Inorganic Perovskite Films Research Articles

Luminescence and Structural Characteristics of Lead Halide Perovskite Films Deposited In Situ by a Versatile Multisource Aerosol Assisted Chemical Vapor Deposition (AACVD) Method

AbstractMost solution‐based synthetic routes for perovskite film deposition take place under highly controlled atmospheres and cannot be easily escalated for mass production. Here, the control in situ over luminescent, morphological, and structural characteristics of hybrid and inorganic perovskite films deposited on top of hot glass substrates by multisource AACVD is reported. By simply adjusting the methylammonium chloride (MACl) to lead bromide (PbBr2) molar ratio in the N‐N dimethylformamide (DMF) precursor solution, a gradual transformation from orthorhombic PbBr2 to cubic MAPbBr2Cl hybrid perovskite films is observed, and the generation of highly luminescent MAPbBr3−xClx nanoparticulate domains in a PbBr2 matrix is easily achieved when a specific ratio is used. Additionally, the crystallization of the films is performed in situ modified by the implementation of an antisolvent stream source during deposition which in turn yields films with superior luminescence properties. Finally, an NIR emitting CsPbBr2Cl:Yb inorganic perovskite film is deposited to probe the versatility of the multisource AACVD system, by the simultaneous deposition of separated PbBr2/YbCl3·6H2O/DMF and CsCl/methanol solutions. The high degree of control on the final properties of the films indicates that AACVD could be a breakthrough for low‐cost, scalable, high‐throughput metal‐halide perovskite film deposition.

Growth and Degradation Kinetics of Organic–Inorganic Hybrid Perovskite Films Determined by In Situ Grazing‐Incidence X‐Ray Scattering Techniques

Organic-inorganic halide perovskite (OIHP) solar cells hold a great promise for commercial breakthrough since their power conversion efficiency has been pushed beyond the mark of 25%, making them capable of competing with traditional crystalline silicon solar cells. The key to achieve efficient and stable perovskite solar cells is inherently related to the film morphology. The understanding of the kinetic processes of film formation and degradation opens up possibilities to tailor the film morphology via the regulation of precursor and processing parameters. In situ grazing-incidence X-ray scattering (GIXS) techniques allow for tracking the morphology evolution of thin films at different length scales and with high temporal resolution. In this review, the selected examples for application of in situ grazing-incidence wide-angle X-ray scattering and grazing-incidence small-angle X-ray scattering techniques to the growth and stability of OIHPs are summarized after a brief introduction to both techniques, highlighting particularly the morphological evolution of perovskite films over time. Then the correlated mathematical models are reviewed to give a toolbox for analyzing the mechanisms of film formation and degradation. Thus, an overview on the in situ GIXS methods is linked to the research of OIHP kinetics.

PTB7 as additive in Anti-solvent to enhance perovskite film surface crystallinity for solar cells with efficiency over 21%

Low temperature solution-processed organic–inorganic hybrid perovskite films inevitably encounter defects especially on surface and at grain boundaries. Anti-solvent washing has been widely practiced in fabricating uniform and dense perovskite films, but unfortunately it could cause even more defects on surface. Herein, polymer PTB7 was introduced into anti-solvent as an additive to significantly enhance perovskite film surface crystallinity with fewer defects, as evidenced by depth sensitive grazing incidence X-ray diffraction. Such improvements could be attributed to the Lewis base coordination bonds formed between PTB7 and Pb atoms in the surface region which slow down crystallization dynamics for enhanced perovskite surface crystallinity and effectively passivate defects at the perovskite grain boundary and film surface. With PTB7 in anti-solvent, the fabricated perovskite solar cells (PSCs) achieved a champion power conversion efficiency (PCE) of 21.41% from that of 19.79% for the control devices without PTB7. In addition, the hydrophobic alkyl chains in PTB7 were shown to improve film surface hydrophobicity with enhanced environmental stability of both the fabricated films and PSCs. Thus, addition of PTB7 in anti-solvent is proven to effectively improve the performance and stability of PSCs which could be easily applied in the fabrication of PSCs and other perovskite-based optoelectronics.

