Fabrication Of Perovskite Films Research Articles

Anion-exchange assisted sequential deposition for stable and efficient FAPbI3-based perovskite solar cells

PbI2 as precursor has been extensively employed for the fabrication of organic–inorganic hybrid perovskite films for high-efficiency perovskite solar cells (PSCs) by using two-step solution deposition method. However, the resultant perovskite film suffers from the incomplete reaction of PbI2 and the volumetric expansion of the film, affecting both the performance and stability of the PSCs. Here, a single-crystal complex FA4Pb3I6Ac4 (Ac−: CH3COO−) is synthesized, and utilized to replace PbI2 for the fabrication of FAPbI3-based perovskite film in ambient conditions. The solution-processed crystal complex has good film-forming ability, and can be directly converted into stable black-phase FAPbI3 perovskite at room temperature through anion exchange reaction between Ac− and I− upon coating with iodide salt solution. By the strategy, a dense and uniform perovskite film is obtained with reduced trap-state density and prolonged charge lifetime. The champion device delivers a power conversion efficiency (PCE) of 23.65% with high reproductivity. Importantly, the unencapsulated device exhibits a dramatically improved operational stability under temperature and humidity conditions.

Intermolecular interaction assisted fabrication of Dion-Jacobson perovskite film with promoted photovoltaic property

Two dimensional (2D) perovskite solar cells have attracted lots of attentions due to the better stability than their three dimensional counterparts. The interaction between the spacer cations of the 2D perovskite has great impact on the quality of the film. While, as to 2D Dion-Jacobson (DJ) perovskites, few studies are reported on this topic. Herein, we choose 2,2′-disulfanediylbis(ethan-1-ammonium) (DSDEA) with SS unit as spacer cation to introduce intermolecular interaction, which promotes the crystallinity and oriented growth of the quasi-2D DJ perovskite film, and the charge transport. The device with structure of ITO/PEDOT:PSS/(DSDEA)MA4Pb5I16/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/bathocuproine (BCP)/Ag reaches a PCE of 14.12 %, much higher than 1,6-hexamethylenediamonium-based devices. The unsealed device retains about 87 % of its original PCE in the air atmosphere with humidity of 45 ± 5 % after 35 days’ storage.

Improving the efficiency and stability of in-air fabricated perovskite solar cells using the mixed antisolvent of methyl acetate and chloroform

Antisolvents play a significant role in obtaining high-quality perovskite films during the fabrication process. This paper reports a novel mixture of two antisolvents (methyl acetate and chloroform) that proves effective for fabricating high-quality perovskite films in a high humidity ambient. The results show that the use of methyl acetate alone as the antisolvent enables the fabrication of dense perovskite films (MAPbI 3 ) in a high humidity ambient, but with a rough surface, while mixing methyl acetate with an appropriate amount of chloroform produces not only dense perovskite films but also smooth surfaces. As a result, the power conversion efficiency (PCE) is increased from 17.1% of the devices treated with methyl acetate alone to 18.6% of the devices treated with the mixed antisolvent of methyl acetate (70%) and chloroform (30%). The stability of the devices was also improved significantly for the devices treated with the mixed antisolvent of methyl acetate (85%) and chloroform (15%), which exhibit a slow degradation of 7% in PCE after 552 h of storage, compared to 22% for the devices treated with methyl acetate alone. • Improving the stability of perovskite solar cell by the mixed antisolvent treatment. • Enabling fabrication of high-performance perovskite solar in a high humidity ambient. • Demonstrating the benefit of mixed antisolvent treatment in MAPbI 3 layer preparation.

