Chen Weijie

The interaction between carbonyl and uncoordinated lead atoms achieves a good passivation effect. The champion performance of the device based on the TPD-Br additive achieves 20.74%

The rapid development of perovskite solar cells (PSCs) perovskite is inseparable from the investigation of plentiful new additive materials. Herein, a conjugated organic material called TPD-Br containing two carbonyl groups and Br atoms is synthesized. TPD-Br with Lewis-base groups can provide excellent passivation for defects between perovskite layer and electron transport layer. Furthermore, Br atom can also interact with iodine ions via halogen bonds. TPD-Br passivates the perovskite defects because it can interact with undercoordinated Pb²⁺ ions by forming PbO bond, lower defect density and larger grain size occur in the perovskite can be obtained. Consequently, high-quality perovskite films with fewer defects can be fabricated. The PSCs with TPD-Br additive achieve a champion power conversion efficiency of 20.74%. These results illustrate that TPD-Br, as a superior passivate defect additive, can improve the performance and stability of PSCs.

An organic ammonium ion, ethylammonium (EA), is introduced to passivate defects caused by PbI₂ residue at the bottom of the perovskite film. EA also contributes to increasing crystallization quality and energy-level alignment at the interface. These changes are directly demonstrated by exposing the bottom interface. All photovoltaic parameters of perovskite solar cells are improved by introducing EA.

Abstract

The interface of perovskite solar cells (PSCs) plays a significant role in influencing their performance, yet there is still scarce research focusing on their difficult-to-expose bottom interfaces. Herein, ethylammonium bromide (EABr) is introduced into the bottom interface and its passivation effects are studied directly. First, EABr can improve substrate wettability, which is beneficial for the perovskite-film deposition. By lifting off the perovskite film spontaneously from the substrate, it is found that EABr can significantly reduce the amount of unreacted PbI₂ at the bottom interface. These PbI₂ crystals have been recently identified as a major defect source and degradation site for perovskite film. Meanwhile, EABr also lifts the valence band maximum at the bottom side of perovskite from -5.38 to -5.09 eV, facilitating better hole transfer. Such a improvement is also verified by the study of charge carrier dynamics. Through introducing EABr, all photovoltaic parameters of the inverted PSCs are improved, and their power conversion efficiency (PCE) increases from 20.41% to 21.06%. The study highlights the importance of direct characterization of the bottom interface for a better passivation effect.

The V_Br are easy to form in wide-bandgap perovskite films, and the introduction of I-rich alkali metal small-molecule compounds is demonstrated to heal the V_Br defects and increase the V _OC of perovskite indoor photovoltaic cells. In this work, a stable perovskite indoor photovoltaic module with an independent certified efficiency of 36.36% at 1000 lux TL84 illumination is also reported.

Abstract

Indoor photovoltaics (IPVs) are expected to power the Internet of Things ecosystem, which is attracting ever-increasing attention as part of the rapidly developing distributed communications and electronics technology. The power conversion efficiency of IPVs strongly depends on the match between typical indoor light spectra and the band gap of the light absorbing layer. Therefore, band-gap tunable materials, such as metal-halide perovskites, are specifically promising candidates for approaching the indoor illumination efficiency limit of ∼56%. However, perovskite materials with ideal band gap for indoor application generally contain high bromine (Br) contents, causing inferior open-circuit voltage (V _OC). By fabricating a series of wide-bandgap perovskites (Cs_0.17FA_0.83PbI_{3− x} Br _x , 0.6 ≤ x ≤ 1.6) with varying Br contents and related band gaps, it is found that, the high Br vacancy (V_Br) defect density is a significant reason that leading to large V _OC deficits apart from the well-accepted halide segregation. The introduction of I-rich alkali metal small-molecule compounds is demonstrated to suppress the V_Br and increase the V _OC of perovskite IPVs up to 1.05 V under 1000 lux light-emitting diode illumination, one of the highest V _OC values reported so far. More importantly, the modules are sent for independent certification and have gained a record efficiency of 36.36%.

