Perovskite Precursor Films Research Articles

Studying the effect of ambient temperature variations on perovskite precursor film formation using different antisolvents

This study investigates the sensitivity of two antisolvents to ambient temperature fluctuations during the fabrication of triple-cation perovskite thin films. Chlorobenzene (CB) and ethyl acetate (EA) were employed as antisolvents in the preparation of perovskite solar cells (PSCs) under identical ambient temperature variation conditions. The experimental results reveal that the quality of the perovskite films does not exhibit a consistent trend in response to ambient temperature changes depending on the antisolvent used. When CB was used as the antisolvent, the highest-performing device, produced at an ambient temperature of 18 °C, achieved a power conversion efficiency (PCE) of 19.9 %. In contrast, when EA was employed as the antisolvent, the highest-performing device was fabricated at 25 °C, reaching a PCE of 20.5 %. Furthermore, when the ambient temperature exceeded 30 °C, all films prepared with either antisolvent exhibited significant cracking, indicating that elevated temperatures adversely affect perovskite film formation. To further investigate the mechanism through which ambient temperature affects the film-forming process, antisolvents at varying temperatures were used during perovskite film preparation to simulate transient temperature increases during formation. This study reveals that the impact of ambient temperature variations on perovskite film formation does not exhibit a uniform trend but is significantly influenced by the choice of antisolvent. Moreover, this work offers valuable insights for optimizing the fabrication of high-quality perovskite thin films.

Spiro-OMeTAD Anchoring perovskite for gradual homojunction in stable perovskite solar cells

The role of interface energetics-modification in interface-defect passivation and optimal interface energy-level matching is assumed to be a crucial aspect. Enhancing the performance and durability of perovskite solar cells (PSCs) can be achieved through this strategy. Here, spiro-OMeTAD [2,2′,7,7′-tetrakis (N, N-di-p-methoxyphenylamine)-9,9′-spirobifluorene] has been pipetted onto the spinning perovskite precursor film via a chlorobenzene anti-solvent strategy. It is found that spiro-OMeTAD serves as not only the filler at grain boundaries, but also the coverage on perovskite’s grain, and then forms the gradual homojunction interface from perovskite to spiro-OMeTAD hole transport layer, which can make spiro-OMeTAD anchor perovskite via the reaction between Pb2+ and C-O groups to decrease the interface barrier and obtain the optimal interface energy-level match between them for hole −migration and −collection. Moreover, these fillers or coverages can prevent moisture invading perovskite. Consequently, the counterpart PSC achieves a champion efficiency of 24.46 %, and has retained more than 88 % of the initial efficiency after 224 days of storage.

Scalable In‐Plane Directional Crystallization for The Printable Hole‐Conductor‐Free Perovskite Solar Cell Based on The Carbon Electrode

AbstractPopular solution‐processed approaches for producing the active layer of perovskite solar cells (PSCs) generally have to make compromise between crystallinity and compactness by inducing a rapid crystallization process with explosive nucleation and limited growth via removing solvent quickly. Here, a practical growth‐dominated in‐plane directional crystallization technique (IPDC) with a deeply retarded crystallization process for the scalable preparation of PSCs are reported. During the low‐temperature annealing, a tiny chamber with a small height is built atop the wet perovskite precursor film to restrain the vertical diffusion and removal of solvent vapor. The chamber eliminates the vertical solvent vapor gradient and induce a horizonal in‐plane gradient of solvent vapor pressure (SVP) toward the preset exhaust port which allows the slow escape of solvent vapor to outer space. In this way, nucleation is induced preferentially near the port and the as‐formed heterogeneous nuclei then grow continuously and directionally. With IPDC, sufficient filling of perovskite with high crystallinity and obvious growth orientation is realized in non‐ordered mesoporous scaffolds. An encouraging power conversion efficiency of 19.35% and 16.53% is achieved respectively for the 0.1 and 52.3‐cm2 printable mesoscopic hole‐conductor‐free PSCs with carbon electrodes.

