Sequential Deposition Method Research Articles

Real time nanoplasmonic sensing for monitoring CH3NH3PbI3 perovskite formation in mesoporous TiO2 films

The formation of methylammonium lead iodide (CH3NH3PbI3) perovskite into mesoporous titania (TiO2) scaffold via a sequential deposition method is known to offer high quality films for good photovoltaic device performance. The local kinetics at the lower interface between the mesoporous TiO2 film and the collecting electrode govern perovskite growth and formation. Here, we have used a NanoPlasmonic Sensing (NPS) approach with gold (Au) nanosensors to monitor the formation of CH3NH3PbI3 perovskite at the lower interface of up to 650 nm mesoporous TiO2 films. This technique provides time-resolved spectral shifts of the localized surface plasmon resonance at different operating temperatures and methylammonium iodide (CH3NH3I3) concentrations by recording changes in the local vicinity of the Au nanosensors at the mesoporous TiO2 film interface. Analytical studies included ellipsometry, scanning electron microscopy, X-ray diffraction, and photoluminescence spectroscopy. The results show that both the intensity of the NPS response and NPS rate constants are correlated with the operating concentrations and temperatures of CH3NH3I3 as well as CH3NH3PbI3 perovskite growth in mesoporous TiO2.

Enhanced electron transport induced by a ferroelectric field in efficient halide perovskite solar cells

Perovskite solar cells have been appearing as a superior photovoltaic device owing to their high photovoltaic performance and low cost of fabrication. The formation of a compact and uniform perovskite layer with large crystal size is a significant factor to get the best device performance. In this work, polyvinylidene difluoride (PVDF) was used as a ferroelectric polymer additive to fabricate high-performance mesoporous CH3NH3PbI3-xClx mixed-halide perovskite solar cells in a sequential deposition method. Power conversion efficiency has been enhanced from 10.4 to 16.51% in an ambient atmosphere in the presence of an optimized amount of PVDF assuring continuous and smooth layers with large grain size. Besides morphological improvements, this progress in the photovoltaic performance is attributed to the dipole field exerted by PVDF that leads to enhanced charge separation. Further improvements in efficiency (18.60%) have been achieved by directing the dipoles under an external field.

Halogen Engineering for Operationally Stable Perovskite Solar Cells via Sequential Deposition

AbstractThe performance of perovskite solar cells (PSCs) relies on the synthesis method and chemical composition of the perovskite materials. So far, PSCs that have adopted two‐step sequential deposited perovskite with the state‐of‐art composition (FAPbI3)1−x(MAPbBr3)x (x < 0.05) have achieved record power conversion efficiency (PCE), while their one‐step antisolvent dripping counterparts with typical composition Cs0.05FA0.81MA0.14Pb(I0.85Br0.15)3 with more bromine have exhibited much better long‐term operational stability. Thus, halogen engineering that aims to elevate bromine content in sequential deposited perovskite film would push operational stability of PSCs toward that of antisolvent dripping deposited perovskite materials. Here, a Br‐rich seeding growth method is devised and perovskite seed solution with high bromine content is introduced into a PbI2 precursor, leading to bromine incorporation in the resulting perovskite film. Photovoltaic devices fabricated by Br‐rich seeding growth method exhibit a PCE of 21.5%, similar to 21.6% for PSCs having lower bromine content. Whereas, the operational stability of PSCs with higher bromine content is significantly enhanced, with over 80% of initial PCE retained after 500 h tracking at maximum power point under 1‐sun illumination. This work highlights the vital importance of halogen composition for the operational stability of PSCs, and introduces an effective way to incorporate bromine into mixed‐cation‐halide perovskite film via sequential deposition method.

