Sequential Evaporation Research Articles

Additive-Free Sequential Thermal Evaporation of Near-Intrinsic Pb-Sn Perovskites.

To boost the efficiency of perovskite solar cells beyond the limit of a single-junction cell, tandem cells are employed, requiring low bandgap materials. This is realized by partially substituting lead(II) (Pb2+) with tin(II) (Sn2+) in the perovskite structure. In this work, a scalable method is presented to produce formamidinium lead tin iodide (FAPb0.5Sn0.5I3) films by sequential thermal evaporation (sTE) of PbSnI4, which is an alloy of SnI2 and PbI2, and FAI, in vacuum. Annealing at 200°C yields a highly oriented and crystalline layer comprising grains over 1µm on average. Photoconductance measurements reveal carrier lifetimes exceeding 2µs and mobilities ≈100cm2/(Vs). Structural analysis confirms that, while interdiffusion is abundant even at room temperature, the complete conversion requires high temperatures. Although the incorporation of Cs+ into the A-site of the perovskite increases the grain size, charge carrier dynamics are reduced. A comparison between the sTE films and spin-coated samples of the same composition demonstrates the superior photoconductance of the sTE films, without the need for any additives. Overall, this study showcases the potential of sTE for producing high-quality low band gap (LBG) perovskite materials.

Evaluation of the optical, structural, morphological and electronic properties of Rb3Bi2I9 Perovskites films prepared by Sequential Evaporation

Evaluation of the optical, structural, morphological and electronic properties of Rb3Bi2I9 Perovskites films prepared by Sequential Evaporation

Controlled Crystal Growth of All-Inorganic CsPbI2Br via Sequential Vacuum Deposition for Efficient Perovskite Solar Cells.

Vacuum deposition of perovskites is a promising method for scale-up fabrication and uniform film growth. However, improvements in the photovoltaic performance of perovskites are limited by the fabrication of perovskite films, which are not optimized for high device efficiency in the vacuum evaporation process. Herein, we fabricate CsPbI2Br perovskite with high crystallinity and larger grain size by controlling the deposition sequence between PbI2 and CsBr. The nucleation barrier for perovskite formation is significantly lowered by first evaporating CsBr and then PbI2 (CsBr-PbI2), followed by the sequential evaporation of multiple layers. The results show that the reduced Gibbs free energy of CsBr-PbI2, compared with that of PbI2-CsBr, accelerates perovskite formation, resulting in larger grain size and reduced defect density. Furthermore, surface-modified homojunction perovskites are fabricated to efficiently extract charge carriers and enhance the efficiency of perovskite solar cells (PeSCs) by modulating the final PbI2 thickness before thermal annealing. Using these strategies, the best PeSC exhibits a power conversion efficiency of 13.41% for a small area (0.135 cm2), the highest value among sequential thermal deposition inorganic PeSCs, and 11.10% for a large area PeSC (1 cm2). This study presents an effective way to understand the crystal growth of thermally deposited perovskites and improve their performance in optoelectronic devices.

Kinetic, products and shrinkage for the pyrolysis of flax fibers

Biomass pyrolysis is a thermochemical process used for renewable products and energies. However, there are still issues that need to be addressed for process modeling and optimization. This study focuses on the relationship between heating rate, shrinkage, and products from flax fibers using thermogravimetric analysis (TGA), microscopic observation, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TGA confirms sequential evaporation of water then decomposition of hemicellulose, cellulose, and lignin. Observations from the micro-reactor show that flax fibers undergo shrinkage within the temperature range of 335–370 ∘C, depending on the heating rate. Pyrolysis products were analyzed using Py-GC/MS at four different final temperatures from 350 to 500 ∘C, revealing the presence of anhydrosugars, furans, ketones, phenols, esters, alcohols, aldehydes, and acids. The results indicate a correlation between temperature and the increase in furans and ketones. The analysis suggests that furans and ketones are associated with shrinkage.