Large-Area Perovskite Film Prepared by New FFASE Method for Stable Solar Modules Having High Efficiency under Both Outdoor and Indoor Light Harvesting.

High-quality perovskite film is deposited on a 30cm× 40cm LiCoO2 -coated ITO/glass via newly developed freely falling anti-solvent extraction (FFASE) method followed by post watervapor annealing in an ambient atmosphere. Perovskite solar modules (PSMs, active area of 25.2cm2 with mask) based on this high-quality film achieve the highest efficiency of 16.04 and 30.76% under 1sun (100mW cm-2 ) and 945 lux fluorescent light illumination, respectively. The encapsulated PSMs are stable at -20 to 80°C thermal cycling and keep high efficiency at temperature as low as -20°C and as high as 80°C. When the encapsulated PSM is heated at 85°C and 85% relative humidity under room lighting or heated at 60°C under AM1.5 (100mW cm-2 ) illumination for 1000h, loses only ≈8% of its original efficiency. The high stability of PSMs is due to very high quality perovskite absorber being used. The underlying concept of the FFASE method for extracting the solvent from the large-area perovskite precursor film is that the whole precursor film contacts with the fresh anti-solvent during the crystallization stage.

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.

Binary antisolvent bathing enabled highly efficient and uniform large-area perovskite solar cells

There is a high commercial demand for the scaled-up perovskite solar cells (PSCs) with excellent power-conversion efficiency. However, only a limited number of fabrication methods for the formation of large-area perovskite films with uniform morphology and high crystallinity have been reported. Herein, we propose a facile binary antisolvent bathing approach for triple-cation-based perovskite, which is highly compatible with large-area fabrication. The wet perovskite precursor films were submerged in a binary antisolvent bath comprising ethyl acetate and diethyl ether, resulting in crystallization retardation. The decelerated nucleation and growth induced enlarged perovskite crystals with highly preferential orientation alignment along the [100] direction, perpendicular to the substrate. The increased grain size and highly preferred crystal orientation not only benefit effective charge extraction but also suppress non-radiative recombination by reducing the defect density of the perovskite films. The photovoltaic performance was greatly improved from 17.30% (single antisolvent bath) to 19.38% (binary antisolvent bath). Furthermore, the binary antisolvent approach successfully tuned the vapor pressure of the binary antisolvent, facilitating rapid elimination of the residual antisolvent in the wet precursor film after bathing and enabling the fabrication of uniform large-area PSCs with high performance.

Study on the Ion Substitution Mechanism of CsPbIBr2 Films Prepared by a Drop-Coating Method

In this paper, the ion substitution mechanism of CsPbIBr2 films prepared by a drop-coating method is studied. CsI/CsBr methanol solution is drop-coated on a CsPbIBr2 precursor film to prepare the CsPbIBr2 perovskite film. After drop-coating, it is found that the color of the perovskite film changes with CsI/CsBr methanol solution drop-coated on the perovskite precursor film. When CsBr methanol solution is drop-coated on a CsPbIBr2 precursor film, the color of the obtained CsPbIBr2 film is orange. The color of the obtained CsPbIBr2 film is brown while CsI methanol solution is drop-coated on a CsPbIBr2 precursor film. Then, the hole-free, carbon-based CsPbIBr2 perovskite solar cells (FTO/ZnO/CsPbIBr2/C) are fabricated. For the solar cells fabricated by drop-coating with 30 μL of CsBr, without methanol solution, with 10 μL of CsI, with 50 μL of CsI, and with 90 μL of CsI, the power conversion efficiency (PCE) values are 2.98, 3.99, 6.04, 7.60, and 8.42%, respectively. The short-circuit current density (JSC) also increases with the changing of drop-coating solution. Therefore, we suppose that perhaps there is an ion substitution during the preparation of the CsPbIBr2 films. The ion substitution supposition is verified by the results of X-ray diffraction, ultraviolet–visible spectra, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy. Specifically, the I element is replaced by the Br element while drop-coating CsBr methanol solution. The Br element is substituted by the I element by drop-coating CsI methanol solution. Also, it is verified that the ion substitution occurs in the entire perovskite film.

