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ABSTRACT Wide-bandgap (WBG) perovskite solar cells (PSCs) are employed as top cells of tandem cells to break through the theoretical limits of single-junction photovoltaic devices. However,

WBG PSCs exhibit severe open-circuit voltage (_V_oc) loss with increasing bromine content. Herein, inhomogeneous halogen-phase distribution is pointed out to be the reason, which hinders

efficient extraction of carriers. We thus propose to form homogeneous halogen-phase distribution to address the issue. With the help of density functional theory, we construct a double-layer

structure (D-2P) based on 2-(9H-Carbazol-9-yl)ethyl]phosphonic acid molecules to provide nucleation sites for perovskite crystallization. Homogeneous perovskite phase is achieved through

bottom-up templated crystallization of halogen component. The efficient carrier extraction reduces the Shockley-Read-Hall recombination, resulting in a high _V_oc of 1.32 V. As a result,

D-2P-treated device (1.75 eV) achieves a record power conversion efficiency of 20.80% (certified 20.70%), which is the highest value reported for WBG (more than 1.74 eV) PSCs. SIMILAR

CONTENT BEING VIEWED BY OTHERS HETEROJUNCTION FORMED VIA 3D-TO-2D PEROVSKITE CONVERSION FOR PHOTOSTABLE WIDE-BANDGAP PEROVSKITE SOLAR CELLS Article Open access 06 November 2023 A UNIVERSAL

CLOSE-SPACE ANNEALING STRATEGY TOWARDS HIGH-QUALITY PEROVSKITE ABSORBERS ENABLING EFFICIENT ALL-PEROVSKITE TANDEM SOLAR CELLS Article 21 July 2022 DEFECT ENGINEERING IN WIDE-BANDGAP

PEROVSKITES FOR EFFICIENT PEROVSKITE–SILICON TANDEM SOLAR CELLS Article 18 July 2022 INTRODUCTION Mixed-halogen wide-bandgap (WBG) perovskite materials is often employed as the top cells of

tandem solar cells, by combining with narrow-bandgap (NBG) bottom cells such as silicon solar cells, organic solar cells, tin-lead hybrid perovskites solar cells (PSCs), etc1,2,3,4,5,6. Due

to the strong photon absorption capability in the long-wavelength range, the bottom cells are beneficial to obtain a larger photocurrent, but usually exhibit a low photovoltage. It is

crucial for tandem cells to achieve the largest possible voltage output through WBG top cells7. Nevertheless, WBG PSCs suffer from severe open-circuit voltage (_V_oc) loss compared to NBG

photovoltaic devices8. Minimizing the _V_oc loss of WBG PSCs should be one of the important issues that need to be addressed urgently in the field of efficient tandem solar cells9,10.

Inorganic nickel oxide (NiOx) film is often employed as hole transport layers (HTL) in WBG PSCs due to its remarkable thermal stability, chemical stability, and high light

transmittance11,12. It is well known that high defect states and mismatched energy levels alignment at the interface between NiOx HTL and perovskite, results in a low _V_oc13. The

application of self-assembled monolayer (SAM) is an important attempt to solve this problem, which has greatly improved the _V_oc of the PSCs14,15,16. Despite this, there is still a large

_V_oc loss in WBG PSCs, according to the Shockley-Queisser (S-Q) limit efficiency theory17. As the optical bandgap of perovskite material widens, the bromine (Br) content of films inevitably

increases, and the resulting device exhibits increasingly severe _V_oc loss18. It is generally recognized that phase separation of perovskite films during the crystallization process is a

prominent problem leading to large _V_oc loss, especially in perovskite systems with Br content exceeding 20 mol%7,19. Br-based perovskites possess lower solubility than iodine (I)-based

analogues, making it easier to nucleate and grow rapidly7. Therefore, for the commonly used solution method, the Br-rich perovskite phase preferentially crystallizes at the perovskite/air

interface at the top of the film, while the I-rich phase is deposited at the bottom of the film20. Such asynchronous crystallization is the root cause of perovskite phase separation.

Inhomogeneous phase distribution impairs efficient extraction and collection of carriers, leading to the severe nonradiative recombination, which has been demonstrated in

quasi-two-dimensional perovskite systems and formamidine (FA) perovskite systems21,22,23,24. Thus, regulating the crystallization kinetics of mixed-halogen perovskites, and achieving

homogeneous halogen-phase distribution should be an important strategy to reduce the _V_oc loss of WBG PSCs. Based on the above inspiration, it is an ideal choice to prepare a functionalized

molecular layer that acts on the buried interface of perovskite film to regulate the crystallization behavior of halides. Considering the advantages of SAM molecules in passivating defects

of NiOx film, we envision to construct a double-layer SAM film at the interface between HTL and perovskite. With the help of density functional theory (DFT) calculations, we have

successfully achieved a double-layer structure (D-2P) based on a single-layer 2-(9H-Carbazol-9-yl)ethyl]phosphonic acid (S-2P) molecules. D-2P structure could be formed through the strong

π-π interaction between the carbazole groups located at the head end of the S-2P molecule16,25,26. Meanwhile, the phosphate group located at the tail end of the S-2P molecule can anchor the

