Surface modified perovskite and preparation method thereof

Abstract

The invention provides surface modified perovskite and a preparation method thereof. In one embodiment, the perovskite is a mixed cationic lead halide perovskite; and the surface modification comprises a DPGABr: PbI2 composite layer. In one embodiment, the method for preparing the surface modified perovskite comprises the following steps: a) providing perovskite with a surface to be modified; b) treating the surface to be modified with DPGABr; and c) annealing to form the surface modified perovskite.

Description

Field of the Invention

[0001] The present invention relates to solar cells, in particular to perovskite solar cells. Background of the Invention

[0002] In recent years, metal halide perovskite solar cells (PSCs) have gained great attention in scientific research and industrial work in the photovoltaic community due to their rapid improvement in power conversion efficiency (PCE) [1-5]. Blade coating in air is a scalable and cost-effective technique for preparing PSCs [6,7]. In the early stage, researchers focused on the operating conditions of blade coating, including substrate temperature [8], flow rate and direction of N2 blade [9], and air humidity

[10] . Subsequently, more strategies, such as solvent engineering and additive engineering [11,12], successfully promoted the production of high-quality and large-area perovskite films. It is worth noting that compared with the ordered crystal structure in the bulk, the atoms on the perovskite surface are more susceptible to environmental influences during the crystallization process. Environmental factors such as humidity [13-15], temperature [16,17], and atmosphere

[18] can affect the lattice and disturb the atomic periodicity of the surface. Therefore, the surface of the blade-coated perovskite film, which is closely related to charge trapping, carrier recombination, charge transfer, and ion diffusion, plays a key role in the performance of PSCs [19-21].

[0003] There have been many efforts to improve the surface quality of perovskite films through surface treatments, such as surface modification or surface reconstruction [22, 23]. In general, surface modification involves optimizing the chemical or physical properties of the perovskite surface without changing its bulk properties, usually achieved by introducing small molecule / polymer treatments [24, 25] (e.g., Lewis acid / base) or physical modifications (e.g., mechanical exfoliation of defect layers

[26] ). These processes can improve the quality of the perovskite surface and reduce the defect density. On the other hand, surface reconstruction is a spontaneous process that usually occurs when molecules are introduced on the perovskite surface to react and form new, more stable structures. The PbI2 ends or MAI ends of the perovskite film serve as the basis for surface reconstruction at the molecular level, stimulating physical and chemical changes on the film surface

[27] . For example, Wu et al. introduced FAI on the surface of MAPbI3 and spontaneously formed FAPbI3 by immersing the blade-coated MAPbI3 in a hot bath of FAI to react with the PbI2 ends. This surface reconstruction can effectively reduce the surface defect density and promote charge transport on the perovskite surface. However, achieving surface reconstruction during the blade coating process is challenging as the retention time is estimated to be only a few milliseconds[6]

[28] . Therefore, selecting appropriate solvents and modifiers for post-treatment after blade coating is crucial to achieving effective perovskite surface reconstruction. Summary of the Invention

[0004] The present invention provides a surface-modified perovskite. In one embodiment, the perovskite is a mixed cation lead halide perovskite; and the modified surface comprises a DPGABr:PbI2 composite layer.

[0005] The present invention also provides a perovskite solar cell, comprising the perovskite of the present invention.

[0006] The present invention also provides a method for preparing a surface-modified perovskite. In one embodiment, the method comprises the following steps: a) providing a perovskite surface to be modified; b) treating the surface to be modified with DPGABr; and c) annealing to form the surface-modified perovskite. Graphical Introduction

[0007] Figure 1 (a) MA reconstructed by doctor blade coating and DPGABr treatment 0.7 FA 0.3 Schematic diagram of the surface of PbI3 film. (b) XRD patterns of perovskite films with or without post-treatment. (c) GIXRD diffraction patterns of reference perovskite, pure IPA-treated film, and pure ACN-treated film measured at an incident angle of ω = 0.5°. (d) XRD patterns of DPGABr powder and [DPGABr]2PbI2.

[0008] Figure 2 Shown are the GIXRD diffraction patterns of pure ACN treated films measured at an incident angle of ω = 0.5° or 1.0°.

[0009] Figure 3 XPS spectra showing the Pb 4f and I 3d peaks of perovskite films, with the insets showing the calculated I:Pb ratios of the films: (a) reference perovskite, (b) pure IPA-treated perovskite, and (c) pure ACN-treated perovskite.

[0010] Figure 4 (a) pure DPGABr and DPGABr+PbI2 compound 1 H-NMR spectra. TOF-SIMS profile of perovskite film, and (b) Pb4f spectra of reference film and DPGABr-ACN treated film. (c) Top surface SEM image of reference perovskite film, (d) DPGABr-ACN treated film. (e) Simulated charge density distribution of MAPbI3 with PbI (I replaced by Pb) antisite defects passivated by DPGABr defects. (f) Pristine MAPbI3, MAPbI3 with PbI antisite defects, and DPGABr modified MAPbI3 with Pb I DOS of antisite-defective MAPbI3.

[0011] Figure 5Atomic force microscopy (AFM) images showing perovskite films with and without surface treatment.

[0012] Figure 6 TOF-SIMS profile showing the perovskite film post-treated with DPGABr-ACN.

[0013] Figure 7 DFT calculations showing different perovskite supercells: (a,b) perfect MAPbI3, (c,d) MAPbI3 with PbI antisite defects and (e,f) MAPbI3 with PbI passivated by DPGABr defects. I Antisite-defective MAPbI3.

