Hybrid organic-inorganic perovskite solar cells (PSCs) have attracted global attention as one of the most promising photovoltaic materials due to their high efficiency, low energy consumption and low cost. However, non-radiative recombination caused by interface defects severely inhibits the performance of PSCs. To solve this critical issue, the particle size of nickel oxide (NiO_x) hole transport layer was reduced to improve the particle size uniformity and achieve efficient hole transport. Furthermore, the antisolvent acting time of the perovskite film was optimized to reduce the interfacial non-radiative recombination and interfacial defect. As a result, the crystalline quality is improved and power conversion efficiency (PCE) of the perovskite solar cells increase from 10.11% to 18.37%. Kelvin probe atomic force microscopy (KPFM) study shows that the contact potential difference (CPD) of the optimized perovskite film in the illumination condition increases by 120.39 mV compared with that under the dark condition. Analysis by piezoelectric atomic force microscopy (PFM) reveals that the ferroelectric polarization of the optimized interfacial perovskite films hardly changes from illumination to dark states, indicating that reducing interfacial defects can decrease the hysteresis effect of the PSCs. It is concluded that optimizing the NiO_x hole transport layer and improving the quality of perovskite film can reduce the interface defects, the non-radiative recombination and the hysteresis effect, and improve PCE of perovskite solar cells.

Perovskite solar cells (PSCs) are developing rapidly and their power conversion efficiency (PCE) has been repeatedly refreshed, but their long-term stability still needs to be improved. At present, most of the preparation of high-efficiency PSCs is completed in the inert gas, with high cost and limited operating space, which is not conducive to its industrial application. Here, perovskite solar cells with mixed cation, displaying ultra-long stability, were successfully prepared in the air. Effects of A-site cation doping on the microstructure, optoelectronic properties and stability of the perovskite were systematically investigated. The experimental results show that FA⁺ and Cs⁺ co-doping improves the quality of perovskite films, modulates the energy level arrangement of perovskite/SnO₂, suppresses carrier complexation, and significantly improves the PCE, long-term, wet and thermal stability of the cell. The optimal PCE of Cs_0.05MA_0.35FA_0.6PbI₃ cells is 19.34%, maintaining 85% of the initial efficiency after reserving for 242 d in dark environment at (20±5) ℃ and <5% relative humidity. In contrast, the PCE of the MAPbI₃ cell decreased to 30% of the initial value after reserving for 112 d under the same test conditions. FA⁺ and Cs⁺ co-doping also significantly improved the thermal and moisture resistance of the cells. Cs_0.05MA_0.35FA_0.6PbI₃ PSCs remain 99% and 84% of initial PCE after aging for 96 h at (85±5) ℃ and 20%-30% relative humidity, (20±5) ℃ and 80%-90% relative humidity in the dark, respectively. In contrast, PCEs of MAPbI₃ PSCs under the same conditions remain only 70% and 56%. This study provides a reference for the preparation of highly efficient and ultra-long stable mixed cation solar cells in the air.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted widespread attention due to their high power conversion efficiency (PCE) and low manufacturing cost. Although the certified PCE has reached 25.8%, the stability of PSCs under high temperature, high humidity, and continuous light exposure is still significantly inferior to that of traditional cells, which hinders their commercialization. Developing and applying highly stable inorganic hole transport materials (HTMs) is currently one of the effective methods to solve the photo-thermal stability of devices, which can effectively shield water and oxygen from corroding the perovskite absorption layer, thereby avoiding the formation of ion migration channels. This paper outlines the approximate classification and photoelectric properties of inorganic HTMs, introduces relevant research progress, summarizes performance optimization strategies for inorganic HTMs devices, including element doping, additive engineering, and interface engineering, and finally prospects the future development directions. It is necessary to further study the microstructure of inorganic HTMs and their relationship with the performance of PSCs to achieve more efficient and stable PSCs.