Sequential deposition method of TiO2/CH3NH3PbI3 films for solar cell application

Seeking to study innovative solar cell compositions with the goal to reach the highest energy efficiency level attainable, the aim of this study was to develop a route to obtain a solar cell composed by hybrid perovskite (CH3NH3PbI3) using a sequential deposition method through the techniques of spin-coating and immersion. Initially, the deposition of PbI2 thin film of was performed on a FTO/glass substrate coated with TiO2, which was subsequently converted into perovskite crystals through spin coating using a CH3NH3I solution. The influence of the PbI2 layer thickness on the formation of CH3NH3PbI3 crystals was evaluated. The hydrophilic characteristic of TiO2 affects the distribution of the crystals nucleation sites, since PbI2 possesses a non-polar liquid characteristic. The characterization of the perovskite thin films showed that thickness affects directly the bandgap and the surface morphology, revealing the presence of dendritic structures and acicular crystals. Both growth and coverage increased for thinner layers of PbI2. It was also possible to observe an increased uniformity in the film for smaller PbI2 layers.

Sequentially Deposited Compact and Pinhole-Free Perovskite Layers via Adjusting the Permittivity of the Conversion Solution

Abstract The preparation of compact and pinhole-free absorber layers is a major step towards device reproducibility and high performance for planar organic-inorganic perovskite solar cells. It is well known that the sequential deposition method exhibits some advantages over the common one-pot synthesis in terms of controlling the surface coverage. However, it still miscarries to produce pinhole-free layers from solution, mainly due to the occurrence of dissolution and recrystallisation processes. We show that by a careful choice of the permittivity of the alcoholic solvent in the conversion step the surface morphology can be finely modified, thereby yielding pinhole-free and compact absorber films comparable to that from vapour-assisted solution techniques. It is observed that the permittivity controls the intensity of the Ostwald ripening effect and that a low value of the former enables an in situ intercalation of precursor materials into the lead halide framework. We successfully prepared smooth and mirror-like perovskite surfaces that demonstrate enhanced optoelectronic properties and photovoltaic performance compared to films from the native two-step deposition in isopropanol. This strategy provides a facile approach for obtaining high-quality layers in the planar architecture by simple solution processing.

Спектральные и проводящие характеристики тонкопленочных структур на основе фуллерена

In the present paper we consider carbon films obtained by the method of sequential deposition from fullerene solutions in various types of solvents. Micrographs are presented to estimate the surface geometry of thin-film structures. So, using various solvents, it is possible to form various geometrical objects depending on the functional purpose of the films. At the same time, nanostructured objects can have the form of both bulk polygons (in our case, hexagons) and star-shaped branching structures. The IR spectra of the obtained samples were analyzed and their comparative characteristics were given for a volume of a precipitated solution of 0.15 ml and 1 ml. Depending on the type of initial solvent, both solvent peaks, fullerene, and complex organic impurities can be present in the fabricated samples. From the presence of solvent peaks, it is possible to make an assumption about the crystallization of solvates and their preservation in the film after drying. The conductive properties of thin-film structures are investigated. The use of five types of solvents made it possible to change linear resistances from hundreds to thousands of GOhms with a volume of 0.15 ml applied. An increase in the volume of the nanocrystalline fraction (1 ml of solution) made it possible to reduce the resistance to tens of GOhms It is worth noting that the mechanisms of the action of the active solvent environment on the morphology of the synthesized objects are not entirely clear, however, studies conducted to obtain nanostructures from fullerene solutions will be effective and, in our opinion, for controlled self-assembly of other functional organic systems.