[0014] Figure 8 Spectra showing (a) steady-state photoluminescence (PL) and (b) time-resolved photoluminescence (TRPL) of perovskite films with and without DPGABr treatment. (c) Structure of ITO / SnO2 / MA 0.7 FA 0.3 Dark IV curves of pure electronic devices of PbI3 / PC70BM / Ag. (d, e) UPS spectra of perovskite with and without DPGABr-ACN treatment. (f) UPS spectra of MA treated with DPGABr-ACN 0.7 FA 0.3 Energy level alignment of PbI3 PSCs.

[0015] Fig. 9 Display structure: ITO / PTAA / MA 0.7 FA 0.3 Dark IV curve of pure hole device of PbI3 / Spiro-OMeTAD / Au.

[0016] Fig.10 Tauc plot showing DPGABr / PbI2 composite film.

[0017] Fig.11 J-V curves of PSCs with different pure IPA and ACN treatments are shown. Insets are performance parameters.

[0018] Fig.12 (a) Device structure of PSC. JV curves of PSCs treated with (b) DPGABr-IPA and (c) DPGABr-ACN at different concentrations. Inset is the performance parameter. (d) -2 The MA measured at a bias voltage of 0.80 V under illumination 0.7 FA 0.3 EIS of PbI3 PSCs. (e) at 100 mW cm -2MA obtained from EIS at various voltages under illumination 0.7 FA 0.3 R of PbI3 PSCs rec (f) V of PSCs with and without DPGABr-ACN treatment as a function of light intensity. oc .

[0019] Fig.13 Showing the absorption spectra of perovskite films with and without DPGABr-ACN treatment. .

[0020] Fig.14 Displayed at 100mW cm -2 Electrochemical impedance spectra (EIS) of PSCs measured at different voltages under illumination: (a) reference PSC, (b) DPGABr-ACN treated PSC. (c) Equivalent circuit diagram of EIS measurement. (d) Recombination lifetime of devices with or without DPGABr-ACN obtained from EIS at different bias voltages.

[0021] Fig.15 Dark J-V curves of PSCs with and without DPGABr-ACN treatment are shown.

[0022] Fig.16 (a) JV curve of the best PSC treated with DPGABr-ACN. Inset is the performance parameter. (b) EQE spectrum of the champion PSC treated with DPGABr-ACN. (c) 1 cm 2 (a) JV curves of PSCs treated with DPGABr-ACN. (b) PCE statistics of PSCs with and without DPGABr-ACN. (c) MPP tracking of PSCs under continuous AM 1.5G illumination. (d) Long-term stability in ambient.

[0023] Fig.17 Statistics showing device performance parameters with and without DPGABr-ACN: (a) V oc ,(b)J sc ,and(c)FF. Detailed Description of the Invention

[0024] The present invention provides a surface-modified perovskite. In one embodiment, the perovskite is a mixed cation lead halide perovskite; and the surface modification comprises a DPGABr:PbI2 composite layer.

[0025] In one embodiment, the perovskite comprises MA (1-x) FA x PbI3 where 0≤x≤1.

[0026] In one embodiment, the perovskite comprises MA 0.7 FA 0.3 One or more of PbI3, MAPbI3 or FAPbI3.

[0027] In one embodiment, the surface modification exhibits one or more photovoltaic properties selected from the following: a) PCE>20%; b) V oc >1.1V; c)J sc >23mA cm -2 ; and d) fill factor>75%. In another embodiment, the surface modification exhibits one or more photovoltaic properties selected from the following: a) PCE is 21.82±1.55%; b) V oc is 1.154±0.02V; c)J sc 24.30±0.55mA cm -2 ; and d) a filling factor of 78.42±1.69%.

[0028] In one embodiment, the surface modification is of n-type relative to the unmodified surface.

[0029] In one embodiment, the surface modification forming step comprises: a) providing a perovskite having a surface to be modified; b) treating the surface to be modified with DPGABr; and c) annealing to form the surface modified perovskite.

[0030] The present invention also provides a perovskite solar cell comprising the perovskite of the present invention.

[0031] In one embodiment, the perovskite solar cell comprises a structure of ITO / PTAA / perovskite of claim 1 / PC70BM / BCP / Ag.

[0032] The present invention also provides a method for preparing a surface-modified perovskite. In one embodiment, the method comprises the following steps: a) providing a perovskite having a surface to be modified; b) treating the surface to be modified with DPGABr; and c) annealing to form the surface-modified perovskite.

[0033] In one embodiment, step (a) comprises doctor blade coating the perovskite solution on a surface.

[0034] In one embodiment, the perovskite solution includes MA (1-x) FA x PbI3, where 0≤x≤1.

[0035] In one embodiment, the perovskite solution includes MA 0.7 FA 0.3 PbI3 solution.

[0036] In one embodiment, the MA 0.7 FA 0.3 The PbI3 solution was prepared by mixing 2.5M MAPbI3 and 1.67M MAPbI3 followed by dilution to form 1.37M MAPbI3. 0.7 FA 0.3 PbI3 solution.

[0037] In one embodiment, the MA 0.7 FA 0.3 The PbI3 solution also included 1.84 mg ml -1 MACl, 1.15 mg ml -1 MABr and 2.8% v / v DMSO.

[0038] In one embodiment, the surface is PTAA and the knife coating is performed at 20 mm s -1 The speed is carried out with a gap of 200 μm

[0039] In one embodiment, step (b) comprises doctor blade coating the DPGABr solution on the surface to be modified.

[0040] In one embodiment, the DPGABr solution includes DPGABr dissolved in ACN.

[0041] In one embodiment, the concentration of the DPGABr solution is 0.25-1.0 mg / ml.

[0042] In one embodiment, step (c) comprises annealing at 100-120°C.