Organic planar heterojunctions are fabricated by matching the thickness of a non-fullerene acceptor to its exciton diffusion length. Additional hole transfer mediated by the exciton diffusion generates a photocurrent over 10 mA cm⁻² in the planar heterojunction. Well-defined planar interfaces reduce the dark leakage current, resulting in 83 times higher photodetector detectivity than the corresponding bulk heterojunction device.

Abstract

While non-fullerene acceptors (NFAs) have recently been demonstrated to exhibit long-range exciton diffusion, most organic photovoltaic and photodetector studies still focus on blended polymer: NFA systems. Herein, a 40 nm exciton diffusion length for IT4F excitons is determined, and it is demonstrated that sharp interface, planar heterojunction (PHJ) IT4F/PM6 devices with the IT4F layer thickness matched to this diffusion length yield optimized photovoltaic and photodetector performance. The PHJ devices yield an enhanced device open-circuit voltage relative to bulk heterojunction (BHJ) devices, associated with suppressed bimolecular recombination losses. The PHJ architecture also results in a ≈100-fold increase in electroluminescence (EL) quantum efficiency relative to the BHJ device, correlated with a shift from charge transfer state EL for the BHJ to IT4F exciton dominated EL for the PHJ, attributed to significant hole injection from PM6 into IT4F. Of particular note, the PHJ architecture is shown to suppress dark leakage current, resulting in 83 times higher photodetector detectivity at −2 V bias than the equivalent BHJ device.

A unique conformation lock is formed in a polymer donor using an unconventional carbamate side chain. It gives wide band-gap polymer donors for application in organic solar cells. Devices incorporating these donors yield power conversion efficiencies up to 18.76 %.

Abstract

Side-chain engineering with heteroatoms is not only effective in tuning frontier molecular orbitals, but also possible for forming secondary bonds which can be utilized to planarize the molecular backbone, hence, improving the photon absorption as well as charge-transport abilities of polymer solar-cell (PSC) materials. Herein, two types of unconventional side chains, namely carboxylate and carbamate, containing various heteroatoms are introduced to the thiophene bridges in high performance benzodithiophene (BDT) based donor polymers to from the novel polymers PTzTz-C and PTzTz-N, respectively. In these polymers, non-covalent O⋅⋅⋅S and N⋅⋅⋅H interactions induce a high tendency to aggregation. In a ternary-blend PSC with PTzTz-N added to the high-performance D18 : BTP-eC9 blend, complimentary absorption and improved thin-film morphology were observed with a top power conversion efficiency of 18.76 %, which is an improvement of almost 5 % over the D18 : BTP-eC9 binary blends.

The halide diffusion from perovskite can chemically dope the electron transport layer and bring forth the nonstoichiometric surface, leading to initial enhancement but long-term loss of the photovoltaic efficiency of p-i-n cells. A predoping strategy is developed to reach the diffusion equilibrium state for the fresh-fabricated device and delivers a power conversion efficiency of 23.13% with stable power output.

Abstract

Understanding the degradation mechanism of perovskite solar cells (PSCs) is of particular importance to solve their instability issue, which is one of the major hindrances toward commercialization. Here, it is shown that a halide diffusion equilibrium exists at the heterointerface of perovskite devices, which strongly impacts the evolution of device performance. The combined experimental and theoretical studies reveal that halide components diffuse from perovskite to fullerene layers in a p-i-n PSC device and equilibrate with an iodine density of 10¹⁸–10¹⁹ cm⁻³ within 80 h under dark aging condition. It is found that there is a strong correction between the device efficiency and halide diffusion equilibrium of PSCs, as the diffused halides can chemically dope the transport layer and result in the nonstoichiometric perovskite surface, leading to both initial enhancement and long-term loss of the photovoltaic efficiency of solar cells. In response to this issue, a predoping strategy is developed to attain the halide diffusion equilibrium once the device is fabricated, thereby avoiding the further halide migration and initial efficiency variations. As a result, the as-prepared PSC achieved an efficiency of 23.13% as well as stable power output under continuous one sun illumination.

The 4,4′-cyclohexylidenebis [N,N-bis(4-methylphenyl) benzene amine] is introduced to form a p/p⁺ homojunction on the top surface of the perovskite layer and the 2-thiophenethylammonium iodide forms an interface electric field at the SnO₂/perovskite interface, which reduces nonradiative recombination loss and increases the power conversion efficiency to 23.44%.

