A 0D/3D Heterostructured All-Inorganic Halide Perovskite Solar Cell with High Performance and Enhanced Phase Stability

Oxygen-Mediated (0D) Cs4PbX6 Formation during Open-Air Thermal Processing Improves Inorganic Perovskite Solar Cell Performance

The desire to commercialize perovskite solar cells continues to mount, motivating the development of scalable production. Evaluations of the impact of open-air processing have revealed a variety of physical changes in the fabricated devices─with few changes having the capacity to be functionalized. Here, we highlight the beneficial role of ambient oxygen during the open-air thermal processing of metastable γ-CsPbI3-based perovskite thin films and devices. Physiochemical-sensitive probes elucidate oxygen intercalation and the formation of Pb-O bonds in the CsPbI3 crystal, entering via iodine vacancies at the surface, creating superoxide (O2-) through electron transfer reactions with molecular oxygen, which drives the formation of a zero-dimensional Cs4PbI6 capping layer during annealing (>330 °C). The chemical conversion permanently alters the film structure, helping to shield the subsurface perovskite from moisture and introduces lattice anchoring sites, stabilizing otherwise unstable γ-CsPbI3 films. This functional modification is demonstrated in γ-CsPbI2Br perovskite solar cells, boosting the operational stability and photoconversion efficiency of champion devices from 12.7 to 15.4% when annealed in dry air. Such findings prompt a reconsideration of glovebox-based perovskite solar cell research and establish a scenario where device fabrication can in fact greatly benefit from ambient oxygen.

A Self-Assembled 3D/0D Quasi-Core-Shell Structure as Internal Encapsulation Layer for Stable and Efficient FAPbI3 Perovskite Solar Cells and Modules

FAPbI3 perovskites have garnered considerable interest owing to their outstanding thermal stability, along with near-theoretical bandgap and efficiency. However, their inherent phase instability presents a substantial challenge to the long-term stability of devices. Herein, this issue through a dual-strategy of self-assembly 3D/0D quasi-core-shell structure is tackled as an internal encapsulation layer, and in situ introduction of excess PbI2 for surface and grain boundary defects passivating, therefore preventing moisture intrusion into FAPbI3 perovskite films. By utilizing this method alone, not only enhances the stability of the FAPbI3 film but also effectively passivates defects and minimizes non-radiative recombination, ultimately yielding a champion device efficiency of 23.23%. Furthermore, the devices own better moisture resistance, exhibiting a T80 lifetime exceeding 3500 h at 40% relative humidity (RH). Meanwhile, a 19.51% PCE of mini-module (5 × 5 cm2) is demonstrated. This research offers valuable insights and directions for the advancement of stable and highly efficient FAPbI3 perovskite solar cells.

Facile Dimension Transformation Strategy for Fabrication of Efficient and Stable CsPbI3 Perovskite Solar Cells

All-inorganic cesium lead triiodide (CsPbI₃) perovskite has received increasing attention due to its intrinsic thermal stability and suitable band gap for photovoltaic applications. However, it is difficult to deposit high-quality pure-phase CsPbI₃ films using CsI and PbI₂ as precursors due to the rapid nucleation and crystal growth by the solution coating method. Here, a simple cation-exchange approach is employed to fabricate all-inorganic 3D CsPbI₃ perovskite, where 1D ethylammonium lead (EAPbI₃) perovskite is first solution-deposited and then transformed to 3D CsPbI₃ via ion exchange between EA⁺ and Cs⁺ during thermal annealing. The large space between the PbI₃^- skeletons in 1D EAPbI₃ favors the cation interdiffusion and exchange for the formation of pure-phase 3D CsPbI₃ with full compactness and high crystallinity and orientation. The resulting CsPbI₃ film exhibits a low trap density of state and high charge mobility, and the perovskite solar cell shows a power-conversion efficiency of 18.2% with enhanced stability. This strategy provides an alternative and promising fabrication route for the fabrication of high-quality all-inorganic perovskite devices.