Plasmon-induced trap filling at grain boundaries in perovskite solar cells

The deep-level traps induced by charged defects at the grain boundaries (GBs) of polycrystalline organic–inorganic halide perovskite (OIHP) films serve as major recombination centres, which limit the device performance. Herein, we incorporate specially designed poly(3-aminothiophenol)-coated gold (Au@PAT) nanoparticles into the perovskite absorber, in order to examine the influence of plasmonic resonance on carrier dynamics in perovskite solar cells. Local changes in the photophysical properties of the OIHP films reveal that plasmon excitation could fill trap sites at the GB region through photo-brightening, whereas transient absorption spectroscopy and density functional theory calculations correlate this photo-brightening of trap states with plasmon-induced interfacial processes. As a result, the device achieved the best efficiency of 22.0% with robust operational stability. Our work provides unambiguous evidence for plasmon-induced trap occupation in OIHP and reveals that plasmonic nanostructures may be one type of efficient additives to overcome the recombination losses in perovskite solar cells and thin-film solar cells in general.

High‐Stability Patterned CsPbIxBr3−x Thin Films with Tunable Crystal Size Prepared by Solid‐Phase Reaction

AbstractDownsides such as pollution, stability, and cost limit the further optoelectronic applications of cesium lead halide inorganic perovskite thin films, prepared using traditional liquid‐phase and vapor‐phase reactions. This study investigates the preparation of inorganic perovskite CsPbIxBr3−x (x = 0, 1, 2, 3) thin films based on a solid‐phase reaction. Two solid‐phase precursor thin films, with an appropriate thickness ratio, are deposited by pulsed laser deposition (PLD) and subsequently react under high temperature, without any by‐products or gas volatilization. Relying on lower structural destruction from solution evaporation, and a reduced intermolecular distance of PLD‐prepared solid‐phase precursors, the inorganic perovskite photodetectors based on a solid‐phase reaction demonstrate enhanced stability under ultrahigh humidity (90–95%). By altering the thickness of the two precursors, the crystal size of the inorganic perovskite thin films can be adjusted within the range from 40 to 150 nm. Reusable metallic masks can be applied on the PLD‐prepared precursors to prepare high‐precision inorganic perovskite arrays (9.6 µm). The results demonstrate the significance of a solid‐phase reaction method in the commercial application of inorganic perovskite optoelectronic devices.

Few-layer fluorine-functionalized graphene hole-selective contacts for efficient inverted perovskite solar cells

Charge-selective contacts can play a critical role in enhancing the efficiency of perovskite solar cells (PSCs). In this study, we employed fluorine-functionalized graphene (FGr) layers having finely tunable energy levels as hole transport layers (HTLs) to improve the power conversion efficiency (PCE) and stability of inverted PSCs. The non-wetting surface of the FGr enhanced the crystallinity of organic–inorganic perovskites films with large aspect ratios, relative to that of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS). Combining the high work function of the HTL interface with the enhanced crystallinity and limited grain boundary area dramatically decreased the charge recombination losses in organic–inorganic trihalide perovskite (OTP) films. Thus, when incorporating FGr HTLs in inverted PSCs, the best PCE reached 19.34%—the highest efficiency reported to date for any PSC featuring a functionalized graphene HTL. Furthermore, we used this HTL to prepare flexible PSCs and obtained a highest efficiency of 17.50%. Therefore, this highly applicable and facile interface strategy using functionalized graphene HTLs provides stable PSCs displaying high PCEs.

Enhancing the performance of CsPbIBr2 solar cells through zinc halides doping

B-site doping is an effective strategy to improve the performance of inorganic perovskite solar cells. Zinc halides (ZnX2, XI, Br, Cl) doped CsPbIBr2 solar cells were prepared by simply introducing ZnX2 salts into the precursor solution for one step spin-coating process. The doped inorganic perovskite films exhibit enhanced crystallinity and improved surface morphology. More over, the photoluminescence and single-carrier device characterizations confirm that the internal defect density of CsPbIBr2 films decreases remarkably after ZnX2 doping and the non-radiative recombination is suppressed. The CsPbIBr2 solar cells based on the ZnI2 doped films achieve a champion efficiency of 8.15%, outperforming that (6.93%) of the pristine counterpart.

