Inorganic Mixed Halide Perovskite Research Articles

Visualization of Ion Migration in an Inorganic Mixed Halide Perovskite by One-Photon and Multiphoton Absorption: Effect of Guanidinium A-Site Cation Incorporation.

In this work, we present the ion migration of CsPbIBr2 under illumination and impede it by incorporating the large cations of guanidinium (GA). A series of "probe-set-probe" operations are applied to assess the photoluminescence (PL) behavior spectrally and spatially, which is correlated to the ion migration-induced phase separation, of CsPbIBr2 and GAxCs1-xPbIBr2 perovskites. The local lattice distortion introduced by GA could reduce the strain gradient in GAxCs1-xPbIBr2 to inhibit the ion migration, leading to a stable PL spectrum and enhanced device stability under light stimulation. A solar cell with an optimized stoichiometric composition of GA0.1Cs0.9PbIBr2 delivers comparable photovoltaic performance and improved stability compared to those of CsPbIBr2-based perovskite solar cells, retaining 80% of its initial power conversion efficiency after being continuously bathed in light for 8 h under ambient conditions without encapsulation, while the CsPbIBr2 counterpart shows an efficiency that is <30% of its initial value under the same test condition.

Improving inorganic perovskite photovoltaic performance via organic cation addition for efficient solar energy utilization

Organic cations help in executing better crystal growth of halide perovskites. Herein, we have realized improved all-inorganic cesium lead halide perovskite film quality with reduced pinholes and high crystallinity in phenylethylammonium (PEA+) assisted perovskite. Additionally, PEA+ cation acts as an additive to control intermediate perovskite phase and executes pure phase perovskite crystal growth as compared to MA+ and FA+ cations assisted perovskite films. X-ray photoelectron and UV–vis spectroscopy results revealed that adding PEA+ in the perovskite helps in almost uniform distribution of Br− ion after post-annealing process. Furthermore, depth profiling analysis reveals that PEA+ in the intermediate phase perovskite interacts more with the ZnO layer beneath perovskite, which helps in the fabrication of compact film. PEA+ sublimates after post-annealing treatment of 300 °C, as no evidence of PEA+ existence was found in characterizations for post-annealed perovskite films. This brings multiple benefits to inorganic mixed halide perovskite film formation. The best performing perovskite solar cell (PSC) exhibits a high conversion efficiency of 14.75% as well as enhanced stability of maintaining almost 83% of its initial efficiency for 400 h. Electrochemical impedance spectroscopy and space-charge-limited current results suggests reduced recombination loss and defect densities in PEA+ assisted PSC.

Terbium-Doped and Dual-Passivated γ-CsPb(I1- x Brx )3 Inorganic Perovskite Solar Cells with Improved Air Thermal Stability and High Efficiency.

Realizing photoactive and thermodynamically stable all-inorganic perovskite solar cells (PSCs) remains a challenging task within halide perovskite photovoltaic (PV) research. Here, a dual strategy for realizing efficient inorganic mixed halide perovskite PV devices based on a terbium-doped solar absorber, that is, CsPb1- x Tbx I2 Br, is reported, which undertakes a bulk and surface passivation treatment in the form of CsPb1- x Tbx I2 Br quantum dots, to maintain a photoactive γ-phase under ambient conditions and with significantly improved operational stability. Devices fabricated from these air-processed perovskite thin films exhibit an air-stable power conversion efficiency (PCE) that reaches 17.51% (small-area devices) with negligible hysteresis and maintains >90%of the initial efficiency when operating for 600 h under harsh environmental conditions, stemming from the combined effects of the dual-protection strategy. This approach is further examined within large-area PSC modules (19.8 cm2 active area) to realize 10.94% PCE and >30days ambient stability, as well as within low-bandgap γ-CsPb0.95 Tb0.05 I2.5 Br0.5 (Eg = 1.73eV) materials, yielding 19.01% (18.43% certified) PCE.