Fabrication of phase-pure and large-grained Cu3BiS3 films by a two-stage process for thin film solar cells

Copper-bismuth-sulfide (Cu3BiS3) has gained great interest as solar cell absorber owing to the advantages of being cheap, abundant, and non-toxic. Fabrication of phase-pure and large-grain absorbers are desirable for their integration in solar cells. Herein, we have used a sequential evaporation and chalcogenization (350–450 oC) process to fabricate phase-pure and large-grain Cu3BiS3 films. X-ray diffraction indicated a CuS secondary phase at 350 °C and single-phase Cu3BiS3 at 400 and 450 °C in the sulfurized films. Elemental analysis revealed a near-stoichiometric Cu3BiS3 composition for all the films. X-ray photoelectron spectroscopy was used to assess the valence states of elements. Microstructural analysis confirmed the formation of compact and large-grained Cu3BiS3 films with an average grain size of 5 μm at 350 °C. The grain size decreased with increasing sulfurization temperature (400–450 °C). The direct bandgap decreases from 1.42 eV to 1.32 eV with increasing sulfurization temperature from 350 to 450 °C. Hall measurements indicated decreased electrical resistivity and increased hole mobility and carrier concentration with increasing the sulfurization temperature. From this study, the Cu3BiS3 absorbers produced at 400 oC exhibited superior phase purity and good quality suitable for the solar cells.

Structural Evolution of Sequentially Evaporated (Cs,FA)Pb(I,Br)3 Perovskite Thin Films via In Situ X‐Ray Diffraction

Evaporation of perovskite thin films for solar cell applications is a solvent‐free, well controllable, and scalable deposition path with promising prospects for commercialization. Compared to commonly applied simultaneous co‐evaporation of various halide precursor salts, sequential evaporation followed by an annealing step allows to better control the amount of deposited precursors, and has the potential to largely improve reproducibility. In this work, Cs/formamidinium (FA)‐based lead iodide perovskites are deposited via sequential evaporation in a vacuum chamber and the phase formation and evolution of different precursor‐stacking sequences and annealing conditions are investigated with in situ X‐ray diagnostics. In addition, some Br is added to investigate the effect of halide intermixing. The stacking sequence is found to strongly influence the formation of dominant phases as well as the preferential orientation and HGHmorphology of the as‐deposited films. These variations in turn affect the diffusion and conversion during thermal annealing and ultimately the conversion ratio of the final perovskite layers. For example, it is found that starting the stacking sequences with the A cations (CsI, FAI) favors a fast and complete conversion of the perovskite phase. However, the result is the formation of perovskite layers with large voids.

Stable, self-biased Cs2AgBiBr6 thin-film based photodetector by three-step vapor-deposition

A lead-free, pure phase double perovskite Cs2AgBiBr6 thin film (TF) is fabricated on an ITO glass plate through a three-step sequential vacuum thermal evaporation method followed by annealing. X-ray diffraction (XRD) analysis of the synthesized material revealed a cubic phase with a lattice constant of α = 11.26 Å. The TF exhibits UV and visible absorption with a bandgap estimated at 2.31 eV (303 K) and a red shift of 0.04 eV (363 K). The optical absorption spectrum is simulated using the modified band anti-crossing (BAC) model, determining the Cs2AgBiBr6 TF's theoretical relative refractive index (r.i.) as 2.10 (303 K) and 1.90 (363 K). Furthermore, a photodetector based on Ag/Cs2AgBiBr6/ITO/glass architecture was fabricated, showcasing excellent stability and self-powered photodetection properties under continuous illumination across a wide temperature range of 303–373 K. The device demonstrates a fast temporal response (13/9 ms), a responsivity of ∼1.0 × 10−4 A/W, and a detectivity of ∼2.5 × 107 Jones. Light sensitivity measurements reveal that the device is twice as sensitive at 373 K compared to room temperature, with negligible (1%) degradation in light sensitivity after 60 days of storage under normal ambient conditions.

Unveiling the optimal selenization temperature for enhancing efficiency in flexible Cu(In,Ga)Se2 thin film solar cells

This work is centered on the growth of metallic precursors (Cu/In/Ga) through sequential evaporation, followed by a controlled ramping step selenization process aimed at synthesizing thin films based on copper indium gallium diselenide (CIGSe) on stainless steel substrates. Selenization temperatures ranging from 475 to 525 °C were employed to optimize the most suitable recrystallization temperature. A comprehensive characterization was conducted, covering structural, morphological, topographical, optical, and electrical aspects, revealing the distinct role of selenization temperature. Subsequently, solar cells were fabricated using the synthesized absorbers, resulting in an impressive efficiency of 15.89 % for the absorber selenized at 525 °C. This observation underscores the pivotal role of selenization parameters in shaping the quality of CIGSe, directly influencing the performance of solar cells. Consequently, this research not only focuses on refining the growth process of CIGSe through a modified approach but also provides valuable insights for the advancement of flexible solar cell technology.