Novel ytterbium-doped CsPbI2Br thin-films–based inorganic perovskite solar cells toward improved phase stability

In this study, we used ytterbium (Yb2+) as a dopant in the CsPbI2Br inorganic perovskite thin film and stabilized its black phase. Here, we varied the Yb2+ doping concentration in the CsPb1−xYbxI2Br (x = 0–0.04) perovskite phase through simple solution method. The optimum concentration of Yb2+ showed improved morphology and crystal growth. The fabricated all-inorganic perovskite solar cells (IPVSCs) having CsPb0.97Yb0.03I2Br-based champion device showed the highest 15.41% power conversion efficiency (PCE) for a small area of 0.09 cm2 and 14.04% PCE for a large area of 1 × 1 cm2 with excellent reproducibility, which is higher than the controlled CsPbI2Br device. Detailed photovoltaic analysis revealed that the PCE, open-circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF) of the final IPVSC device attributed to the suppressed charge recombination, better film quality, and well growth orientation of the perovskite film. Moreover, the champion CsPb0.97Yb0.03I2Br device retains >85% initial efficiency after 280 h under 85 °C thermal annealings. Our results provide a new method to boost the performance of the photovoltaic application.

Antisolvent engineering for mixed tin-lead inorganic perovskite solar cells

Recently, inorganic perovskite has been a research hotspot due to its thermal stability and promising photovoltaic performance. Here, we demonstrate the antisolvent engineering can assist the fabrication of the mixed tin-lead inorganic perovskite films. The treated devices exhibit enhanced stability in atmosphere air. The champion perovskite solar cells (PSCs) treated with anisole exhibits a power conversion efficiency of 9.3% with an open-circuit voltage over 0.8 V.

Over 23% power conversion efficiency of planar perovskite solar cells via bulk heterojunction design

The planar organic–inorganic hybrid perovskite solar cells (PSCs) have in recent years had remarkable success due to their superior optoelectronic performance. However, their power conversion efficiency is significantly inferior compared to mesoporous structure PSCs. Unlike most other advances focusing on non-perovskite materials to improve device performance, herein a multifunctional double perovskite material, Cs2PtI6, is proposed as the grain boundary modifier of organic–inorganic hybrid perovskite films. Results show three main benefits of introducing Cs2PtI6 into perovskite films: (1) it prompts growth of perovskite crystals, resulting in improved crystallinity and enlarged crystals; (2) it suppresses the trap assisted recombination at grain boundaries thanks to the formation of heterojunction and interface passivation; (3) it raises the efficiency of carrier collection and transport at grain boundaries owing to the high carrier mobility of Cs2PtI6. Consequently, a PCE of 23.56% is achieved. The unencapsulated devices show less than 10% degradation compared to the initial performance after storage in ambient (≈ 30%) humidity for 2000 h. This study outlines a simple yet effective strategy for boosting the performance of planar PSCs.

Laser fabricated carbon quantum dots in anti-solvent for highly efficient carbon-based perovskite solar cells

Additive passivation can be an effective strategy to regulate and control the properties of organic–inorganic halide perovskite film. In this article, carbon quantum dots (CQDs), fabricated by non-focused laser irradiation of carbon nanomaterial diluted in anti-solvent ethyl acetate, denoted as EACQDs, were adopted for perovskite film defect passivation and modification of carbon-based CH3NH3PbI3 perovskite solar cells (PSCs). The size of EACQDs can be tuned by manipulating the laser fluence. The morphology of perovskite film was uncovered through scanning electron microscopy and atomic force microscopy. After embedding of EACQDs, the defect in perovskite crystal was reduced, resulting in the decreased carrier recombination and accelerated carrier transportation, which were demonstrated by electrochemical impedance spectroscopy, photoluminescence and time-resolved photoluminescence. As a consequence, with the optimization of 0.01 mg/mL EACQDs (1064 nm–300 mJ·pulse−1·cm−2–10 min), the power conversion efficiency (PCE) of carbon-based PSCs achieved a maximum value of 16.43%, which improved 23.81% when compared with the pristine PSCs of 13.27%. Furthermore, the EACQDs optimized PSCs also exhibited an excellent stability and still retained 86% of its initial PCE after 50-day storage at the room atmosphere with a humidity of 30–50%.