Abstract

The severe nonradiative recombination losses limit the further improvement of open-circuit voltage (V _oc) and power conversion efficiency (PCE) of perovskite solar cells (PVSCs). In this work, the 4,4′-cyclohexylidenebis [N,N-bis(4-methylphenyl) benzene amine] is dissolved into the antisolvent to prepare perovskite films, which reduces defects, improves the crystallinity, and induces a p/p⁺ homojunction on the top surface of perovskite film. Besides, the 2-thiophenemethylammonium iodide and 2-thiophenethylammonium iodide form interface electric field and passivate defects on the bottom surface of perovskite film. The p/p⁺ homojunction and interface electric field enhance the charges’ separation and transportation efficiencies in the bulk perovskite film and at the perovskite/charge transport layer interfaces, which effectively reduces nonradiative recombination losses and V _oc loss of PVSCs. Consequently, low V _oc loss of 0.348 V is realized, resulting in the increase in V _oc from 1.082 to 1.172 V and PCE from19.15% to 23.44%. The optimized PVSCs without encapsulation maintain 88.23% of the original PCE after exposing in the air for 1500 h. This work provides a strategy to reduce the nonradiative recombination losses and V _oc loss by forming p/p⁺ homojunction and interface electric field on the surfaces of perovskite film, which advances the development of high-performance PVSCs.

Constructive ionic-bonding heterointerfaces through interfacial embedding of nano-MXenes with rationally terminated halogen in formamidinium-based perovskite films, have been used to efficiently stabilize the soft lattice of hybrid perovskite and modulate the carrier dynamics of its film, which results in an n-i-p perovskite solar cell with a champion efficiency up to 24.17% and both light and thermal stability over 1000 h.

Abstract

Formamidinium (FA)-based perovskite promises high power conversion efficiency in photovoltaics while it faces awkward spontaneous yellow phase transition even at ambient conditions. This has spurred intensive efforts which leave a formidable challenge on robust anchoring of the soft perovskite lattice. Present work pioneers the rational design of interfacial ionic-bonding between halogen-terminated nano-MXenes and perovskite for effective retarding of the lattice instability in FA-based perovskites. The robust heterointerface between perovskite and nano-MXenes results also in effectively modulating the deep-energy-level defects, lowering the interfacial charge transfer barrier, and tuning the work function of perovskite films. Benefiting from these merits, unencapsulated FA-based perovskite solar cells after the ionic stabilization (champion efficiency up to 24.17%), maintain over 90% of their initial efficiency after operation at maximum power point under continuous illumination for 1000 h, and retain more than 85% of their initial efficiency even after annealing for 1000 h at 85 °C in inert atmosphere.

Publication date: 16 November 2022

Source: Joule, Volume 6, Issue 11

Author(s): Chunqing Ma, Min-Chul Kang, Sun-Ho Lee, Seok Joon Kwon, Hyun-Woo Cha, Cheol-Woong Yang, Nam-Gyu Park

The interfacial dynamics and electrochemical interactions of hybrid perovskites prepared by an anion-exchange process in the photoelectrochemical system is investigated through computational simulation, experimental photophysical, and (photo)electrochemical analysis. The synergically interfacial dynamics and electrochemical analysis help to discover the intrinsic and interfacial properties of semiconductor materials.

Abstract

An environmentally friendly mixed-halide perovskite MA₃Bi₂Cl_{9− x} I _x with a bandgap funnel structure has been developed. However, the dynamic interfacial interactions of bandgap funneling in MA₃Bi₂Cl_{9− x} I _x perovskites in the photoelectrochemical (PEC) system remain ambiguous. In light of this, single- and mixed-halide lead-free bismuth-based hybrid perovskites—MA₃Bi₂Cl_{9− y} I _y and MA₃Bi₂I₉ (named MBCl-I and MBI)—in the presence and absence of the bandgap funnel structure, respectively, are prepared. Using temperature-dependent transient photoluminescence and electrochemical voltammetric techniques, the photophysical and (photo)electrochemical phenomena of solid–solid and solid–liquid interfaces for MBCl-I and MBI halide perovskites are therefore confirmed. Concerning the mixed-halide hybrid perovskites MBCl-I with a bandgap funnel structure, stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions results in more efficient exciton transport. Besides, MBCl-I's effective diffusion coefficient and electron-transfer rate demonstrate efficient heterogeneous charge transfer at the solid–liquid interface, generating improved photoelectrochemical hydrogen production. Consequently, this combination of photophysical and electrochemical techniques opens up an avenue to explore the intrinsic and interfacial properties of semiconductor materials for elucidating the correlation between material characterization and device performance.

