Close-spaced Sublimation Research Articles

Low-temperature conformal vacuum deposition of OLED devices using close-space sublimation

Close-space sublimation (CSS) has been demonstrated as an alternative vacuum deposition technique for fabricating organic light-emitting diodes (OLEDs). CSS utilizes a planar donor plate pre-coated with organic thin films as an area source to rapidly transfer the donor film to a device substrate at temperatures below 200 °C. CSS is also conformal and capable of depositing on odd-shaped substrates using flexible donor media. The evaporation behaviors of organic donor films under CSS were fully characterized using model OLED materials and CSS-deposited films exhibited comparable device performances in an OLED stack to films deposited by conventional point sources. The low temperature and conformal nature of CSS, along with its high material utilization and short process time, make it a promising method for fabricating flexible OLED displays.

Photodetector properties of CdSe thin films grown by close space sublimation method

Photodetector properties of CdSe thin films grown by close space sublimation method

Improvement of crystallinity of CdZnTe epilayers on GaSb substrates by ZnTe buffer layer

Thick CdZnTe epitaxial film is a promising alternative for X-ray detectors, especially in the case of large-area imaging application. One of the key issues in growing thick heteroepitaxial film with high crystallinity is to reduce the mismatch dislocations that appear at the interface between CdZnTe epilayer and the substrate. In this paper, we prepared CdZnTe films without and with ZnTe buffer layers on GaSb (001) substrates by the closed space sublimation. All preparation conditions for ZnTe buffer layers, CdZnTe epilayers on ZnTe buffers and GaSb substrates, as well as the pretreatment of GaSb surface have been optimized through tremendous experiments. The results of electron backscatter diffraction and transmission electron microscope observation prove that ZnTe buffer layers suppress (1‾1‾1)M twins extending from GaSb. The deposition temperature for inserting ZnTe buffer about 495 K is optimized for getting smooth ZnTe surface, on which high crystalline quality CdZnTe epilayer with a narrower full-width at half-maximum (85 arcsec) of double crystal X-ray rocking curve for (004) reflection and lower intensity ratio IDcomplex/I(D0, h) of low-temperature photoluminescence spectroscopy were produced.

Growth of CdZnTe (2 1 1) epilayers on GaAs by close spaced sublimation as an alternative substrate for HgCdTe growth

Cd0.96Zn0.04Te crystals are perfect substrates for epitaxial growth of HgCdTe films due to good lattice matching, but they are limited by cost factors. To grow a replacement substrate for the subsequent growth of low-cost, high-yield HgCdTe IR materials, CdZnTe epitaxial films have been fabricated by close-spaced sublimation on GaAs substrates, and the effect of substrate temperature on the crystalline quality of CdZnTe films has been investigated. The results of EBSD and TEM indicate that the surface is oriented in (211) and the low temperatures enhance the crystalline quality of the film. The results of dislocation density (average etch pit density ∼3.6 × 105 cm−2) and energy dispersive spectrometer (Zn content ∼5 %) indicate that CdZnTe films with appropriate Zn content and excellent crystal quality can be obtained by the close spaced sublimation method, which is expected to be applied for molecular beam epitaxy growth of HgCdTe films.

One-dimensional scintillator film with benign grain boundaries for high-resolution and fast x-ray imaging.

Fast and high-resolution x-ray imaging demands scintillator films with negligible afterglow, high scintillation yield, and minimized cross-talk. However, grain boundaries (GBs) are abundant in polycrystalline scintillator film, and, for current inorganic scintillators, detrimental dangling bonds at GBs inevitably extend radioluminescence lifetime and increase nonradiative recombination loss, deteriorating afterglow and scintillation yield. Here, we demonstrate that scintillators with one-dimensional (1D) crystal structure, Cs5Cu3Cl6I2 explored here, possess benign GBs without dangling bonds, yielding nearly identical afterglow and scintillation yield for single crystals and polycrystalline films. Because of its 1D crystal structure, Cs5Cu3Cl6I2 films with desired columnar morphology are easily obtained via close space sublimation, exhibit negligible afterglow (0.1% at 10 ms) and high scintillation yield (1.2 times of CsI:Tl). We have also demonstrated fast x-ray imaging with 27 line pairs mm-1 resolution and frame rate up to 33 fps, surpassing most existing scintillators. We believe that the 1D scintillators can greatly boost x-ray imaging performance.