Vitrification Transformation of Poly(Ethylene Oxide) Activating Interface Passivation for High‐Efficiency Perovskite Solar Cells

Interface engineering is critical for achieving high‐efficiency and high‐stability perovskite solar cells (PSCs). Herein, a new interface engineering approach—poly(ethylene oxide) (PEO) modification of SnO2 quantum dot (QD) film—to improve electron transport is introduced. It is found that when the PEO film is annealed over its glass‐transition temperature, the ether‐oxygen unshared electron pair in the PEO film activates to form a crosslinking complex with metal ions at the SnO2 QD and perovskite interface, which triggers heterogeneous nucleation over the perovskite precursor film and is beneficial for achieving uniform and dense perovskite films. PEO is also shown to passivate the bulk defects of perovskite films and the interface defects between SnO2 QD and perovskite, which promotes electron‐transferring from the perovskite layer to cathode. PSCs based on SnO2 QD with PEO treatment exhibit an enhanced efficiency, leading to a champion PCE of 20.23%, with good reproducibility and stability.

Adduct phases induced controlled crystallization for mixed-cation perovskite solar cells with efficiency over 21%

Organic-inorganic perovskite solar cells have attracted extensive attentions due to the advantages such as high power conversion efficiency and easy fabrication over other counterparts. Mixed-cation perovskite is considered as one of the most efficient light absorbers for perovskite solar cells and the device performance has a close connection to the quality of the perovskite thin film. Herein, we systematically investigate the influence of adduct phase in the mixed-cation perovskite precursor film on the crystallization of the perovskite. By tuning the adduct phase through solvent engineering, we successfully optimize the morphology and optoelectronic properties of the perovskite film and the planar-type perovskite solar cells with a power conversion efficiency over 21% can be achieved. Our work provides an effective method to control the growth of the mixed-cation perovskite film and thus boost the device performance with enhanced efficiency and stability.

Steering the crystallization of perovskites for high-performance solar cells in ambient air

We developed a “humidity-insensitive antisolvent method” for highly efficient PSCs by steering the crystallization of perovskite precursor films.

20% Efficient Perovskite Solar Cells with 2D Electron Transporting Layer

AbstractHerein, a 2D SnS2 electron transporting layer is reported via self‐assembly stacking deposition for highly efficient planar perovskite solar cells, achieving over 20% power conversion efficiency under AM 1.5 G 100 mW cm−2 light illumination. To the best of the authors' knowledge, this represents the highest efficiency that has so far been reported for perovskite solar cells using a 2D electron transporting layer. The large‐scaled 2D multilayer SnS2 sheet structure triggers a heterogeneous nucleation over the perovskite precursor film. The intermolecular Pb⋅⋅⋅S interactions between perovskite and SnS2 could passivate the interfacial trap states, which suppress charge recombination and thus facilitate electron extraction for balanced charge transport at interfaces between electron transporting layer/perovskite and hole transporting layer/perovskite. This work demonstrates that 2D materials have great potential for high‐performance perovskite solar cells.

Tetra‐ammonium Zinc Phthalocyanine to Construct a Graded 2D–3D Perovskite Interface for Efficient and Stable Solar Cells

Summary of main observation and conclusionThe crystallographic defects inevitably incur during the solution processed organic‐inorganic hybrid perovskite film, especially at surface and the grain boundaries (GBs) of perovskite film, which can further result in the reduced cell performance and stability of perovskite solar cells (PSCs). Here, a simple defect passivation method was employed by treating perovskite precursor film with a hydrophobic tetra‐ammonium zinc phthalocyanine (ZnPc). The results demonstrated that a 2D‐3D graded perovskite interface with a capping layer of 2D (ZnPc)0.5MAn − 1PbnI3n + 1 perovskite together with 3D MAPbI3 perovskite was successfully constructed on the top of 3D perovskite layer. This situation realized the efficient GBs passivation, thus reducing the defects in GBs. As expected, the corresponding PSCs with modified perovskite revealed an improved cell performance. The best efficiency reached 19.6%. Especially, the significantly enhanced long‐term stability of the responding PSCs against humidity and heating was remarkably achieved. Such a strategy in this work affords an efficient method to improve the stability of PSCs and thus probably brings the PSCs closer to practical commercialization.