NiOx and the [PbX6]4- octahedron respectively, thereby forming a stable bond bridge structure27,28. More importantly, the phosphate group acts on the [PbX6]4- octahedron through -P-OH···X

bonds, reducing the formation energy of Br-phase and I-phase perovskite simultaneously. The nucleation sites provided by the D-2P structure induce bottom-up homogeneous crystallization of

the halogen component. The reversed crystallization process and homogeneous halogen-phase distribution have been demonstrated through in-situ grazing-incident wide-angle X-ray scattering

(GIWAXS) and depth-profiling X-ray photoelectron spectroscopy (XPS) characterization, etc. Benefiting from optimized energy level alignment and efficient carrier extraction, non-radiative

recombination is effectively suppressed. As a result, D-2P-treated WBG PSCs (1.75 eV) achieved a record power conversion efficiency (PCE) of 20.80% (certified 20.70%), accompanied by a high

_V_oc of 1.32 V. And a semitransparent PSC was employed as four-terminal (4 T) perovskite/perovskite tandem with a PCE of 28.08%. Furthermore, the homogeneous phase distribution alleviated

the lattice strain of the WBG perovskite film and ensured the long-term operational stability. The unencapsulated device still maintains more than 90% of the original PCE after being stored

under nitrogen conditions for 2500 h. RESULTS HALOGEN-PHASE SEPARATION ISSUE AND D-2P STRUCTURE CONSTRUCTION Previous reports have demonstrated that homogeneous phase distribution in

perovskite films is crucial to achieve high-performance photovoltaic devices19. Therefore, we investigate the phase distribution of mixed-halide WBG perovskite films based on a common

FA0.8Cs0.15MA0.05Pb(I0.7Br0.3)3 system (1.75 eV). In-situ GIWAXS technique is an effective characterization to reveal the crystallization dynamics of perovskite films. Various grazing

incidence angles (_θ_) are applied to detect crystal structure information at different depths of perovskite films29. As shown in Fig. 1a, the (001) plane of the S-2P-treated perovskite film

corresponds to a constant _q_ value at 1.03 nm−1 when the top of the film (_θ_ = 0.3°) was probed during the spin-coating stage. Crystallization situation at the bottom of the film can also

be detected by increasing the grazing incidence angle (_θ_ = 1°), and a broader diffraction signal was showed in Fig. 1b. Moreover, the _q_ value continuously decreases from 1.03 to 1.01 

nm−1 throughout the spin-coating stage. Considering that perovskite films preferentially crystallize at the air/solution interface20, the initial GIWAXS signal should mainly depend on the

crystal structure of the film surface (Fig. 1d). As the film crystallizes sequentially from top to bottom, the crystal structure at the bottom begins to dominate the GIWAXS signal. The

decreased _q_ value represents that the perovskite at the bottom film possesses a larger interplanar spacing than at the top film. The _q_ values at the top and bottom films are almost

constant during the annealing stage (Supplementary Fig. 1), indicating that an inhomogeneous perovskite phase is formed during the spin-coating stage. We further qualitatively analyzed the

phase distribution of perovskite films by depth-profiling XPS spectra (Fig. 1c). As the profiling depth increases, the intensity of I 3_d_5/2 and I 3_d_3/2 spectra (619.5 and 631.0 eV)

gradually increases, while the intensity of Br 3_d_5/2 and Br 3_d_3/2 spectra (68.6 and 69.7 eV) at the corresponding film depth gradually decreases, which is consistent with the GIWAXS

results. It is easy to understand that the [PbBr6]4- octahedron preferentially crystallizes on the top film, due to its solubility is lower than [PbI6]4- octahedron7. This results in

excessive consumption of the Br component, and hence the I-rich phase is deposited at the bottom film (Fig. 1d). Such phase distribution signifies an inhomogeneous energy landscape, which

would lead to large _V_oc loss and low PCE18. Achieving homogeneous halogen-phase distribution through crystallization kinetics regulation should be an effective strategy to address this

issue. Thereupon, we propose to construct D-2P structure based on 2P molecules to regulate the crystallization kinetics of perovskite films. D-2P structure could be formed through the strong

π-π interaction between the carbazole groups located at the head end of the S-2P molecule (Fig. 1e). We used DFT calculations to simulate the binding energy of 2P pairs in three stacking

model: parallel stacking, intersecting stacking, and antiparallel stackings (Fig. 1h)30. For parallel stacking (inset i), the benzene rings at the heads of the two 2P molecules are arranged

in parallel, and the phosphate groups at their tails extend in same directions. For intersecting stacking (inset ii), the benzene rings at the heads of the two 2P molecules intersect with

each other at a certain angle, and the phosphate groups at their tails extend in opposite directions. For parallel stacking (inset iii), the benzene rings at the heads of the two 2P

molecules are arranged in parallel, and the phosphate groups at their tails extend in opposite directions. As shown, intersecting stacking mode exhibits a larger binding energy (10.847 eV)

than parallel stacking (0.014 eV) and antiparallel stacking mode (0.018 eV), which indicates that this stacking mode should be the most stable form of D-SP structure. The electrostatic

potential distribution of 2P molecules also proves that intersecting stacking is the optimal arrangement of 2P pairs (Supplementary Fig. 2). We then construct the D-2P structure based on the

