nsurface (Supplementary Fig. 10c of the Supplementary Information). Both the low trap\nstate density and high exciton binding energy promote a largely improved emission\nefficiency of the perovskite films for high-performance devices.\nTable R1 Comparison of the trap state densities of the blue-emissive perovskites with\nsimilar thickness and composition.\nControl Target\nPerovskite Published journals\n(cm-3) (cm-3)\n(Cs/PEA)Pb(Cl/Br) 2.28 × 1017 1.93 × 1017 ACS Energy Lett. 10, 3638 (2025)\n(Cs/FA/pFPEA)Pb(Cl/Br) 4.21 × 1018 2.92 × 1018\n3\n(2024).\n(Cs/GA/pFPEA)Pb(Cl/Br) 2.81 × 1018 1.02 × 1018 Adv. Mater. 35, 2302161 (2023)\n(Cs/FA/K/PEA)Pb(Cl/Br) 2.80 × 1018 1.70 × 1018\n3\ndoi.org/10.1002/adma.202521547 (2026)\n(Cs/GA/4F- ACS Energy Lett. 10, 11, 5405–5413\n3.90 × 1018 3.25 × 1018\nPEA/PEA)Pb(Cl/Br) (2025)\n3\n(Cs/FA/p-\n3.99 × 1018 2.88 × 1018 Nat. Commun.15, 10621 (2024)\nPEA/K)Pb(Cl/Br)\n3\n(Cs/Rb/FA)Pb(Cl/Br) 4.50 × 1017 9.79 × 1016 Our work\n3\n3. The control sample shows a consistent curve trend with the target one in power density-\ndependent PLQYs, absent of the apparent trap-filled region, which is contradicted with the\nassertion of the massive trap in the control film.\nR: Sorry for the confusion. The seemingly consistent curve trend of the power density-\ndependent PLQYs for the control perovskites is induced by the large range of the PLQY\nvalues in y-axis. When we narrow the y-axis range (shown in Supplementary Fig. 11\nbelow), a trap saturation process at low excitation intensity is observed for the control\nperovskites. Whereas the target perovskites show nearly a consistent curve trend,\nshowing fewer trap states in the perovskite films.\nSupplementary Fig. 11 Fluence-dependent PLQYs for control and target perovskites.\nAccordingly, we have updated the y-axis range in Supplementary Fig. 11 of the\nSupplementary Information (page S9)\n4. What is the reason for the significant increase in current density for the target device?\nWill the additive affect the electrical properties of the perovskite film? As different facets may\nshow distinct carrier mobilities, more related analyses are needed to fully uncover the\nmechanism of the device performance.\nR: The significant increase in current density for the target device can be attributed to\nthe increased carrier mobility. The carrier mobility of the perovskite films was\nmeasured in Supplementary Fig. 10 of the Supplementary Information, where the\nobtained carrier mobility for the target perovskites is 2.93 × 10-4 cm2 V-1 s-1, which is\nlarger than 9.95 × 10-5 of the control perovskites, indicating the preferred (100) facet\nfor enhanced carrier mobility. The improved carrier mobility also benefits the high\ndevice performance.\nAccordingly, we have extended the following discussion in the manuscript (lines 5 and\n6, page 11).\nWhile the significant increase in current density for the target device can be attributed\nto the improved carrier mobility (Supplementary Fig. 10).\n5. Generally, the stretching vibration signals from groups such as C-O or NH2 on the additive\nwill shift to lower wavenumbers after interacting with the perovskite. But they shift to a higher\nwavenumbers in the BAPEG-Pb(Br/Cl)2 complex. Please clarify this apparent discrepancy.\nR: Besides the coordination interaction between BAPEG and the lead-halide complex,\nwe also demonstrated the hydrogen bonding interaction between BAPEG and the halide\nions, which shifts the stretching vibration of N-H to a high wavenumber due to the\nstrengthened stretching vibration by accepting the electron from the halide ions. This\ntrend has been widely observed in previous works (e.g., Angew. Chem. Int. Ed. 2024,\n63, e202411361; Adv. Mater. 2024, 36, 2400658; Nano Energy 2022, 95, 107000; Adv.\nMater. 2019, 31, 1904319, shown in Fig. R4a, b below)\nBesides, the characteristic shifts to higher wavenumbers after the interaction with the\nperovskite for C-O bond were also extensively demonstrated previously due to the\nincreased bond order of the C-O bond by coordination with the perovskite (e.g., Adv.\nFunct. Mater. 2024, 34, 2311527; Device 2024, 2, 100285; J. Am. Chem. Soc. 2020,\n142, 47, 19980–19991; Nat. Commun. 2021, 12, 3383, shown in Fig. R4c, d below).\n[FIGURE REDACTED]\nFig. R4 FT-IR signals of a, b) -NH and c, d) C-O groups before and after interaction\n2\nwith the perovskites in previous works."}, {"round": 3, "reviewer_comments": {"reviewer_2": "The authors have well revised the manuscript with the point-by-point responses to my concerns and now the qualilty of the paper is improved significantly, and thus I recommend the publication of this article."}, "author_response": ""}]

Decision letter