Spacer Cation Tuning Enables Vertically Oriented and Graded Quasi-2D Perovskites for Efficient Solar Cells

Halide substitution in phenethylammonium spacer cations (X-PEA⁺, X  = F, Cl, Br) is a facile strategy to improve the performance of PEA based perovskite solar cells (PSCs). However, the power conversion efficiency (PCE) of X-PEA based quasi-2D (Q-2D) PSCs is still unsatisfactory and the underlying mechanisms are in debate. Here, the in-depth study on the impact of halide substitution on the crystal orientation and multi-phase distribution in PEA based perovskite films are reported. The halide substitution eliminates n  =  1 2D perovskite and thus leads to the perpendicular crystal orientation. Furthermore, nucleation competition exists between small-n and large-n phases in PEA and X-PEA based perovskites. This gives rise to the orderly distribution of different n-phases in the PEA and F-PEA based films, and random distribution in Cl-PEA and Br-PEA based films. As a result, (F-PEA)₂MA₃Pb₄I₁₂ (MA = CH₃NH₃⁺, n = 4) based PSCs achieve a PCE of 18.10%, significantly higher than those of PEA (12.23%), Cl-PEA (7.93%) and Br-PEA (6.08%) based PSCs. Moreover, the F-PEA based devices exhibit remarkably improved stability compared to their 3D counterparts.     

In Situ Growth of 2D Perovskite Capping Layer for Stable and Efficient Perovskite Solar Cells

2D halide perovskites have recently been recognized as a promising avenue in perovskite solar cells (PSCs) in terms of encouraging stability and defect passivation effect. However, the efficiency (less than 15%) of ultrastable 2D Ruddlesden–Popper PSCs still lag far behind their traditional 3D perovskite counterparts. Here, a rationally designed 2D‐3D perovskite stacking‐layered architecture by in situ growing 2D PEA₂PbI₄ capping layers on top of 3D perovskite film, which drastically improves the stability of PSCs without compromising their high performance, is reported. Such a 2D perovskite capping layer induces larger Fermi‐level splitting in the 2D‐3D perovskite film under light illumination, resulting in an enhanced open‐circuit voltage (V_oc) and thus a higher efficiency of 18.51% in the 2D‐3D PSCs. Time‐resolved photoluminescence decay measurements indicate the facilitated hole extraction in the 2D‐3D stacking‐layered perovskite films, which is ascribed to the optimized energy band alignment and reduced nonradiative recombination at the subgap states. Benefiting from the high moisture resistivity as well as suppressed ion migration of the 2D perovskite, the 2D‐3D PSCs show significantly improved long‐term stability, retaining nearly 90% of the initial power conversion efficiency after 1000 h exposure in the ambient conditions with a high relative humidity level of 60 ± 10%.     

Managing Interfacial Hot-Carrier Cooling and Extraction Kinetics for Inverted Ma-Free Perovskite Solar Cells Over 23% Efficiency via Dion–Jacobson 2D Capping Layer

While quasi-2D perovskite is often used in inverted perovskite solar cells (PSCs) to improve the interfacial carrier transfer, the development of pure 2D perovskite with superior stability is rarely seen and the corresponding carrier-extraction kinetics remains unclear. Here, a variety of hexatomic ring cations including piperidine, pyridine, and cyclohexane are introduced to modify the perovskite/electron transport layer interface. The Dion–Jacobson phase 2D cladding (n = 1) based on 3-(aminomethyl) piperidinium is proved to form a coordinated energy landscape and homogeneous surface potential distribution, and effectively prolong the electron diffusion length (≈1.58 µm) and accelerate the hot-carrier extraction rate (2.5 times that of Control at 400 K). Furthermore, the quasi-2D treatment (n ≈ 3,4) demonstrated a slight escalation in short-circuit current, but failed to inhibit the interdiffusion of Ag, Pb, and I under illumination. Finally, one of the state-of-art power conversion efficiency (PCE) for MA-free inverted PSCs is achieved at 23.62% with increased open-circuit voltage (≈1.15 V) and fill factor (≈82.8%). Most importantly, 89% and 93.6% of initial PCE are retained after 720 h under 85 °C heating and 1000 h under maximum power point tracking, illustrating satisfactory thermal and operational stability with pure 2D perovskite capping layer.     