ITO/ NiOx substrate by a simple solution method (Supplementary Figs. 3, 4). A thin 2P film is deposited on the NiOx layer using spin-coating method at step I (Fig. 1f). The resulting film

spontaneously forms an S-2P structure, and the phosphate group located at the tail end of the oriented 2P molecule can anchor the NiOx layer31. Meanwhile, some non-oriented 2P molecules are

inevitably attached to the surface of the S-2P structure. S-2P structure without residual molecules can be obtained by removing attached 2P molecules with the help of absolute ethanol rinse

(step II). The benzene ring groups exposed on the surface of the S-2P layer increase the hydrophobicity of the film, and thus the film obtained at stage II exhibits a larger contact angle

(61.9°) compared with the film (35.1°) obtained at stage I. D-2P structure can be obtained by re-depositing an anhydrous ethanol solution of 2P molecules (phase III) and rinse again (phase

IV). The smallest contact angles (22.2°) can be obtained in the final film, because the intersecting π-π stacking of 2P pairs exposes the hydrophilic phosphate groups on the film surface.

This strong π-π force can also be demonstrated through C 1 _s_ spectra of XPS16. As shown in Fig. 1g, a peak at binding energy of 291.6 eV could be observed, which is consistent with the π-π

bonding collaboration. The resulting D-2P structure (stage IV) exhibited the strongest π-π interaction. The anchoring action of Ni=O bonds between the phosphate group of the D-2P structure

and the NiOx film has been demonstrated by XPS spectra (Supplementary Fig. 5), thereby forming a stable bond bridge structure. HOMOGENEOUS HALOGEN-PHASE PEROVSKITE FILM INDUCED BY THE D-2P

STRUCTURE The phosphate groups on the top layer of the D-2P structure are exposed, which is an opportunity to anchor the [PbX6]4- octahedron (Supplementary Fig. 6) and provide nucleation

sites for the crystallization of perovskite films. We then performed in-situ GIWAXS with different _θ_ angles. The characteristic signal of ITO can be observed in the GIWAXS patterns of

perovskite films (_θ_ = 1°) (Fig. 2c, Supplementary Figs. 7 and 8), indicating that the signal at the bottom of perovskite film can be detected. As shown in Fig. 2a, b, the (001) plane of

the D-2P-treated perovskite film exhibited an almost constant _q_ value of 1.02 nm−1 at spin-coating stage, both on the top (_θ_ = 0.3°) at and bottom (_θ_ = 1°) of the film29,32. The

annealed perovskite film also showed an almost the same diffraction ring of (001) plane for different incident angles (Fig. 2c, Supplementary Fig. 9), meaning that the perovskite phase is

uniformly distributed throughout the film. This is in sharp contrast to the inhomogeneous phase distribution exhibited by the surface and bottom of the S-2P-treated film. Meanwhile, the

strong perovskite signal at the top of the S-2P-treated perovskite film is detected earlier than that at the bottom (Fig. 2a), indicating that the perovskite crystallizes preferentially at

the top. This up-bottom crystallization approach allows stronger (001) signals to be detected at the top. In general, Br-based perovskite exhibits a lower formation energy than I-based one

(Fig. 2e). Thus, the Br-rich phase preferentially crystallizes at the top of the S-2P-treated perovskite film, resulting in an inhomogeneous halogen-phase distribution. In stark contrast,

the strong perovskite signal was first detected at the bottom of the D-2P-treated perovskite film rather than the top (Fig. 2b). The slower crystallization rate at the top of the film

results in a weaker (001) signal compared to that at the bottom. This bottom-up crystallization approach is attributed to the D-2P structure, and the phosphate group provides nucleation

sites for the crystallization of perovskite films. Furthermore, the D-2P-treated perovskite film displayed a faster crystallization rate than the S-2P-treated perovskite film, which can be

determined from the faster increase in GIWAXS signal intensity of the former. The in-situ laser scanning confocal microscope (LSCM) images further supports this conclusion that shorter

crystallization time is observed for the D-2P-treated perovskite film compared to S-2P-treated one (Fig. 2d and Supplementary Fig. 10). The crystallization kinetic behavior of the above

films confirms our previous assumptions. The phosphate groups exposed in the D-2P structure could simultaneously anchor the [PbI6]4- and [PbB6]4- through -P-OH···X- and -P = O···Pb2+ bonds33

(Fig. 2f). As shown in the XPS spectra of the perovskite film at the bottom, Pb 4 _f_, Br 3_d_ and I 3_d_ peaks were all shifted towards the high energy region (Fig. 2g, h), demonstrating

the strong interaction between the D-2P structure and the perovskite crystal34. The formation energy of I-based and Br-based perovskites could be reduced and closer after the introduction of

2P (2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) (Fig. 2e). This indicates that the phosphate groups will interact with both I and Br components and provide nucleation sites for perovskite

crystallization, which will induce the homogeneous crystallization of the halogen phase. As expected, depth-profiling XPS spectra showed the same Br 3_d_ and I 3_d_ signal intensity at

various depths of the film (Fig. 2h, Supplementary Fig. 11). Moreover, the double-layered materials based on other carbazole-based phosphonic acids also showed similar effects, such as such

as [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (2M) and [4-(3,6-dimethoxy-9H-carbazol-9-yl) butyl]phosphonic acid (4M) (Supplementary Figs. 12, 13). We further quantitatively

analyzed the halogen content based on the focused ion beam (FIB)-prepared flakes located on the top and bottom of the perovskite film35. As shown in the energy dispersive spectroscopy (EDS)

combined transmission electron microscopy (TEM) (Supplementary Fig. 14), the S-2P-treated films exhibited distinguishable Br/(I+Br) ratios for the top (38.63%) and bottom (22.82%) samples.