As a reversible, non-volatile, and resistive state mutation information storage and processing device, the resistive switching (RS) memory is expected to solve the inherent physical limitations of the traditional memory and von Neumann bottleneck, and has received widespread attention. Taking advantage of rapid carrier migration characteristics and excellent photoelectric conversion performance, halide perovskite optoelectronic RS memory devices present excellent resistive switching performance. In recent years, researches on storage and computing applications of the halide perovskite RS memory developed unprecedentedly; whereas, the working mechanisms of halide perovskite RS memory still remain unclear. This review analyzes the working mechanism of halide perovskite RS memory, compares the regulation characteristics of conduction filaments (CFs) and energy level matching (ELM), summarizes the constraints of various mechanisms, reveals the repeated formation and dissolution of CFs under light illumination and electric field, as well as Schottky barrier between the perovskite transfer layer and other layer, dominates the On/Off ratio, threshold (Set/Reset) voltage and performance stability of halide perovskite optoelectronic RS memory, and prospects the applications of halide perovskite RS memory in artificial intelligence bionic synapses, in-memory computing, and machine vision.

Power conversion efficiency of single-junction solar cells is fundamentally limited by the Shockley- Queisser (S-Q) limit. The most promising practical technology to break through the S-Q limit is to use two-terminal tandem structure which can simultaneously solve the problems, spectral mismatch and thermal relaxation energy loss, in single-junction devices. As one of the important components of the interconnecting layer, the recombination layer in the two-terminal tandem solar cells can provide recombination sites for electrons and holes extracted from the electron transporting layer and the hole transporting layer, avoiding the open-circuit voltage loss caused by charge accumulation and promoting the current flow of tandem solar cells. The recombination layer is considered as one of the key factors of achieving high-performance tandem devices. The ideal recombination layer should possess high conductivity to improve the charge recombination rate, high optical transmittance to ensure effective light absorption of the rear subcells, good chemical stability to reduce the damage caused by the solvent, and low preparation cost to promote the commercial production process. At present, a variety of materials have been used in two-terminal tandem solar cells, such as thin metals, transparent conductive oxides, conductive polymers, graphene oxide, etc., which play an important role in perovskite-perovskite, perovskite-organic, and perovskite-silicon two terminal tandem devices. In this review, the research progress of recombination layers in different types of tandem solar cells is summarized, together with types, design principles, preparation processes, and their advantages and disadvantages. Meanwhile, problems and challenges of the current recombination layers are proposed, which provides a useful reference for the design of high-performance tandem cells.

In recent years, organic-inorganic hybrid perovskite solar cells have received a lot of attention for their excellent performance and low manufacturing cost. However, the toxicity of lead in organic-inorganic hybrid perovskite solar cells and instability inhibits its further commercialization. Double perovskite Cs₂AgBiBr₆ possess excellent stability, low toxicity, long carrier lifetime, and small effective carrier mass, and is considered as a promising photovoltaic material. It has been applied in solar cells and displayed superior performance. However, the power conversion efficiency of Cs₂AgBiBr₆ perovskite solar cell still lags behind organic-inorganic hybrid perovskite solar cells, and its development faces various challenges. This review firstly introduces the crystal structure and the structural parameters such as tolerance factor of Cs₂AgBiBr₆. And then, the progress of thin film preparation technologies such as solution processing method, anti-solvent assisted film forming method, vapor deposition processing method, vacuum-assisted film forming method, spray-coating method are summarized, and the advantages and disadvantages of various preparation technologies are discussed. The performance optimization strategies of Cs₂AgBiBr₆ perovskite solar cells are analyzed from three aspects: element doping, additive engineering, and interface engineering (interface energy level matching and interface defect passivation), and the research progress in recent years is reviewed. Finally, the challenges faced by Cs₂AgBiBr₆ perovskite solar cells are pointed out, and future research directions are prospected from three aspects: precursor solvent engineering, bandgap engineering, and device degradation mechanism.