Fully Inorganic CsSnI3 Mesoporous Perovskite Solar Cells with High Efficiency and Stability via Coadditive Engineering

The small optical bandgap of a CsSnI3‐based inorganic perovskite film makes it a hopeful candidate as an absorber layer in solar cell applications. Herein, a coadditive 2‐aminopyrazine (APZ) in the precursor solution to form SnF2−APZ complex with the aim to restrain Sn2+ oxidation and thus improve the CsSnI3‐based device performance is proposed. It is found that the amino group of APZ significantly suppresses oxidation of Sn2+ through a Lewis acid–base addition reaction. Consequently, the CsSnI3‐based mesoporous perovskite solar cells that use a printable c‐TiO2/m‐TiO2/Al2O3/NiO/carbon framework with high reproducibility achieve a power conversion efficiency of 5.12%. This is a champion efficiency for fully inorganic CsSnI3‐based mesoporous devices reported up to now. Furthermore, after 60 days of storage in a N2‐filled glovebox, the device still maintains an initial efficiency of 92%.

A bilateral cyano molecule serving as an effective additive enables high-efficiency and stable perovskite solar cells

The existence of defects in perovskite films is a major obstacle that prevents perovskite solar cells (PSCs) from high efficiency and long-term stability. A variety of additives have been introduced into perovskite films for reducing the number of defects. Lewis base-based additive engineering has been considered as an effective way to eliminate defects, especially the defects caused by the uncoordinated Pb2+. In this work, for the first time, a bilateral cyano molecule (succinonitrile, SN) which is a commonly used plasticizer in solid electrolyte of solid-state lithium batteries was selected as an additive to modify organic–inorganic hybrid perovskite films in PSCs. SN is featured with two cyano groups (–C≡N) distributing at both terminals of the carbon chain, providing two cross-linking points to interact with perovskites crystals via coordinating with uncoordinated Pb2+ and forming hydrogen bonds with –NH2 groups in perovskite. It was found that the addition of SN into perovskite precursor solution could effectively reduce defects, particularly inhibit the appearance of Pb0 and thus suppress trap-assisted nonradiative charge carrier recombination. As a result, the efficiency of CH3NH3PbI3(Cl) (MAPbI3(Cl))-based PSCs was improved from 18.4% to 20.3% with enhanced long-term stability at N2 and humid air atmosphere. This work provides a facile and effective strategy to enhance the PCE and stability of PSCs simultaneously, facilitating the commercialization of PSCs.

Tailored Design‐of‐Experiments Approach for Device Performance Prediction and Optimization of Flash‐Evaporated Organic–Inorganic Halide Perovskite‐Based Photodetectors

AbstractSingle‐source flash evaporation method has recently gained attention for its potential as a rapid and solvent‐free deposition method for producing organic–inorganic halide perovskite (OHP) films in large‐scale. However, due to a complex nature of the different experimental parameters involved in the deposition process, it is not straightforward to obtain the optimal condition for producing high‐quality OHP films. In this study, this problem is tackled by employing the design‐of‐experiment (DoE) process, which is an efficient statistical analysis for finding an optimized condition with a minimized number of experiments. The DoE process is used for optimizing the responsivity of the OHP photodetector devices against the input variables used in the deposition that yielded an enhanced responsivity of 112.2 mA W−1, which is up to an order of magnitude higher than that of the unoptimized devices. The experimental results using the DoE method provide not only the conditions required for enhancing the device performance but also the guidelines for improving the overall film quality through exploring the variable space of the flash evaporation technique.

Morphology controlled nanocrystalline CsPbBr3 thin-film for metal halide perovskite light emitting diodes

Morphology and crystal grain size of inorganic CsPbBr3 metal halide perovskite (MHP) films are controllable through a diffusion-controlled anti-solvent dripping crystallization method using an anti-solvent mixture of toluene (Tol):isopropanol (IPA). The 8:2 (v:v) Tol:IPA anti-solvent enables the production of a pinhole-free CsPbBr3 MHP film with the smallest crystal grain size and the brightest photoluminescence (PL). Accordingly, the 8:2 CsPbBr3 MHP film reveals a very uniform and strong PL mapping image. As a result, the 8:2 CsPbBr3 MHP light emitting diode (LED) exhibits ∼12.8, ∼7.4, and ∼7.9 fold enhanced maximum electroluminescence (ELmax), current efficiency (CEmax), and external quantum efficiency (EQEmax) compared to the 10:0 pristine device. The optimized 8:2 MHP LED shows an ELmax of 22,298cd/m2, CEmax of 36.65cd/A and EQEmax of 9.64%, respectively. In addition, the 8:2 CsPbBr3 MHP LED with controlled morphology and grain size has better operating stability than the pristine device.