In contrast, a close to theoretical Br/(I+Br) ratio (30%) is detected for both the top (31.42%) and bottom (29.16%) samples treated with D-2P structure (Fig. 2i). The same conclusion can be

obtained through the statistical Br/(I+Br) ratio at different spatial positions (Supplementary Fig. 15). Such halogen-phase distribution is attributed to the anchoring effect of the D-2P

structure on the buried interface of perovskite film. CARRIER TRANSPORT BEHAVIOR OF HOMOGENEOUS HALOGEN-PHASE PEROVSKITE FILM We then investigated the carrier transport behavior at the top

and bottom of the perovskite film. Kelvin probe force microscopy (KPFM) provides a channel to detect the surface electronic state information of perovskite films. According to previously

reported methods36, we stripping perovskite films form substrates (Supplementary Figs. 16, 17). EDS mapping of the substrate after stripping exhibited that the signal of the Pb element is

negligible (Supplementary Fig. 18), indicating that the complete perovskite film is stripped, which allows the information at the bottom of the film to be effectively detected. As shown in

Fig. 3a–c, similar to the top film, the bottom film also exhibits a uniform potential distribution in different regions. This also proves that the bottom films of two perovskite samples

exhibit almost negligible crystal damage after peeling off. Moreover, the top (0.482 V) exhibited significantly larger contact potential difference (CPD) than the bottom (0.188 V) of

S-2P-treated perovskite film. This is exactly in line with the situation caused by halogen-phase segregation37,38. In contrast, the D-2P-treated perovskite film exhibited close CPD at the

top (0.251 V) and bottom (0.223 V), and more uniform CPD distribution further confirmed the homogeneous halogen-phase distribution throughout the perovskite film. In general, changes in the

CPD of films are accompanied by rearrangements of the energy landscape. Thereupon, we measured the ultraviolet-visible (UV-vis) absorption spectra (Supplementary Fig. 19) and the ultraviolet

photoelectron spectroscopy (UPS) of the films to characterize the energetics (Fig. 3d–f). Considering that long-term UV-light irradiation would damage the perovskite film39, we peeled the

buried bottom surface of the perovskite film off the substrate to minimize the error in UPS measurements. As displayed on the bottom of films, the D-2P-treated perovskite film possessed a

shallower Fermi level (5.0 eV) than the S-2P-treated film (5.4 eV), showing more N-type characteristics40, which is beneficial to achieving high _V_oc. Moreover, the valence band maximum

(VBM) of the former is closer to the highest occupied molecular orbital (HOMO) of 2P molecule10, and optimized energy level alignment is achieved between the photoactive layer and the hole

transport layer. Moreover, the top of the S-2P-treated perovskite film showed more Br components than the D-2P-treated film, which means a larger _E_g. The former exhibited smaller _E_VBM

value than the latter according to their UPS measurements (Supplementary Fig. 20). Therefore, we can deduce that the D-2P-treated perovskite film possessed a larger _E_CBM value than the

S-2P-treated one. This is a smaller energy barrier between the perovskite film and the electron transport layer, which is conducive to electron extraction41. The matched energy level

structure ensures effective carrier extraction. The steady-state photoluminescence (PL) spectra of ITO/NiOx/D-2P/Perovskite film showed a lower PL intensity than that of

ITO/NiOx/S-2P/Perovskite film (Fig. 3g). And a full width at half maxima (FWHM) could also be observed, which is closely related to the homogeneous halogen-phase. In general, low PL

intensity may be caused by the following two factors. In the first case, the high defect states lead to strong PL quenching in perovskite films42. We then measured the defect states of two

perovskite films using thermal admittance spectroscopy (TAS)43. As shown, Band 1 ( < 0.4 eV) represents shallow level, Band 2 (0.4–0.5 eV) and Band 3 ( > 0.5 eV) represent deep level

(Supplementary Fig. 21). Deep level defects are the main factors affecting device performance. The density of defect states (_t_DOS) was in the order of 1016 to 1019 m−3 eV−1 in the both

devices. Meanwhile, the D-2P-treated perovskite device displayed the reduced _t_DOS over the entire trap depth compared with S-2P-treated film. Therefore, we can confirm that the low defect

state of the D-2P-treated perovskite film is not responsible for the low PL intensity. For the second case, the rapid hole extraction from the perovskite film to the hole transport layer

film induces strong PL quenching44,45. As shown in Fig. 3d–f, the valence band maximum (VBM) of the D-2P-treated perovskite film is closer to the highest occupied molecular orbital (HOMO) of