X-ray detection has been widely used in medical imaging, security inspection, and industrial non-destructive tests. Halide perovskite X-ray detectors have attracted increasing attention due to their high sensitivity and low detection limit, but the notorious ion migration leads to poor operational stability. It is reported that the low dimensional structure can effectively suppress the ion migration of perovskites, thus greatly improving the stability of the detectors. This review introduces the working mechanism, key performance parameters of perovskite X-ray detectors, and summarizes the recent progress of low-dimensional perovskite materials and their application in direct X-ray detectors. The relationship between the structural characteristics of low-dimensional perovskite materials and their X-ray detection performance was systematically analyzed. Low-dimensional perovskite is a promising candidate for the preparation of X-ray detectors with both high sensitivity and stability. Further optimization of detection material and device structure, preparation of large-area pixelated imaging devices, and study of working mechanism in-depth of the detector are expected to promote the practical application of perovskite X-ray detectors.

Perovskite light-emitting diodes (PeLEDs), owing to their unique photoelectric performance, show promising prospects in display applications. Red, green, and blue monochromatic PeLEDs have achieved remarkable breakthroughs, but the study of red/green/blue perovskite co-electroluminescence is still delayed. This study proposed a strategy that an intermediate connection layer (ICL) with hole/electron generation and transport capability is introduced between perovskites. On the one hand, introduction of the ICL can inhibit ion exchange and energy transfer. On the other hand, ICL has a charge-generation function that ensures different perovskite centers capture enough carriers. Furthermore, the thickness of the hole transport layer (NPB) is optimized. Furthermore, the thickness of the hole transport layer (NPB) is regulated, the blue/green tandem PeLED achieved relatively balanced luminescence and exhibits the largest EQE of 0.33%. The developed red/green/blue tandem PeLED exhibits the highest EQE of 0.5%, which is the first report in the field of PeLEDs, and exhibits the largest External Quantum Efficiency(EQE) of 0.33%. The developed red/green/blue tandem PeLED exhibits the highest EQE of 0.5%. In conclusion, this work provides a reference strategy for the co-electroluminescence of multicolor perovskites, which is expected to promote the development of perovskite in display applications.

With a bandgap of 1.1-1.4 eV, Sn/Pb mixed halide perovskites are ideal materials for single-junction solar cells to reach the power conversion efficiencies (PCEs) limit of Shockley-Queisser (S-Q) theory. Their chemical composition gradient in the vertical direction of the perovskite films affect the transport and separation of carriers by changing the energy band structures. Therefore, it is very important to control the crystallization process of tin-lead mixed perovskite thin films. In this work, it was found that different vertical composition gradients were formed when tin-lead mixed perovskites were prepared with different amounts of the anti-solvent. Larger amounts of anti-solvent was contributed to higher lead content on the film surface. The vertical composition gradient of tin-lead mixed perovskite could be regulated by adjusting the solvent composition, among which increasing V(DMSO):V(DMF) in the solvent could form a vertical composition gradient with a lead-rich bottom and a tin-rich surface. When V(DMSO):V(DMF) in lead-based precursor solutions was optimized to 1 : 2, compared with the control group of 1 : 4, open circuit voltage of the device under standard light conditions increased from 0.725 to 0.769 V, short circuit current density from 30.95 to 31.65 mA·cm^-2, and PCE from 16.22% to nearly 18%. Numerical simulations using SCAPS further proved the necessity of forming a vertical composition gradient. When the bottom of the perovskite film is rich in lead and the top is rich in tin, the recombination of carriers in the hole transport layer interface region is reduced, which can improve the device’s performance.

Organic-inorganic hybrid perovskite is an ideal light absorption material due to its high light absorption coefficient, adjustable band gap and bipolar charge conduction characteristics. However, perovskite thin films prepared by solution method possess various defects in the surface and interface, which inhibit carrier transport and trigger recombination. In this study, a multifunctional amino acid derivative, 9-fluorenylmethoxycarbonyl- L-phenylalanine-L-phenylalanine (Fmoc-FF-OH), was selected as an additive to reduce defects of perovskite film and to inhibit carrier recombination at grain boundaries. When the concentration of Fmoc-FF-OH is 0.6 g·L^-1, the particle size of the perovskite thin film increases from 138 to 210 nm, and the defect state density decreases from 2.46×10¹⁵ to 2.17×10¹⁵ cm^-3. Perovskite solar cells also exhibit optimal performance with open circuit voltage increasing from 1.05 to 1.10 V, and photoelectric conversion efficiency (PCE) improved from 15.50% to 17.44%. After stability test for 220 h, the photoelectric conversion efficiency of the device can still maintain 71% of the initial.