Heterostructured CdS Buffer Layer for Sb2Se3 Thin Film Solar Cell

The antimony selenide thin film solar cells technology becomes promising due to its excellent anisotropic charge transport and brilliant light absorption capability. Especially, the device performance heavily relies on the vertically oriented Sb2Se3 grain to promote photoexcited carrier transport. However, crystalline orientation control has been a major issue in Sb2Se3 thin film solar cells. Herein, a new strategy has been developed to tailor the crystal growth of Sb2Se3 ribbons perpendicular to the substrate by using the structural heterostructured CdS buffer layer. The heterostructured CdS buffer layer is formed by a dual layer of CdS nanorods and nanoparticles. The hexagonal CdS nanorods passivated by a thin cubic CdS nanoparticle layer can promote [211] and [221] directional growth of Sb2Se3 ribbons using a close space sublimation approach. The improved buffer/absorber interface, reduced interface defects, and recombination loss contribute to the improved device efficiency of 7.16%. This new structural heterostructured CdS buffer layer can regulate Sb2Se3 nanoribbons crystal growth and pave the way to further improve the low‐dimensional chalcogenide thin film solar cell efficiency.

The effect of SbCl3 treatment on CdTe produced by close space sublimation method

In this study, influence of SbCl3 treatment on CdTe films deposited by the close space sublimation method was investigated. SbCl3 treatment was compared with conventional CdCl2 treated and untreated samples. It was determined that CdTe grew as Cd-rich and there was a slight decrease in Cd-amount after SbCl3 and CdCl2 treatments. In addition, a significant amount of Sb was detected in the SbCl3 treated sample. The samples crystallized in the cubic structure of CdTe. However, graded structures such as phase-I and phase-II with different structural parameters were formed. In the SbCl3 sample, it was revealed that the presence of Sb- caused a slight increase in the lattice parameter, compared to the other samples. Morphological analyses of the samples showed facet and large-small grain structures. CdCl2 treatment caused a slight decrease in grain size, while SbCl3 treatment resulted in a coarser and rougher grain structure. CdCl2 treatment increased transmittance, whereas SbCl3 treatment caused a decrease in transmittance (hence, an increase in absorbance). It was observed that the bandgaps were ∼1.49 eV in all samples, and annealing, as well as CdCl2 and SbCl3 heat treatments did not cause a sharp change in the bandgaps. Photoluminescence spectra revealed the presence of band-edge and shallow-level defect transitions (except CdCl2 treated) in the samples. All results suggest that SbCl3 heat treatment has a significant effect on CdTe and may be an alternative to CdCl2.

The Growth Pits Filling Mechanism of CdZnTe Epitaxial Film Prepared by Close-Spaced Sublimation Based on the First-Principles Calculation

The preparation of high quality II-VI semiconductor single crystal still is a challenging task. The II-VI ternary compound Cd1-xZnxTe is an outstanding candidate for room temperature nuclear radiation detectors. Therefore, the epitaxial mechanism of its film is profound to clarify for accurate growth regulation and quality improvement. However, determining the essence of epitaxial growth remains challenge only using experiments to explore the effects of growth conditions on film epitaxy. In this work, the growth pits filling mechanism of CdZnTe epitaxial film has been elucidated by combining the experimental results with the first-principles calculation. Based on the Atomic Force Microscope data, the structural characteristics of growth pits were analyzed, and the layered growth model and the lateral step growth model were proposed. According to Gibbs-Wulff crystal growth law, the stability of two growth pits filling models was compared through the first-principles simulations. By comparing surface energies, we identified that the filling process of growth pits relies on the movement of steps along the interface. These results well describe the deposition mechanism of CdZnTe film prepared by close-spaced sublimation and provide inspirations to accurately regulate the II-VI film growth and obtain high quality films.

Development of Bi2S3 thin film solar cells by close-spaced sublimation and analysis of absorber bulk defects via in-depth photoluminescence analysis

Development of Bi2S3 thin film solar cells by close-spaced sublimation and analysis of absorber bulk defects via in-depth photoluminescence analysis

Post deposition annealing effect on properties of CdS films and its impact on CdS/Sb2Se3 solar cells performance