[0043] The present invention will be better understood by reference to the following examples, but those skilled in the art will readily appreciate that the detailed description is for exemplary purposes only and is not meant to limit the invention described herein, which is defined by the claims that follow. Various references or publications are cited in this application. In order to more fully describe the state of the art related to the present invention, the entire disclosure of these references or publications has been incorporated into this application by reference. It should be noted that the transitional word "comprising", which is synonymous with "including", "comprising" or "having", is inclusive or open-ended and does not exclude additional unspecified elements or method steps. example

[0044] Experimental Section

[0045] In this study, the effects of solvents such as isopropyl alcohol (IPA) and acetonitrile (ACN) on the performance of hybrid perovskite MA 0.7 FA 0.3Effect of post-treatment surface of blade coating of PbI3. It was found that ACN can partially remove MAI / FAI and expose the PbI2 ends on the surface, while IPA has little effect on the surface, proving that ACN is a suitable solvent for further surface reconstruction. Subsequently, a new surface modifier, N,N-diphenylguanidine monohydrobromide (DPGABr), was introduced to reconstruct the surface of the perovskite film. The results show that this treatment can significantly improve the photovoltaic performance due to the effective surface reconstruction on the perovskite layer. The results found that due to the formation of an ultra-thin composite layer of DPGABr / PbI2 on the perovskite surface, the surface Fermi level was modulated, non-radiative recombination was significantly reduced and electron transfer was promoted. Based on this technology, the blade-coated inversion PSCs achieved a best PCE of 23.37%, an open circuit voltage (Voc) of 1.174V and excellent long-term stability, with an average PCE increase of 6% compared to the control device.

[0046] Materials: Lead iodide (99.99%) (PbI2) and N,N-diphenylguanidine monohydrobromide (DPGABr) from Alfa Aesar. Formamide iodide (99.99%) (FAI) and methylammonium iodide (99.99%) (MAI) purchased from Greatcell Solar Materials. 2-Methoxyethanol (2ME), chlorobenzene (CB), isopropyl alcohol (IPA), toluene and dimethyl sulfoxide (DMSO) purchased from Sigma-Aldrich. Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (Mn=15000-25000) (PTAA) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (96%) (BCP) purchased from Xi'an Polymer Optoelectronics Technology Co., Ltd. Phenyl-C71-butyric acid methyl ester (99%) (PC70BM) purchased from Nano-C.

[0047] Solar cell preparation: ITO glass was ultrasonically cleaned with deionized water, acetone, and isopropanol for 15 minutes. The cleaned glass was then dried with nitrogen and treated with oxygen plasma for 10 minutes. -1 The PTAA was spin coated on the ITO glass substrate at 5000 rpm for 30 seconds and then annealed at 100 °C for 10 minutes. Before doctor blade coating, the precursor solutions (2.5 M MAPbI3 and 1.67 M FAPbI3) were mixed and diluted to 1.37 M MAPbI3. 0.7 FA 0.3 PbI3 solution, and then add MACl (1.84 mg ml -1 ), MABr (1.15 mg ml-1) and 2.8% (v / v) DMSO as additives. -1MA was coated on the PTAA surface with a knife at a speed of 200 μm and a gap of 200 μm. 0.7 FA 0.3 PbI3 solution and annealed at 105 °C for 10 min. Perovskite films treated with DPGABr were first doctor-bladed with DPGABr dissolved in IPA or CAN at different concentrations and then annealed at 105 °C for 5 min. 20 mg mL dissolved in CB -1 PCBM was spin-coated at 1500 rpm for 60 seconds and annealed at 60°C for 5 minutes. Then, 0.5 mg mL PCBM dissolved in IPA was spin-coated at 4500 rpm. -1 The BCP was then heated for 30 s. Finally, a 200 nm Ag film was deposited as an electrode by thermal evaporation.

[0048] Characterization: XPS was measured using an XPS instrument (ESCALAB250XI, Thermo Fisher Scientific). Rigaku-2500 X-ray diffractometer and X-ray tube (Cu Kα, ) measured X-ray diffraction patterns. Top and cross-sectional SEM images were obtained using a scanning electron microscope (Tescan MAIA3). EQE was recorded using a Newport Oriel QE-200 with a power source (Newport 300W xenon lamp, 66920) and a monochromator (Newport Cornerstone 260). All JV curves were obtained at 100mWcm provided by a solar simulator (Newport 66902). -2 The light intensity was calibrated using a single crystal silicon reference cell (Newport, Oriel 91150) with a KG5 window. The impedance spectrum (IS) was measured by Zennium (Zahner). PL was measured by FLS 920 (Edinburgh Instruments, Ltd).

[0049] DFT calculations: DFT simulations were performed using Quantum Espresso (version 6.5). All structures were fully relaxed using the Perdew, Burke, and Ernzerhof (PBE) exchange-correlation functional and the projected augmented wave (PAW) method before DOS and charge density calculations. The electronic convergence criterion was set to 10 –6 eV, and a plane wave basis set with a cutoff energy of 450 eV was used.