Introduction of Hydrophobic Ammonium Salts with Halogen Functional Groups for High‐Efficiency and Stable 2D/3D Perovskite Solar Cells

2D perovskites have attracted extensive attention due to their excellent stability compared with 3D perovskites. However, the intrinsic hydrophilicity of introduced alkylammonium salts effects the humidity stability of 2D/3D perovskites. Devices based on longer chain alkylammonium salts show improvement in hydrophobicity but lower efficiency due to the poorer charge transport among various layers. To solve this issue, two hydrophobic short‐chain alkylammonium salts with halogen functional groups (2‐chloroethylamine, CEA⁺ and 2‐bromoethylamine, BEA⁺) are introduced into (Cs_0.1FA_0.9)Pb(I_0.9Br_0.1)₃ 3D perovskites to form 2D/3D perovskite structure, which achieve high‐quality perovskite films with better crystallization and morphology. The optimal 2D/3D perovskite solar cells (PSCs) with 5% CEA⁺ display a power conversion efficiency (PCE) as high as 20.08% under 1 sun irradiation. Because of the notable hydrophobicity of alkylammonium cations with halogen functional groups and the formed 2D/3D perovskite structure, the optimal PSCs exhibit superior moisture resistance and retain 92% initial PCE after aging at 50 ± 5% relative humidity for 2400 h. This work opens up a new direction for the design of new‐type 2D/3D PSCs with improved performance by employing proper alkylammonium salts with different functional groups.     

Modifying Surface Termination of CsPbI3 Grain Boundaries by 2D Perovskite Layer for Efficient and Stable Photovoltaics

It is highly desirable for all-inorganic perovskite solar cells (PVSCs) to have reduced nonideal interfacial charge recombination in order to improve the performance. Although the construction of a 2D capping layer on 3D perovskite is an effective way to suppress interfacial nonradiative recombination, it is difficult to apply it to all-inorganic perovskites because of the resistance of Cs⁺ cesium ions in cation exchange reactions. To alleviate this problem, a simple approach using an ultra-thin 2D perovskite to terminate CsPbI₃ grain boundaries (GBs) without damaging the original 3D perovskite is developed. The 2D perovskite at the GBs not only enhances the charge-carrier extraction and transport but also effectively suppresses nonradiative recombination. In addition, because the 2D perovskite can prevent the moisture and oxygen from penetrating into the GBs and at the same time suppress the ion migration, the 2D terminated CsPbI₃ films exhibit significantly improved stability against humidity. Moreover, the devices without encapsulation can retain ≈81% of its initial power conversion efficiency (PCE) after being stored at 40 ± 5% relative humidity for 84 h. The 2D-based champion device exhibits a high PCE of 18.82% with a high open-circuit voltage of 1.16 V.     

Multi-Site Intermolecular Interaction for In Situ Formation of Vertically Orientated 2D Passivation Layer in Highly Efficient Perovskite Solar Cells

Surface passivation via 2D perovskite is critical for perovskite solar cells (PSCs) to achieve remarkable performances, in which the applied spacer cations play an important role on structural templating. However, the random orientation of 2D perovskite always hinder the carrier transport. Herein, multiple nitrogen sites containing organic spacer molecule (1H-Pyrazole-1-carboxamidine hydrochloride, PAH) is introduced to form 2D passivation layer on the surface of formamidinium based (FAPbI₃) perovskite. Deriving from the interactions between PAH and PbI₂, the defects of FAPbI₃ perovskite are effectively passivated. Interestingly, due to the multiple-site interactions, the 2D nanosheets are found to grow perpendicularly to the substrate for promotion of charge transfer. Therefore, an impressive power conversion efficiency of 24.6% and outstanding long-term stability are achieved for the 2D/3D perovskite devices. The findings further provide a perspective in structure design of novel organic halide salts for the fabrication of efficient and stable PSCs.     