Ammonia for post-healing of formamidinium-based Perovskite films

Solvents employed for perovskite film fabrication not only play important roles in dissolving the precursors but also participate in crystallization process. High boiling point aprotic solvents with O-donor ligands have been extensively studied, but the formation of a highly uniform halide perovskite film still requires the participation of additives or an additional step to accelerate the nucleation rate. The volatile aliphatic methylamine with both coordinating ligands and hydrogen protons as solvent or post-healing gas facilitates the process of methylamine-based perovskite films with high crystallinity, few defects, and easy large-scale fabrication as well. However, the attempt in formamidinium-containing perovskites is challenged heretofore. Here, we reveal that the degradation of formamidinium-containing perovskites in aliphatic amines environment results from the transimination reaction of formamidinium cation and aliphatic amines along with the formation of ammonia. Based on this mechanism, ammonia is selected as a post-healing gas for a highly uniform, compact formamidinium-based perovskite films. In particular, low temperature is proved to be crucial to enable formamidinium-based perovskite materials to absorb enough ammonia molecules and form a liquid intermediate state which is the key to eliminating voids in raw films. As a result, the champion perovskite solar cell based on ammonia post-healing achieves a power conversion efficiency of 23.21% with excellent reproducibility. Especially the module power conversion efficiency with 14 cm2 active area is over 20%. This ammonia post-healing treatment potentially makes it easier to upscale fabrication of highly efficient formamidinium-based devices.

Solvent-Induced Crystallization Method for High-Performance and Long-Term Stability Flexible Perovskite Photodetectors

Herein, we report a novel solvent-induced fabrication method to synthesize a perovskite thin film on flexible substrates. The high-quality CH3NH3PbI3 (MAPbI3) thin film is successfully fabricated, which is applied to prepare the stable flexible photodetector (PD). Compared with the reported results, this method achieved a low-temperature and low-cost perovskite thin film fabrication process on a flexible substrate. The constructed MAPbI3 layer possesses the advantages of being highly crystalline, uniform, and compact in a large area. The flexible PD based on the as-prepared perovskite thin film exhibits excellent performance and long-term stability. The EQE and R of the flexible PDs reached 8 × 102% and 3.6 A/W, respectively. At the same time, the flexible PDs still showed superior stability and high performance after 15 days of continuous working. The presented high-quality perovskite thin-film fabrication method and high-performance flexible perovskite PDs are expected for application in the development of novel optoelectronic devices.

Tailoring Phase Alignment and Interfaces via Polyelectrolyte Anchoring Enables Large-Area 2D Perovskite Solar Cells.

Ruddlesden-Popper phase 2D perovskite solar cells (PSCs) exhibit improved lifetime while still facing challenges such as phase alignment and up-scaling to module-level devices. Herein, polyelectrolytes are explored to tackle this issue. The contact between perovskite and hole-transport layer (HTL) is important for decreasing interfacial non-radiative recombination and scalable fabrication of uniform 2D perovskite films. Through exploring compatible butylamine cations, we first demonstrate poly(3-(4-carboxybutyl)thiophene-2,5-diyl)-butylamine (P3CT-BA) as an efficient HTL for 2D PSCs due to its great hydrophilicity, relatively high hole mobility and uniform surface. More importantly, the tailored P3CT-BA has an anchoring effect and acts as the buried passivator for 2D perovskites. Consequently, a best efficiency approaching 18 % was achieved and we further first report large-area (2×3 cm2 , 5×5 cm2 ) 2D perovskite minimodules with an impressive efficiency of 14.81 % and 11.13 %, respectively.

Tailoring Phase Alignment and Interfaces via Polyelectrolyte Anchoring Enables Large‐Area 2D Perovskite Solar Cells

AbstractRuddlesden–Popper phase 2D perovskite solar cells (PSCs) exhibit improved lifetime while still facing challenges such as phase alignment and up‐scaling to module‐level devices. Herein, polyelectrolytes are explored to tackle this issue. The contact between perovskite and hole‐transport layer (HTL) is important for decreasing interfacial non‐radiative recombination and scalable fabrication of uniform 2D perovskite films. Through exploring compatible butylamine cations, we first demonstrate poly(3‐(4‐carboxybutyl)thiophene‐2,5‐diyl)‐butylamine (P3CT‐BA) as an efficient HTL for 2D PSCs due to its great hydrophilicity, relatively high hole mobility and uniform surface. More importantly, the tailored P3CT‐BA has an anchoring effect and acts as the buried passivator for 2D perovskites. Consequently, a best efficiency approaching 18 % was achieved and we further first report large‐area (2×3 cm2, 5×5 cm2) 2D perovskite minimodules with an impressive efficiency of 14.81 % and 11.13 %, respectively.