[0050] Results and discussion

[0051] For MA 0.7FA 0.3 Solvent Effects on PbI3 Blade Coated Surfaces

[0052] Preparation of MA by knife coating in air 0.7 FA 0.3 The PbI3 perovskite film was then annealed in air at 105 °C for 15 min (see Figure 1 a). Then, different solvents including ACN and IPA were coated on the film by doctor blade coating, as these solvents can slowly dissolve the 3D perovskite on the surface

[29] . The obtained film was characterized by X-ray diffraction (XRD). Figure 1 As shown in b, the main peaks of all films can be attributed to MA 0.7 FA 0.3 It is noteworthy that in the sample treated with ACN solvent, the

[001] peak of PbI2 crystals was observed at 12.5°, indicating that MAI / FAI initially dissolved in ACN in a fast dynamic process to form PbI2 ends on the surface. However, after IPA treatment, the MAI / FAI 0.7 FA 0.3 PbI3 did not show PbI2 phase after the knife coating process, which can be attributed to the lower solubility of MAI / FAI in IPA than ACN. During the knife coating process, the trace presence of IPA and the short exposure time on the perovskite surface made it difficult for MAI or FAI to dissolve. Then, the films were characterized by oblique incidence X-ray diffraction (GIXRD). At an incident angle of 0.5°, the peak of PbI2 was directly detected in the pure ACN treated film ( Figure 1 c). In addition, when the incident angle increases to 1°, PbI2:MA 0.7 FA 0.3 The peak intensity ratio of PbI3 decreases ( Figure 2 ), indicating that PbI2 is mainly located on the perovskite surface. In contrast, no new peaks were observed in the pure IPA-treated film under the same characterization conditions, further confirming that pure IPA treatment cannot induce the formation of PbI2 on the perovskite surface.

[0053] Figure 3ac shows the X-ray photoelectron spectroscopy (XPS) of the pristine perovskite film or the film after treatment with ACN or IPA. The Pb 4f core electron level spectrum of the comparative perovskite film shows two major peaks at 138.79 and 143.73 eV, corresponding to Pb 4f7 / 2 and Pb 4f5 / 2. The I:Pb ratio can be calculated by the integrated area of ​​the I 3d and Pb 4f peaks. A decrease in the I:Pb ratio from 3.15 to 2.71 after pure ACN post-treatment is observed, confirming the presence of PbI2 terminations on the surface due to the limited detection depth. However, the I:Pb ratio of the pristine film or the film treated with IPA remains unchanged, again demonstrating the significant effect of IPA treatment on MA during the blade coating process. 0.7 FA 0.3 There is no apparent effect on the surface composition or chemical properties of PbI3.

[0054] DPGABr vs. MA 0.7 FA 0.3 Surface reconstruction of PbI3

[0055] like Figure 1 As shown in Fig. b, although the perovskite film treated with pure ACN shows the

[001] peak of PbI2, the film coated with a doctor blade of a solution of DPGABr dissolved in ACN does not show the PbI2 peak, indicating that DPGABr can interact with PbI2 and form another phase. To study their interaction, a mixture of DPGABr and PbI2 was dissolved in dimethyl sulfoxide (DMSO) and thermally annealed at 120 °C for 10 min on a glass substrate to form a solid film, which was then characterized by X-ray diffraction (XRD), as shown in Fig. Figure 1 d. The broad peak of the mixture film indicates that DPGABr and PbI2 can form an amorphous composite. Based on the experimental results, a surface reconstruction process was proposed, in which a large amount of MAI / FAI was quickly dissolved using ACN as a solvent to expose PbI2, and then DPGABr interacted with PbI2 to form a DPGABr:PbI2 composite.

[0056] To further understand the interaction between DPGABr molecules and PbI2, nuclear magnetic resonance (NMR) measurements were performed on DPGABr dissolved in d6-dimethyl sulfoxide (d-DMSO) solvent or DPGABr+PbI2 (1:1) solution. Figure 4 As shown in a, NMR analysis showed that 1 The H resonance signals appeared at 9.94 and 8.00 ppm, corresponding to -NH2 of pure DPGABr, respectively. + and -NH2 environment[30,31]. For DPGABr:PbI2 mixture, -NH2 + of 1The H resonance signal shifted to 9.90 ppm, while the -NH2 resonance signal remained unchanged, proving that -NH2 was formed in the solvent. + and hydrogen bonds between I-Pb-I

[32] . Then, XPS characterization of the perovskite film before and after treatment with DPGABr-ACN solution was performed. Figure 4 As shown in Fig. 2b, after DPGABr-ACN treatment, the characteristic peak of Pb4f in the XPS spectrum shifted from 137.90 eV to 137.98 eV with a higher binding energy, indicating that the chemical environment of Pb changed, thus forming a new phase on the perovskite surface

[33] . These results all indicate that DPGABr can interact with PbI2 caused by ACN coating and form a thin composite on the perovskite surface.

[0057] Figure 4 cd shows MA treated with DPGABr-ACN and without treatment 0.7 FA 0.3 Scanning electron microscopy (SEM) image of PbI3. Notably, the lower surface roughness observed in the atomic force microscopy (AFM) image confirms that ( Figure 5 ), the DPGABr-ACN treated perovskite surface exhibited a smoother and more compact morphology compared to the reference film. These results indicate that surface reconstruction was successfully achieved by DPGABr-ACN post-treatment.

[0058] In order to explore whether DPGABr can penetrate into the perovskite layer, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to detect DPGA + The vertical distribution of ions. Figure 6 As shown, the molecular ion (C 13 H 14 N3+), DPGA + The depth profile of DPGABr decreases rapidly at the surface. This observation suggests that DPGABr can only penetrate to a very shallow depth and is mainly localized on the perovskite surface. This limited penetration may be attributed to the short residence time of the DPGABr solution on the perovskite film. + The strength is higher than Pb + The intensity of DPGABr is two orders of magnitude lower, indicating that DPGABr only partially covers the film surface.