Effects of Bromide-mixing in Methylammonium Lead Iodide on Photovoltaic Properties of ZnO-based Perovskite Solar Cells

To improve efficiency of ZnO-based perovskite solar cells, a mixture iodide-bromide (I-Br) of FA0.4MA0.6Pbl3-2xBr2x perovskite structure was prepared by two-step sequential deposition method and used as photo absorber layer. Solar cells with structure of ITO/ZnO/PCBM/perovskite/P3HT/Au were fabricated and characterized. The perovskite films were prepared by mixing precursor PbI2 and PbBr2 at various molar ratio. It was found that the grain sizes and crystallite sizes of perovskite crystal were comparable for different Br doping. The existence of Br ions in perovskite layer was confirmed. In addition, the increase in band gap energy was observed. The highest average power conversion efficiency (PCE) of 2.17% was achieved from the device with FA0.4MA0.6PbI2.8Br0.2 layer. This PCE value is higher than the FA0.4MA0.6PbI3 device which exhibited 1.53%-efficiency. The enhancement in PCE could be explained by the development of light absorption and charges transport.

Ultrasensitive electrochemical biosensor of interferon-gamma based on gold nanoclusters-graphene@zeolitic imidazolate framework-8 and layered-branched hybridization chain reaction

In this work, a novel electrochemical biosensor was constructed for ultrasensitive interferon-gamma (IFN-γ) detection based on graphene@zeolitic imidazolate framework-8 hybrids anchored gold nanoclusters (AuNCs-GR@ZIF-8) and hemin/G-quadruplex DNAzyme decorated layered-branched hybridization chain reaction (LB-HCR). The two-dimensional GR@ZIF-8 hybrids were utilized as template to anchor AuNCs through a sequential deposition method. On the AuNCs-GR@ZIF-8 platform, an improved and efficient LB-HCR pattern was designed on the strength of traditional HCR with the cascade-like assembly of four hairpins. In which, HP1 and HP2 participated in traditional HCR process to form long double-helix DNA, AD1 and AD2 assembled alternately to facilitate the layerly chain-branching growth of DNA nanostructures. The target-triggered LB-HCR resulted in the generation of dendritic DNA nanostructures integrated with numerous in-situ formed hemin/G quadruplex DNAzyme as amplifying labels, which catalyzed the reduction of H2O2 with thionine acted as the electron mediator to realize amplified signal output. This multiple-amplified strategy exhibited good analytical performance towards IFN-γ with a wide linear range form 1 fM to 50 pM and a low detection limit of 0.6 fM, holding promising application in disease diagnosis and monitoring.

Enhanced Crystallization and Optimized Morphology of Perovskites Through Doping an Indium‐Based Metal–Organic Assembly: Achieving Significant Solar Cell Efficiency Enhancements

Perovskite crystallization and morphology are two essential factors to the photoelectric performances of perovskite solar cells (PSCs). A 3D metal–organic assembly [In2(phen)3Cl6]·CH3CN·2H2O (In2) is introduced for the first time into lead iodide precursor to modify the quality of a perovskite thin film through a two‐step sequential deposition method. As a result, both the lead iodide and perovskite exhibit improved crystallization and modified morphology. The optimized film presents less trap states and is thus in favor of the charge transfer as well as charge collection. Consequently, open circuit voltage (Voc) and fill factor obviously show enhancements from 0.99 to 1.04 V and from 0.66 to 0.71, respectively, yielding a significant increase in a power conversion efficiency from 15.41% to 17.15%. Meanwhile, the hydrophobic property of In2 can increase the moisture resistance of the perovskite, which offers a simple and effective method to improve the stability of PSCs.

Moisture assisted CsPbBr3 film growth for high-efficiency, all-inorganic solar cells prepared by a multiple sequential vacuum deposition method

We developed a multiple sequential vacuum deposition method for the preparation of CsPbBr3 film with pure phase. Meanwhile, we found the annealing humidity plays an important role for the growth of CsPbBr3 crystal. By controlling the relative humidity at 30%, we obtained high-quality CsPbBr3 film with large grain size. As a result, a PCE of 8.86% has been achieved in the all-inorganic PSCs with a planar structure of FTO/compact TiO2/CsPbBr3/carbon.