2P molecule, compared with that the S-2P-treated perovskite film. The optimized energy level alignment between the photoactive layer and the hole transport layer ensures a more efficient

hole extraction rate, which can be the reason for the low PL intensity. We then operated solar cells as light-emitting diodes (Supplementary Fig. 22), and D-2P-treated PSC device showed

enhanced electroluminescence (EL) intensity compared with S-2P-treated one. This directly demonstrates that non-radiative recombination at the interface between the perovskite and the

transport layer is reduced in the D-2P-treated devices. Furthermore, we measured the confocal laser microscopy (TCFM) mappings of the films to study the carrier lifetime distribution in

different regions. As shown in Fig. 3h, i, the overall fluorescence lifetime of the D-2P-treated film is nearly an order of magnitude lower than that of the S-2P-treated film. The

corresponding time-resolved PL (TRPL) decay also exhibited the same trend (Supplementary Fig. 23). Benefiting from the templated crystallization induced by the D-2P structure, the

high-quality and homogeneous halogen-phase perovskite film exhibited the efficient carrier extraction (Supplementary Fig. 24). Therefore, the improved optical and electrical properties lay a

solid foundation for the efficient photovoltaic devices. RELATIONSHIP BETWEEN HOMOGENEOUS HALOGEN PHASE AND THE _V_ OC LOSS We fabricated a p-i-n planar heterojunction WBG PSCs (1.75 eV)

with an architecture of ITO/NiOx/D-2P(S-2P)/Perovskite/PEAI/C60/BCP/Ag. The S-2P-treated PSC showed a PCE of 18.33% with a low _V_oc of 1.25 V (Fig. 4a). In contrast, the optimized

D-2P-treated PSC achieved a champion PCE of 20.80% (Supplementary Fig. 25, Supplementary Table 1). And a certified PCE of 20.7% was obtained at SIMIT (Fig. 4b, Supplementary Fig. 26), which

is the highest value reported for a WBG PSC with a bandgap wider than 1.74 eV (Fig. 4c, Supplementary Table 2). A short-circuit current density (_J_sc) of 18.81 mA cm−2 obtained by current

density-voltage (_J_-_V_) curve was verified by the external quantum efficiency (EQE) spectra (Supplementary Fig. 27). Moreover, the D-2P-treated PSC with high repeatability exhibited

negligible hysteresis and stable maximum power point output (Supplementary Fig. 28, 29, Supplementary Table 3). We also investigated the effects of the number of 2P layer and the bilayer

structure of other carbazole-phosphate-based acids on WBG PSCs (Supplementary Figs. 30–34, Supplementary Tables 4 and 5). In contrast, NiOx-based D-SP-treated PSCs exhibited the best

photovoltaic performance (Supplementary Figs. 35, 36, Supplementary Table 6). The remarkably high _V_oc (1.32 V) can also be obtained, and reduced _V_oc loss is a crucial factor in achieving

PCE improvement. The dependence of _V_oc on illumination intensity is an effective strategy to evaluate the internal recombination mechanism in PSCs. The ideality factor _n_ can be obtained

by calculating the slope of the fitted straight line. As shown in Fig. 4d, D-2P-treated PSC displayed a smaller _n_ value (1.21) than S-2P-treated PSC (1.88), and _n_ value close to 1

indicates that Shockley-Read-Hall recombination is substantially suppressed. This can also be demonstrated by the low reverse saturation current under dark conditions (Supplementary Fig. 

37). The larger recombination resistance (_R_rec = 22.52 KΩ) and smaller transport resistance (_R_tr = 125.61 Ω) for D-2P-treated PSC corresponds to more efficient hole transport and

extraction (Supplementary Fig. 38). Therefore, a longer charge-recombination lifetime (_τ_rec = 53.33 μs) and a shorter charge-extraction time (_τ_tra = 0.38 μs) were obtained according to

the transient photovoltage (TPV) and transient photocurrent (TPC) measurements (Supplementary Fig. 39). A similar conclusion could be also obtained from the capacitance-voltage (_C_-_V_)

characteristics of PSCs (Fig. 4e). The D-2P-treated PSC displayed an increased built-in potential (_V_bi) from 1.01 to 1.16 V, implying an enlarged driving force of carrier extraction and

separation, which is contributing to the large _V_oc46. To quantitatively evaluate and correlate the recombination rate with the _V_oc and device performance, we operated solar cells as

light-emitting diodes (Fig. 4f), as follows47: $${V}_{{{{\rm{oc}}}}}={V}_{{{{\rm{oc}}}},\! {{{\rm{rad}}}}}-\frac{{kT}}{e}{ln}{{EQE}}_{{{{\rm{EL}}}}}^{-1}$$ (1) where _V_oc,rad, _EQE_EL, _k_,