A facile strategy to obtain phase-pure α-FAPbI₃ perovskite films by introducing N-(2-aminoethyl) acetamide into perovskite precursors is reported. The additive reduces the potential barrier in the phase transition process, passivates the defects of the film, and leads to a high-quality and phase-pure α-FAPbI₃ perovskite. The resultant self-powered photodetector based on the as-fabricated FAPbI₃ film exhibits superior performance.

Abstract

Formamidinium–lead triiodide (FAPbI₃) perovskite is considered as one of the most promising perovskite materials for high-performance photodetectors because of its narrow bandgap and superior thermal stability. Nevertheless, to realize efficient carrier transport and highly performing photodetectors, it imposes the requirement of fabricating α-FAPbI₃ with pure phase, preferred crystal orientation, large grain size, and passivated interface, which still remains challenging. Here, a facile strategy based on additive engineering to obtain pure-phase FAPbI₃ perovskite films by introducing N-(2-aminoethyl) acetamide into perovskite precursors is reported. The formation of chemical bond and hydrogen bond between N-(2-aminoethyl) acetamide and perovskite reduces the potential barrier in the phase-transition process from an intermediate yellow phase to a final black phase, passivates the defects of the film, and leads to a high-quality and phase-pure α-FAPbI₃ perovskite. A self-powered photodetector based on the as-fabricated FAPbI₃ film exhibits a maximum responsivity of 0.48 A W⁻¹ at 700 nm with a peak external quantum efficiency of 95% at 440 nm. Moreover, the optimized device remains 83% of the initial performance after 576 h storage at ambient condition. This work provides a simple and feasible scheme for the preparation of high-quality phase-pure α-FAPbI₃ perovskite and associated devices.

Bulky cations are widely used in the halide perovskite field to reduce nonradiative recombination at interfaces. In this work, a critical perspective on the use of these organohalide salts is provided. It is demonstrated that some of these capping layers are unstable and prolonged annealing is proposed as a critical way to drive the selection between different bulky cations for improved stability.

Abstract

The impact of the bulky-cation-modified interfaces on halide perovskite solar cell stability is underexplored. In this work, the thermal instability of the bulky-cation interface layers used in the state-of-the-art solar cells is demonstrated. X-ray photoelectron spectroscopy and synchrotron-based grazing-incidence X-ray scattering measurements reveal significant changes in the chemical composition and structure at the surface of these films that occur under thermal stress. The changes impact charge-carrier dynamics and device operation, as shown in transient photoluminescence, excitation correlation spectroscopy, and solar cells. The type of cation used for surface treatment affects the extent of these changes, where long carbon chains provide more stable interfaces. These results highlight that prolonged annealing of the treated interfaces is critical to enable reliable reporting of performances and to drive the selection of different bulky cations.

Highly efficient and stable perovskite solar cells (PSCs) via the two-step sequential method are fabricated using organic–inorganic (OI) complexes as multifunctional interlayers. OIcomplexes not only passivate the metal ions related trap states but also introduce dipole moment which can enhance the built-in electric field, thus facilitating charge carrier extraction. The resulting devices perform a champion efficiency of 23.55% with excellent long-term air stability.

Abstract

Perovskite solar cells (PSCs) via two-step sequential method have received great attention in recent years due to their high reproducibility and low processing costs. However, the relatively high trap-state density and poor charge carrier extraction efficiency pose challenges. Herein, highly efficient and stable PSCs via a two-step sequential method are fabricated using organic—inorganic (OI) complexes as multifunctional interlayers. In addition to reduce the under-coordinated Pb²⁺ ions related trap states by forming interactions with the functional groups, the complexes interlayer tends to form dipole moment which can enhance the built-in electric field, thus facilitating charge carrier extraction. Consequently, with rational molecular design, the resulting devices with a vertical dipole moment that parallels with the built-in electric field yield a champion efficiency of 23.55% with negligible hysteresis. More importantly, the hydrophobicity of the (OI) complexes contributes to an excellent ambient stability of the resulting device with 91% of initial efficiency maintained after 3000 h storage.