Tailoring perovskite conversion and grain growth by in situ solvent assisted crystallization and compositional variation for highly efficient perovskite solar cells

Abstract The performance of perovskite solar cell devices is strongly dependent on the morphology, crystallinity, and phase purity of perovskite films. However, the complete conversion of PbI2 into perovskite and tailoring perovskite grain growth as well as its surface morphology are challenging in the conventional two-step sequential deposition method. In this study, a facile and effective approach was developed to improve perovskite conversion rate and film quality via in situ solvent assisted crystallization (ISAC) and compositional adjustment. It was found that in the presence of in situ solvent molecules, CH3NH3I (MAI) molecules readily intercalated in the PbI2 lattice to form small-grain (∼210 nm) MAPbI3 perovskite. By partially substituting MAI with a small amount of CH(NH2)2I (FAI), flat FAxMA1–xPbI3 films composed of much larger grains (∼450 nm) could be obtained due to the in situ formation and decomposition of (MA)2Pb3I8(DMSO)2 intermediates. Photovoltaic devices based on ISAC-FAxMA1–xPbI3 films exhibited an enhanced efficiency of 17.31% under AM 1.5G solar illumination at 100 mW cm−2 when compared to the devices based on ISAC-MAPbI3 films (14.30%), which can be mainly ascribed to the higher optical absorption and reduced defect density of the former. The results highlight the distinct effects of in situ solvent molecules on perovskite crystallization dynamics in various material systems and the importance of in situ solvent molecules in perovskite conversion, film morphology, and even device performance.

Direct Evidence of Ion-Migration-Induced Degradation of Ultrabright Perovskite Light-Emitting Diodes.

Low operational lifetime is a critical issue in perovskite light-emitting diodes. The forward-bias currents for light emission accelerate device degradation, which needs to be identified and understood to be able to improve the device stability. Here, we systematically analyze the degradation mechanism of perovskite light-emitting diodes (PeLEDs) fabricated with a sequential deposition method that produce a compact and pinhole-free perovskite film. The device exhibits an efficient green electroluminescence (peak wavelength at 533 nm and full width at half-maximum of 22 nm) with a maximum luminance of more than 67 000 cd/m2. The lifetime, however, is quite short; under the constant current bias for an initial luminance of 1000 cd/m2, the decay time to reach half of the initial luminance is approximately 13 min. Dark spots are created and enlarged as a result of perovskite film deterioration and ion migration. By investigating morphological changes in the perovskite films and the amount of ion accumulation under the Al electrode for the unoperated, T50 (luminance decay to 50% of the initial value), and T10 (luminance decay to 10% of the initial value) devices, we propose a degradation mechanism for PeLEDs. The ion migration from the perovskite layer experienced electrochemical interactions with the Al electrode, causing device degradation.

Physical Synthesis and Study of Ag@CaF2 Core@Shell Nanoparticles: Morphology and Tuning of Optical Properties

Pre‐formed Ag nanoparticles (NPs) and Ag@CaF2 core–shell NPs are physically synthesized using DC magnetron‐based NP source and deposited on Si‐SiOx wafers. The samples are prepared by co‐depositing Ag nanoparticles and CaF2 produced by an evaporation source, or by sequential deposition method, i.e., by depositing in a sequence a CaF2 buffer layer, the Ag NPs generated by the NP source and a capping CaF2 layer. The supported films are characterized by Scanning Electron Microscopy (SEM), X‐ray Photoelectron Spectroscopy (XPS), and Surface Differential Reflectivity (SDR). SEM shows that Ag NPs deposited directly on Si‐SiOx tend to diffuse and to agglomerate, affecting the size distribution of the nanostructures. The presence of a CaF2 buffer layer between Ag and Si‐SiOx limits this effect, while XPS reveals electrical charging, caused by the insulating nature of the CaF2 continuous film. The surface plasmon resonance behavior for different samples is analyzed using SDR with p‐polarized light. There is a clear evidence of a blue shift in the plasmon excitation due to the presence of CaF2 on Si, which can represent a potential advantage for the technological applications in photovoltaics and optoelectronics.