Vacuum Deposited Perovskites with a Controllable Crystal Orientation.

The preferential orientation of the perovskite (PVK) is typically accomplished by manipulation of the mixed cation/halide composition of the solution used for wet processing. However, for PVKs grown by thermal evaporation, this has been rarely addressed. It is unclear how variation in crystal orientation affects the optoelectronic properties of thermally evaporated films, including the charge carrier mobility, lifetime, and trap densities. In this study, we use different intermediate annealing temperatures Tinter between two sequential evaporation cycles to control the Cs0.15FA0.85PbI2.85Br0.15 orientation of the final PVK layer. XRD and 2D-XRD measurements reveal that when using no intermediate annealing primarily the (110) orientation is obtained, while when using Tinter = 100 °C a nearly isotropic orientation is found. Most interestingly for Tinter > 130 °C a highly oriented PVK (100) is formed. We found that although bulk electronic properties like photoconductivity are independent of the preferential orientation, surface related properties differ substantially. The highly oriented PVK (100) exhibits improved photoluminescence in terms of yield and lifetime. In addition, high spatial resolution mappings of the contact potential difference (CPD) as measured by KPFM for the highly oriented PVK show a more homogeneous surface potential distribution than those of the nonoriented PVK. These observations suggest that a highly oriented growth of thermally evaporated PVK is preferred to improve the charge extraction at the device level.

A compact dication source for Ba2+ tagging and heavy metal ion sensor development

We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cadmium samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean Ba2+ ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb2+ and Cd2+ also demonstrated for this purpose.

Fast Fabrication of Porous Amphiphilic Polyamides via Nonconventional Evaporation Induced Phase Separation.

In the present work, we report a facile approach for the fast fabrication of porous films and coatings of long-chain polyamides through a nonconventional evaporation induced phase separation. Because of its amphiphilic nature, polyamide 12 can be dissolved in the mixture of a high-polarity solvent and a low-polarity solvent, while it could not be dissolved in either solvent solely. The sequential and fast evaporation of the solvents leads to the formation of porous structures within 1 min. Moreover, we have investigated the dependence of the pore structures on composition of the solutions, and have demonstrated that our approach can be applied to other long-chain polycondensates, too. Our findings can provide insight on the fabrication of porous materials by using amphiphilic polymers.

Sequential Vacuum Evaporated Copper Metal Halides for Scalable, Flexible, and Dynamic X‐Ray Detection

AbstractCopper metal halides have emerged as a strong contender in the scintillator field due to the self‐trapped excitons (STEs) mechanism. However, their development has been hindered by the preparation process. Single crystals have long growth cycles and cannot achieve large areas and flexibility. Quantum dots have a low yield and can easily cause chemical pollution, and the thickness of films prepared by the spin coating cannot be controlled. To address these challenges, a new method for preparing Cs3Cu2Cl5 using sequential vacuum evaporation is developed. This allows successful preparation of large‐area (≈100 cm2) and flexible films. The STEs mechanism of Cs3Cu2Cl5 gives it unique properties such as a large Stokes shift that reduces self‐absorption effects, and a wide full width at half‐maximum that improves coupling with photodiodes. Therefore, Cs3Cu2Cl5 is applied to X‐ray imaging with a light yield of ≈30 000 photons MeV−1, a spatial resolution of over 10 lp mm−1, and a low detection limit below 0.8 µGyair s−1. In addition, the flexible Cs3Cu2Cl5 film enables effective dynamic imaging and clear imaging on non‐planar objects. It also exhibits good resistance to harsh environments, maintaining good imaging performance after 150 days. It is believed that sequential vacuum evaporation provides an important idea for preparing scintillators.

Structural and Optical Properties of Vacuum‐Evaporated Mixed‐Halide Perovskite Layers on Nanotextured Black Silicon

Vacuum-Evaporated Mixed-Halide Perovskite Layers In article number 2200482, Ashok Vaseashta and co-workers investigate the structural and optical properties of mixed-halide perovskite layers deposited on black silicon by sequential and co evaporation methods. The black silicon is formed using plasma reactive ion etching. The authors demonstrate a significant reduction in the reflection of the perovskite layers. This is achieved without compromising the structural quality of the perovskite layer as a photoabsorber. The results confirm the promise of using black silicon for perovskitesilicon tandem junction solar cells.