[0059] Density functional theory (DFT) calculations were used to investigate the surface properties of the films after surface reconstruction. To simplify the calculations but maintain generality, a unit cell of MAPbI3 perovskite with PbI2 terminations was constructed. It is well known that the band edges of organic-inorganic perovskites are dominated by Pb and I orbitals, which are crucial to the band structure and are closely related to defects in the unit cell. Antisite defects associated with these ions are known to be located deep in the band gap and act as carrier recombination centers that reduce carrier lifetimes [34-36]. As a Lewis base, the electron pair of the N element in DPGABr enables it to react with Pb by bonding to the Pb 2+ The coordination bonding of effectively passivates the antisite defect, which is also considered to be the main interaction in the present invention

[35] . Figure 7 The perovskite supercell with DPGABr passivation defects is shown, providing the relationship between the N element in DPGABr and the Pb on the film surface. 2+ To further elucidate the passivation effect of DPGABr, simulations and Figure 4 f shows the original MAPbI3, MAPbI3 with PbI antisite defects, and MAPbI3 with PbI passivated by DPGABr. I Density of states (DOS) of anti-site defective MAPbI3. Calculations show that Pb I Antisite defects can lead to mid-gap trap states, but after DPGABr passivation, these trap states move toward the conduction band edge. Therefore, it is concluded that DPGABr passivates Pb I Antisite defects effectively reduce the number of carriers in non-radiative recombination centers.

[0060] Photoluminescence (PL) measurements were performed on the perovskite films before and after surface reconstruction to evaluate the passivation effect. The perovskite side was excited with 435 nm excitation light in the glass / perovskite structure. Figure 8 a shows that both films emit infrared light in the wavelength range of about 750nm to 840nm, proving that the introduction of DPGABr into the surface of the perovskite film has little effect on the radiative recombination mechanism. However, the perovskite film treated with DPGABr-ACN exhibits a stronger PL intensity, which means that the non-radiative recombination centers on the surface are reduced. Figure 8 b, the time-resolved PL (TRPL) results support this inference. A double exponential decay function was used to fit the data, and the average lifetime τ was calculated using the following equation ave

[37] :

[0061] The results show that the τ of the reference perovskite film and DPGABr-ACN film ave are 452ns and 791ns respectively. The increase in τ aveIt is demonstrated that after surface reconstruction, the non-radiative recombination centers on the perovskite surface are reduced, which is beneficial to improving the photovoltaic performance of PSCs.

[0062] To investigate the trap density in perovskite films, space charge limited current (SCLC) tests were performed. Figure 8 The inset of c shows the electron-only device of the ITO / SnO2 / perovskite / PC70BM / Ag structure. Figure 8 c shows the trap filling limit voltage (V TFL ) is 0.22 V, while the V TFL The trap density (N t ) is calculated using the following equation

[38] :

[0063] L represents the thickness of the perovskite film, ε r represents the relative dielectric constant of perovskite, ε0 represents the vacuum permittivity, and q represents the electron charge. The trap density of perovskite treated with DPGABr-ACN is 0.87×10 15 cm -3 , untreated is 1.61×10 15 cm -3 . Fig. 9 The hole-only device test results shown in Figure 2 are similar. After DPGABr-ACN treatment, the trap density increased from 1.32×10 15 cm -3 Reduced to 0.95×10 15 cm -3 The decrease in trap density in films after DPGABr-ACN treatment highlights the potential of surface reconstruction in achieving higher quality film surfaces, which is important for improving V in PSCs. oc It is crucial.

[0064] According to the optical absorption spectrum of the DPGABr:PbI2 composite layer, the absorption edge is 397 nm (see Supporting Information Fig.10 ), with a corresponding band gap of 3.12 eV, indicating that the composite layer is an insulator. Partial coverage of the insulator on the perovskite surface can passivate the traps without affecting charge transfer, similar to previous reports on the effect of ultrathin polymethyl methacrylate (PMMA) spacer layers on improving PSC performance [39,40].

[0065] To gain a deeper understanding of the charge transfer after surface reconstruction, the energy level alignment of the perovskite film was analyzed by ultraviolet photoelectron spectroscopy (UPS). Figure 8 d and e show the E extracted from the cutoff of the linear extension line, respectively. f -E VBMand work function (W f ) value. The results show that after surface reconstruction, E f and E VBM The energy gap between them becomes wider, indicating that the film surface is more n-type and the number of free electrons on the surface increases

[41] . f The increase from 4.61eV to 4.38eV results in a built-in electric field in the bulk material, which promotes charge separation and transfer under light illumination [42,43]. Fig.11 ) Extracted E f -E VBM , W f and band gap (E g ) value, determine the valence band (E v ) and conduction band (E c ) position. The energy level of the device is aligned as Figure 8 f, from which the charge transfer characteristics can be analyzed. The energy gap between the Ec of perovskite and PCBM provides sufficient driving force for electron transfer (~0.11 eV). More importantly, the band bending on the perovskite surface is conducive to charge transfer when photocarriers are generated under light.

[0066] Photovoltaic performance of DPGABr-treated PSCs

[0067] In order to explore the effect of different post-treatments on photovoltaic performance, the prepared structure is ITO / PTAA / MA 0.7 FA 0.3 PbI3 / PC 70 BM / BCP / Ag PSCs( Fig.12 a), modified with DPGABr-IPA and DPGABr-ACN, respectively. Fig.12 The results in b show that DPGABr-IPA treatment has little effect on the PCE of PSCs. Fig.12 As shown in c, DPGABr-ACN treatment significantly increased the PCE from 21.31% to 22.65%, accompanied by a oc (1.15V), short circuit current (J sc )(24.92 mA cm -2 ) and fill factor (FF) (79.14%). These findings suggest that specific surface reconstructions can enhance the photovoltaic performance of PSCs, depending on the choice of post-treatment solvent and surface modifier. To demonstrate that the difference in photovoltaic performance is caused by surface reconstruction rather than pure solvent effects, PSCs modified with two different pure solvents were prepared. Fig.13 As shown, pure solvent surface treatment does not significantly improve the photovoltaic performance of the device.