Flexible Photodetector Arrays Based on Patterned CH3 NH3 PbI3- x Clx Perovskite Film for Real-Time Photosensing and Imaging.

The quest for novel deformable image sensors with outstanding optoelectronic properties and large-scale integration becomes a great impetus to exploit more advanced flexible photodetector (PD) arrays. Here, 10 × 10 flexible PD arrays with a resolution of 63.5 dpi are demonstrated based on as-prepared perovskite arrays for photosensing and imaging. Large-scale growth controllable CH3 NH3 PbI3- x Clx arrays are synthesized on a poly(ethylene terephthalate) substrate by using a two-step sequential deposition method with the developed Al2 O3 -assisted hydrophilic-hydrophobic surface treatment process. The flexible PD arrays with high detectivity (9.4 × 1011 Jones), large on/off current ratio (up to 1.2 × 103 ), and broad spectral response exhibit excellent electrical stability under large bending angle (θ = 150°) and superior folding endurance after hundreds of bending cycles. In addition, the device can execute the functions of capturing a real-time light trajectory and detecting a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, digital display, and artificial electronic skin applications.

High‐Performance Large‐Area Organic Solar Cells Enabled by Sequential Bilayer Processing via Nonhalogenated Solvents

AbstractWhile the performance of laboratory‐scale organic solar cells (OSCs) continues to grow over 13%, the development of high‐efficiency large area OSCs still lags. One big challenge is that the formation of bulk heterojunction morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. The morphology control becomes much more challenging when the device area is scaled up. In this work, a highly efficient (12.9%) nonfullerene organic solar cell processed using a sequential bilayer deposition method from nonhalogenated solvents, is reported. Using this bilayer processing method, the organic solar cells can be scaled up to a larger area (1 cm2) while maintaining a high performance of 11.4% using doctor‐blade‐coating technique. Moreover, as the acceptor is hidden behind the polymer donor, the possibility of degradation by sunlight is lessened. Thus, improved photostability is observed in the bilayer structure device when compared with the bulk heterojunction device. This method offers a truly compatible processing technique for printing large‐area OSC modules.

Decoration of 3D ZnO nanoelectrodes with CuInS2 for solar water splitting

This study reports the decoration of zinc oxide (ZnO) nanosheets with copper indium sulfide (CuInS2) via sequential metal deposition and post sulfurization methods for photoelectrochemical solar cell application. The three dimensional (3D) ZnO nanosheets are hydrothermally grown on conductive glass substrates by chemical bath deposition. Then, copper/indium metallic alloy is deposited via magnetron sputtering and annealed at high temperature in the presence of elemental sulfur to form CuInS2 absorber on the surface of 3D nanosheets. Photoelectrochemical measurements indicate that the decoration of CuInS2 layer over the ZnO nanosheets results in significant increase in the photocurrent density to 28 mA cm−2 (at 0.5 V vs Ag/AgCl) leading a remarkable amount of hydrogen generation during solar water splitting process, 1387 μmol measured at 0 V vs Ag/AgCl under 1 sun-illumination for 4 h.

Fabrication of BiVO4/RGO/Ag3PO4 ternary composite photocatalysts with enhanced photocatalytic performance

A novel BiVO4/RGO/Ag3PO4 ternary composite photocatalyst was fabricated through a two-step method of solvothermal assisted in situ ion sequential deposition method. The morphological structure, composition and optical properties were characterized by SEM, XRD, FT-IR, XPS, PL and UV–vis. The photocatalytic activities were assessed by the photocatalytic degradation process of Rhodamine B (RhB) and 4-nitrophenol (4-NP), and its photocatalytic mechanism was analyzed by conducting active radicals trapping experiments. The as-obtained BiVO4/RGO/Ag3PO4 composite photocatalysts exhibited enhancement in photocatalytic activities compared with the pure BiVO4, Ag3PO4 and BiVO4/Ag3PO4 composite photocatalysts, which can degrade 98.2% of RhB and 82.1% of 4-NP in 45 min under the simulated sunlight irradiation when the mass ratio of Ag3PO4 to BiVO4/RGO composites was 0.6:1. The photo-generated holes (h+) and the superoxide radicals (O2−) radicals were the dominant active species during the photocatalytic degradation process. The enhancement in photocatalytic performance can be ascribed to the synergistic effect of BiVO4 and Ag3PO4, and the incorporation of reduced graphene oxide (RGO) which can promote the transfer and separation of photogenerated carriers at their interfaces.