_T_ and _e_ are the radiative limit of _V_oc, electroluminescence external quantum efficiency, Boltzmann’s constant, thermodynamic temperature and elementary charge. D-2P-treated device

showed a detected EL emission even under a low bias voltage of 1.10 V (Supplementary Fig. 40). The _V_oc loss was calculated by measuring the _EQE_EL of the device. D-2P-treated device

obtained an improved _EQE_EL value (0.437%), which was an order of magnitude higher than S-2P-treated device (0.034%). This demonstrated the substantially reduced _V_oc loss of 0.15 V,

agreeing well with the improved _V_oc of 1.32 V. To show the application potential of WBG PSCs with D-2P structure, we fabricated a semitransparent device to construct four-terminal (4-T)

all-perovskite tandem solar cell with NBG perovskite bottom cell41,48 (Fig. 4g). The resulting semitransparent WBG PSC yielded a PCE of 19.35% with a _V_oc of 1.30 V. The filtered NBG PSC

possessed a PCE of 8.73% based on an initial PCE of 21.70% (Fig. 4h and Supplementary Table 7). The reduced PCE of the filtered NBG PSC is mainly ascribed to the sharp decline in _J_sc from

31.52 to 12.87 mA cm−2, which is in accordance with the corresponding EQE spectra (Fig. 4i). The most of the short wavelength photons (300 – 700 nm) can be absorbed by the top

semitransparent PSC, which allows that the long wavelength photons are absorbed by the bottom PSC. As a result, 4-T all-perovskite tandem solar cell achieved a PCE of 28.08%, which is one of

the highest PCE reported for 4-T all-perovskite tandem cell. Subsequently, we investigative the stability of WBG perovskite materials and photovoltaic devices. Residual lattice strain is

usually one of the crucial factors affecting the stability of perovskite crystal structures, which could be characterized by grazing incident X-ray diffraction (GIXRD) via the 2_θ_-sin2_φ_

method49,50. As shown in Fig. 5a–c, D-2P-treated perovskite film displayed relieved lattice strain (10.0 MPa) compared to the S-2P-treated perovskite film (59.8 MPa), which is attributed to

the homogeneous halogen-phase distribution. We evaluated the migration ability of halide ions by temperature-dependent conductivity measurements51. The ion migration activation energy (_E_a)

is obtained by fitting the corresponding plots with the Nernst-Einstein equation52 (Fig. 5d). A larger _E_a (0.58 eV) is observed in the D-2P-treated perovskite film than that in the

S-2P-treated one (0.17 eV). The relieved lattice strain and increased halogen ion migration barrier facilitate the realization of robust stability of mixed-halide perovskite films. The EL

spectra of PSCs at various bias voltages are showed in the Fig. 5e, f. Distinguishable phase separation can be observed in S-2P-treated PSC when the bias voltage exceeds 3.0 V. In contrast,

D-2P-treated PSC exhibit continuously enhanced EL signals at constant wavelength with increasing bias voltage from 2.0 to 6.0 V. In addition to the improved electric field stability, the

light stability of the D-2P-treated perovskite is also impressive. Time-dependent PL measurements of perovskite films were carried out in air during continuous 1-sun light illumination (Fig.

 5g, h). The D-2P-treated film still exhibited a constant PL intensity at 708 nm after 400 h, while the S-2P-treated perovskite film showed a split and blue-shifted PL peak after being

soaked for a very short time. We further studied the phase separation of perovskite films under long-term light illumination conditions by the SEM coupled with EDS mappings (Supplementary

Fig. 41). For perovskite films, the contents of I and Br elements are large enough, so the influence of possible presence of background noise on the analysis of their distribution is

negligible. After two months of continuous light illumination, the S-2P-treated perovskite film showed an inhomogeneous halogen (Br and I) distribution compared with the pristine one. And no

obvious holes were found in the main aggregation areas of I and Br elements. It can be observed that the halogen inhomogeneous perovskite phase at different film depths will aggravate the

phase separation of the entire film. In contrast, the D-2P-treated perovskite film still exhibited homogeneous halogen distribution under the same light illumination conditions. The electric

field stability and light stability of perovskite film guarantee the long-term stability of solar cells. The PCE evolution of the unencapsulated WBG PSCs were monitored in accordance with

the ISOS-L-1 test standard53 (Fig. 5i). D-2P-treated PSC still maintained more than 90% of its initial PCE after continuous 1-sun illumination conditions in nitrogen for 2500 h, while the

S-2P-treated device has rapidly degraded to less than half its initial PCE after only 1000 h. DISCUSSION In conclusion, we demonstrate an efficient and stable WBG PSC with the homogeneous

halogen-phase distribution. Guided by DFT calculations, we design the D-2P structure through π-π interactions between 2P molecules. The phosphate groups exposed on the surface of the D-2P

structure provide nucleation sites for the homogeneous halogen-phase perovskite. Bottom-up templated crystallization results in the homogeneous perovskite phase distribution. The efficient

carrier extraction between the perovskite and the charge transport layer reduces _V_oc loss of WBG PSC. As a result, D-2P-treated PSC (1.75 eV) achieved a champion PCE of 20.80% (certified