Highly Efficient and Stable MAPbI₃ Perovskite Solar Cell Induced by Regulated Nucleation and Ostwald Recrystallization.

Perovskite solar cells have attracted great attention in recent years, due to their high conversion efficiency and solution-processable fabrication. However, most of the solar cells with high efficiency in the literature are prepared employing TiO2 as electron transport material, which needs sintering at a temperature higher than 450 °C, and is not applicable to flexible device and low-cost fabrication. Herein, the MAPbI3 perovskite solar cells are fabricated at a low temperature of 150 °C with SnO2 as the electron transport layer. By dropping the antisolvent of ethyl acetate onto the perovskite precursor films during the spin coating process, compact MAPbI3 films without pinholes are obtained. The addition of ethyl acetate is found to play an important role in regulating the nucleation, which subsequently improves the compactness of the film. The quality of MAPbI3 films are further improved significantly through Ostwald recrystallization by optimizing the thermal treatment. The crystallinity is enhanced, the grain size is enlarged, and the defect density is reduced. Accordingly, the prepared MAPbI3 perovskite solar cell exhibits a record-high conversion efficiency, outstanding reproducibility, and stability, owing to the reduced electron recombination. The average and best efficiency reaches 19.2% and 20.3%, respectively. The device without encapsulation maintains 94% of the original efficiency after storage in ambient air for 600 h.

Synergistic improvement of perovskite film quality for efficient solar cells via multiple chloride salt additives

Perovskite crystal film quality is critical for obtaining efficient perovskite solar cells. Anti-solvent processing was used for fast crystallization of perovskite precursor film, which can form dense perovskite film. However, the crystals from this method are usually small due to the fast crystal growth process, which could lead to grain boundary recombination. Here, element chloride is introduced to enhance the perovskite layer crystallinity via slowing down the perovskite crystallization process by simultaneous introduction of methylammounium chloride (MACl) and cesium chloride (CsCl) into precursor solution. As a result, we achieve high quality of pin-hole free perovskite film with large crystal size. A power conversion efficiency of 21.55% with free of hysteresis of the device is obtained, which is among the highest efficiency of planar structure perovskite solar cells.

High annealing temperature induced rapid grain coarsening for efficient perovskite solar cells

Thermal annealing plays multiple roles in fabricating high quality perovskite films. Generally, it might result in large perovskite grains by elevating annealing temperature, but might also lead to decomposition of perovskite. Here, we study the effects of annealing temperature on the coarsening of perovskite grains in a temperature range from 100 to 250 °C, and find that the coarsening rate of the perovskite grain increase significantly with the annealing temperature. Compared with the perovskite films annealed at 100 °C, high quality perovskite films with large columnar grains are obtained by annealing perovskite precursor films at 250 °C for only 10 s. As a result, the power conversion efficiency of best solar cell increased from 12.35% to 16.35% due to its low recombination rate and high efficient charge transportation in solar cells.

Stable and Efficient Organo-Metal Halide Hybrid Perovskite Solar Cells via π-Conjugated Lewis Base Polymer Induced Trap Passivation and Charge Extraction.

High-quality pinhole-free perovskite film with optimal crystalline morphology is critical for achieving high-efficiency and high-stability perovskite solar cells (PSCs). In this study, a p-type π-conjugated polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl) thiophen-2-yl)-benzo[1,2-b:4,5-b'] dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl) benzo[1',2'-c:4',5'-c'] dithiophene-4,8-dione))] (PBDB-T) is introduced into chlorobenzene to form a facile and effective template-agent during the anti-solvent process of perovskite film formation. The π-conjugated polymer PBDB-T is found to trigger a heterogeneous nucleation over the perovskite precursor film and passivate the trap states of the mixed perovskite film through the formation of Lewis adducts between lead and oxygen atom in PBDB-T. The p-type semiconducting and hydrophobic PBDB-T polymer fills in the perovskite grain boundaries to improve charge transfer for better conductivity and prevent moisture invasion into the perovskite active layers. Consequently, the PSCs with PBDB-T modified anti-solvent processing leads to a high-efficiency close to 20%, and the devices show excellent stability, retaining about 90% of the initial power conversion efficiency after 150 d storage in dry air.