The effect of solution process control on the formation of the α-FAPbI3 perovskite: FAPbI3 versus MAPbI3 solar cells

This study aims at the fabrication of hole-conductor-free perovskite solar cells by the sequential deposition method. To develop the cells, MAPbI3 (CH3NH3PbI3) and FAPbI3 (HC(NH2)2PbI3) perovskites were used as light-absorbing materials. It is difficult to achieve a black α-FAPbI3 perovskite due to the unwanted yellow δ-FAPbI3 phase that is usually first formed at a low temperature and then converted into a black α-FAPbI3 perovskite at a high annealing temperature. A high annealing temperature can also lead to the uncontrollable degradation of the α-FAPbI3 perovskite. Here, we report the effect of various temperatures of a dipping solution of formamidine iodide (FAI) in isopropanol on the formation of black α-FAPbI3 perovskites from the initial stage. The effects of various annealing temperatures on the surface morphology and the optical properties of the perovskite layer are also studied. The optimum temperatures of the FAI solution and annealing for making an FAPbI3 perovskite were 80 °C and 170 °C respectively. A stable black FAPbI3 perovskite layer was formed in these optimum conditions. Moreover, the short-circuit current density and the efficiency of the fabricated FAPbI3 and MAPbI3 perovskite solar cells were approximately the same.

Effects of the concentration of PbI2 and CH3NH3I on the perovskite films and the performance of perovskite solar cells based on ZnO-TiO2 nanorod arrays

To date the research of the effects of the concentration of PbI2 and CH3NH3I in the two-step sequential deposition process on the perovskite films and the performance of the perovskite solar cells (PSCs) based on nanorod arrays is rarely reported. In this paper, the perovskite films and the PSCs based on ZnO-TiO2 nanorod arrays were prepared by two-step sequential deposition method in ambient atmosphere. The effects of the concentration of PbI2 and CH3NH3I solution on the morphology, structure, optical absorption and luminescence properties of perovskite films and cell performance were systematically investigated by using field emission scanning electron microscope, X-ray diffractometer, UV–vis spectrophotometer, fluorophotometer, and photocurrent density-voltage (J-V) curves. The best power conversion efficiency (PCE) of perovskite solar cell reaches 10.38% by using PbI2 with a concentration of 1.0 M and CH3NH3I with a concentration of 0.063 M in ambient atmosphere with a relative humidity of about 40%. The PCE of the device may be further improved by optimizing the density and length of nanorod arrays and using glove box. These results provide valuable information for preparing more efficient all-solid-state PSC based on nanorod arrays.

Application of copper phthalocyanin for surface modification of perovskite solar cells

The photovoltaic performance of perovskite solar cells is promoted by addition of different amounts of copper phthalocyanine (CuPc) to the Methylammonium lead Iodide (CH3NH3PbI3)–CuPc composite. Solar cells using CH3NH3PbI3-0.05 wt% CuPc were fabricated by a sequential deposition method. Higher short-circuit current density and efficiency were achieved for the CH3NH3PbI3-0.05 wt% CuPc solar cells as compared to those of the reference perovskite solar cells. This suggests that increased light absorption and improvement in quality of perovskite active films is due to the application of CuPc that leads to a higher crystallinity of CH3NH3PbI3.