20.70%), which is the highest value reported for a WBG PSC with a bandgap wider than 1.74 eV. Benefiting from improved electric field stability and light stability of perovskite film, the

resulting PSC achieves improved long-term stability, and maintained more than 90% of its initial PCE after continuous 1-sun illumination conditions for 2500 h. This work will provide a route

for minimizing _V_oc loss in WBG PSC, and pave the way for the development of perovskite tandem solar cells. METHODS MATERIALS _N,N_-dimethylformamide (DMF, 99.8%, anhydrous),

dimethylsulfoxide (DMSO, ≥ 99.9%, anhydrous), 2-Propanol (IPA, 99.5%, anhydrous) and chlorobenzene (CB, 99.8%, anhydrous) were obtained from Sigma-Aldrich. Tin (II) iodide (SnI2, 99.99%) and

tin (II) fluoride (SnF2, 99%) were purchased from Sigma-Aldrich. Formamidinium iodide (FAI, 99.9%), methylammonium iodide (MAI, 99.9%), cesium iodide (CsI, 99.999%), lead iodide (PbI2,

99.999%), lead bromide (PbBr2, 99.999%), methylammonium chloride (MACl, 99.9%), 2-phenylethylamine hydroiodide (PEAI, 99.5%) and indium tin oxide (ITO, 15 Ω) glass were obtained from

Advanced Election Technology Co., Ltd. [2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid (2P, > 98%), [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic Acid (MeO-2PACz > 98%) and

[4-(3,6-Dimethoxy-9H-carbazol-9-yl)butyl]phosphonic Acid (MeO-4PACz > 98%) were purchased from TCI. Nickel oxide (NiOx, 99.999%) was from Xi ‘an E-light New Material Co., LTD. Fullerene

(C60, 99.9%) and bathocuproine (BCP, 99%) were obtained from Xi’an Polymer Light Technology Corporation. PEDOT:PSS (CLEVIOS P VP Al 4083) was purchased from Heraeus, LLC. None of the above

chemicals received further purification, were used directly. SINGLE-JUNCTION PEROVSKITE DEVICE FABRICATION The pre-patterned ITO substrates were placed in cleaning agent, deionized water,

anhydrous ethanol, and acetone in sequence cleaning for 20 min. The cleaned ITO substrates were treated with UV-zone for 20 min. NiOx nanoparticles (10 mg) were dissolved in 1 ml of pure

water, ultrasonic shock for 20 min, and then filtered by a filter head with an aperture of 0.22 μm for reserve use. The NiOx film was prepared by spin-coating NiOx solution on the ITO

substrate at 3000 rpm for 30 s, and then annealed at 110 °C for 15 min in air. S-2P film is formed by spinning ethanol solution of 2P molecule coating at 3000 rpm for 30 s, annealing at 100 

°C for 10 min, rinsing with anhydrous ethanol, repeat twice to form D-2P film. For 1.5 M FA0.8Cs0.15MA0.05Pb(I0.7Br0.3)3 perovskite, PbI2, PbBr2, FAI, MAI and CsI are dissolved into a mixed

solvent of DMF and DMSO (4:1) at the stoichiometric ratio. The perovskite layer was fabricated by spin coating 30 µl perovskite precursor solution at a speed of 5000 rpm for 32 s in a N2

glovebox. At the time of 22 s, 110 µl CB was dropped as an anti-solvent. The fabricated film was annealed at 100 °C for 60 min. For PEAI treatment, the 3 mg PEAI was dissolved in 1 ml IPA

and spin-coated onto the perovskite surface at 4000 rpm for 30 s. Finally, it is transferred to a high vacuum chamber (6 × 10−4 Pa), and the C60 (35 nm), BCP (6 nm) and Ag (100 nm) are

thermally evaporated. 4 T ALL-PEROVSKITE TANDEM CELLS FABRICATION SEMI-TRANSPARENT WBG PSCS Preparation of WBG perovskite films as shown above, after depositing 35 nm C60, the substrates

were then transferred to the atomic layer deposition (ALD) system where 40 nm of SnO2 was deposited at 80 °C. Next, a 100 nm-thick indium zinc oxide film (IZO) was sputtered. NBG PSCS The

PEDOT:PSS solution was spin-coated onto ITO and annealed in air at 100 °C for 15 min. Immediately after annealing the substrates were placed in the glove box to deposit NBG perovskite films.

For 2 M FAPb0.5Sn0.5I3 perovskite, PbI2, FAI, SnI2, and SnF2 are dissolved into a mixed solvent of DMF and DMSO (2:1) at the stoichiometric ratio. NBG perovskite precursor solution was

deposited on the substrate by two-part spin coating process: 1000 rpm for 10 s and 4000 rpm for 50 s. At the last 20 s, 200 μl of CB was dripped and then annealed at 100 °C for 10 min.