Surface Passivation for Promotes Bi-Excitonic Amplified Spontaneous Emission in CsPb(Br/Cl)3 Perovskite at Room Temperature.

Perovskite-type lead halides exhibit promising performances in optoelectronic applications, for which lasers are one of the most promising applications. Although the bulk structure has some advantages, perovskite has additional advantages at the nanoscale owing to its high crystallinity given by a lower trap density. Although the nanoscale can produce efficient light emission, its comparatively poor chemical and colloidal stability limits further development of devices based on this material. Nevertheless, bulk perovskites are promising as optical amplifiers. There has been some developmental progress in the study of optical response and amplified spontaneous emission (ASE) as a benchmark for perovskite bulk phase laser applications. Therefore, to achieve high photoluminescence quantum yields (PLQYs) and large optical gains, material development is essential. One of the aspects in which these goals can be achieved is the incorporation of a bulk structure of high-quality crystallization films based on inorganic perovskite, such as cesium lead halide (CsPb(Br/Cl)3), in polymethyl methacrylate (PMMA) polymer and encapsulation with the optimal thickness of the polymer to achieve complete surface coverage, prevent degradation, surface states, and surface defects, and suppress emission at depth. Sequential evaporation of the perovskite precursors using a single-source thermal evaporation technique (TET) effectively deposited two layers. The PL and ASEs of the bare and modified films with a thickness of 400 nm PMMA were demonstrated. The encapsulation layer maintained the quantum yield of the perovskite layer in the air for more than two years while providing added optical gain compared to the bare film. Under a picosecond pulse laser, the PL wavelength of single excitons and ASE wavelength associated with the stimulated decay of bi-excitons were achieved. The two ASE bands were highly correlated and competed with each other; they were classified as exciton and bi-exciton recombination, respectively. According to the ASE results, bi-exciton emission could be observed in an ultrastable CsPb(Br/Cl)3 film modified by PMMA with a very low excitation energy density of 110 µJ/cm2. Compared with the bare film, the ASE threshold was lowered by approximately 5%. A bi-exciton has a binding energy (26.78 meV) smaller than the binding energy of the exciton (70.20 meV).

Solvent-vapor assisted conversion process for hybrid perovskites coupling thermal evaporation and slot-die coating

The present paper reports for the first time on the fabrication of highly efficient solar cells based on a perovskite layer produced by a sequential deposition method coupling thermal evaporation and slot-die coating. Thermally evaporated PbI2 films were converted into perovskite by slot-die coating a solution containing the organic MA and FA cations. Careful optimization of the coating parameters resulted in uniform double-cation perovskite films with an optical band gap of 1.64 eV. This work highlights the need for a DMSO (Dimethyl Sulfoxide) vapor treatment performed on the evaporated PbI2 film to obtain high-quality perovskite layers after the conversion step. Thus, a simple and short pre-treatment has been designed to induce the formation of porous PbI2(DMSO)x complex phases enabling a fast and complete perovskite conversion process. Thereby, the champion device delivers a power conversion efficiency of 19.8% with enhanced short-circuit current, open-circuit voltage, and fill factor compared to control devices without treatment.

Structural and Optical Properties of Vacuum‐Evaporated Mixed‐Halide Perovskite Layers on Nanotextured Black Silicon

To improve the absorption of light in two‐junction tandem perovskite–silicon solar cells, antireflective textures are often created on the front surface in the form of micronsized pyramids using wet‐chemical etching. It is known that single‐junction silicon solar cells with nanotextured black silicon (BS) formed by dry‐etching techniques are more efficient than pyramidal microtextures. Herein, experimental evidence of enhanced efficiency of structures using BS between the perovskite layer and the silicon substrate for the first time is demonstrated. BS is fabricated using plasma‐based reactive‐ion etching on the front surface of the crystalline silicon. The deposition of mixed‐halide perovskite layers is performed by vacuum coevaporation and sequential evaporation. The structural and optical properties of evaporated perovskite layers with various thicknesses are investigated. It is found that the structural‐phase quality (viz., surface coverage, chemical composition, dimensionality, crystallinity, and phase purity) of perovskite layers on planar and nanotextured substrates is similar. However, the root mean square roughness of the perovskite layers on nanotextured substrates is much higher, which reduces the reflection significantly, especially, in the range of radiation incidence angle up to 60°. These results pave the way for the development of high‐performance perovskite–silicon tandem solar cells for improved efficiency.