Interface engineering utilizing bifunctional metformin for high performance inverted perovskite solar cells

Hydrophobic nature of hole transporting layers commonly employed in inverted perovskite solar cells (iPSCs), such as PTAA, hampers the fabrication of compact and high quality perovskite films above. Moreover, the defects at perovskite interface and grain boundaries directly deteriorate the power conversion efficiency (PCE) and stability of solar cells. Hence, the realization of high quality perovskites with reduced defects on hydrophobic substrate is critical but still challenging to further enhance the performance of iPSCs. It has been succeeded in this work through rational approach of interface engineering. Metformin, a preferred medicine for diabetes mellitus, is introduced as a bifunctional interfacial layer on PTAA surface. It is revealed that metformin can substantially improve the wettability of PTAA, and facilitate the fabrication of compact perovskite films. In addition, as a biguanidine molecule, it can effectively passivate the defects at the interface. Consequently, iPSCs with a dramatic PCE enhancement from 16.54% to 19.73% have been succeeded. Moreover, metformin can promote the device stability by maintaining the 90% of the initial PCE after a 600 h storage. • Metformin can substantially improve the wettability of PTAA, and facilitate the fabrication of compact perovskite films. • Metformin can effectively passivate the defects at the interface. • Metformin can enhance the PCE of iPSCs from 16.54% to 19.73%. • Metformin can promote the device stability by maintaining the 90% of the initial PCE after a 600 h storage.

A facile fabrication of lead-free Cs2NaBiI6 double perovskite films for memory device application

The environment-friendly Cs 2 NaBiI 6 double perovskite films have been fabricated using a one-step solution spin coating method in air. The X-ray diffraction analyzer, Ultraviolet-visible spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscopy were carried out to characterize the films. The films were used to prepare the memory devices with the structure of Al/Cs 2 NaBiI 6 /ITO. The current−voltage characteristics of the devices clearly showed a bipolar resistive switching behavior. The estimated activation energy (~0.11 eV) proves that the conduction mechanism is mainly derived from the migration of iodine vacancies. Moreover, the devices showed the memory performances with an endurance up to 200 cycles, a higher ON/OFF ratio of over 10 2 , a long retention time ~10 4 s, and outstanding reproducibility. Especially, the devices still keep excellent memory behaviors with the increase of measurement temperatures up to 403 K or after 90 days exposure in the air. The results indicate that the present double perovskite memory devices with a remarkable stability offer a great potential for future applications. • Lead-free Cs 2 NaBiI 6 double perovskite films were fabricated by a one-step solution spin coating method. • The memory devices show large ON/OFF ratios, good endurance and long retention time. • The devices maintain excellent memory behaviors after 90 days exposure in the air.

The strategies for widening processing windows for perovskite solar cells: a mini review on the role of solvent/antisolvent

ABSTRACT Perovskite solar cells are promising candidates for next-generation photovoltaic devices with certified power-conversion efficiency for single-junction perovskite-based devices exceeded 25%. However, it remains challenging to fabricate a large-area and dense perovskite film using solution-based deposition methods. This is due to perovskite wet films being highly sensitive and unstable, and thus having only a narrow processing window. There is therefore a demand for ways to expand the processing window in the fabrication of perovskite films. Herein, we systematically review research on the role of precursor solutions and antisolvents during the perovskite formation process, and reveal the fundamental factors governing the width of the perovskite film-processing window. Then, we give an overview of current strategies for enlarging the processing window, which includes solvent and antisolvent engineering strategies. We conclude by summarizing current challenges in the development of perovskite solar modules with a wide processing window and provide perspectives for future development.