Functional organic cation induced 3D-to-0D phase transformation and surface reconstruction of CsPbI3 inorganic perovskite

Efficiency and stability are the main research focuses for perovskite solar cells. Inorganic perovskites like CsPbI₃ possess higher chemical stability than those with organic A-site cations, while they also exhibit higher defect density. Nonetheless, it is highly challenging to induce orderly secondary arrangement or reconstruction of inorganic perovskites with reduced defects because of their unique chemical properties. In this work, in-situ three-dimension-to-zero-dimension (3D-to-0D) phase transformation and surface reconstruction on CsPbI₃ film is achieved as induced by a functional organic cation, benzyldodecyldimethylammonium (BDA), a process of which that is similar to phase-transfer catalysis. With the help of BDABr salt treatment, 0D Cs₄PbI₆ perovskites are secondarily formed along CsPbI₃ grain boundaries with Cs-related cationic defects passivated, yielding structures of higher stability. The BDA-CsPbI₃ films exhibit reduced non-radiative recombination and promoted charge transfer, leading to inorganic perovskite solar cells with a high power conversion efficiency of 20.63% and good operational stability.

Preparation of High-Efficiency (>14%) HTL-Free Carbon-Based All-Inorganic Perovskite Solar Cells by Passivation with PABr Derivatives

Due to the advantages of low cost and good thermal stability, all-inorganic CsPbI2Br carbon-based perovskite solar cells (C-PSCs) without a hole transport layer have been rapidly developed in recent years. While the carbon electrode is in direct contact with the CsPbI2Br film, higher requirements are placed on the defects and energy level arrangement of the CsPbI2Br layer, which leads to the relatively low photoelectric conversion efficiency (PCE) of C-PSCs. Herein, propylamine hydrobromide (PABr) and its derivative 3-bromopropylamine hydrobromide (3Br-PABr) were used to passivate the surface defects of CsPbI2Br C-PSCs for the first time. The results show that passivation molecules are modulated by the substituent effect, leading to a stronger interaction between amino groups and uncoordinated Pb2+ ions, which facilitates a better passivation effect of 3Br-PABr. In addition, 3Br-PABr promotes the gradient arrangement of energy levels while passivating surface defects, which accelerates the rapid extraction of holes. After the passivation by PABr and 3Br-PABr, the PCE of HTL-free CsPbI2Br C-PSCs increased from 12.15% for the control device to 13.15 and 14.04%, respectively, which are among the highest reported values of CsPbI2Br C-PSCs.

0D/3D direct Z-scheme heterojunctions hybridizing by MoS2 quantum dots and honeycomb conjugated triazine polymers (CTPs) for enhanced photocatalytic performance

Herein, a novel direct Z-scheme photocatalyst was accomplished by hybridization of 0D MoS₂ quantum dots (MSQDs) and 3D honeycomb-like conjugated triazine polymers (CTP) (namely, CTP-MSQD). The unique 0D/3D hierarchical structure significantly enhanced the exposure of active sites and light harvesting property, while the formed p-n junction enabled the direct strong interface coupling without the necessity of any mediators. The optimized CTP-MSQD3 exhibited continuously increased visible-light-driven photocatalytic activity and strong durability both in Cr(VI) reduction and H₂ evolution, featured a rate of 0.069 min^-1 and 1070 µmol/(hr∙g), respectively, which were 8 times than those of pure 3D-CTP (0.009 min^-1 and 129 µmol/(hr∙g)). We believe that this work provides a promising photocatalyst system that combines a 0D/3D hierarchical structure and a Z-scheme charge flow for efficient and stable photocatalytic conversion.