Glow discharge optical emission spectroscopy technique has emerged recently as a powerful tool to get major information in the field of perovskite solar cells research. In this review paper, the wide palette of information that has been accessed by implementing this elemental profiling technique on films and devices is summarized.

Abstract

The emerging broad range of applications of the glow discharge optical emission spectroscopy (GD-OES) technique in the field of perovskite solar cells (PSCs) research is reviewed. It can provide a large palette of information by easily and quickly tracking the depth distribution of light to heavy elements. After a discussion of the advantages and the limitations of the technique and a comparison with other analytical techniques, how GD-OES is employed to give structural information on perovskite solar cells is shown. GD-OES has allowed the full perovskite film formation process investigation, from the initial precursor layers containing soaking and complexed solvent to the final crystallized 3D perovskite layers. The A-site elemental cations distribution is followed-up during the film formation. In addition, this technique gives a deep insight into the action mechanism of additives and their effects on the film formation. It provides fruitful information on optimized light absorbing layers and on the selective contact layers which ensure the charge transport in PSCs. It allows to directly visualize halide ions migration and their blocking by ad-hoc chemical engineering and to study the films and PSCs ageing. GD-OES opens new perspectives to explain the final performances of the devices.

Herein, a novel multifunctional passivator trifluoroacetamidine (TFA) is introduced to decrease the defect density and improve the photovoltaic performance of CsPbI₃ perovskite solar cells. Under the synergistic passivation of the C=O bonds and the amino groups in TFA, the optimized device performs champion power conversion efficiency of 19.82% as well as superior environmental stability with no encapsulation.

All-inorganic CsPbI₃ perovskite solar cells (PSCs) possess great potential of development with the suitable bandgap and outstanding chemical stability in recent years. However, due to the low tolerance factor of the crystal structure and the high defect density of states within the absorbing layer, CsPbI₃ perovskite film displays poor phase stability at room temperature and severe exciton nonradiative loss under illumination conditions. Therefore, a novel multifunctional passivator trifluoroacetamidine (TFA) is introduced to decrease the defect density and improve the photovoltaic performance of CsPbI₃ PSCs. The amino groups in TFA not only form hydrogen bonds with I⁻ to suppress the oxidation of I⁻ in the perovskite, but also interact with noncoordinated Pb²⁺ in conjunction with C=O bonds to passivate Pb-related defects. Furthermore, the hydrophobic characteristic of –CF₃ in TFA could efficiently protect the perovskite layer from moisture damage in the external environment. Consequently, the 0.3 mol% TFA additive based-device possesses an optimal power conversion efficiency of 19.82% and the excellent fill factor of 0.81. In addition, the optimized PSCs retain 80% of their original efficiency under 1000 h of illumination in ambient conditions without encapsulation.

A sulfur-containing Lewis base 2-(methylthio)ethylamine hydrochloride (MTEACl) as a perovskite precursor additive for p-MPSCs is adopted. The sulfur donor in MTEACl can interact with uncoordinated Pb²⁺, and thus effectively passivate defects in MAPbI₃ perovskite. Correspondingly, the trap density of the perovskite is reduced, contributing to the improvement of the power conversion efficiency from 15.18% to 17.17% and open circuit voltage to 995 mV.

In the rapid development of perovskite solar cells (PSCs), additive engineering has played a significant role for perovskite crystallization and passivation. The high density of defects at perovskite grain boundaries in the mesoporous scaffold leads to severe nonradiative recombination, which results in severe voltage loss. Herein, a sulfur-containing Lewis base 2-(methylthio)ethylamine hydrochloride (MTEACl) is applied in the perovskite precursor solution for printable mesoscopic PSCs with triple-mesoscopic layer structure. Due to the strong electron donating ability of sulfur, the MTEACl can strongly interact with Pb²⁺, which can effectively passivate the defects of the perovskite. Correspondingly, the trap density of the perovskite is reduced, contributing to the improvement of power conversion efficiency from 15.18% to 17.17% and open circuit voltage to 995 mV.