Two-dimensional (2D) perovskite displays great potential in optoelectronic applications due to its inherent quantum well structure, large exciton binding energy and good stability. However, facile preparation of high-quality 2D perovskite films with low cost remains a huge challenge. In this work, high-quality two-dimensional perovskite (PEA)₂PbI₄ films were prepared by solution method at low annealing temperature(80 ℃) without other special treatments, and further applied in the field of photodetectors. The results show that this photodetector possessed a low dark current (10^-11 A), good responsiveness illuminated at a wavelength of 450 nm (107 mA·W^-1), high detection rate (2.05×10¹² Jones) and fast response time (250 μs/330 μs). After 1200 s continuous illumination, the device maintains 95% initial photocurrent. In addition, the photocurrent remains almost unchanged after storage for 30 d. This work provides promising strategy to develop stable and high-performance optoelectronic devices.

Carbon-based perovskite solar cells (C-PSCs) play an important role in industrialization research due to their stability and low cost. In this work, high-quality NiO_x mesoporous layer was selected as a hole transport layer (HTL) based on MAPbI₃ material to enhance the performance of C-PSCs. The effect of preparation methods of the NiO_x mesoporous layer on the solar cell performance and the optimum thickness of the NiO_x mesoporous layer were investigated. It was found that mesoporous layers prepared by screen-printing process with well-distributed pores facilitated the filling of perovskite (PVK) precursor solution in the underlayer mesoporous scaffold. Finally, an HTL-contained perovskite solar cell with high efficiency and almost negligible hysteresis was achieved, possessing an open-circuit voltage (V_OC) of 910 mV, a power conversion efficiency (PCE) of 14.63%, and certified efficiency reached 14.88%. Moreover, PCE of the solar cell displayed outstanding stability after being stored in air for nearly 900 h.

Density functional theory calculations play an important role in the study of defects in halide perovskites. Although the traditional semi-local functionals (such as PBE) can obtain the band gaps close to the experiments, they fail to accurately describe the positions of the band edges. Utilizing more accurate hybrid functionals combined with the spin-orbit coupling (SOC) effect with full structure relaxation is considered to be necessary for the prediction of defect properties. There are two types of hybrid functionals in the literature, namely the screened HSE and the unscreened PBE0. In this study, taking the orthorhombic phase CsPbI₃ as an example, these methods were compared for the calculation of defect properties. The results show that there is no obvious difference between two methods for bulk properties, but qualitative differences appear for the defect properties. Most of the shallow-level defects predicted in the HSE calculations become deep-level defects in the PBE0 calculations. Meanwhile, there are qualitative differences between the defect transition levels and the Kohn-Sham levels. The origin of above differences lies in the fact that the Hartree-Fock exchange potential has long-range interaction. Therefore, in unscreened hybrid functionals, such as PBE0, it is more difficult to obtain convergent results with a manageable supercell size. In contrast, HSE exhibits a screening effect on the Hartree-Fock exchange potential and can obtain accurate defect energy levels using relatively small supercell sizes. Therefore, all results here demonstrate that the HSE hybrid functional owns a significant advantage in dealing with this problem even though a large Hartree-Fock mixing parameter (about 0.43) is needed.