[0068] To gain deeper insights into the underlying mechanisms of charge transport and recombination in PSCs, electrochemical impedance spectroscopy (EIS) analysis was employed. Fig.12 d shows at 100 mW cm -2 Nyquist plot measured at 0.80V bias under illumination. Fig.14 c to obtain the charge transfer resistance (R tr ) and composite resistance (R rec ). Generally speaking, R tr represents the high frequency part and R rec represents the low-frequency part

[44] . Specifically, it was observed that the Rtr of the device decreased from 55.38Ω to 26.68Ω and the Rrec increased from 885.4Ω to 1094Ω before and after DPGABr-ACN treatment. These findings suggest that surface reconstruction leads to faster charge transport and reduces non-radiative recombination at the perovskite / PCBM interface, which is beneficial to the J of PSCs. sc and V oc At 100 mW cm - 2 Rrec values ​​under different applied voltages at different light intensities are shown in Fig.12 e. It can be observed that the target device has a higher Rrec than the control device at each bias voltage. This finding provides strong evidence that the surface reconstruction caused by defect passivation of DPGABr can significantly reduce the recombination rate in PSCs. The increase in Rrec is expected to enhance the shunt resistance of PSCs, which is a key factor leading to the improvement of FF in the target PSCs

[45] .

[0069] Fig.12 f shows the V in PSCs treated with DPGABr-ACN and without treatment oc dependence on light intensity. The slopes of the target device and the control device were determined to be 1.36 KT / q and 1.51 KT / q, respectively. In general, a larger deviation from the ideal slope of 1 KT / q indicates the presence of more trap-assisted recombination centers. A lower slope was observed in the DPGABr-CAN treated PSCs, indicating that non-radiative recombination was effectively suppressed. In addition, dark IV curve measurements were performed to examine the reverse saturation current density of the PSCs. Fig.15 As shown in Figure 4, the reverse saturation current density of the target PSC is lower than that of the control device, indicating that the former has a lower carrier generation rate in the dark due to the lower trap density

[46] . This result is consistent with the reduced recombination rate in the target PSC.

[0070] After successfully passivating the surface defects and forming a more n-type perovskite surface, a promising perovskite with a PCE of 23.37%, V oc (1.174V), J sc (24.85mA cm-2 ) and FF (80.11%) excellent devices ( Fig.16 a). In addition, the external quantum efficiency (EQE) measurement results ( Fig.16 b) shows that the integrated photocurrent of the excellent device is 23.67 mA cm -2 , and J obtained from the JV curve sc The values ​​are consistent. It is worth noting that using 1cm 2 The device area treated with DPGABr-ACN achieved a maximum PCE of 20.44% ( Fig.16 c) These results demonstrate the effectiveness of DPGABr-ACN post-treatment in achieving high-performance PSCs.

[0071] To evaluate the repeatability of the DPGABr-ACN post-treatment, a batch of 30 devices was prepared to assess their performance. Fig.16 d shows that the DPGABr-ACN based device outperforms the reference device in terms of average PCE and improves V oc , J sc and the average value of FF ( Fig.17 The operational stability of PSCs is evaluated by measuring the steady-state output at the maximum power point (MPP). Fig.16 e, the results show that at V MPP At 0.992 V, the PSC treated with DPGABr-ACN exhibited a higher output PCE (22.35%), while the control device had a PCE of 20.95% at an applied voltage of 0.94 V. It is worth noting that both devices maintained stable output during operation. In addition, the long-term stability of PSCs is crucial for practical applications. Fig.16 f depicts the long-term stability of unencapsulated PSCs under ambient conditions (25 ± 5 °C, 15% ± 5% RH). The target devices with surface reconstruction exhibit superior stability performance relative to the control devices, which can be attributed to the significantly reduced trap density on the perovskite surface.

[0072] in conclusion

[0073] In summary, this paper proposes a facile surface modification method to achieve efficient blade-coated PSCs by removing part of the MAI / FAI components on the surface and reconstructing the surface with the help of DPGABr. Compared with IPA, ACN can quickly dissolve and remove MAI / FAI on the perovskite surface and lead to the exposure of PbI2. After adding DPGABr to ACN, the reconstruction of the perovskite surface is achieved through the reaction between the PbI2 end and DPGABr, generating an amorphous composite that partially covers the perovskite surface. The DPGABr:PbI2 composite layer can passivate defects and adjust the perovskite surface to make it more n-type. Therefore, the PCE of the treated device is higher, with a relative increase of 6%, while the PCE of the best device reaches 23.37%, V oc The results show that the surface of perovskite films can be reconstructed by blade coating, which is compatible with the scale-up of large-area PSCs and other optoelectronic devices.

[0074] References [1]A.Kojima,K.Teshima,Y.Shirai,T.Miyasaka,J.Am.Chem.Soc.2009,131,6050. [2] A. Mei, X. Li, L. Liu, Z. Ku, T. Liu, Y. Rong, M. Xu, M. Hu, J. Chen, Y. Yang, M. H. Han, Science 2014, 345, 295. [3]Z.Xiao,Q.Dong,C.Bi,Y.Shao,Y.Yuan,J.Huang,Adv.Mater.2014,26,6503. [4]JHHeo,DHSong,HJHan,SYKim,JHKim,D.Kim,HWShin,TKahn,C.Wolf,TWLee,SHIm,Adv.Mater.2015,27,3424. [5]NJJeon,JHNoh,WSYang,YCKim,S.Ryu,J.Seo,SISeok,Nature2015,517,476. [6]Y.Deng,E.Peng,Y.Shao,Z.Xiao,Q.Dong,J.Huang,EnergyEnviron.Sci.2015,8,1544. [7]Y.Deng,Q.Dong,C.Bi,Y.Yuan,J.Huang,Adv.Energy Mater.2016,6,1600372. [8]Y.Zhong,R.Munir,J.Li,M.-C.Tang,MRNiazi,D.-M.Smilgies,K.Zhao,A.Amassian,ACS Energy Lett.2018,3,1078. [9]PW-K.Fong,H.Hu,Z.Ren,K.Liu,L.Cui,T.Bi,Q.Liang,Z.Wu,J.Hao,G.Li,Adv.Sci.2021,8,2003359.