Ion-exchange-induced slow crystallization of 2D-3D perovskite thick junctions for X-ray detection and imaging

<h2>Summary</h2> Metal-halide perovskites have recently emerged as promising candidates for next-generation X-ray detectors, mainly benefiting from their low-temperature solution processability, chemical versatility, low cost, and excellent and tunable optoelectronic properties. However, the fabrication of perovskite thick junctions is very challenging, particularly for solution-processed thick photodiodes. Here, we report an ion-exchange strategy to prepare two-dimensional (2D)-3D perovskite thick films for directly detecting X-rays. This approach provides a facile and generic fabrication of high-quality perovskite films with various perovskite precursors, achieving uniform morphology, tunable thickness, and vertically monolithic crystal phase. The dynamic processes of the ion exchange were fully characterized and studied with multiple <i>in situ</i> and <i>ex situ</i> techniques, e.g., photoluminescence spectroscopy and X-ray diffraction. After optimization, record-high X-ray sensitivity of 1.36 × 10⁴ μC Gy_air^-1 cm^-2 and ultra-low detection limit of 4.2 nGy_air s^-1 were achieved based on the optimized (BA₂PbBr₄)_0.5FAPbI₃ detectors, demonstrated along with 32 × 32 pixel prototypical photodetector arrays.

Revealing the vertical structure of in-situ fabricated perovskite nanocrystals films toward efficient pure red light-emitting diodes

The development of efficient perovskite light-emitting diodes (PeLEDs) relies strongly on the fabrication of perovskite films with rationally designed structures (grain size, composition, surface, etc.). Therefore, an understanding of structure-performance relationships is of vital importance for developing high-performance perovskite devices, particularly for devices with in-situ fabricated perovskite nanocrystal films. In this study, we reveal the vertical structure of an in-situ fabricated quasi-two-dimensional perovskite film. By combining time-of-flight secondary ion mass spectrometry, energy dispersive spectroscopy, grazing incidence wide-angle X-ray scattering (GIWAXS), and low-temperature photoluminescence spectra, we illustrate that the resulting in-situ fabricated DPPA2Csn-1Pbn(Br0.3I0.7)3n+1 (DPPA+: 3,3-diphenylpropylammonium) film has a gradient structure with a very thin layer of ligands on the surface, predominantly small-n domains at the top, and predominantly large-n domains at the bottom owing to the solubility difference of the precursors. In addition, GIWAXS measurements show that the domain of n = 2 on the top layer has an ordered in-plane alignment. Based on the understanding of the film structure, we developed an in-situ fabrication process with ligand exchange to achieve efficient pure red PeLEDs at 638 nm with an average external quantum efficiency (EQE) of 7.4%. The optimized device had a maximum luminance of 623 cd/m2 with a peak EQE of 9.7%.

Efficient Perovskite Light‐Emitting Diodes with a Siloxane‐Blended Organic Hole Transport Layer

Metal halide perovskite light‐emitting diodes (LEDs) are promising for future display applications because of their excellent advantages, such as high external quantum efficiency, emission color tunability, and high emission color purity. Although solution processing widely used for perovskite film fabrication is an additional advantage, there are cases in which fabricating a perovskite‐emitting layer with spin‐coating results in the dissolution of an underlying organic hole transport layer (HTL). As a result, since a perovskite layer comes into partial contact with an indium tin oxide (ITO) anode layer, excited states formed in a perovskite‐emitting layer are quenched by charge transfer to ITO. In this study, it is shown that adding tetraethyl orthosilicate (TEOS) into a HTL material of poly(N‐vinylcarbazole) (PVCz) is an effective method used to overcome this issue. Upon heating, the hydrolysis reaction of TEOS molecules takes place in PVCz films to form a siloxane network, which makes PVCz films insoluble and, therefore, alleviates the excited‐state quenching. It is demonstrated that using the siloxane‐blended PVCz HTL increases external quantum efficiencies of perovskite LEDs to 15.4 ± 0.3% from the original 10.4 ± 0.3% by about 1.5 times.