Stable one dimensional (1D)/three dimensional (3D) perovskite solar cell with an efficiency exceeding 23%

AbstractThe interface properties of organic–inorganic mixed halide perovskite solar cells play a significant role in their photovoltaic performance. Defect states at the interface can decrease the power conversion efficiency through defect‐assisted charge recombination and degrade the long‐term stability. Low‐dimensional perovskites exhibit excellent stabilities. They can be combined with three dimensional (3D) perovskites to utilize their advantages for fabrication of high‐performance devices. In this study, we successfully construct a robust interface for perovskite films through mixed‐dimensional engineering. After the introduction of a one dimensional (1D)‐structured capping layer on the 3D perovskite through post‐treatment, the number of defect states in the perovskite film is significantly decreased, while the lifetime of the photocarriers is increased. In addition, the 1D capping layer can serve as a diffusion barrier to reduce the ion migration and protect the vulnerable 3D perovskite against moisture. Perovskite solar cells based on stacked 1D/3D structures exhibit a power conversion efficiency of 23.3% and maintain 80% of the initial efficiency after storage for over 800 h under ambient conditions with a humidity of 50%. Their performances are superior to those of the 3D devices. This study provides a simple approach to simultaneously enhance the efficiency and stability of perovskite solar cells and may guide the development of other solar cells.image

Homologous Bromides Treatment for Improving the Open-Circuit Voltage of Perovskite Solar Cells.

The power conversion efficiency (PCE) of solution-processed organic-inorganic mixed halide perovskite solar cells has achieved rapid improvement. However, it is imperative to minimize the voltage deficit (Woc = Eg /q- Voc ) for their PCE to approach the theoretical limit. Herein, the strategy of depositing homologous bromide salts on the perovskite surface to achieve a surface and bulk passivation for the fabrication of solar cells with high open-circuit voltage is reported. Distinct from the conclusions given by previous works, that homologous bromides such as FABr only react with PbI2 to form a large-bandgap perovskite layer on top of the original perovskite, this work shows that the bromide also penetrates the perovskite film and passivates the perovskite in the bulk. This is confirmed by the small-bandgap enlargement observed by absorbance and photoluminescence, and the bromide element ratio increasing in the bulk by time-of-flight secondary-ion mass spectrometry and depth-resolved X-ray photoelectron spectroscopy. Furthermore, a clear suppression of non-radiative recombination is confirmed by a variety of characterization methods. This work provides a simple and universal way to reduce the Woc of single-junction perovskite solar cells and it will also shed light on developing other high-performance optoelectronic devices, including perovskite-based tandems and light-emitting diodes.

Halide Perovskites: A New Era of Solution-Processed Electronics.

Organic-inorganic mixed halide perovskites have emerged as an excellent class of materials with a unique combination of optoelectronic properties, suitable for a plethora of applications ranging from solar cells to light-emitting diodes and photoelectrochemical devices. Recent works have showcased hybrid perovskites for electronic applications through improvements in materials design, processing, and device stability. Herein, a comprehensive up-to-date review is presented on hybrid perovskite electronics with a focus on transistors and memories. These applications are supported by the fundamental material properties of hybrid perovskite semiconductors such as tunable bandgap, ambipolar charge transport, reasonable mobility, defect characteristics, and solution processability, which are highlighted first. Then, recent progresses on perovskite-based transistors are reviewed, covering aspects of fabrication process, patterning techniques, contact engineering, 2D versus 3D material selection, and device performance. Furthermore, applications of perovskites in nonvolatile memories and artificial synaptic devices are presented. The ambient instability of hybrid perovskites and the strategies to tackle this bottleneck are also discussed. Finally, an outlook and opportunities to develop perovskite-based electronics as a competitive and feasible technology are highlighted.

Phase segregation in inorganic mixed-halide perovskites: from phenomena to mechanisms

Halide perovskites, such as methylammonium lead halide perovskites ( MAPbX 3 , X = I , Br, and Cl), are emerging as promising candidates for a wide range of optoelectronic applications, including solar cells, light-emitting diodes, and photodetectors, due to their superior optoelectronic properties. All-inorganic lead halide perovskites CsPbX 3 are attracting a lot of attention because replacing the organic cations with Cs + enhances the stability, and its halide-mixing derivatives offer broad bandgap tunability covering nearly the entire visible spectrum. However, there is evidence suggesting that the optical properties of mixed-halide perovskites are influenced by phase segregation under external stimuli, especially illumination, which may negatively impact the performance of optoelectronic devices. It is reported that the mixed-halide perovskites in forms of thin films and nanocrystals are segregated into a low-bandgap I-rich phase and a high-bandgap Br-rich phase. Herein, we present a critical review on the synthesis and basic properties of all-inorganic perovskites, phase-segregation phenomena, plausible mechanisms, and methods to mitigate phase segregation, providing insights on advancing mixed-halide perovskite optoelectronics with reliable performance.

