CsPbI2Br Film Research Articles

Surface Management for Carbon‐Based CsPbI2Br Perovskite Solar Cell with 14% Power Conversion Efficiency

Carbon‐based hole transport material (HTM)‐free CsPbI2Br perovskite solar cells (C‐PSCs) have garnered considerable attention due to their super thermal stability. The energy‐level mismatch between the CsPbI2Br perovskite and carbon electrodes, however, results in major energy loss and reduced power conversion efficiency (PCE) of C‐PSCs. Herein, 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF4) is used to manage the energy level, reduce defect densities, and improve the interface quality between CsPbI2Br and carbon electrodes. Preliminary results demonstrate that the BMIMBF4 modifier can passivate the surface defects of the perovskite film and reduce the energy‐level mismatch between the CsPbI2Br layer and the carbon electrode. A PCE of 14.03% is achieved by introducing BMIMBF4 which is improved by 23% compared with the control device (11.37%). Moreover, stability—whether in the case of C‐PSCs or CsPbI2Br films—is also improved.

Ambient Air Temperature Assisted Crystallization for Inorganic CsPbI2Br Perovskite Solar Cells.

Inorganic cesium lead halide perovskites, as alternative light absorbers for organic–inorganic hybrid perovskite solar cells, have attracted more and more attention due to their superb thermal stability for photovoltaic applications. However, the humid air instability of CsPbI2Br perovskite solar cells (PSCs) hinders their further development. The optoelectronic properties of CsPbI2Br films are closely related to the quality of films, so preparing high-quality perovskite films is crucial for fabricating high-performance PSCs. For the first time, we demonstrate that the regulation of ambient temperature of the dry air in the glovebox is able to control the growth of CsPbI2Br crystals and further optimize the morphology of CsPbI2Br film. Through controlling the ambient air temperature assisted crystallization, high-quality CsPbI2Br films are obtained, with advantages such as larger crystalline grains, negligible crystal boundaries, absence of pinholes, lower defect density, and faster carrier mobility. Accordingly, the PSCs based on as-prepared CsPbI2Br film achieve a power conversion efficiency of 15.5% (the maximum stabilized power output of 15.02%). Moreover, the optimized CsPbI2Br films show excellent robustness against moisture and oxygen and maintain the photovoltaic dark phase after 3 h aging in an air atmosphere at room temperature and 35% relative humidity (R.H.). In comparison, the pristine films are completely converted to the yellow phase in 1.5 h.

Improved Photovoltaic Performance of CsPbI2Br Perovskite Films via Bivalent Metal Chloride Doping

Cesium-based all-inorganic perovskite absorbers have attracted increasing attention due to their superior thermal stability, compared to their organic–inorganic counterparts. Up to now, it is a challenge to fabricate high-efficiency all-inorganic perovskite solar cells (PSCs) with low defect densities. Herein, we used bivalent metal chloride salts (SrCl2 and NiCl2) to optimize CsPbI2Br films. The experimental results indicate that this method could deliver high-quality films with improved electronic property. As a result, the champion device based on the 0.01 M SrCl2–doped CsPbI2Br film achieved a power conversion efficiency (PCE) of 16.07% with a high open voltage (VOC) of 1,322 mV, which is about 18% higher than that of the pristine device.

A Stable CsPbI2Br Perovskite Film Prepared in Air Atmosphere by Mesophase Transformation Strategy

A black phase CsPbI2Br film was prepared by mesophase transformation strategy in air atmosphere, and a methylamine acetate vapor-assisted annealing method was applied. The CsPbI2Br film exhibits a stable α phase in air atmosphere through the characterization of time-dependent photoluminescence. The process of methylamine acetate not only improves quality of CsPbI2Br film but also optimizes its phase stability. We demonstrate efficient solar cells based on CsPbI2Br film exhibiting 8.7% power conversion efficiency initial and 5.9% after 7 days in air atmosphere.