Antimony selenide (Sb2Se3) is one of the emerging photovoltaic absorber materials possessing abundance and non-toxicity as the main attributes. Following CdTe technology, CdS is a widely used partner layer for Sb2Se3 solar cells. Related to CdS/Sb2Se3 device configuration, a number of studies reported findings and challenges regarding the intermixing phenomenon at the main interface and suitability of various annealing for CdS (and related interface) and still, significant room remains in developing strategies for interface optimization and understanding of the physiochemistry behind. In this perspective, this work provides a systematic investigation of the effect of vacuum and air annealing at temperatures between 200 and 400°C on the properties of CdS deposited by chemical bath deposition and combined with Sb2Se3 absorber obtained by close-spaced sublimation the direct impact of the CdS annealing on the device performance is illustrated. It is found that by varying the annealing temperature from 200 to 400°C in both, vacuum and air ambient, the morphology of CdS changes from highly dispersed small grain structure to sintered dense grains, the band gap decreases from 2.43 to 2.35 eV and the electron density drops from ∼1018 to ∼1011 cm−3. These changes were correlated with the changes in the CdS lattice and connected with the mobility of the OH group and the presence of secondary phases in CdS layers. 200°C air annealing of CdS was found as an optimal treatment resulting in 2.8% Sb2Se3/CdS cell efficiency - a 60% boost compared to the 1.8% performance of the device with as-deposited CdS. Material and device characterization analysis is performed, providing complementary insights on the interrelation between the physicochemical mechanism of the CdS annealing processes and device functionality.

Cu2ZnSnS4 films properties deposited by spray pyrolysis, subjected to a combined novel thermal treatment: CSS sulfurization and RTA post-treatment

CZTS films were obtained by spray pyrolysis, a low-cost technique implemented on an industrial scale. Sulfurization processes generally enhance CZTS properties for its use in solar cells; however, these require high temperatures and long times. In this work, CZTS films properties were studied after being subjected to a combined novel thermal treatment which involved two stages. Sulfur incorporation using close space sublimation technique (CSS) at a temperature (TCSS) in the 350–500 °C range for 60 s, and after a rapid thermal annealing post-treatment (RTA) at TRTA = 500 °C for 10 s, with a heating ramp of 5 °C/s under argon atmosphere. Morphological, structural, chemical composition, optical and electrical properties were studied for CZTS films subjected to CSS as CSS+RTA treatments for all TCSS values. From the results, efficient sulfur incorporation by CSS was obtained without substantial sulfur concentration loss after RTA treatment, associated with the short treatment time. In addition, significant enhancement of crystalline quality and electrical resistivity diminished of the films is obtained after the CSS+RTA process for all TCSS. CZTS films with the best properties are those obtained at TCSS of 400 °C, having Cu/(Zn+Sn) = 0.79 and Zn/Sn = 1.3 ratios, a direct bandgap value of 1.5 eV, and resistivity of 4 Ω-cm. These films can be candidates for their characteristics as an absorbent layer in solar cells.

Preparation and characterization of Sb2S3 thin films for planar solar cells via close space sublimation method

Sb2S3 has a unique one-dimensional structure-composed (Sb4S6) n ribbons leads to strong anisotropic carrier transport characteristic: carrier transport along the (Sb4S6) n ribbon is more efficient than other ribbons. Therefore, it's crucial to control the direction of grain growth along the (hk1) orientation. In this work, the close space sublimation method was utilized to fabricate Sb2S3 thin films with a systematical regulation of substrate temperature. The results demonstrate that optimized Sb2S3 thin film presented preferred orientation at the direction of (hk1). The champion device based on Au and Ni electrodes achieved a power conversion efficiency (PCE) of 3.06% and 1.69%, respectively.

Electro-optical characterization of arsenic-doped CdSeTe and CdTe solar cell absorbers doped in-situ during close space sublimation

Electro-optical characterization of arsenic-doped CdSeTe and CdTe solar cell absorbers doped in-situ during close space sublimation

Low processing temperatures explored in Sb2S3 solar cells by close-spaced sublimation and analysis of bulk and interface related defects

Low processing temperatures explored in Sb2S3 solar cells by close-spaced sublimation and analysis of bulk and interface related defects

Effect of phosphoric acid treatment on the physical properties of zinc telluride thin films

Zinc Telluride (ZnTe) films were prepared by the closed space sublimation (CSS) method. The effect of chemical treatments with concentrated phosphoric acid, on the optical, electric and structural properties of the films was studied. Zinc-blend structure of the polycrystalline nature of the films was confirmed by x-ray diffraction (XRD) spectra. The energy dispersive x-ray (EDX) shows an increase in Te ratio on the surface of the film as exposed to phosphoric acid. In addition, the dc electrical resistivity of the films was dropped considerably. The refractive index, thickness, and thickness irregularity of the films were determined by fitting of the optical transmittance spectra in the wavelength range 400 to 2500 nm. The effect, of treatment, on the optical parameters is also reported.