Manipulating the Formation of 2D/3D Heterostructure in Stable High-Performance Printable CsPbI3 Perovskite Solar Cells

Manipulating the formation process of the 2D/3D perovskite heterostructure, including its nucleation/growth dynamics and phase transition pathway, plays a critical role in controlling the charge transport between 2D and 3D crystals, and consequently, the scalable fabrication of efficient and stable perovskite solar cells. Herein, the structural evolution and phase transition pathways of the ligand-dependent 2D perovskite atop the 3D surface are revealed using time-resolved X-ray scattering. The results show that the ligand size and shape have a critical influence on the final 2D structure. In particular, ligands with smaller sizes and more reactive sites tend to form the n = 1 phase. Increasing the ligand size and decreasing the reactive sites promote the transformation from 3D to n = 3 and n < 3 phases. These findings are useful for the rational design of the phase distribution in 2D perovskites to balance the charge transport and stability of the perovskite films. Finally, solar cells based on ambient-printed CsPbI₃ with n-butylammonium iodide treatment achieve an improved efficiency of 20.33%, which is the highest reported value for printed inorganic perovskite solar cells.

Dimethyl sulfoxide: a promising solvent for inorganic CsPbI3 perovskite

Inorganic CsPbI₃ perovskite is an important photovoltaic material due to its suitable band gap and high chemical stability. However, it is a challenge to grow high-quality CsPbI₃ perovskite because the stability of perovskite phase is low and is sensitive to solvent. So far, most of CsPbI₃ perovskites in high-performance perovskite solar cells (PSCs) were prepared from N,N-dimethylformamide, a highly toxic solvent, and no successful case has been reported for dimethyl sulfoxide (DMSO), which is environmentally-friendly with considerably higher complexation capability. Herein, we reveal that forming DMSO-based adduct is the main cause for limiting the quality of CsPbI₃ perovskite from DMSO-based solutions, which would inhibit the formation of DMAPbI₃ (DMA = dimethylammonium, (CH₃)₂NH₂⁺) intermediate. Then, by introducing a vacuum treatment, DMSO molecules could be efficiently extracted from the adduct to induce the formation of DMAPbI₃ intermediate. After annealing, the intermediate is transitioned to the CsPbI₃ perovskite with enhanced crystallinity, high orientation, low defect density, and high uniformity. By using the CsPbI₃ perovskite as a light absorber, the PSCs based on carbon electrode (C-PSCs) achieve an efficiency of 16.7%, a new record for inorganic C-PSCs.

Intermediate-Phase-Modified Crystallization for Stable and Efficient CsPbI3 Perovskite Solar Cells

All-inorganic CsPbI₃ perovskite solar cells (PSCs) are becoming desirable for their excellent photovoltaic ability and adjustable crystal structure distortion. However, the unsatisfactory crystallization of the perovskite phase is unavoidable and leads to challenges on the road to the development of high-quality CsPbI₃ perovskite films. Here, we reported the intermediate-phase-modified crystallization (IPMC) method, which introduces pyrrolidine hydroiodide (PI) before the formation of the perovskite phase. The hydrogen bonding, which originates from the interaction between the -NH in PI and the dimethylammonium iodide (DMAI) from the precursor solution, improved the crystallization conditions and further prompted the transition from the DMAPbI₃ phase to CsPbI₃ perovskite phase. The application of the IPMC method not only decreased the trap density but also changed the energy alignment for better separation of electron-hole pairs. As a result, the devices based on the PI-CsPbI₃ perovskite films reached an efficiency of 18.72% and maintained 85% of their initial PCE after 1000 h of being stored in an ambient environment (∼25% RH, 25 °C). This work stimulates inspiration on how to conveniently fabricate high-quality perovskite films in industry.

Temperature-Insensitive Efficient Inorganic Perovskite Photovoltaics by Bulk Heterojunctions

Inorganic perovskite solar cells (IPSCs) emerge as an ideal candidate for applications beyond terrestrial implementation due to their robustness. However, underlying mechanisms regarding their photovoltaic process at different temperatures remain unclear. Based on a stable absorber of CsPbI_2.85 (BrCl)_0.15 , considerable variation of corresponding device performance is revealed over temperature and further demonstrates a simple approach to an effective reduction of such variation. Interestingly, this absorber is found to be excitonic with poor carrier transport even at an ambient temperature of 285 K and below. With a novel device configuration of a PTB7-th/perovskite bulk heterojunction, exciton dissociation and carrier extraction is facilitated. The resultant solar cell attains a best power conversion efficiency (PCE) of 17.2% with the fill factor of ≈84%, which represents the highest-efficiency γ-phase IPSCs reported to date. Importantly, this device is less sensitive to operation temperature, wherein the PCE variation over the temperature range from 210 to 360 K is 60% suppressed compared with the reference. The approach is effectively extended to other IPSCs with different photoactive phases, which may shed light on realizing highly efficient IPSCs for specific scenarios such as polar regions, near-space, and exoplanet exploration.