Fully-inorganic strontium incorporated CsPbI2Br perovskite solar cells with promoted efficiency and stability

In the present investigation, we fabricated strontium (Sr2+) incorporated CsPbI2Br-based inorganic perovskite solar cells in ambient conditions. The morphology, crystallinity, absorption, elemental composition and photoluminescence analysis of the bare CsPbI2Br and CsPb1-xSrxI2Br perovskite thin films were studied systematically to investigate the role of Sr2+ incorporation. It is observed that the surface morphology of the CsPbI2Br perovskite thin film has been improved by partial substitution of Pb2+ by Sr2+ which facilitates photoactive black phase-stabilization and defect passivation. The champion device having CsPb0.98Sr0.02I2Br composition exhibited a power conversion efficiency (PCE) of 16.61% which is much higher than the bare device (13.65%). Furthermore, our CsPb0.98Sr0.02I2Br-based devices maintain > 85% of its initial efficiency over 100 h in ambient conditions.

Dual Passivation Strategy for High Efficiency Inorganic CsPbI2Br Solar Cells

Inorganic metal halide perovskite solar cells have achieved incredible progress in recent years. However, the power conversion efficiency of the inorganic perovskite solar cells is still low compared with their hybrid counterparts due to the inescapable nonradiative losses from the charge recombination. Herein, a strategy is demonstrated to minimize the nonradiative recombination loss in CsPbI2Br solar cells by establishing a synergetic passivation from the mutual effect of alkali‐ and alkylammonium‐salt. Accordingly, a sequential passivation process employing KBr and phenethylammonium chloride overcomes their limited passivation effect in one single step. This dual passivation is beneficial to an improved CsPbI2Br film with reduced trap defects, enlarged grain size, as well as to form an ultrathin low‐dimensional perovskite surface layer. As a result, a very high power conversion efficiency of 16.9% is obtained for inorganic CsPbI2Br solar cells. The proposed dual passivation scheme provides a feasible route not only for the design of high‐efficiency perovskite solar cells but also for other perovskite‐related optoelectronic devices.

High-Efficiency (>14%) and Air-Stable Carbon-Based, All-Inorganic CsPbI2Br Perovskite Solar Cells through a Top-Seeded Growth Strategy

The inferior crystallinity and phase stability of CsPbI2Br films have severely hindered the development of carbon-based, all-inorganic perovskite solar cells (PSCs). Herein, we demonstrate the prep...

PMMA passivated CsPbI2Br perovskite film for highly efficient and stable solar cells

Cesium-based inorganic perovskite solar cells (PSCs), especially for the CsPbI2Br-based solar cells, have attained extensive attention due to its excellent thermal and phase stability. Solution-prepared CsPbI2Br films usually have some defects which demand to be passivated for PSCs and also their degradations often happen at the grain boundaries (GBs). Herein, by using polymethylmethacrylate (PMMA) solution, we optimize the perovskite film growth and further investigate the effect of PMMA treatment on the properties of the CsPbI2Br films. Time-resolved photoluminescence (TRPL) displays that the PMMA coating can improve the photoluminescence lifetime of CsPbI2Br perovskite films. Therefore, it is proved that PMMA coating film can effectively passivate the defects of the pure CsPbI2Br films, suppress the charge recombination with increased electron extraction efficiency, which improves the performance of solar cells. Consequently, the devices based on CsPbI2Br films with PMMA solution treatment exhibit average power conversion efficiency (PCE) over 11.18%, which is much higher than the efficiency of 9.69% for pure CsPbI2Br-based solar cells.

An aerosol-liquid-solid process for the general synthesis of halide perovskite thick films for direct-conversion X-ray detectors

Summary Medical X-ray computed tomography requires imaging at a low dose rate and in a large area. Halide perovskites have shown high potential for X-ray detection, but a pressing challenge is the current lack of low-cost methods for large-scale fabrication of high-quality thick perovskite films. Here we demonstrate and elucidate an aerosol-liquid-solid process to enable continuous growth of uniform halide perovskite films at low temperature over a large area of 100 cm2, which are vertically monolithic, and thus beneficial to carrier transport. Direct-conversion X-ray detectors based on the representative CsPbI2Br films in conjunction with a deliberated, interface-engineered C-electrode have realized an unprecedented sensitivity (≥1.48 × 105 μC Gyair−1 cm−2) and a low limit of detection (280 nGyair s−1). We have further demonstrated the high-resolution radiographic imaging capability of these films. These results lay the groundwork for large-scale application of halide perovskites in radiation detectors.