Study the Structural/Microstructural and Electrical Properties of CdTe:Sb Thin Films Deposited by Flash Evaporation

in this research studied the structure and electrical properties of the Pure CdTe and metal Sb-doped CdTe thin films with 0.5, 1, and 1.5 wt.%, respectively. Theydeposited on glass substrates using flash evaporation technique. It was found that theprepared films had a cubic structure and a strong preferred <111> crystal orientation.Atomic force microscopy (AFM) results showed that the film surface doped Sb wasmore compact and uniform and also the root mean squared (RMS) roughnessincreased with Sb contents. The electrical properties were investigated as function ofSb wt.% doping. The results showed that the electrical conductivity (6) increasingtrend with increasing the wt.% of dopant , while the activation energies (E,i, E,2)showed an opposite trend, where the activation energies decreased with dopant.1. Introduction Thin films of II-VI semiconductors are widely used in many semiconductordevices such as photo electrochemical cells, field effect transistors, IR detectors,photodiodes, photo conductors and photovoltaic solar cells[1, 2]. CdTe has long beenidentified as a candidate for the absorber layer in low cost thin film photovoltaic solarcells because of its direct bandgap, high absorption coefficient and the possibility of avariety of preparation techniques such as close spaced sublimation (CSS)[3], vacuumdeposition [4], electrodeposition [5], and RF sputtering[6], close spaced vaportransport [7]. In this present work we focused attention on the prominent techniquesfor the deposition of thin films of multicomponent alloys whose constituents havedifferent vapor pressures. Thin films of CdTe have been prepared under suitablegrowth conditions by a simple flash evaporation (FE) technique. This techniquerequires only one boat maintained at sufficiently high temperature to evaporate theleast volatile component of the alloy. The main advantage of (FE) is that it does notrequire maintaining the critical vapor pressures of the components and temperatures ofthe boats unlike multisource thermal evaporation[8] . CdTe thin film still has many defects, such as it has extremely high resistivity. Tosolve this issue, the implying of the technique Sb-doped CdTe film to change electricalproperties [9]. In this work deposited Sb-doped CdTe films using the mixed powder of TO -AA suet Talal = - VN - Kya lal ayy cll 212 alae

Sb2Se3 Polycrystalline Thin Films Grown on Different Window Layers

Sb2Se3 is a typical V2VI3 binary chalcogenide compound characterized by a single crystalline phase and a fixed composition. Sb2Se3 displays a narrow energy gap ranging from 1.1 to 1.3 eV, which are quite optimal values for single-junction solar cells. Earth-abundant and non-toxic components make this material a good candidate for low-cost thin-film solar cells. In substrate configuration, a world record efficiency of 9.2% was recently obtained. Sb2Se3 thin films exhibit an accentuated predisposition to form (Sb4Se6)n ribbons along the [001] direction. This anisotropy heavily influences the charge transport of the photogenerated carriers. In this work, structural characterization of the Sb2Se3 films showed that the crystalline quality and preferential orientation are strongly dependent on the window layer used. To better understand the growth mechanism, Sb2Se3 thin films were deposited by close-spaced sublimation on five different window layers, such as CdS, CdS:F, CdSe, As2S3, and ZnCdS. Sb2Se3-based solar cells, realized in superstrate configuration on these different substrates, evidently demonstrate the influence of the Sb2Se3 preferential orientation on the photovoltaic parameters.

Effect of argon pressure on the physical characteristics of cadmium telluride (CdTe) thin films by close-spaced sublimation

Effect of argon pressure on the physical characteristics of cadmium telluride (CdTe) thin films by close-spaced sublimation

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

A comprehensive material study of CdSeTe films deposited with differing selenium compositions

The addition of selenium into CdTe to create the ternary alloy CdSeTe has been one of the most impactful advancements to CdTe-based photovoltaics in the last decade. CdSeTe/CdTe bilayer device structures have enabled a gain in short-circuit current due to the narrower bandgap of the alloy, with minimal to no loss in voltage. Intensity of photoluminescence and time-resolved photoluminescence measurements suggest this is due to an increase in carrier lifetime and concomitant greater fraction of radiative vs non-radiative recombination events which allows for a reduction in the voltage deficit. Here, we study the properties of as-deposited and CdCl2-treated CdSeTe films deposited by close-space sublimation under varying conditions from CdSeTe source charges with both 20 and 40 mol% CdSe. We find that the selenium content in the deposited films are substantially reduced from that of the source material. Additionally, deposition temperature, particularly that of the substrate, considerably affects the grain size, crystallinity, and photoluminescence of the material, illustrating the importance of source material selection and process optimization. Finally, we present evidence that the source material, and therefore the properties of the deposited films, change over time as the source material is used.