Fabrication Strategies and Optoelectronic Applications of Perovskite Heterostructures

Metal halide perovskites (MHPs) are emerging low‐cost and multifunctional semiconductor materials. They have been widely used in optoelectronic devices such as perovskite solar cells, light‐emitting diodes, photodetectors, memristors, and lasers. Developing new MHPs, defects passivation, optimizing device structures, and packaging techniques are all effective methods to improve photoelectric performance and stability of perovskite devices. Particularly, the fabrication of perovskite/perovskite heterostructures (PPHSs) is a novel and arresting method to obtain stable and high‐performing optoelectronic perovskite devices since it can passivate defects, regulate energy gaps, and provide new carrier transmission modes of MHPs for multiple semiconductor applications. In this paper, representative fabrication strategies of PPHSs including films and single‐crystal heterostructures are reviewed, and their applications in optoelectronic devices are summarized. Furthermore, the challenges and prospects of PPHSs are discussed based on the current status.

A double perovskite participation for promoting stability and performance of Carbon-Based CsPbI2Br perovskite solar cells

All-inorganic perovskite materials (Typically: CsPbI₂Br) have attracted enormous attention due to their illustrious thermal stability and appropriate bandgap, and their use in perovskite solar cells (PSCs) has been extensively investigated. However, the inevitable defects of the perovskite layer, energy level mismatch between perovskite and carbon electrodes, and the phase instability of CsPbI₂Br limit the power conversion efficiency (PCE) and stability of carbon-based CsPbI₂Br PSCs. Herein, we demonstrate a simple and effective strategy for regulating energy level, inhibiting carrier recombination, and delaying the degradation of perovskite by modifying the surface of CsPbI₂Br with a new type of 2D perovskite Cs₂PtI₆. The carbon-based CsPbI₂Br PSCs achieve a higher PCE (13.69 %) than the control device (11.10 %). The excellent matching of the energy level and suppression of charge carrier recombination should be responsible for the improvement in efficiency. Furthermore, the excellent hydrophobic performance of Cs₂PtI₆ enhances the moisture resistance of the device. This study provides a potential strategy for improving the performance and stability of all-inorganic CsPbI₂Br PSCs.

Hetero-perovskite engineering for stable and efficient perovskite solar cells

This review summarizes and discusses the HPSC engineering and optimization mechanism, and provides systematic knowledge and prospects of their development in the photovoltaic field.

0D Perovskites: Unique Properties, Synthesis, and Their Applications

0D perovskites have gained much attention in recent years due to their fascinating properties derived from their peculiar structure with isolated metal halide octahedra or metal halide clusters. However, the systematic discussion on the crystal and electronic structure of 0D perovskites to further understand their photophysical characteristics and the comprehensive overview of 0D perovskites for their further applications are still lacking. In this review, the unique crystal and electronic structure of 0D perovskites and their diverse properties are comprehensively analyzed, including large bandgaps, high exciton binding energy, and largely Stokes-shifted broadband emissions from self-trapped excitons. Furthermore, the photoluminescence regulation are discussed. Then, the various synthetic methods for 0D perovskite single crystals, nanocrystals, and thin films are comprehensively summarized. Finally, the emerging applications of 0D perovskites to light-emitting diodes, solar cells, detectors, and some others are illustrated, and the outlook on future research in the field is also provided.