Cs₂NaBiCl₆ double perovskite with indirect band demonstrates near-infrared (NIR) wide-band emission, but its low efficacy limits its potential applications in the field of NIR. In this work, micron-sized Cs₂Ag_0.1Na_0.9BiCl₆:Tm³⁺ double perovskites were synthesized via the coprecipitation method, which shows enhanced NIR emission. Their optical absorption, photoluminescence emission (PL) and excitation (PLE), time-resolved photoluminescence, and photoluminescence quantum yield (PLQY) were investigated. The Cs₂Ag_0.1Na_0.9BiCl₆:Tm³⁺ shows optical bandgap of 3.06 eV and NIR broad emission peaking at 680 nm under 350 nm excitation due to recombination of self-trapped excitons (STEs). Meanwhile, a new emission peak could be observed at 810 nm due to Tm³⁺ doping. The PLQY in the band range of 780-830 nm can be increased by 6.05 times from 1.67% to 11.77% and in the band range of 650-900 nm can reach 25.22%. This study proves the feasibility of Cs₂Ag_0.1Na_0.9BiCl₆:Tm³⁺ double perovskite as new NIR emission material.

Solution-processed perovskite films usually contain a large quantity of grain boundaries, which decrease the film crystalline quality and introduce severe defect recombination, hindering performance of the devices based on them. Therefore, preparation of high-quality films to achieve high power conversion efficiencies remains a great challenge for perovskite solar cells. Due to high abilities of self-assembly and morphology-tuning for liquid crystal molecules, a single-molecule liquid crystal 4-cyano-4′-pentyl biphenyl (5CB) was employed as additive in CH(NH₂)₂PbI₃ (FAPbI₃) precursor solution to increase the perovskite grain size and decrease the grain boundaries. In addition, the cyano group in 5CB passivates the uncoordinated Pb²⁺ in the perovskite films, which reduces the trap density concentration and inhibits the nonradiative recombination. The resulting perovskite solar cells with 0.2 mg/mL 5CB in the precursor achieve an efficient power conversion efficiency of 21.27% with an open circuit voltage of 1.086 V, a current density of 24.17 mA/cm², and a fill factor of 80.96%. In conclusion, introducing single-molecule liquid crystal as additive is a facile and efficient strategy for improving the performance of FAPbI₃ solar cells.

AgBi₂I₇ thin film is one of the important candidates for constructing heterojunction ultraviolet photodetectors, due to their great optoelectronic properties and environmental stability. In this study, AgBi₂I₇ thin films were prepared by solution method and their photodetecting properties were investigated. By optimizing technological parameters such as concentration of the precursor solution and type of solvent (n-butylamine and DMSO), their photodetecting performance were investigated. AgBi₂I₇ thin films were fabricated on wide-bandgap GaN by optimal scheme to construct an AgBi₂I₇/GaN heterojunction. The heterojunction has a great selective detection of UVA-ray of which full width at half maximum is about 30 nm. Under 3 V bias and 350 nm UV irradiation, the On/Off ratio of the device exceeds 5 orders of magnitude, achieving a high responsivity of 27.51 A/W and a high detection rate of 1.53×10¹⁴ Jones. Therefore, the present research indicates that AgBi₂I₇ thin films prepared by solution method are promising to be applied to construct high-performance heterojunction ultraviolet photodetectors.

Perovskite solar cells (PSCs) with structure of TiO₂/ZrO₂/carbon triple-layer are attractive recently because of their inexpensive raw materials, scalable fabrication process, and outstanding stability. But little progress has been made in the low temperature fabrication of TiO₂/ZrO₂/carbon triple-layer structured PSCs. A major reason is that it is rather difficult to construct the ZrO₂ spacer layer at low temperature. Herein, we report a facile low-temperature spray-coating method to prepare effective ZrO₂ spacer layer in TiO₂/ZrO₂/carbon triple-layer PSCs using urea to tune the porosity. After optimizing the amount of urea and the thickness of zirconia to 1100 nm, power conversion efficiencies (PCE) of 14.7% for a single cell and 10.8% for a module with 5 cells connected in series (5×0.9 cm× 2.5 cm) were achieved. Furthermore, the PSCs could be stable for 200 d at constant temperature (25 ℃) and humidity (40%). With this spray coating method, the zirconia layer on flexible substrate can endure 50 times of bending without any cracking. Compared to the conventional screen-printing method of ZrO₂ spacer layer, the spray-coating alternative developed in this work shows advantages of more convenient to process, preparation under lower temperature, and compatibility to flexible substrate.