Reducing defect of inorganic perovskite film by sulphur-containing Lewis base for robust photodetectors

Sluggish charge transfer in perovskite film induced by inherent defects such as uncoordinated Pb2+ undoubtedly hinders the rapid response of self-powered photovoltaic-typed detector. Based on interaction between Lewis acids and bases, herein, we employ thiourea molecule as a multifunctional Lewis base to significantly improve the quality of all-inorganic CsPbIBr2 perovskite film. After careful characterizations, the quality of perovskite film has been well regulated. Arising from the reduced defect and the reinforced the interfacial charge extraction owing to the strong interaction between uncoordinated Pb2+ ions and the -C = S groups in thiourea and the formation of hydrogen bond at perovskite/TiO2 interface, an enhanced responsivity of 0.335 A W−1 and specific detectivity of 3.92 × 1012 Jones has been achieved for the self-powered, carbon-electrode based photodetector, which is comparable to the state-of-the-art device based on CsPbIBr2 film. More importantly, the device free of encapsulation remains 82.8% of initial performance after storage over 56 days in ambient atmosphere, promoting the practical deployment of perovskite products.

Large-Area Nanocrystalline Caesium Lead Chloride Thin Films: A Focus on the Exciton Recombination Dynamics.

Caesium lead halide perovskites were recently demonstrated to be a relevant class of semiconductors for photonics and optoelectronics. Unlike CsPbBr3 and CsPbI3, the realization of high-quality thin films of CsPbCl3, particularly interesting for highly efficient white LEDs when coupled to converting phosphors, is still a very demanding task. In this work we report the first successful deposition of nanocrystalline CsPbCl3 thin films (70–150 nm) by radio frequency magnetron sputtering on large-area substrates. We present a detailed investigation of the optical properties by high resolution photoluminescence (PL) spectroscopy, resolved in time and space in the range 10–300 K, providing quantitative information concerning carriers and excitons recombination dynamics. The PL is characterized by a limited inhomogeneous broadening (~15 meV at 10 K) and its origin is discussed from detailed analysis with investigations at the micro-scale. The samples, obtained without any post-growth treatment, show a homogeneous PL emission in spectrum and intensity on large sample areas (several cm2). Temperature dependent and time-resolved PL spectra elucidate the role of carrier trapping in determining the PL quenching up to room temperature. Our results open the route for the realization of large-area inorganic halide perovskite films for photonic and optoelectronic devices.

Engineering inorganic lead halide perovskite deposition toward solar cells with efficiency approaching 20%

AbstractInorganic perovskite materials have gained tremendous attention due to their superior chemical and thermal stability than organic‐inorganic hybrid perovskites. In the past years, substantial research efforts have been devoted to developing uniform and pin‐hole free inorganic perovskite films with high electronic quality. As a result, power conversion efficiency of inorganic perovskite solar cells (PSCs) has boosted to over 19%, which presents a promising potential for technology commercialization. Herein, we give a comprehensive review of the recent progress on state‐of‐the‐art inorganic cesium lead halide based PSCs, particularly on the perovskite deposition approaches. We show a clear roadmap to fabricate high electronic quality inorganic perovskite films by tuning the precursor crystallization kinetics, performing post‐deposition treatments, and passivating surface/interface defects. Inorganic perovskite films prepared by these approaches exhibit not only high crystallinity, favorable morphology, and low trap densities but also improved phase stability. The advanced deposition approaches lay the foundation for further improving the performance and long‐term operational stability of inorganic perovskite photovoltaics.