Ambient air processed highly oriented perovskite solar cells with efficiency exceeding 23% via amorphous intermediate

The preparation of perovskite solar cells (PSCs) in ambient air can effectively reduce the production cost and is more conducive to commercial production. However, ambient air fabrication of perovskite film always causes rough surface and nonuniform coverage which increase non-radiative recombination in PSCs. In this work, we adopted an amorphous intermediate strategy in lead iodide (PbI2) film to prepare the oriented perovskite film under ambient air condition. This amorphous intermediate formed by the interaction force between cesium iodide (CsI) and PbI2, which promotes perovskite phase inversion in perovskite precursor film and finally the perovskite grains grow perpendicular to the substrate in the ambient air. As a result, this ambient air processed-PSCs with the perovskite film passivated with butylammonium iodide (BAI) obtained a power conversion efficiency (PCE) of 23.46%, which is equivalent to that of two-step preparation in glovebox. Furthermore, the PSC maintains 85% of its initial efficiency under more than 1000 h of continuous illumination and processes a recoverable PCE at temperatures below 65 °C under photothermal cycling stress.

All-Inorganic Perovskite Solar Cells: Recent Advancements and Challenges.

Organic–inorganic metal-halide-based hybrid perovskite solar cells (SCs) have attracted a great deal of attention from researchers around the globe with their certified power conversion efficiencies (PCEs) having now increased to 25.2%. Nevertheless, organic–inorganic hybrid halide perovskite SCs suffer the serious drawback of instability with respect to moisture and heat. However, all-inorganic perovskite SCs have emerged as promising candidates to tackle the thermal instability problem. Since the introduction of all-inorganic perovskite materials to the field of perovskite photovoltaics in 2014, a plethora of research articles has been published focusing on this research topic. The PCE of all-inorganic PSCs has climbed to a record 18.4% and research is underway to enhance this. In this review, I survey the gradual progress of all-inorganic perovskites, their material design, the fabrication of high-quality perovskite films, energetics, major challenges and schemes opening new horizons toward commercialization. Furthermore, techniques to stabilize cubically phased low-bandgap inorganic perovskites are highlighted, as this is an indispensable requirement for stable and highly efficient SCs. In addition, I explain the various energy loss mechanisms at the interface and in the bulk of perovskite and charge-selective layers, and recap previously published reports on the curtailment of charge-carrier recombination losses.

A route towards the fabrication of large-scale and high-quality perovskite films for optoelectronic devices.

Halide perovskite materials have been extensively explored for their unique electrical, optical, magnetic, and catalytic properties. Most notably, solar cells based on perovskite thin films have improved their power conversion efficiency from 3.8% to over 25% during the last 12 years. However, it is still a challenge to develop a perovskite-based ink, suitable for upscaling the fabrication process of high-quality perovskite films with extreme purity, good crystallinity, and complete coverage over the deposition area. This is particularly important if the perovskite films are to be used for the scaled production of optoelectronic devices. Therefore, to make halide perovskites commercially available for various applications, it is vital to develop a reliable and highly robust deposition method, which can then be transferred to industry. Herein, the development of perovskite precursor inks suitable for use at low-temperature and vacuum-free solution-based deposition processes is reported. These inks can be further tailored according to the requirements of the deposition method, i.e., we propose their use with the industrially viable deposition technique called “slot-die coating”. Furthermore, a route for the preparation of low-cost and high-volume manufacturing of perovskite films on both rigid and flexible substrates is suggested in this paper. The presented approach is suitable for the fabrication of any functional layers of perovskites, that can be employed in various scaled applications, and it seeks the potential and the methodology for perovskite film deposition that is scalable to industrial standards.

Single-crystalline TiO2 nanoparticles for stable and efficient perovskite modules.

Despite the remarkable progress in power conversion efficiency of perovskite solar cells, going from individual small-size devices into large-area modules while preserving their commercial competitiveness compared with other thin-film solar cells remains a challenge. Major obstacles include reduction of both the resistive losses and intrinsic defects in the electron transport layers and the reliable fabrication of high-quality large-area perovskite films. Here we report a facile solvothermal method to synthesize single-crystalline TiO2 rhombohedral nanoparticles with exposed (001) facets. Owing to their low lattice mismatch and high affinity with the perovskite absorber, their high electron mobility and their lower density of defects, single-crystalline TiO2 nanoparticle-based small-size devices achieve an efficiency of 24.05% and a fill factor of 84.7%. The devices maintain about 90% of their initial performance after continuous operation for 1,400 h. We have fabricated large-area modules and obtained a certified efficiency of 22.72% with an active area of nearly 24 cm2, which represents the highest-efficiency modules with the lowest loss in efficiency when scaling up.