Perovskite solar cells have become a research hotspot in the field of new energy due to the excellent performance and potential in application, but it still displays some disadvantages such as high defect density and poor stability. In this study, L-arginine, a small molecule of organic matter, was doped into the perovskite precursor soLution as compared with the other amino acids, and the perovskite solar cells were prepared by a two-element and two-step preparation method. The test results show that L-arginine doping improves the photoelectric performance of the device, which photoelectric efficiency increases from 18.81% to 21.86%. L-arginine reduces the nonradiative recombination of carriers and increases the average carrier life by reducing the defect density of perovskite layer from 4.83×10¹⁶ cm^-3 to 3.45×10¹⁶ cm^-3. In addition, the perovskite grain size increases, grain boundaries decrease, the light absorption ability and stability of the film are enhanced, while the hysteresis effect is suppressed. Improvement of the photovoltaic performance is due to the passivation of defects by interaction between multi-groups of L-arginine and perovskite materials. This study provides an optimization method for perovskite solar cells.

Defects at the surface and grain boundary of the three-dimensional (3D) organic-inorganic metal halide perovskite film incline to cause non-radiative recombination of charge carriers and accelerate decomposition of 3D perovskite, in turn deteriorating the power conversion efficiency (PCE) and stability of the perovskite solar cells (PSCs). In this study, the organic 4-chlorobenzylamine cation was applied to react with 3D perovskite and the residual PbI₂ to in-situ form a two-dimensional (2D) perovskite top layer, which can passivate the surface and grain boundary defects of the 3D perovskite film, and improve the surface hydrophobicity. Based on this strategy, 2D/3D-PSCs with higher PCE and better stability were successfully obtained. Their structure, morphology photoelectric propery and stability of PSCs were systematically studied. All results show that 2D/3D-PSCs achieve PCEs up to 20.88%, much higher than that of 18.70% for the 3D-PSCs. In addition, 2D/3D-PSCs can maintain 82% of the initial PCE after 200 h continuous operation under 1-sun illumination in N₂ atmosphere, exhibiting excellent stability.

Printable perovskite solar cells employ a device structure for which the organic-inorganic perovskite absorber is hosted by an inorganic mesoporous scaffold. Its advantages include simple fabrication process, low material cost and relatively high stability. However, it is challenging to homogeneously deposit high-quality perovskite crystals on the mesoporous scaffold. Herein, by incorporating lead acetate (Pb(Ac)₂) in the typical perovskite precursor, methylamine lead iodine (MAPbI₃), the crystal growth and pore-filling of the perovskite crystals in the mesoporous scaffold is improved by facilitating the crystal nucleation. Meanwhile, Ac^- and MA⁺ form MAAc which releases during thermal annealing process, resulting in excess PbI₂ in the perovskite layer which passivates the grain boundaries. By incorporating 1% molar ratio of Pb(Ac)₂ in the perovskite precursor, a power conversion efficiency of 15.42% is obtained for printable perovskite solar cells. This indicates that it is feasible to enhance the performance of printable perovskite solar cells by employing additives to tune the crystallization of the perovskite absorbers.

Solar thermal radiant energy is abundant in storage and pollution-free, and is one of the most competitive clean energies in the future. In recent years, halide perovskite quantum dots (PQDs) are widely used in solar cells and luminescent concentrator solar cells due to their excellent photoelectric properties and unique advantages such as quantum confinement effect and solution processing, and possess vast application prospects, but they are still facing many challenges in future commercial applications. In this review, optimization strategies for improving cell performance are emphatically summarized combined with the domestic and foreign research progress in the field of PQD solar cells. The application of PQDs in luminescent concentrator cells is introduced. Finally, the current challenges in this field are elaborated, and its development trends are prospected. This review provides some ideas for the design and development of the photovoltaic technology in the future.