Finally, it was transferred to the evaporation system, depositing 35 nm C60, 6 nm BCP and 100 nm Ag, respectively. DEVICE CHARACTERIZATION The _V_oc and _J_sc were measured using a Keithley

2400 instrument. Instantaneous _J-V_ curves then measured with a scanning rate of 100 mV s−1 (voltage step of 20 mV and delay time of 200 ms). The devices were measured by a customized mask

with an effective area of 0.089 cm−2. The output of the light source was adjusted using a calibrated silicon photodiode (Newport) at 1 sun (100 mW cm−2). The _J-V_ curves is measured in

atmospheric conditions. Through the silicon standard cells (SRC-00288, Enli Tech) and sun simulator (SS-F5, Enli Tech) for light intensity calibration. Electroluminescence efficiency

(_EQE_EL) was performed via a system containing a Keithley 2400 digital source meter for current injection, a Keithley 6482 picometer, and the Si photodiode for quantifying the photons

emitted from PSCs. OTHER CHARACTERIZATIONS The in-situ GIWAXS measurements were performed at BL 17B1 beamline of the Shanghai Synchrotron Radiation Facility (SSRF). X-ray with a wavelength

of 1.238 Å was utilized for incident-angle-depending measurements, and the incident angle was fixed at 0.3° and 1°. GIWAXS data was collected at every 1 s. The ex-situ GIWAXS patterns with

various grazing incident angles of perovskite films were measured using monochromatic beam (1.54 Å) on the beamline 1W1A at Beijing Synchrotron Radiation Facility (BSRF), China. The XPS was

measured at a vacuum chamber (ESCALAB 250Xi), with a base pressure of 2 × 10−10 mbar, for XPS depth profiling measurements. XPS measurements were performed using a double-differentially

pumped He gas discharge lamp emitting He I radiation (_hν_ = 21.22 eV). REPORTING SUMMARY Further information on research design is available in the Nature Portfolio Reporting Summary linked

to this article. DATA AVAILABILITY All the data supporting the findings of this study are available within this article and its Supplementary Information. Any additional information can be

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ACKNOWLEDGEMENTS We acknowledge the National Natural Science Foundation of China (No. 52403373, T.H.), the Natural Science Foundation of Hebei Province (No. E2024201002, T.H.), the Advanced

Talents Incubation Program of the Hebei University (No. 521100222047, T.H.), the Hebei Province Optoelectronic Information Materials Laboratory Performance Subsidy Fund Project

(No.22567634H, S.Y.). The work is funded by the Researchers supporting project number (RSPD2024R762, S.M.H.Q.), King Saud University, Riyadh, Saudi Arabia. The authors gratefully acknowledge

the cooperation of the beamline scientists at BSRF-1W1A beamline. The authors thank the staff at BL17B1 beamline of the National Facility for Protein Science in Shanghai (NFPS), Shanghai

Advanced Research Institute, CAS, for providing technical support in X-ray diffraction data collection and analysis. AUTHOR INFORMATION Author notes * These authors contributed equally: Rui

Wang, Xiaoyu Liu, Shan Yan. AUTHORS AND AFFILIATIONS * College of Physics Science and Technology, Hebei University, Baoding, 071002, China Rui Wang, Xiaoyu Liu, Shan Yan, Ni Meng, Xinmin

Zhao, Shaopeng Yang & Tingwei He * Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, CAS, Beijing, 100049, China Yu Chen * College of Polymer Science and

Engineering State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, 610065, China Hongxiang Li * Department of Physics & Astronomy, College of Sciences, King

Saud University, Riyadh, Saudi Arabia Saif M. H. Qaid * College of Chemistry, Nankai University, Tianjin, 300071, China Mingjian Yuan * Hebei Key Laboratory of Optic-Electronic Information

and Materials, Hebei University, Baoding, 071002, China Tingwei He * National-Local Joint Engineering Laboratory of New Energy Photoelectric Devices, Hebei University, Baoding, 071002, China

Tingwei He * Province-Ministry Co-construction Collaborative Innovation Center of Hebei Photovoltaic Technology, Hebei University, Baoding, 071002, China Tingwei He * Institute of Life

Science and Green Development, Hebei University, Baoding, 071002, China Tingwei He Authors * Rui Wang View author publications You can also search for this author inPubMed Google Scholar *

Xiaoyu Liu View author publications You can also search for this author inPubMed Google Scholar * Shan Yan View author publications You can also search for this author inPubMed Google

Scholar * Ni Meng View author publications You can also search for this author inPubMed Google Scholar * Xinmin Zhao View author publications You can also search for this author inPubMed 

Google Scholar * Yu Chen View author publications You can also search for this author inPubMed Google Scholar * Hongxiang Li View author publications You can also search for this author

inPubMed Google Scholar * Saif M. H. Qaid View author publications You can also search for this author inPubMed Google Scholar * Shaopeng Yang View author publications You can also search

for this author inPubMed Google Scholar * Mingjian Yuan View author publications You can also search for this author inPubMed Google Scholar * Tingwei He View author publications You can

also search for this author inPubMed Google Scholar CONTRIBUTIONS R.W., X.L., and S.Y. contributed equally to this work. T.H. conceived the idea and supervised the work. R.W., X.L., and S.Y.

fabricated devices and analyzed the data. R.W., N.M., S.M.H.Q., and X.Z. performed DFT simulation. Y.C. and H.L. guided the GIWAXS and GIXRD measurements. R.W. and X.L cowrote the paper.

S.M.H.Q., R.W., X.L., M.Y., and T.H. revised the paper. All authors read and commented on the paper. CORRESPONDING AUTHORS Correspondence to Shaopeng Yang or Tingwei He. ETHICS DECLARATIONS

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perovskite photovoltaics with homogeneous halogen-phase distribution. _Nat Commun_ 15, 8899 (2024). https://doi.org/10.1038/s41467-024-53344-9 Download citation * Received: 07 March 2024 *

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