Insights on the opto-electronic structure of the inorganic mixed halide perovskites γ-CsPb(I1-xBrx)3 with low symmetry black phase

Abstract Inorganic halide perovskites especially CsPbI3 have attracted great attention in optoelectronics and photovoltaic fields due to their good thermal stability and comparable efficiency with organometallic perovskites. CsPbI3 has two main phases, active black phase at high temperature and inactive yellow phase at low temperature. To obtain the perovskite phase, thin films should be heated above 320 °C, this high temperature can damage the flexible substrates. Recently, it has been suggested that partial or total substitution of iodide by bromide such as CsPbI3−xBrx, could stabilize the preferred perovskite black phase at lower temperature. Hence, it was very necessary to investigate the electronic and optical characteristics of these materials. The structural, electronic, some carrier transport and optical properties of all-inorganic cesium lead mixed halide perovskite with a low symmetry orthorhombic structure were methodically investigated using density functional theory.

Thermally Stable, Efficient, Vapor Deposited Inorganic Perovskite Solar Cells

We report on thermally stable inorganic mixed halide perovskite solar cells deposited using a vapor deposition technique with no loss in device performance at 200 °C for 72 h. X-ray diffraction ana...

All Inorganic Mixed Halide Perovskite Nanocrystal-Graphene Hybrid Photodetector: From Ultrahigh Gain to Photostability.

Hybrid graphene-perovskite photodetectors embrace the excellent photoabsorption properties of perovskites and high carrier mobility of graphene in a single device. Here, we demonstrate the integration of halide-ion-exchanged CsPbBrxI3-x nanocrystals (NCs) as a photoabsorber and graphene as a transport layer. The NCs conform to a cubic lattice structure and exhibit an optical band gap of 1.93 eV. The hybrid device attained a maximum responsivity of 1.13 × 104 A/W and specific detectivity of 1.17 × 1011 Jones in low light intensity (∼80 μW/cm2). Specifically, an ultrahigh photoconductive gain of 9.32 × 1010 is attained because of fast hole transit time in the graphene transistor and long recombination lifetime in the perovskite NCs simultaneously. The phototransistor also shows good stability and can maintain ∼95% of the photocurrent under continuous illumination over 5 h and ∼82% under periodic illumination over 37 h. Our results also revealed that the common issue of ion separation and segregated halide domains in mixed halide perovskite NCs do not occur under low light intensities. The intensive degradation of CsPbBrxI3-x NCs is only observed under stronger light excitation (≥55 mW/cm2), reflecting as emission shifts. Our work establishes the use of fully inorganic perovskite NCs as highly stable photodetectors with high responsivity and low power light detection.

Postsynthesis Spontaneous Coalescence of Mixed-Halide Perovskite Nanocubes into Phase-Stable Single-Crystalline Uniform Luminescent Nanowires.

All inorganic mixed-halide perovskite, CsPb(Br xI1- x)3 (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb(Br xI1- x)3 nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.

High Efficiency Blue and Green Light-Emitting Diodes Using Ruddlesden–Popper Inorganic Mixed Halide Perovskites with Butylammonium Interlayers

Ruddlesden–Popper phase inorganic metal halide perovskites are promising candidates for efficient light-emitting diodes (LEDs) with high brightness and color purity. Here, we demonstrate LEDs made from in situ grown CsPbX3 quasi 2D/3D thin films that are color tunable across the entire visible spectrum. CsPbX3 nanosheets are used to produce RP phase perovskites using butylammonium as a separating ligand to create BA2Csn–1Pbn(Br/Y)3n+1 2D/3D mixed halide thin films, where Y = Cl or I. The number of CsPbBr3 monolayers in these crystals was optimized by changing the butylammonium concentration. We demonstrate a stable perovskite phase with thin emission line widths providing points covering the edge of the CIE triangle and a maximum red/green/blue coverage of ∼130% of the National Television System Committee color standard. Additionally, we are able to report record efficiencies for blue emitting perovskite nanocrystal LEDs with a maximum external quantum efficiency (EQE) of 2.4% and 6.2% at 465 and 487 nm a...