The investigation of defects in perovskite crystals is essential to promote the development of perovskite solar cells. The defects result in non-radiative recombination as well as the deterioration of device stability. To reduce the impact of material defects on photovoltaic performance, it is necessary to deeply understand the types of perovskite film defects and the routes of suppression methods. According to electronic characteristics, defects can be divided into electron-rich and electron-deficient defects. Based on Lewis acid-base theory, electron-rich defects can be passivated by Lewis acid, and electron-deficient defects can be passivated by Lewis base or ionic liquids. These passivation additives can be added during the formation of perovskite film, or used to post-treat the surface of the films. This review summarized the defect passivation cases reported in recent years to visually present design strategies of additives and the effects of defect passivation on photovoltaic performance. Finally, developing multi-functional passivators, large-area passivation strategy and advanced charge transport layer were proposed for future perspective. This review is expected to promote the development of perovskite solar cells in the future.

Cs₂SnI₆ is a stable and environmentally friendly halide perovskite material with great potential for photovoltaic and optoelectronic applications. While the surface properties are of paramount importance for device fabrications, there have been no such theoretical studies on this material. Using density functional theory calculations with the SCAN+rVV10 functional, the (001), (011) and (111) surfaces of Cs₂SnI₆ were studied to reveal their thermodynamic stability. We constructed seven models for these surfaces, including two along the (001) orientation (CsI₂- and SnI₄-terminated surfaces), two along the (011) orientation (I₄- and Cs₂SnI₂-terminated surfaces) and three along the (111) orientation (non-stoichiometric CsI₃-, Sn- and stoichiometric CsI₃-terminated surfaces). Because most of the surfaces are non-stoichiometric, their relative stability depends on the experimental preparation condition, which is reflected by the chemical potentials of the constituent elements in the calculation. By determining the allowed chemical potential region, the thermodynamic stability of these Cs₂SnI₆ surfaces is analyzed. The results show that the surface energies of the (001) and (011) surfaces are affected by the chemical potentials, while the stoichiometric CsI₃-terminated (111) surface is unaffected by the chemical potentials and is energetically the most stable surface of Cs₂SnI₆. Thus, the observed exposure of (111) surface of Cs₂SnI₆ crystals in several recent experiments is determined to be driven by thermodynamics.

Luminescent materials have been widely used in confidential information protection and anticounterfeiting. Luminescent lead halide perovskite nanocrystals, which can be converted from the lead source through a two-step method, are attractive candidates for information encryption and decryption. Herein, the reversible conversion between the invisible lead-organic framework and the luminescent MAPbBr₃ nanocrystals is achieved, together with their further application on information storage by inkjet printing technology. The lead ions are embedded into the metal-organic frameworks through coordination with the 2-methylimidazole linkers. The inherent confined distribution of lead ions facilitates the in-situ growth of perovskite nanocrystals in the second step without the assistance of external bulky ligands. The recorded information was firstly encrypted by the lead organic frameworks, which is invisible under ambient and UV light. After reacting with methylammonium bromide, the perovskite nanocrystals are in-situ formed, and the information becomes readable under UV light. Using methylammonium bromide and water as the decryption and encryption reagents could also switch on/off the luminescence, therefore, realizing the confidential information storage.

0.96NaNbO₃-0.04CaZrO₃(NNCZ) ceramic shows stable double hysteresis loops at room temperature, but the property of energy density, energy storage efficiency and breakdown strength of NNCZ are terrible, which limit NNCZ to be used as energy storage materials. In this work, Fe₂O₃ was chosen to modify the energy storage property of NNCZ. (0.96NaNbO₃-0.04CaZrO₃)-xFe₂O₃ (NNCZ-xFe) antiferroelectric ceramics were prepared by traditional solid reaction method. The phase, morphology, dielectric property and energy storage property of NNCZ-xFe were characterized. The results indicated that the crystal structures of NNCZ-xFe ceramics were pure perovskite structure. The sintering temperature of NNCZ ceramic was decreased with addition of Fe₂O₃. With the increase of Fe₂O₃ content, the grain size of NNCZ-xFe were decreased firstly and then raised. The NNCZ-0.02Fe ceramic obtained the smallest grain size (5.04 μm) and the best energy storage property. The breakdown strength of NNCZ-0.02Fe was 230 kV/cm at room temperature (RT). The recoverable energy density and energy storage efficiency before breakdown were 1.57 J/cm ³and 55.74% respectively. At 125 ℃ and 180 kV/cm, the energy density of NNCZ- 0.02Fe was 4.53 J/cm ³. Fe₂O₃ doping decreased the sintering temperature of NNCZ ceramics, reduced the the migration rate of oxygen vacancies and inhibited the growth of grains. At the same time, it reduced the dielectric loss and improved the breakdown strength. The oxygen vacancies pinning made antiferroelectric phase switch to ferroelectric phase harder, avoided appearance dumbbell-shaped double hysteresis loops, so the energy storage efficiency was improved. This research shows that NNCZ-xFe has a good potential application in the field of dielectric energy storage.