24.64%-Efficiency MA-Free Perovskite Solar Cell with Voc of 1.19 V Enabled by a Hinge-Type Fluorine-Rich Complex

High density of defects at interface severely affects the performance of perovskite solar cells (PSCs). Herein, cobalt (II) hexafluoro-2,4-pentanedionat (CoFAc), a hinge-type fluorine-rich complex, is introduced onto the surface of formamidinium cesium lead iodide (FACsPbI₃) film to address the issues of perovskite/Spiro-OMeTAD interface. The existence of CoFAc passivates both organic cation and halide anion vacancies by establishing powerful hydrogen bonds with HC(NH₂)₂⁺ (FA⁺) and strong ionic bonds with Pb²⁺ in perovskite films. In addition, CoFAc serves as a connecting link to enhance interfacial hole-transport kinetics via interacting with Spiro-OMeTAD. Consequently, FACsPbI₃ PSCs with CoFAc modification display a champion power conversion efficiency (PCE) of 24.64% with a charming open-circuit voltage (V_OC) of 1.191 V, which is the record V_OC among all the reported organic-inorganic hybrid PSCs with TiO₂ as electron transport layer. Furthermore, CoFAc-modified devices exhibit an outstanding long-term stability, which can maintain 95% of their initial PCEs after exposure to ambient atmosphere for 1500 h without any encapsulation.     

3D Polydentate Complexing Agents for Passivating Defects and Modulating Crystallinity for High-Performance Perovskite Solar Cells

The grain boundaries (GBs)/surface defects within perovskite film directly impede the further improvement of photoelectric conversion efficiency (PCE) and stability of planar perovskite solar cells (PSCs). Herein, 3D phytic acid (PA) and phytic acid dipotassium (PAD) with polydentate are explored to synchronously passivate the defects of perovskite absorber directly in multiple spatial directions. The strong electron-donating groups ( H₂PO₄) in the PA molecule afford six anchor sites to bind firmly with uncoordinated Pb²⁺ at the GBs/surface and modulate perovskite crystallization, thus enhancing the quality of perovskite film. Particularly, PAD containing an additional (K→PO) push–pull structure promotes the dominant coordination of phosphate group (PO) with Pb²⁺ and passivates halide anion defects due to the complexation of potassium ions (K⁺) with iodide ions (I^-). Consequently, the PAD-complexed PSCs deliver a champion PCE of 23.18%, which is remarkably higher than that of the control device (19.94%). Meanwhile, PAD-complexed PSCs exhibit superior moisture and thermal stability, remaining 79% of their initial PCE after 1000 h under continuous illumination, while the control device remain only 48% of their PCE after 1000 h. This work provides important insights into designing multifunctional 3D passivators for the purpose of simultaneously enhancing the efficiency and stability of devices.     

Spidermen Strategy for Stable 24% Efficiency Perovskite Solar Cells

The interface energetics-modification plays an important role in improving the power conversion efficiency (PCE) among the perovskite solar cells (PSCs). Considering the low carrier mobility caused by defects in PSCs, a double-layer modification engineering strategy is adopted to introduce the “spiderman” NOBF₄ (nitrosonium tetrafluoroborate) between tin dioxide (SnO₂ and perovskite layers. NO⁺, as the interfacial bonding layer, can passivate the oxygen vacancy in SnO₂, while BF₄⁻ can optimize the defects in the bulk of perovskite. This conclusion is confirmed by theoretical calculation and transmission electron microscopy (TEM). The synergistic effect of NO⁺ and BF₄⁻ distinctly heightens the carrier extraction efficiency, and the PCE of PSCs is 24.04% with a fill factor (FF) of 82.98% and long-term stability. This study underlines the effectiveness of multifunctional additives in improving interface contact and enhancing PCE of PSCs.     

Rubidium Fluoride Modified SnO2 for Planar n-i-p Perovskite Solar Cells

Regulating the electron transport layer (ETL) has been an effective way to promote the power conversion efficiency (PCE) of perovskite solar cells (PSCs) as well as suppress their hysteresis. Herein, the SnO₂ ETL using a cost-effective modification material rubidium fluoride (RbF) is modified in two methods: 1) adding RbF into SnO₂ colloidal dispersion, F and Sn have a strong interaction, confirmed via X-ray photoelectron spectra and density functional theory results, contributing to the improved electron mobility of SnO₂; 2) depositing RbF at the SnO₂/perovskite interface, Rb⁺ cations actively escape into the interstitial sites of the perovskite lattice to inhibit ions migration and reduce non-radiative recombination, which dedicates to the improved open-circuit voltage (V_oc) for the PSCs with suppressed hysteresis. In addition, double-sided passivated PSCs, RbF on the SnO₂ surface, and p-methoxyphenethylammonium iodide on the perovskite surface, produces an outstanding PCE of 23.38% with a V_oc of 1.213 V, corresponding to an extremely small V_oc deficit of 0.347 V.     