[10] J.Hidalgo,CARPerini,A.-F.Castro-Mendez,D.Jones,H. B.Lai,R.Li,S.Sun,A.Abate,J.-P.Correa-Baena,ACS Energy Lett.2020,5,3526.

[11] S.Chen,X.Dai,S.Xu,H.Jiao,L.Zhao,J.Huang,Science 2021,373,902.

[12] S.Chen,X.Xiao,H.Gu,J.Huang,Sci.Adv.7,eabe8130.

[13] G.Wang,Q.Lian,D.Wang,F.Jiang,G.Mi,D.Li,Y.Huang,Y.Wang,X.Yao,R.Shi,Adv.Mater.2022,34,2205143.

[14] PWKFong,H.Hu,Z.Ren,K.Liu,L.Cui,T.Bi,Q.Liang,Z.Wu,J.Hao,G.Li,Adv.Sci.2021,8,2003359.

[15] H.Li,X.Feng,K.Huang,S.Lu,X.Wang,E.Feng,J.Chang,C.Long,Y.Gao,Z.Chen,C.Yi,J.He,JYang,Small 2023,n / a,2300374.

[16] Y.Chen,X.Liu,Y.Zhao,Angew.Chem.Int.Ed.2022,61,e202110603.

[17] J.A.Aguiar,S.Wozny,N.R.Alkurd,M.Yang,L.Kovarik,T.G.Holesinger,M.Al-Jassim,K.Zhu,W.Zhou,J.Berry,ACS Energy Lett.2016,1,155.

[18] S.Pathak,A.Sepe,A.Sadhanala,F.Deschler,A.Haghighirad,N.Sakai,K.C.Goedel,S.D.Stranks,N.Noel,M.Price,ACS Nano 2015,9,2311.

[19] Q.Jiang,Y.Zhao,X.Zhang,X.Yang,Y.Chen,Z.Chu,Q.Ye,X.Li,Z.Yin,J.You,Nat.Photonics 2019,13,460.

[20] D.Luo,X.Li,A.Dumont,H.Yu,Z.H.Lu,Adv.Mater.2021,33,2006004.

[21] G.Wu,R.Liang,M.Ge,G.Sun,Y.Zhang,G.Xing,Adv.Mater.2022,34,2105635.

[22] Q.Jiang,J.Tong,Y.Xian,R.A.Kerner,S.P.Dunfield,C.Xiao,R.A.Scheidt,D.Kuciauskas,X.Wang,M.P.Hautzinger,R.Tirawat,M.C.Beard,D.P.Fenning,J.J.Berry,B.W.Larson,Y.Yan,K.Zhu,Nature 2022,611,278.

[23] Z.Li,B.Li,X.Wu,S.A.Sheppard,S.Zhang,D.Gao,N.J.Long,Z.Zhu,Science2022,376,416.

[24] M.Yang,T.Zhang,P.Schulz,Z.Li,G.Li,D.H.Kim,N.Guo,J.J.Berry,K.Zhu,Y.Zhao,Nat.Commun.2016,7,12305.

[25] F.Li,X.Deng,F.Qi,Z.Li,D.Liu,D.Shen,M.Qin,S.Wu,F.Lin,S.-H.Jang,J.Zhang,X.Lu,D.Lei,C.-S.Lee,Z.Zhu,AKY20,J.01,J.Am31c.420

[26] S.Chen,Y.Liu,X.Xiao,Z.Yu,Y.Deng,X.Dai,Z.Ni,J.Huang,Joule 2020,4,2661.

[27] Y.Yang,W.Zhao,T.Yang,J.Liu,J.Zhang,Y.Fang,S.Liu,J.Mater.Chem.A2021,9,23597.

[28] Y.Deng,CHVan Brackle,X.Dai,J.Zhao,B.Chen,J.Huang,Sci.Adv.2019,5,eaax7537.

[29] S.Sidhik,Y.Wang,M.De. Siena,R.Asadpour,AJTorma,T.Terlier,K.Ho,W.Li,ABPuthirath,X.Shuai,A.Agrawal,B.Traore,M.Jones,R.Giridharagopal,PMAjayan,J.Strzalka,DSGinger,ADcienceKatan.MGedis,MAAlam 2022,377.

[30] J.Zhu,S.Park,OYGong,C.Sohn,Z.Li,Z.Zhang,B.Jo,W.Kim,GShan,DHKim,TKAhn,J.Lee,HSJung,Energy Environ.Sci.2021,14,4903.

[31] X.Li,M.Ibrahim Dar,C.Yi,J.Luo,M.Tschumi,SMZakeeruddin,MKNazeeruddin,H.Han,M. Nature Chemistry 2015,7,703.

[32] T.Yang,L.Gao,J.Lu,C.Ma,Y.Du,P.Wang,Z.Ding,S.Wang,P.Xu,D.Liu,H.Li,X.Chang,J.Fang,W.Tian,Y.Yang,S.Liu,K.Zhao,Nat.Commun.2023,14,839.

[33] S.Tan,T.Huang,I.Yavuz,R.Wang,M.H.Weber,Y.Zhao,M.Abdelsamie,M.E.Liao,H.-C.Wang,K.Huynh,K.-H.Wei,J.Xue,F.Babbe,M.S.Goorsky,J.-W.Lee,C.M.Sutter-Fella,Y.Yang,J.Am.Chem.Soc.2021,143,6781.