Benefitting from Synergistic Effect of Anion and Cation in Antimony Acetate for Stable CH3 NH3 PbI3 -Based Perovskite Solar Cell with Efficiency Beyond 21

Both the film quality and the electronic properties of halide perovskites have significant influences on the photovoltaic performance of perovskite solar cells (PSCs) because both of them are closely related to the charge carrier transportation, separation, and recombination processes in PSCs. In this work, an additive engineering strategy using antimony acetate (Sb(Ac)₃ ) is employed to enhance the photovoltaic performance of methylammonium lead iodide (MAPbI₃ )-based PSCs by improving the film quality and optimizing the photoelectronic properties of halide perovskites. It is found that Ac^- and Sb³⁺ of Sb(Ac)₃ play different roles and their synergistic effect contributed to the eventual excellent photovoltaic performance of MAPbI₃ -based PSCs with a power conversion efficiency of above 21%. The Ac^- anions act as a crystal growth controller and are more involved in the improvement of perovskite film morphology. By comparison, Sb³⁺ cations are more involved in the optimization of the electronic structure of perovskites to tailor the energy levels of the perovskite film. Furthermore, with the assistance of Sb(Ac)₃ , MAPbI₃ -based PSCs deliver much improved moisture, air, and thermal stability. This work can provide scientific insights on the additive engineering for improving the efficiency and long-term stability of MAPbI₃ -based PSCs, facilitating the further development of perovskite-based optoelectronics.

Strain Engineering in Electrochemical Activity and Stability of BiFeO3 Perovskites

Strain engineering is widely employed to manipulate the intrinsic relationship of activity and the crystal structure, while the mechanism and rational strategy toward high-performance devices are still under investigation. Here straining engineering is utilized to manipulate a series of a typical perovskite structures via introducing different types of heteroions (Bi_1-xM_xFeO₃, M = Ca²⁺ or Y³⁺ ion). The space group R3c in BiFeO₃ perovskites is found to be maintained with substituting a certain amount of heteroions at Bi³⁺ sites (<5%), while it would shift into either space groups P4mm (with Ca²⁺ substitute) or Pnma (with Y³⁺ substitute) beyond some critical doping amounts (>5%). Such a transformation is linked with the mismatched crystal strain induced by the heteroions substituted at Bi³⁺ sites, while the activity, stability, and energy storage capability of Bi_1-xM_xFeO₃ have been essentially varied. The results offer a strategy for manipulating stability and activity of perovskites in electrochemical energy conversion and storage.

Synthesis of Red Cesium Lead Bromoiodide Nanocrystals Chelating Phenylated Phosphine Ligands with Enhanced Stability

Two new phosphine ligands, diphenylmethylphosphine (DPMP) and triphenylphosphine (TPP), were introduced onto cesium lead bromoiodide nanocrystals (CsPbBrI₂ NCs) to improve air stability in the ambient atmosphere. Incorporating DPMP or TPP ligands can also enhance film-forming and optoelectronic properties of the CsPbBrI₂ NCs. The results reveal that DPMP is a better ligand to stabilize the emission of CsPbBrI₂ NCs than TPP after storage for 21 days. The increased carrier lifetime and photoluminescence quantum yield (PLQY) of perovskite NCs are due to the surface passivation by DPMP or TPP ligands, which reduces nonradiative recombination at the trap sites. The DPMP and TPP-treated CsPbBrI₂ NCs were successfully utilized as red emitters for fabricating perovskite light-emitting diodes with enhanced performance and prolonged device lifetime relative to the pristine one.

Engineering bandgap of CsPbI3 over 1.7 eV with enhanced stability and transport properties

Potential multijunction application of CsPbI₃ perovskite with silicon solar cells to reach efficiencies beyond the Shockley-Queisser limit motivates tremendous efforts to improve its phase stability and further enlarge its band gap between 1.7 and 1.8 eV. Current strategies to increase band gap via conventional mixed halide engineering are accompanied by detrimental phase segregation under illumination. Here, ethylammonium (EA) in a relatively small fraction (x < 0.15) is first investigated to fit into three-dimensional CsPbI₃ framework to form pure-phase hybrid perovskites with enlarged band gap over 1.7 eV. The increase of band gap is closely associated with the distortion of Pb-I octahedra and the variation of the average Pb-I-Pb angle. Meanwhile, the introduction of EA can retard the crystallization of perovskite and tune the perovskite structure with enhanced phase stability and transport properties.