Evolution of the Cu2ZnSnS4 phase based on the sulfurization-crystallisation duration of the CuS/SnS/ZnS stack formed by thermal evaporation

ABSTRACT Binary sulfides were deposited by sequential thermal evaporation with the stacking order glass/CuS/SnS/ZnS and subsequently subjected to a sulfurization-crystallization process, considering two thermal treatment time intervals, 5 and 20 min. The objective of implementing different annealing durations was to identify the best conditions to form CZTS films in the pure kesterite phase. After being subjected to the annealing, the films show structural characteristics of the kesterite phase. However, XRD data showed that prolonged annealing causes degradation of the kesterite phase, leading to the formation of traces of CuS and Cu5Sn2S7. The films annealed for shorter duration, in this case 5 min, present a denser and more uniform surface morphology, better degree of preferential orientation, small Urbach energy of 0.302 eV, and higher photosensitivity. The band gap of the films was 1.46 eV and 1.53 eV for annealing durations 5 and 20 min, respectively.

Synthesis and characterization of Cu-sandwiched Sb2Se3 thin films and numerical simulation of p-Sb2Se3/n-ZnSe heterojunction solar cell

Sb2Se3 and Cu-sandwiched Sb2Se3 thin films were prepared by sequential evaporation of (Sb/Se) × 3 and [(Cu/(Sb/Se) × 3/Cu)] precursor stacks over the glass substrates in a high vacuum using electron beam (e-beam) evaporation followed by annealing in a tubular furnace at various temperatures in Ar atmosphere. The growth of Sb2Se3 and Cu-sandwiched Sb2Se3 films is studied by varying annealing temperature. The Sb2Se3 films grown without copper layers were peeled off from the glass substrates when annealed above 300 °C, whereas the Cu-sandwiched Sb2Se3 films were adherent to substrates up to 450 °C. The XRD of Cu-sandwiched Sb2Se3 films annealed at all temperatures confirms the Sb2Se3 formation with orthorhombic crystal structure. The Cu-sandwiched films annealed at ≤ 250 °C showed the preferred orientation along the (hk0) plane, whereas films annealed at ≥ 300 °C exhibited the (hk1) preferred orientation. The morphology of Cu-sandwiched Sb2Se3 films annealed at 450 °C showed compact and larger grains (∼0.8 μm) with a direct optical band gap of 1.04 eV. Hall effect measurement exhibited a p-type conductivity with a hole concentration of 3.1 × 1015 cm−3. The numerical simulation of the proposed Glass/Ni/p-Sb2Se3/n-ZnSe/ITO/Al heterojunction solar cell showed a power conversion efficiency of 21.51%.

Water Dynamics in Competitive Solvation Assisted Loading of Colloidal Curcumin Nanoparticles onto Mesoporous Silica Nanostructures (Part. Part. Syst. Charact. 8/2022)

In article number 2200062, Nitthin Ananth, Jose, and co-workers studied that the sequential solvent evaporation approach combined with dielectric nano environment tuning mediates the uploading of hydrophobic curcumin nanoparticles onto mesoporous silica. The co-solvents that modulate the water dynamics favor the form of monodispersed, stable nanostructures with high loading fractions.

Sequential vacuum-evaporated perovskite solar cells with more than 24% efficiency.

Vacuum evaporation is promising for the high-throughput fabrication of perovskite solar cells (PSCs) because of its solvent-free characteristic, precise control of film thickness, and compatibility with large-scale production. Nevertheless, the power conversion efficiency (PCE) of PSCs fabricated by vacuum evaporation lags behind that of solution-processed PSCs. Here, we report a Cl-containing alloy-mediated sequential vacuum evaporation approach to fabricate perovskite films. The presence of Cl in the alloy facilitates organic ammonium halide diffusion and the subsequent perovskite conversion reaction, leading to homogeneous pinhole-free perovskite films with few defects. The resulting PSCs yield a PCE of 24.42%, 23.44% (certified 22.6%), and 19.87% for 0.1, 1.0, and 14.4 square centimeters (mini-module, aperture area), respectively. The unencapsulated PSCs show good stability with negligible decline in performance after storage in dry air for more than 4000 hours. Our method provides a reproducible approach for scalable fabrication of large-area, high-efficiency PSCs and other perovskite-based optoelectronics.