Solvent engineering of lead-free bismuth-based perovskite material for potential application of solar cell

In the past few years, hybrid organic–inorganic perovskite materials have attracted great attention due to their impressive properties for solar cells applications. However, perovskite methylammonium lead halide is facing with toxicity issues that may hinder the wide range application of the lead halide-based hybrid perovskite solar cells. The sources of toxicity of these solar cells are the pollution from the B-site of lead ion and the toxic solvents used in the fabricating the devices. Thus, environmentally friendly materials and non-toxic solvents are highly desired for large-scale manufacturing of perovskite solar cells. In this work, the chemical and optical properties of lead-free bismuth based MA3Bi2I9 perovskite fabricated using different compositions of non-toxic solvents are investigated through solvent engineering method. Dimethyl sulfoxide (DMSO) /acetonitrile (ACN) /methyl-acetate (MA) solvents were employed as non-toxic solvent systems for the formation of homogeneous and good quality perovskite film. Hybrid organic–inorganic lead-free perovskite films were fabricated by mixing 1:1 M ratio compositions of CH3NH3I and BiI3 in different mixture of the solvents. The results show that the mixing solvent DMSO / ACN / MA at a volume ratio of 5:2:3 v / v, which incorporates the advantages of each solvent, has the best result among others. It is believed that by optimizing the solvent compositions, high performance lead-free bismuth-based perovskite film using non-toxic solvents could be obtained for potential solar cells application.

High-performance carbon- based CsPbIBr<sub>2</sub> perovskite solar cells fabricated by precursor film preparation process

All-inorganic perovskite has attracted extensive attention due to its photovoltaic properties and stability. Typically, the α-phase CsPbI<sub>3</sub> has an ideal bandgap of 1.73 eV suitable for the construction of high performance inorganic PSCs. But it suffers phase instability under ambient condition because of the unsatisfactory tolerance factor. By incorporating Br atoms into the perovskite structure, can greatly enhance the phase stability can be greatly enhanced. For example, CsPbBr<sub>3</sub> shows an excellent ambient stability and a wide bandgap of 2.3 eV that results in a limited light absorbtion. With the consideration from the unified perspective of the bandgap and the ambient phase stability, CsPbIBr<sub>2</sub> has a relatively appropriate bandgap (2.05 eV) and higher stability than CsPbI<sub>3</sub> and CsPbI<sub>2</sub>Br, which is made a good option for stable and efficient PSCs. However, there exist numerous defects on the CsPbIBr<sub>2</sub> film prepared by conventional one-step deposition method, which seriously affect the photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs). Considering the short dripping time and poor reproducibility of conventional anti-solvent technology, a precursor film preparation process is proposed to fabricate efficient and stable carbon-based CsPbIBr<sub>2</sub> perovskite solar cells. Using isopropyl alcohol (IPA) as the anti-solvent, the nucleation position of perovskite can be adjusted by regulating the evaporation rate of DMSO in the precursor film. In addition, guanidine thiocyanate (C<sub>2</sub>H<sub>4</sub>N<sub>4</sub>S) is added into IPA solution as a passivator to regulate the nucleation and crystallization process of perovskite. The carboxylic acid group of C<sub>2</sub>H<sub>4</sub>N<sub>4</sub>S can crosslink to Pb<sup>2+</sup> of CsPbIBr<sub>2</sub> via a chelating interaction, resulting in the easier decomposition of the CsI-DMSO-PbBr<sub>2</sub> intermediate phase in the spin-coating process of the precursor film. The amino group of C<sub>2</sub>H<sub>4</sub>N<sub>4</sub>S can also promote the crystallization and suppress the ion migration of the perovskite film through hydrogen bonds. The result shows that the compactness of the optimized CsPbIBr<sub>2</sub> film is significantly improved and the average grain size is about 800nm. The crystallinity and grain orientation are improved, and thus achieving better carrier separation and transport efficiency. The highest PCE of carbon-based CsPbIBr<sub>2</sub> PSC is obviously improved from 5.29% to 6.71%, i.e. increased by almost 21.16% compared with the control sample. Furthermore, the PSCs with precursor film preparation process possesses better long-term stability. The results obtained in this paper demonstrate that the new preparation technology can improve the quality of inorganic perovskite films in pure DMSO solvent system.