Influence of the Nature of A Cation on Dynamics of Charge Transfer Processes in Perovskite Solar Cells

The electronic processes occurring within the perovskite solar cells (PSCs) are strongly influenced by the nature of the organic A cations present within the inorganic framework. In this study, the impact of FA (CH(NH₂)₂⁺) and Cs⁺ cations on the intrinsic and interfacial properties in the FAPbBr₃ and CsPbBr₃ PSCs is investigated. The analysis of current density ( J _SC) and photovoltage ( V _OC) as a function of illumination intensity establishes that the interfacial charge transport is more rapid in FAPbBr₃ devices. Small perturbation measurements including intensity modulated photocurrent and photovoltage spectroscopy are applied to explore the resistive and capacitive elements. Furthermore, electrochemical impedance spectroscopy measurements are found to correlate well with the photovoltaic characteristics of FAPbBr₃ and CsPbBr₃ PSCs. Overall, the in‐depth analysis of various phenomena occurring within the bromide PSCs allows to underline the working principle, which provides a key to optimize the device performance. The present protocol is not only valid for PSCs but can also be extended to devices based on alternative light harvesters.     

Fully Printed High-Performance Quasi-Two-Dimensional Perovskite Solar Cells via Multifunctional Interfacial Engineering

Planar n–i–p carbon perovskite solar cells (PSCs) with a hole transport layer that can be fabricated at low temperatures at low-cost exhibit great potential for large-scale manufacturing. Moreover, 2D perovskites have attracted considerable attention owing to their higher stability. In this work, scalable and highly efficient fully printed large-area carbon electrode-based 2D perovskite modules are reported through the insertion of a thin naphthaleneimide derivative (CATNI)-based interfacial layer between tin (IV) oxide and the perovskite layer. The results show that this facilitates the formation of the interfacial contact, suppresses energy losses, and substantially improves the performance parameters of the PSCs, especially their V_OC value. A significantly enhanced V_OC of 1.13 V is achieved resulting in the device PCE value reaching over 18%, which is one of the highest reported for fully printed PSCs so far. It is found that with the deployment of this CATNI-based interfacial layer, a more efficient carrier extraction is achieved. This ultimately contributed to enhanced spectral response as well as improved V_OC for these carbon electrodes based on fully printed devices. Finally, the carbon-perovskite solar modules (carbon-PSMs) are fabricated on ITO glass substrates with dimensions of 5.0 × 5.0 cm. These prepared modules exhibited outstanding photovoltaic performance with the highest PCE value of over 14.6%.     

Design and Synthesis of Fluorinated Quantum Dots for Efficient and Stable 0D/3D Perovskite Solar Cells

Dimensionality engineering involving the low-dimensional and 3D perovskites has been demonstrated as an efficient promising strategy to modulate interfacial energy loss as well as instability in perovskite solar cells (PSCs). Herein, the use of fluorinated Cesium Lead Iodide (CsPbI₃) perovskite quantum dot (PQD) is first reported as interface modification layer for PSCs. The binding between the CsPbI₃ PQD surface and native oleic acid (OLA)/oleylamine (OAm) ligands is governed by a dynamic adsorption–desorption equilibrium. Perfluorooctanoic acid (PFA) with stronger binding affinity and more hydrophobic nature is explored to partially replace OLA to prepare the fluorinated ligand capped CsPbI₃ PQDs (F-CsPbI₃). Through optimization of the addition of PFA during hot-injection synthesis, the in situ treated F-CsPbI₃ PQDs display reduced surface defect states, higher photoluminescence quantum yields together with improved stability. Subsequently, both CsPbI₃ and F-CsPbI₃ PQDs are utilized as interface engineering layer in PSCs, delivering the best efficiency values of 21.99% and 23.42%, respectively, which is significantly enhanced compared to the control device (20.37%). More importantly, benefiting from its more hydrophobic properties, the F-CsPbI₃ PQD treated device exhibits excellent ambient storage stability (25 °C, relative humidity: 35–45%), retaining over 80% of its initial efficiency after 1500 h aging.     