Postsynthetic Surface-Treatment of CsPbX3 (X = Cl, Br, or I) Nanocrystals via CdX2 Precursor Solution toward High Photoluminescence Quantum Yield

The existing defects on the surface of CsPbX₃ nanocrystals (NCs) resulted in the decrease of the photoluminescence quantum yields (PLQYs) of NCs. In this study, we developed a simple strategy, which can make the treated CsPbX₃ NCs exhibit high PLQYs and better stability by CdX₂ post-treatment at room temperature. The treated CsPbX₃ NCs were characterized by X-ray diffraction (XRD) patterns and PL spectra. The shape, size, and crystal structure of the NCs remained unchanged after Cd ion treatment. The PLQYs of CsPbCl₃ increased from 24 to 73% and the PLQYs of CsPbBr₃ NCs increased from 85 to 92% after treatment. The significant enhancement of PLQYs is ascribed to the effective passivation of surface defects, in which Cd²⁺ and X^- ions occupied the Pb-X vacancies existing on the surface of the NCs. In addition, this strategy was also applied to a mixed halide perovskite. The practical application of CsPbX₃ NCs will be extended by this method.

Highly Sensitive and Stable X-ray Detector Based on a 0D Structural Cs4PbI6 Single Crystal

Lead halide perovskite single crystals with a high X-ray stopping power and large μτ product have been successfully used for X-ray detection. However, poor air stability and ionic migration lead to the degradation of the devices for long-term operations. Here, we report a solution-processed lead 0D bulk Cs₄PbI₆ single crystal, which have I atoms in isolated [PbI₆]^4-. This 0D Cs₄PbI₆ single crystal has a μτ product of 9.7 × 10^-4 cm² V^-1 and an activation energy of 321.28 meV. We have fabricated a photoconductor device with a symmetric Au/Cs₄PbI₆/Au sandwich structure, which exhibits a high sensitivity of 451.49 μC Gy^-1 cm^-2 under 30 keV X-ray irradiation at an applied voltage of 30 V. After storing the device in air at room temperature for three months, the device retains nearly the same sensitivity as the original. These results demonstrate that this 0D Cs₄PbI₆ perovskite single crystal has great potential for practical X-ray detection applications.

Historical Analysis of High-Efficiency, Large-Area Solar Cells: Toward Upscaling of Perovskite Solar Cells

The status and problems of upscaling research on perovskite solar cells, which must be addressed for commercialization efforts to be successful, are investigated. An 804 cm² perovskite solar module has been reported with 17.9% efficiency, which is significantly lower than the champion perovskite solar cell efficiency of 25.2% reported for a 0.09 cm² aperture area. For the realization of upscaling high-quality perovskite solar cells, the upscaling and development history of conventional silicon, copper indium gallium sulfur/selenide and CdTe solar cells, which are already commercialized with modules of sizes up to ≈25 000 cm² , are reviewed. GaAs, organic, dye-sensitized solar cells and perovskite/silicon tandem solar cells are also reviewed. The similarities of the operating mechanisms between the various solar cells and the origin of different development pathway are investigated, and the ideal upscaling direction of perovskite solar cells is subsequently proposed. It is believed that lessons learned from the historical analysis of various solar cells provide a fundamental diagnosis of relative and absolute development status of perovskite solar cells. The unique perspective proposed here can pave the way toward the upscaling of perovskite solar cells.