Surface modification with ionic liquid for efficient CsPbI2Br perovskite solar cells

The presence of numerous trap states on the perovskite surface severely affects the performance of inorganic CsPbI2Br perovskite solar cells. Surface modification has been proven to be an effective strategy to passivate the surface trap states of CsPbI2Br perovskite. However, most modifiers behave high volatility and insulation, not enough to further develop the CsPbI2Br solar cells. Herein, an ionic liquid of 1-viny-3-propionate ethyl imidazolium chloride ([PEVIM]Cl) is applied to modify the CsPbI2Br film surface, yielding a compact film with enhanced crystallinity. The surface trap states of CsPbI2Br film are effectively passivated via the interaction between carbonyl group of [PEVIM]Cl and uncoordinated metal cations of CsPbI2Br perovskite, leading to charge recombination suppression and charge transport enhancement. Consequently, the power conversion efficiency (PCE) of [PEVIM]Cl modified CsPbI2Br device is obviously enhanced from 12.49% to 14.19% with an improved open-circuit voltage of 1.160 V. Moreover, the non-encapsulated device presents excellent thermal stability, still maintaining 91% PCE when heated at 85 °C in nitrogen atmosphere for 360 h. Meanwhile, the non-encapsulated device degrades only 11% PCE after stored at 50% relative humidity for 960 h. This simple and efficient approach provides a promising direction to fabricate high-efficiency and stable inorganic perovskite devices.

Intermediate-Adduct-Assisted Growth of Stable CsPbI2 Br Inorganic Perovskite Films for High-Efficiency Semitransparent Solar Cells.

Thanks to the tunable bandgap and excellent photoelectric characteristics, perovskites have been widely used in semitransparent solar cells (ST-SCs). Most works present unsatisfactory power conversion efficiencies (PCEs) through reducing the thickness of the perovskite films because there is a trade-off between PCE and average visible transmittance (AVT). As a consequence, most PCEs are less than 12% when the AVT is higher than 20% due to the limited voltage (Voc ) and short-circuit current (Jsc ). Herein, a strategy of intermediate adduct (IMAT) engineering is developed to improve the film quality of the inorganic perovskite CsPbI2 Br, which is a challenging issue to limit its performance of efficiency and stability. A normal n-i-p-structured PSC based on the optimal CsPbI2 Br film delivers a PCE of 16.02% with excellent stability. Furthermore, through optimizing the electrode type and interface, the ST-PSC shows a high Voc larger than 1.2V and the PCE reaches 14.01% and 10.36% under an AVT of 31.7% and 40.9%, respectively. This is the first demonstration of a CsPbI2 Br ST-PSC, and it outperforms most of other types of perovskites.

Implementing Dopant-Free Hole-Transporting Layers and Metal-Incorporated CsPbI2Br for Stable All-Inorganic Perovskite Solar Cells.

Mixed-halide CsPbI2Br perovskite is promising for efficient and thermally stable all-inorganic solar cells; however, the use of conventional antisolvent methods and additives-based hole-transporting layers (HTLs) currently hampers progress. Here, we have employed hot-air-assisted perovskite deposition in ambient condition to obtain high-quality photoactive CsPbI2Br perovskite films and have extended stable device operation using metal cation doping and dopant-free hole-transporting materials. Density functional theory calculations are used to study the structural and optoelectronic properties of the CsPbI2Br perovskite when it is doped with metal cations Eu2+ and In3+. We experimentally incorporated Eu2+ and In3+ metal ions into CsPbI2Br films and applied dopant-free copper(I) thiocyanate (CuSCN) and poly(3-hexylthiophene) (P3HT)-based materials as low-cost hole transporting layers, leading to record-high power conversion efficiencies of 15.27% and 15.69%, respectively, and a retention of >95% of the initial efficiency over 1600 h at 85 °C thermal stress.