Additive Engineering in Antisolvent for Widening the Processing Window and Promoting Perovskite Seed Formation in Perovskite Solar Cells.

The chlorobenzene (CB) antisolvent is widely used to fabricate high-efficiency perovskite solar cells (PSCs). However, the narrow processing window and the strict volume ratio of a binary mixed solvent limit the fabrication of large-area and high-quality perovskite films. In this work, by systematic investigation of additives with the CB antisolvent, a universal guideline is achieved wherein a small amount of additive with a donor number between 9.0 and 27.0 kcal/mol can significantly widen the antisolvent treating time slot from 2 to 40 s while simultaneously enlarging the processor binary mixed solvent (dimethylformamide/dimethyl sulfoxide) from 7:3 to 0:10. Moreover, this process facilitates the formation of perovskite seeds as templates for perovskite crystal growth, effectively reducing the bulk defects in perovskite films. Finally, the obtained PSCs show remarkable power conversion efficiencies (PCEs) of 22.22 and 19.74% for rigid and flexible devices, respectively.

In Situ Growth Mechanism for High-Quality Hybrid Perovskite Single-Crystal Thin Films with High Area to Thickness Ratio: Looking for the Sweet Spot.

The development of in situ growth methods for the fabrication of high‐quality perovskite single‐crystal thin films (SCTFs) directly on hole‐transport layers (HTLs) to boost the performance of optoelectronic devices is critically important. However, the fabrication of large‐area high‐quality SCTFs with thin thickness still remains a significant challenge due to the elusive growth mechanism of this process. In this work, the influence of three key factors on in situ growth of high‐quality large‐size MAPbBr3 SCTFs on HTLs is investigated. An optimal “sweet spot” is determined: low interface energy between the precursor solution and substrate, a slow heating rate, and a moderate precursor solution concentration. As a result, the as‐obtained perovskite SCTFs with a thickness of 540 nm achieve a record area to thickness ratio of 1.94 × 104 mm, a record X‐ray diffraction peak full width at half maximum of 0.017°, and an ultralong carrier lifetime of 1552 ns. These characteristics enable the as‐obtained perovskite SCTFs to exhibit a record carrier mobility of 141 cm2 V−1 s−1 and good long‐term structural stability over 360 days.

All green solvent engineering of organic–inorganic hybrid perovskite layer for high-performance solar cells

Solvent engineering technology is an important approach for fabrication of high quality perovskite films, and thereby high-performance perovskite solar cells (PSCs). However, it is strongly dependent on the usage of toxic solvents, including the host solvent and anti-solvent to prepare perovskite solutions and control the crystallization of perovskite films, respectively. The usage of toxic solvents poses a serious threat to the health of manufactures and the safety of environment. Therefore, the solvent toxicity has become a burning issue before the forthcoming commercialization of PSCs. Here, we report an all green solvent engineering to prepare high quality (FAPbI3)1-x(MAPbBr3)x (x = 0, 0.05) films, where a green Lewis base solvent of triethyl phosphate (TEP) is used to prepare (FAPbI3)1-x(MAPbBr3)x/TEP solution, and a non-polar solvent of dibutyl ether (DEE) is used as anti-solvent. In this approach, a new intermediate phase film is formed after spin-coating the (FAPbI3)1-x(MAPbBr3)x/TEP solution on substrates, followed by dropping of DEE during spinning, and subsequently convert into perovskite films by annealing. Finally, it enables a PCE of 18.65% (x = 0) and 20.13% (x = 0.05) basing on a typical device configuration of FTO/SnO2/Perovskite/Spiro-OMeTAD/Au, which is the highest value for the all green solvent processed PSCs. More importantly, the all green solvent engineering approach can also be used to prepare another typical perovskite of MAPbI3 films for efficient solar cells. Therefore, this work not only provides an universial approach to prepare typical organic–inorganic hybrid perovskite films, but also addresses the solvent toxicity during the production of perovskite films. The green solvent engineering may pave the way for future industrial scale production of PSCs under environment friendly conditions.