The ultraviolet (UV) part in sunlight causes most damage to organic photovoltaics (OPV). This work shows that once UV is removed by a filter the nonfullerene OPV maintains a stable efficiency. This is in sharp contrast to the continuous decay under UV. Years of outdoor lifetime are projected with the UV filter.

The ultraviolet (UV) part in the sunlight is known to cause most damage to organic photovoltaics (OPV). UV filters therefore can improve stability. The lifetime of the UV-filtered OPV is determined by visible light. Herein, visible sunlight is divided into several bands and modeled by light-emitting diodes to study the stability of ternary OPV. Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)] (PM6) is used as the donor. 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2",3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6) is used as the acceptor. Another polymer is added as the second donor to improve the stability. As expected, the deep and light blue bands dominate the decay under visible light. After about 1200 h of blue irradiation, the devices enter a relatively stable state up to 3000 h of tracking, in sharp contrast to the continuous decay under UV. No chemical reaction is observed under blue light. Years of outdoor lifetime for nonfullerene OPV are projected with the UV filter.

All-polymer solar cells (PSCs) based on a new polymer acceptor PYSe-2FT exhibit highly efficient and mechanically robust properties with simple device technology of free treatment. Power conversion efficiencies of 13.56% also are the best values reported in flexible all-PSCs so far. Good flexibility, favorable universality, and stability hold great potential for future applications where high performances and mechanical stability are anticipated.

The many merits of organic solar cells such as light weight, flexibility, and printability rely heavily on flexible devices. In this regard, all-polymer solar cells (PSCs) are the primary choices due to the superior flexibility and mechanical properties of polymers over small molecule and fullerene materials. However, the polymer batch discrepancy and the multifarious post-treatment steps are serious obstacles to practical applications. Herein, highly efficient and mechanically robust all-PSCs based on a new polymer acceptor PYSe-2FT and polymer donor D18 are developed. Without any post-treatment, the flexible all-PSC exhibits high power conversion efficiency (PCE) of 13.56%, which stands among the best values in flexible all-PSCs so far. Bending tests reveal that the flexible device maintains 86% efficiency of the original PCE after 1000 bending cycles with a narrow curvature radius of 3 mm. More importantly, the all-PSC efficiencies are insensitive to the molecular weight of the newly developed acceptor polymer, which possesses favorable universality and stability when working together with various donors. The superior mechanical properties and the ease of process make this all-PSC a promising candidate for applications in flexible and portable devices.

2D perovskites in situ generated from a series of bulky primary alkylammoniums are found to be volatile and are used to prepare phase- and compositionally-pure α-formamidinium lead triiodide solar cells.

Abstract

Perovskite solar cells with increasingly pure composition of α-formamidinium lead triiodide (α-FAPbI₃) perovskite are utilized to set more and more record-breaking efficiencies. However, pure α-FAPbI₃ perovskite is unstable and difficult to prepare. Here, a series of bulky alkylammoniums known as the spacer cations (RP cations) of 2D Ruddlesden–Popper perovskites (2D perovskites) are used to prepare α-FAPbI₃ perovskite films. The deprotonation process of RP cations during annealing removes the in situ generated 2D perovskites from the film, which determines the phase and compositional purity, crystallinity, and stability of α-FAPbI₃ perovskite films and depends on the design of RP cations. Only a small number of residual RP cations (0.3–2.3%) are found anchoring at grain boundaries. As a result, α-FAPbI₃ perovskite solar cells prepared from RP cations, especially 2-thiophenemethylammonium, show higher efficiency and stability than control devices prepared from the most commonly used methylammonium. It is believed that in situ generated 2D perovskites are ideal additives for α-FAPbI₃ perovskite, because a large addition (20%) of 2D perovskites ensures the preparation of high-quality phase-pure α-FAPbI₃ perovskite films, while a small number of residual RP cations anchored at grain boundaries guarantee the performance and stability of α-FAPbI₃ perovskite solar cells.