Fabrication of Perovskite Films with Large Columnar Grains via Solvent-Mediated Ostwald Ripening for Efficient Inverted Perovskite Solar Cells

Generally, residual solvent is embedded in perovskite precursor films fabricated from the Lewis adduct method. Most of the research focus on the ligand function of the solvent in forming a solvate complex for fabricating high quality perovskite films. However, little attention has been paid to the latent function of the solvent in the perovskite precursor films during the annealing process due to its fast extravasation at high temperature. Here, we develop a sandwich configuration of substrate/perovskite precursor films/PC61BM to retard the extravasation of solvent during annealing. We find that the restrained solvent induces an obvious solvent-mediated dissolution–recrystallization process, leading to high quality perovskite films with large columnar grains. There is mass transportation from small grains to large grains in the dissolution–recrystallization process, which follows the Ostwald ripening model. Inverted planar solar cells are fabricated on the basis of this annealing method. The photovoltaic ...

(Invited) Controlling Solution Chemistry from Lab-Scale Spin Coating to Scalable Deposition for High-Performance Perovskite Solar Cells

Organic-Inorganic hybrid halide perovskites have recently emerged as a new class of light absorbers that have demonstrated a rapid progress and impressive efficiencies (>22%) for solar conversion applications. Despite the rapid progress demonstrated by these light absorbers, there is still a lack of understanding of some fundamental material/physical/chemical properties of these materials. There is also a significant processing gap between the lab-scale spin coating and scalable deposition methods toward future roll-to-roll manufacturing. The challenge results from the sensitivity of perovskite crystallization and film formation to the processing conditions, which depend strongly on the specific deposition method. In this presentation, I will present our recent studies toward a better understanding and control of perovskite nucleation, grain growth, and microstructure evolution using solution processing. The precursor chemistry and growth conditions are found to affect significantly the structural and electro-optical properties of perovskite thin films. We also find that the precursor ink chemistry (solvent, coordination chemistry) of perovskite is critical for scalable deposition; but this has largely been underexplored. We present a rational design of perovskite precursor film formation to achieve highly specular films using scalable deposition methods. Using these high quality perovskite films, we have achieved device efficiencies approaching the values obtained on small scale by spin coating. These findings make a significant advance towards commercialization of the perovskite photovoltaic technology. These results and others will be discussed.

Enhanced performance of perovskite solar cells by strengthening a self-embedded solvent annealing effect in perovskite precursor films

Smooth perovskite films with large grains are fabricated by strengthening the self-embedded solvent annealing effect in the perovskite precursor film via pre-depositing a protective layer.

Morphology Evolution of High Efficiency Perovskite Solar Cells via Vapor Induced Intermediate Phases.

Morphology is critical component to achieve high device performance hybrid perovskite solar cells. Here, we develop a vapor induced intermediate phase (VIP) strategy to manipulate the morphology of perovskite films. By exposing the perovskite precursor films to different saturated solvent vapor atmospheres, e.g., dimethylformamide and dimethylsufoxide, dramatic film morphological evolution occurs, associated with the formation of different intermediate phases. We observe that the crystallization kinetics is significantly altered due to the formation of these intermediate phases, yielding highly crystalline perovskite films with less defect states and high carrier lifetimes. The perovskite solar cells with the reconstructed films exhibits the highest power conversion efficiency (PCE) up to 19.2% under 1 sun AM 1.5G irradiance, which is among the highest planar heterojunction perovskite solar cells. Also, the perovskite solar cells with VIP processing shows less hysteresis behavior and a stabilized power output over 18%. Our work opens up a new direction for morphology control through intermediate phase formation, and paves the way toward further enhancing the device performances of perovskite solar cells.