Structural and Electronic Properties of Inorganic Mixed Halide Perovskites

In this work, we investigate the structural and electronic variations of all‐inorganic mixed halide perovskites CsPb(Cl1−xBrx)3 and CsPb(Br1−xIx)3 upon their halide composition, by the first‐principles calculation with the spin–orbit interaction. We find that these perovskites always keep their direct‐bandgap nature, even though structurally their PbX6 octahedra are more or less distorted with different halide ratios (Cl/Br or Br/I). Their optical bowing parameters show no dependence on such composition ratios, which means their bandgaps can be linearly tuned. Moreover, these perovskites also exhibit rather good bipolar transport character, as both electrons and holes have the effective masses of less than 0.2m0. Therefore, we propose that by properly tuning the halide composition ratio, these mixed halide perovskites can be fabricated into light‐emitting devices with selected frequency in a broad frequency range.

The structural, electronic, and optical properties of organic–inorganic mixed halide perovskites CH3NH3Pb(I1−yXy)3 (X = Cl, Br)**Project supported by the Financial Support from the “12th Five-Year” Science and Technology Research Project of the Education Department of Jilin Province (Grant No. [2016] 494) and the National Natural Science Foundation of China (Grant No. 21173035).

Methylammmonium lead iodide perovskites (CH3NH3PbI3) have received wide attention due to their superior optoelectronic properties. We performed first-principles calculations to investigate the structural, electronic, and optical properties of mixed halide perovskites CH3NH3Pb(I1−yXy)3 (X = Cl, Br; y = 0, 0.33, 0.67). Our results reveal the reduction of the lattice constants and dielectric constants and enhancement of band gaps with increasing doping concentration of Cl−/Br− at I−. Electronic structure calculations indicate that the valance band maximum (VBM) is mainly governed by the halide p orbitals and Pb 6s orbitals, Pb 6p orbitals contribute the conduction band minimum (CBM) and doping does not change the direct semiconductor material. The organic cation [CH3NH3]+ does not take part in the formation of the band and only one electron donates to the considered materials. The increasing trends of the band gap with Cl content from y = 0 (0.793 eV) to y = 0.33 (0.953 eV) then to y = 0.67 (1.126 eV). The optical absorption of the considered structures in the visible spectrum range is decreased but after doping the stability of the material is improving.

Light Soaking Phenomena in Organic–Inorganic Mixed Halide Perovskite Single Crystals

Recently, organic–inorganic mixed halide perovskite (MAPbX3; MA = CH3NH3+, X = Cl–, Br–, or I–) single crystals with low defect densities have been highlighted as candidate materials for high-efficiency photovoltaics and optoelectronics. Here we report the optical and structural investigations of mixed halide perovskite (MAPbBr3–xIx) single crystals. Mixed halide perovskite single crystals showed strong light soaking phenomena with light illumination conditions that were correlated to the trapping and detrapping events from defect sites. By systematic investigation with optical analysis, we found that the pseudocubic phase of mixed halide perovskites generates light soaking phenomena. These results indicate that photoinduced changes are related to the existence of multiple phases or halide migrations.

Effect of Annealing Temperature on Film Morphology of Planar Heterojunction Mixed Halide Perovskite CH3NH3PbI3−xClx Solar Cells Based on Compact ZnO

Abstract A one-step deposition method was adopted to form the organic–inorganic mixed halide perovskite (CH3NH3PbI3−xClx) on compact ZnO in order to study the effect of annealing temperature on perovskite film morphology and photovoltaic performance of solar cells. In contrast to the reported results, the perovskite begins to decompose at a pretty low temperature of 70 °C. Through careful temperature modulation, we achieved a fairly high efficiency of 9.28%.