A Spacer Cation Assisted Nucleation and Growth Strategy Enables Efficient and High-Luminance Quasi-2D Perovskite LEDs

Quasi-2D Ruddlesden-Popper perovskites receive tremendous attention for application in light-emitting diodes (LEDs). However, the role of organic ammonium spacers on perovskite film has not been fully-understood. Herein, a spacer cation assisted perovskite nucleation and growth strategy, where guanidinium (GA⁺) spacer is introduced into the perovskite precursor and at the interface between the hole transport layer (HTL) and the perovskite, to achieve dense and uniform perovskite films with enhanced optical and electrical performance is developed. A thin GABr interface pre-formed on HTL provides more nucleation sites for perovskite crystal; while the added GA⁺ in perovskite reduces the crystallization rate due to strong hydrogen bonding interacts with intermediates, which promotes the growth of enhanced-quality quasi-2D perovskite films. The ionized ammonium group ( NH₃⁺) of GA⁺ also favors formation of polydisperse domain distribution, and amine or imine ( NH₂ or NH) group interact with perovskite defects through coordination bonding. The spacer cation assisted nucleation and growth strategy is advantageous for producing efficient and high-luminance perovskite LEDs, with a peak external quantum efficiency of over 20% and a luminance up to 100 000 cd m⁻². This work can inform and underpin future development of high-performance perovskite LEDs with concurrent high efficiency and brightness.     

Pre-buried Interface Strategy for Stable Inverted Perovskite Solar Cells Based on Ordered Nucleation Crystallization

The buried interface has important effect on carrier extraction and nonradiative recombination of perovksite solar cells (PSCs). Herein, to inactivate the buried interfacial defects of perovskite and boost the crystallization quality of perovskite film, 3-amino-1-adamantanol (AAD) serves as a pre-buried interface modifier on nickel oxide (NiO_x) surface to regulate the nucleation and crystallization process of perovskite precursor. The amino and hydroxyl groups in AAD molecule can synchronously coordinate with nickel ion (Ni³⁺) in NiO_x and lead ion in perovskite, respectively. The dual action favors the ordered arrangement of AAD molecules between NiO_x and perovskite, which not only enhances hole extraction in hole transport layer, but also provides active sites for homogeneous nucleation. Furthermore, AAD modifier blocks the unfavorable reaction between Ni³⁺ and perovskite, and effectively passivates the buried interfacial defects. The optimal inverted PSCs achieve a champion power conversion efficiency of 22.21% with negligible hysteresis, favorable thermal, optical, and long-term stability. Thus, this strategy of modulating perovskite nucleation and crystallization by pre-buried modifier is feasible for achieving efficient and stable inverted perovskite solar cells.     

Efficient and Ambient‐Air‐Stable Solar Cell with Highly Oriented 2D@3D Perovskites

3D organic–inorganic lead halide perovskites have shown great potential in efficient photovoltaic devices. However, the low stability of the 3D perovskite layer and random arrangement of the perovskite crystals hinder its commercialization road. Herein, a highly oriented 2D@3D ((AVA)₂PbI₄@MAPbI₃) perovskite structure combining the advantages of both 2D and 3D perovskite is fabricated through an in situ route. The highest power conversion efficiency (PCE) of 18.0% is observed from a 2D@3D perovskite solar cell (PSC), and it also shows significantly enhanced device stability under both inert (90% of initial PCE for 32 d) and ambient conditions (72% of initial PCE for 20 d) without encapsulation. The high efficiency of 18.0% and nearly twofold improvement of device stability in ambient compared with pure 3D PSCs confirm that such 2D@3D perovskite structure is an effective strategy for high performance and increasing stability and thus will enable the timely commercialization of PSCs.     

Synergetic Excess PbI2 and Reduced Pb Leakage Management Strategy for 24.28% Efficient,Stable and Eco-Friendly Perovskite Solar Cells

Introducing excess PbI₂ has proven to be an effective in situ passivation strategy for enhancing efficiency of perovskite solar cells (PSCs). Nevertheless, the photoinstability and hysteresis are still tough issues owing to the photolysis nature of PbI₂. Moreover, the humidity-related degradation of perovskite films is also a difficult territory to cover in such an in situ passivation strategy. Herein, a synergistic strategy is reported via initiatively inducing vertical graded PbI₂ distribution (GPD) in the whole perovskite film and capping a cis-Ru(H₂dcbpy)(dnbpy)(NCS)₂ (Z907) internal encapsulation (IE) layer on the surface to ameliorate the above issues. The GPD design can enhance luminescence, prolong carrier lifetimes, ascertaining the improvement of efficiency and elimination of photoinstability in the PSCs. Besides, the introduced IE layer not only can promote the moisture and thermal resistance, but also inhibit Pb leakage and ion migration in the PSCs. Through the synergetic regulations, the resultant PSCs exhibit an impressive open circuit voltage (V_OC) of 1.253 V, fill factor of 81.25%, and power conversion efficiency (PCE) of 24.28%. Moreover, the PSCs maintain 91% of its initial PCE at relative humidity of 85% after 500 h aging and 94% under continuous heating at 85 °C after 750 h aging.     