[34] H.Cheng,C.Liu,J.Zhuang,J.Cao,T.Wang,W.Y.Wong,F.Yan,Adv.Funct.Mater.2022,32,2204880.

[35] R.Yu,G.Wu,R.Shi,Z.Ma,Q.Dang,Y.Qing,C.Zhang,K.Xu,Z.a.Tan,Adv.Energy Mater.2023,13,2203127.

[36] J.Cao,C.-K.Liu,V.Piradi,H.-L.Loi,T.Wang,H.Cheng,X.Zhu,F.Yan,ACSEnergy Lett.2022,7,3362.

[37] J.Zhuang,P.Mao,Y.Luan,N.Chen,X.Cao,G.Niu,F.Jia,F.Wang,S.Cao,J.Wang,Adv.Funct.Mater.2021,31,2010385.

[38] J.Cao,H.-L.Loi,Y.Xu,X.Guo,N.Wang,C.-k.Liu,T.Wang,H.Cheng,Y.Zhu,M.G.Li,W.-Y.Wong,F.Yan,Adv.Mater.2022,34,2107729.

[39] H.Kim,K.S.Lee,M.J.Paik,D.Y.Lee,S.-U.Lee,E.Choi,J.S.Yun,S.I.Seok,Adv.Funct.Mater.2022,32,2110473.

[40] B. Yuan, C. Li, W. Yi, F. Juan, H. Yu, F. Xu, C. Li, B. Cao, J. Phys. Chem. Solids 2021, 153, 110000.

[41] Y.-N.Lu, J.-X.Zhong, Y.Yu, X.Chen, C.-Y.Yao, C.Zhang, M.Yang, W.Feng, Y.Jiang, Y.Tan, L.Gong,

[42] W.Yan,Y.Li,Y.Li,S.Ye,Z.Liu,S.Wang,Z.Bian,C.Huang,Nano Energy2015,16,428.

[43] W. Chai, W. Zhu, Z. Zhang, D. Liu, Y. Ni, Z. Song, P. Dong, D. Chen, J. Zhang, C. Zhang, Y. Hao, Chem. Eng. J. 2023, 452, 139292.

[44] H.Li,J.Cao,Q.Zhou,L.Ding,J.Wang,Nano Energy 2015,15,125.

[45] P.You,G.Li,G.Tang,J.Cao,F.Yan,Energy Environ.Sci.2020,13,1187.

[46] T. Wu, P. Xu, D. Wang, X. Jiang, F. Guo, S. Gao, Z. Ge, Y. Zhang, Chem. Eng. J. 2023, 454, 140451.

Claims

1. A surface-modified perovskite, characterized in that: a) the perovskite is a mixed cation lead halide perovskite; and b) The surface modification includes a DPGABr:PbI2 composite layer.

2. The perovskite according to claim 1, characterized in that: The perovskite includes MA (1-x) FA x PbI3, where 0≤x≤1.

3. The perovskite according to claim 1, characterized in that: The perovskite comprises a material selected from MA 0.7 FA 0.3 One or more of PbI3, MAPbI3 and FAPbI3.

4. The perovskite according to claim 1, characterized in that: The surface modification exhibits one or more photovoltaic properties selected from the group consisting of: a. PCE>20%; b.V. oc >1.1V; cJ sc >23mA cm -2 ;and d. Fill factor > 75%.

5. The perovskite according to claim 1, characterized in that: The surface modification is of the n-type relative to the unmodified surface.

6. The perovskite according to claim 1, characterized in that: The surface modification forming step comprises: a. providing a perovskite having a surface to be modified; b. treating the surface to be modified with DPGABr; and c. Annealing to form the surface modified perovskite.

7. A perovskite solar cell comprising the perovskite of claim 1.

8. The perovskite solar cell according to claim 7, characterized in that: The perovskite solar cell comprises a structure of ITO / PTAA / the perovskite of claim 1 / PC70BM / BCP / Ag.

9. A method for preparing a surface-modified perovskite, comprising the following steps: a. providing a perovskite having a surface to be modified; b. treating the surface to be modified with DPGABr; as well as c. Annealing to form the surface-modified perovskite.

10. The method according to claim 9, characterized in that: The step (a) comprises knife coating the perovskite solution onto a surface.

11. The method according to claim 10, characterized in that: The perovskite solution includes MA (1-x) FA x PbI3, where 0≤x≤1.

12. The method according to claim 10, characterized in that: The perovskite solution includes MA 0.7 FA 0.3 PbI3 solution.

13. The method according to claim 12, characterized in that: The MA 0.7 FA 0.3 The PbI3 solution was prepared by mixing 2.5 M MAPbI3 and 1.67M FAPbI3 were then diluted to form 1.37M MA 0.7 FA 0.3 PbI3 solution.

14. The method according to claim 12, characterized in that: The MA 0.7 FA 0.3 The PbI3 solution also contained 1.84 mg ml -1 MACl, 1.15 mg ml -1 MABr and 2.8% v / v DMSO.

15. The method according to claim 10, characterized in that: The surface was PTAA and the knife coating was carried out at 20 mm s -1 The speed was carried out at a gap of 200 μm.

16. The method of claim 9, characterized in that: The step (b) comprises applying a DPGABr solution on the surface to be modified by a doctor blade.

17. The method of claim 16, characterized in that: The DPGABr solution includes DPGABr dissolved in ACN.

18. The method of claim 16, characterized in that: The concentration of the DPGABr solution is 0.25-1.0 mg / ml.

19. The method according to claim 9, characterized in that: The step (c) comprises annealing at 100-120°C.

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