An efficient post-treatment strategy with acetylacetone for low temperature CsPbI2Br solar cells

All inorganic perovskite solar cells (PSCs) have been demonstrated to get tremendous interest recently owing to their better thermal stability. Nevertheless, some CsPbI2Br films prepared at low temperature have lower quality compared to those annealing at high temperature. Herein, to obtain high performance PSCs, a simple post-treatment strategy is presented by spin coating acetylacetone (AA) solution on the CsPbI2Br films. The AA treatment can reduce the density traps on the CsPbI2Br films surface and enlarge the size of grains, resulting in enhanced performance PSCs. After optimizing surface treatment, the devices based on low-temperature-processed CsPbI2Br with AA treatment achieved a power conversion efficiency (PCE) of 14.43%. The better CsPbI2Br films quality and interface contact of hole transport layer (HTL)/CsPbI2Br result in better device stability. Therefore, it could be a promising post treatment method for enhancing the performance of PSCs by introducing AA on the perovskite surface.

Generic Water-Based Spray-Assisted Growth for Scalable, High-Efficiency Carbon-Electrode, All-Inorganic Perovskite Solar Cells

A water-based spray-assisted growth strategy is proposed for the first time to prepare large-area all-inorganic perovskite films for perovskite solar cells (PSCs), which involves the direct spraying of cesium halide water solution onto lead halide films under ambient air, followed by thermal annealing. With CsPbBr3 as an example, we show that the proposed growth strategy yields the films with uniform surface, full coverage, pure phase, large grains, and high crystallinity, which primarily benefit from the controllable CsBr loading quantity and the use of water as the CsBr solvent makes the reaction between CsBr and PbBr2 immune to the underlying PbBr2 film microstructure. As a result, the small-area (0.09 cm2) and large-area (1.00 cm2) carbon-electrode CsPbBr3 PSCs without any interface modification yield record-high power conversion efficiencies (PCEs) of 10.22% and 8.21%, coupled with excellent operational stability in ambient air. We also illustrate that the water-based spray-assisted deposition strategy is suitable to prepare CsPbCl3, CsPbIBr2, and CsPbI2Br films with outstanding PCEs of 1.27%, 10.44%, and 13.30% for carbon-electrode, all-inorganic PSCs.

Effect of doping on the phase stability and photophysical properties of CsPbI2Br perovskite thin films.

In this study, we demonstrate that the crystallization process of CsPbI2Br films can be modulated when small amounts of additives are added to the precursor solution, leading to the formation of the bright brownish α-phase perovskite films with high orientation along the [100] crystallographic direction. Doped CsPbI2Br films exhibit improved crystallinity, with high coverage, large grain size and pinhole-free surface morphology, suitable for making high performance optoelectronic devices. We also explored the role of Cl in the photophysical properties of CsPbI2Br perovskite films using the temperature dependent photoluminescence technique. We found that the Cl ions enhance the photoluminescence emission by reducing the density of trap states, and also decrease the exciton binding energy from (22 ± 3) meV to (11 ± 2) meV. We believe this work contributes to understanding the effect of doping on the crystallization process with an in-depth insight into the photophysical properties of the cesium-based perovskite materials.

An Aerosol-Liquid-Solid Process for the General Synthesis of Halide Perovskite Thick Films for Direct Conversion X-Ray Detectors

Medical X-ray computed tomography requires fast imaging at a low dose rate and in a large area. Halide perovskites have shown high potential for X-ray detection, but a pressing challenge is the current lack of low-cost methods for large-scale fabrication of high-quality thick perovskite films. Here we demonstrate and elucidate an aerosol-liquid-solid process to enable continuous growth of uniform halide perovskites films at low temperature over a large area of 100 cm2, which are vertically monolithic and monocrystalline, and thus beneficial to carrier transport. Direct conversion X-ray detectors based on the representative CsPbI2Br films in conjunction with a deliberated, interface-engineered C-electrode have realized an unprecedented sensitivity (≥1.48×105 μC Gyair−1cm−2). We have further demonstrated the high-resolution radiographic imaging capability of these films. These results lay the groundwork for large scale application of halide perovskites in radiation detectors.