Perovskite manganese oxide (PMO) has attracted extensive attention in the field of heat dissipation because of its discoloration stimulated by external conditions. At present, most of the researchs on the discoloration characteristics of PMO is based on temperature excitation, and there still lacks of heat dissipation equipment excited by electric field. In addition, because the electric field excitation is accompanied by Joule heat, electrochromic property of PMO materials has not been clearly proved. In view of the above challenges, here an electrical modification method for PMO materials is proposed by using influence of electric field excitation on Mn elements in PMO. Thermochromic property of PMO was greatly weakened by electrical modification, and then La_0.7Ca_0.25K_0.05MnO₃ (LCKMO) can eliminate the influence of Joule heat in electric field excitation experiment. We studied the thermochromic and electrochromic properties of LCKMO before and after electrical modification. Emittance of LCKMO before electrical modification increases with the increase of temperature with the maximum increment at 17%. After being excited by 21 V electric field, the emittance increases by 15%, 16%, 10%, 0.6% and 1.4% at 173, 203, 243, 273, and 373 K, respectively. The thermochromic property of electrically modified LCKMO is greatly weakened, and its emittance increases by 10.7% and 9.3% at 273 and 373 K, respectively, after being excited by 21 V electric field. The experimental results before and after electrical modification show that LCKMO has electrochromic property, and there is an obvious regulation mechanism of electric field excitation on the emissivity. Therefore the electrical modification method for PMO materials can not only enable the electrochromic study of PMO materials without the influence of Joule heat, but also provides a new possibility for regulation of the thermochromic property of PMO materials.

Piezoelectric actuators have advantages of fast response, high positioning accuracy, small size, and have received widespread attention in the field of precision drives. Lead-based piezoelectric actuators occupy the main commercial market. To avoid the use of the harmful element lead, a lead-free piezoelectric materials and actuators must be developed. Among them, bismuth sodium titanate (Bi_0.5Na_0.5)TiO₃ (BNT), was reported but it has some disadvantages of higher driving voltage, larger hysteresis, and poor temperature stability. To optimize the strain performance of the lead-free actuator, this study adopted the solid-phase reaction method to prepare (1-x) {0.76(Bi_0.5Na_0.5)TiO₃- 0.24SrTiO₃}-xNaNbO₃ (BNT-ST-xNN, x=0-0.03) lead-free ferroelectric ceramics, systematically studied its field- induced strain performance. The results show that when x=0.01, the strain value of the ceramic can reach 0.278% under a low electric field (E = 4 kV/mm), and the piezoelectric coefficient d^*₃₃ is as high as 695 pm/V. Meanwhile, the ceramic is at the non-ergodic/ergodic relaxation phase boundary, and the electric field induced relaxor-ferroelectric phase transition leads to large field-induced strain. Compared with x=0.01, the strain value at x=0.02 is 0.249%, which is slightly reduced, but the hysteresis is significantly reduced to 43% of the comparator. In addition, the strain remains stable in the temperature range of 25-100 ℃. This study shows that introduction of SrTiO₃ and NaNbO₃ into BNT can increase the field-induced strain value while maintaining a low driving voltage and good temperature stability, indicating suitable for the development of piezoelectric actuators.