Chemical Reduction of Iodine Impurities and Defects with Potassium Formate for Efficient and Stable Perovskite Solar Cells

The performance of perovskite solar cells (PSCs) is negatively affected by iodine (I₂) impurities generated from the oxidation of iodide ions in the perovskite precursor powder, solution, and perovskite films. In this study, the use of potassium formate (HCOOK) as a reductant to minimize the presence of detrimental I₂ impurities is presented. It is demonstrated that HCOOK can effectively reduce I₂ back to I⁻ in the precursor solution as well as in the devices under external conditions. Furthermore, the introduced formate anion (HCOO⁻) and alkali metal cation (K⁺) can reduce the defect density within the perovskite film by modulating perovskite growth and passivating electronic defects, significantly prolonging the carrier lifetime and reducing the J–V hysteresis. Consequently, the maximum efficiency of the HCOOK-doped planar n–i–p PSCs reaches 23.8%. After 1000 h of operation at maximum power point tracking under continuous 1 sun illumination, the corresponding encapsulated devices retain 94% of their initial efficiency.     

Over 24% Efficient Poly(vinylidene fluoride) (PVDF)-Coordinated Perovskite Solar Cells with a Photovoltage up to 1.22 V

Recently, organic–inorganic metal halide perovskite solar cells (PSCs) have achieved rapid improvement, however, the efficiencies are still behind the Shockley–Queisser theory mainly due to their high energy loss (E_LOSS) in open-circuit voltage (V_OC). Due to the polycrystalline nature of the solution-prepared perovskite films, defects at the grain boundaries as the non-radiative recombination centers greatly affect the V_OC and limit the device efficiency. Herein, poly(vinylidene fluoride) (PVDF) is introduced as polymer-templates in the perovskite film, where the fluorine atoms in the PVDF network can form strong hydrogen-bonds with organic cations and coordinate bonds with Pb²⁺. The strong interaction between PVDF and perovksite enables slow crystal growth and efficient defect passivation, which effectively reduce non-radiation recombination and minimize E_LOSS of V_OC. PVDF-based PSCs achieve a champion efficiency of 24.21% with a excellent voltage of 1.22 V, which is one of the highest V_OC values reported for FAMAPb(I/Br)₃-based PSCs. Furthermore, the strong hydrophobic fluorine atoms in PVDF endow the device with excellent humidity stability, the unencapsulated solar cell maintain the initial efficiency of >90% for 2500 h under air ambient of ≈50% humid and a consistently high V_OC of 1.20 V.     

Combined Bulk and Surface Passivation in Dimensionally Engineered 2D-3D Perovskite Films via Chlorine Diffusion

Dimensional engineering of perovskite films is a promising pathway to improve the efficiency and stability of perovskite solar cells (PSCs). In this context, surface or bulk passivation of defects in 3D perovskite film by careful introduction of 2D perovskite plays a key role. Here the authors demonstrate a 2D perovskite passivation scheme based on octylammonium chloride, and show that it provides both bulk and surface passivation of 1.6 eV bandgap 3D perovskite film for highly efficient (≈23.62%) PSCs with open-circuit voltages up to 1.24 V. Surface and depth-resolved microscopy and spectroscopy analysis reveal that the Cl⁻ anion diffuses into the perovskite bulk, passivating defects, while the octylammonium ligands provide effective, localized surface passivation. The authors find that the Cl⁻ diffusion into the perovskite lattice is independent of the 2D perovskite crystallization process and occurs rapidly during deposition of the 2D precursor solution. The annealing-induced evaporation of Cl from bulk perovskite is also inhibited in 2D–3D perovskite film as compared to pristine 3D perovskite, ensuring effective bulk passivation in the relevant film.