Polymer-modified CsPbI2Br films for all-inorganic planar perovskite solar cells with improved performance

All-inorganic CsPbI2Br perovskite with relatively high phase stability and a suitable band gap has been considered as a promising candidate for photovoltaic application. However, in comparison with its organic–inorganic counterparts, it still shows unsatisfactory efficiency and high moisture sensitivity. Here, polyethylene glycol (PEG) is introduced into the CsPbI2Br precursor solution. It is revealed that Lewis base PEG interacts with Pb2+, which can slow down the crystallization rate, regulate the energy levels, and passivate the defect density of CsPbI2Br films. As a result, the optimized devices with PEG exhibit a power conversion efficiency (PCE) of 13.59% under one sun illumination (100 mW cm‒2), which is considerably higher than that of the control devices (10.09%), owing to the reduced nonradiative recombination losses for the former CsPbI2Br films. The results demonstrate that using polymer additives to improve the device performance is an effective strategy for all-inorganic perovskite solar cells.

Unraveling the Impact of Halide Mixing on Crystallization and Phase Evolution in CsPbX3 Perovskite Solar Cells

Summary All-inorganic perovskite solar cells (PSCs) have attracted wide attention for their excellent thermal stability. However, the detailed crystallization process and complicated phase-transition mechanism of the CsPbX3 film with different halide compositions (I, Br, Cl) remain mysterious. In this study, systematic investigations are performed via state-of-art in situ grazing-incidence wide-angle X-ray scattering to understand the role of the halide elements in all-inorganic perovskite crystallization kinetics, phase-transition, and stabilization mechanism as well as how film morphology and grain size are affected. Based on these results, we were able to fabricate high-performance ternary halide (I, Br, Cl) all-inorganic PSCs through a precise compositional engineering. Our results provide guidance for an in-depth understanding of all-inorganic perovskite materials and pave the way to obtain high-performance all-inorganic PSCs.

Lead iodide and cesium lead halide perovskite highly oriented films deposited by spin coating

Spin-coated films are usually polycrystalline or amorphous, while some special materials such as lead iodide (PbI2) and inorganic perovskite could be deposited onto a variety of single-crystal substrates by spin coating obtaining highly oriented films. Herein, we report an effective method for depositing highly textured PbI2 and CsPbI2Br films—via spin coating. An unexpected high-quality PbI2 film with uniform out-plane orientation of the {001} plane was deposited on the gallium nitride substrate, which was benefited from heterogeneous nucleation measured by high-resolution x-ray diffraction (XRD) and Raman mapping. Furthermore, the α-phase CsPbI2Br highly oriented film was deposited on single-crystal (100) silicon with only the (200) plane for the first time. Compressive stress was found both in PbI2 film and in CsPbI2Br film via XRD, Raman spectra, and photoluminescence spectroscopy. Density functional theory calculations were performed to confirm that CsPbI2Br had a tetragonal structure rather than an orthogonal structure.

Organic Ligands Armored ZnO Enhances Efficiency and Stability of CsPbI2Br Perovskite Solar Cells.

Inorganic perovskite solar cells (PSCs) have witnessed great progress in recent years due to their superior thermal stability. As a representative, CsPbI2Br is attracting considerable attention as it can balance the high efficiency of CsPbI3 and the stability of CsPbBr3. However, most research employs doped charge transport materials or applies bilayer transport layers to obtain decent performance, which vastly complicates the fabrication process and scarcely satisfies the commercial production requirement. In this work, all‐layer‐doping‐free inorganic CsPbI2Br PSCs using organic ligands armored ZnO as the electron transport materials achieve an encouraging performance of 16.84%, which is one of the highest efficiencies among published works. Meanwhile, both the ZnO‐based CsPbI2Br film and device show superior photostability under continuous white light‐emitting diode illumination and improved thermal stability under 85 °C. The remarkable enhanced performance arises from the favorable organic ligands (acetate ions) residue in the ZnO film, which not only can conduce to maintain high crystallinity of perovskite, but also passivate traps at the interface through cesium/acetate interactions, thus suppressing the photo‐ and thermal‐ induced perovskite degradation.