Mesoporous-Carbon-Based Fully-Printable All-Inorganic Monoclinic CsPbBr3 Perovskite Solar Cells with Ultrastability under High Temperature and High Humidity

The all-inorganic CsPb(I_xBr_1-x)₃ (0 ≤ x ≤ 1) perovskite solar cells (PSCs) are attractive by virtue of their high environmental and thermal stability. Nevertheless, multiple-step deposition and high annealing temperature (>250 °C) and the structural and optoelectronic properties changes upon temperature-dependent phase-transition are potential impediments for highly efficient and stable PSCs. Herein, a space-confined method to fabricate stable lower-order symmetric pure monoclinic CsPbBr₃ phase at low temperature (<50 °C) is for the first time reported. It is found that the carbon-based mesoporous fully printable area can inhibit the phase transition to get a pure phase. Therefore, the device exhibits a power conversion efficiency of 7.52% with a low hysteresis index of 0.024. Moreover, the device passed the 1000 h 85 °C thermal test and the 200 cycles thermal cycling test according to IEC-61625 stability tests. These are critical progresses for achieving long-term stability and the stable pure inorganic perovskite phase of high-performance photovoltaics.

Chemically Stable Black Phase CsPbI3 Inorganic Perovskites for High-Efficiency Photovoltaics

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high-efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI₃ with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single-junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI₃ exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI₃ induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI₃ perovskite are presented. The development of various solution chemistry approaches for depositing high-quality phase-pure CsPbI₃ perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI₃ are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI₃ have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI₃ materials will further advance inorganic perovskite for highly stable and efficient photovoltaics.

Recent advances in interface engineering of all-inorganic perovskite solar cells

All-inorganic perovskite solar cells (PSCs) have become one of the most attractive research fields in recent years due to their excellent thermal stability and light stability as compared with their organic-inorganic hybrid counterparts. However, there is still a long way to go for their commercial application due to their low efficiency and poor stability under humidity conditions. Herein, an overview of the recent progress of all-inorganic PSCs based on interface engineering is provided. The main roles of interface engineering, adjusting energy-level alignment, enhancing charge transport capacity, passivating interface defects, modulating morphology of perovskite films, stabilizing perovskite phase, broadening spectral absorption, eliminating electrical hysteresis and enhancing operational stability, are summarized with examples, which paves the way for highly efficient and stable all-inorganic PSCs. Some of the latest progress in incorporating dopants to charge transport materials and modifying interface properties in all-inorganic PSCs are also covered.

Dual-Phase CsPbCl3-Cs4PbCl6 Perovskite Films for Self-Powered, Visible-Blind UV Photodetectors with Fast Response

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl₃-Cs₄PbCl₆ films. It is achieved by spin-coating of a certain dose of CH₃NH₃Cl/CsCl solution onto a CsI-PbBr₂-dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl₃-Cs₄PbCl₆ film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl₃-Cs₄PbCl₆ film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310-420 nm, a high responsivity (R) peak value of 61.8 mA W^-1, an exceptional specific detectivity (D*) maximum of 1.35 × 10¹² Jones, and a particularly fast response speed of 2.1/5.3 μs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.

Cs4 PbI6 -Mediated Synthesis of Thermodynamically Stable FA0.15 Cs0.85 PbI3 Perovskite Solar Cells

The stability issue is still one of the main limitations of the commercialization of perovskite photovoltaics. The mixed cation FA_x Cs_{1 -x} PbI₃ has shown great promise owing to its improved thermal and moisture stability. However, the study of FA_x Cs_{1 -x} PbI₃ is concentrated on formamidine (FA)-rich perovskite, whereas cesium (Cs)-rich FA_x Cs_{1 -x} PbI₃ perovskites are barely studied due to the inevitable phase separation when Cs > 30 mol%. Here, a Cs₄ PbI₆ -mediated method is developed to synthesize Cs-rich FA_x Cs_{1 -x} PbI₃ perovskites. It is demonstrated that Cs₄ PbI₆ intermediate phase has a low Cs cation diffusion barrier and therefore offers a fast ion exchange with the preformed FA-rich perovskite phase to finally form the Cs-rich FA_x Cs_{1 -x} PbI₃ perovskite. The results indicate that ≈15% alloying with organic FA cations can sufficiently stabilize the perovskite phase with excellent phase and UV-irradiation stability. The FA_0.15 Cs_0.85 PbI₃ perovskite solar cells achieve a champion power conversion efficiency of 17.5%, showing the great potential of Cs-based perovskites for efficient and stable solar cells.