Multilayer Precursor Research Articles

Low band‐gap CuIn(S,Se)2 thin film solar cells using molecular ink with 9.5% efficiency (Phys. Status Solidi C 6/2017)

In order to achieve low band-gap thin film solar cells which can play an important role in tandem solar cells combined with perovskite top solar cells, the preparation of chalcopyrite absorbers is a major task. Wang et al. (article no. 1600169) report a non-vacuum simple solution coating approach for CuIn(S,Se)2 absorbers using an air stable molecular ink containing metal chlorides and thiourea in organic solvents. Careful balancing of ink concentration, number of precursor deposition cycles, and annealing temperature profile will transform the multilayer precursor into a sufficiently thick, continuous, large grained film as required for high quantum efficiency, and good red response of the cells. These optimizations aimed at high photo current have already led to an efficiency of 9.5% at a band-gap of 1.02 eV.

Another approach for controlling size and distribution of nanoparticles in coated conductors fabricated by the TFA-MOD method

A new process, which is conceptually different from that reported so far, was developed for positive and direct control of the size and distribution of BaZrO3 (BZO) nanoparticles acting as the effective magnetic flux pinning centers for coated conductors (CCs) fabricated on buffered metal substrates by the trifluoroacetate-based metal-organic decomposition method. The (Y,Gd)Ba2Cu3O6+δ (YGdBCO) phase crystallization heat-treatment process was applied one time to a multi-layered precursor prepared by repeating the coating/calcination process of the extremely thin layer of a few tens of nanometers. The size of BZO nanoparticles refined with thinning the once coated film thickness (donce) even in the same total film thickness of 0.6−0.7 μm, consequently the critical current density in magnetic-field (Jc(B)) was increased. A YGdBCO CC fabricated with donce of 30 nm revealed very high Jc(B∣∣c) characteristics of 0.26 and 1.60 MA cm−2 at 77 and 65 K, respectively, for 3.0 T.

Sputtering Deposition of Sandwich-Structured V2O5/Metal (V, W)/V2O5 Multilayers for the Preparation of High-Performance Thermally Sensitive VO2 Thin Films with Selectivity of VO2 (B) and VO2 (M) Polymorph

For specific application to an uncooled infrared detector, VO2 thin films should have a series of characteristics including purposefully chosen polymorphs, accurate stoichiometry, phase stabilization, a high temperature-coefficient of resistance (TCR), and suitable square-resistance. This work reports controllable preparation of high-performance VO2 films via post annealing of a sandwich-structured V2O5/metal (V, W)/V2O5 multilayer precursor, which was deposited by RF magnetron sputtering. This sandwich structure can dynamically regulate oxygen contents and doping element levels in the films, enabling us to achieve accurate regulation of stoichiometry and polymorphs. The precursor films undergo a B to M phase transition depending on the quantity of the metal layers. At the thickness of the metal layer below a limitation, the resulting film after heat treatment was VO2 (B), and above the limitation, the product was VO2 (M). The optical modulation of the VO2 (M) in the near-infrared region can be tuned from 1.2 to 39.8% (ΔT2000nm). TCR values can range from -1.89 to -4.29%/K and the square-resistances at room temperature (R0) from 69.68 to 12.63 kΩ. The simplicity in phase regulation of the present method and the superior optical and electrical properties of the films may allow its wide applications in thermo-opto-electro sensing devices.

Fabrication and characterization of novel multilayered structures by stereocomplexion of poly(D-lactic acid)/poly(L-lactic acid) and self-assembly of polyelectrolytes.

The enantiomers poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) were alternately adsorbed directly on calcium carbonate (CaCO3) templates and on poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) multilayer precursors in order to fabricate a novel layer-by-layer (LBL) assembly. A single layer of poly(L-lysine) (PLL) was used as a linker between the (PDLA/PLLA)n stereocomplex and the cores with and without the polymeric (PSS/PAH)n/PLL multilayer precursor (PEM). Nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) were used to characterize the chemical composition and molecular weight of poly(lactic acid) polymers. Both multilayer structures, with and without polymeric precursor, were firstly fabricated and characterized on planar supports. A quartz crystal microbalance (QCM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and ellipsometry were used to evaluate the thickness and mass of the multilayers. Then, hollow, spherical microcapsules were obtained by the removal of the CaCO3 sacrificial template. The chemical composition of the obtained microcapsules was confirmed by differential scanning calorimetry (DSC) and wide X-ray diffraction (WXRD) analyses. The microcapsule morphology was evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The experimental results confirm the successful fabrication of this innovative system, and its full biocompatibility makes it worthy of further characterization as a promising drug carrier for sustained release.

2D Electronic Transport with Strong Spin-Orbit Coupling in Bi(2-) Square Net of Y2O2Bi Thin Film Grown by Multilayer Solid-Phase Epitaxy.

Highly crystalline Y2O2Bi epitaxial thin film with monatomic Bi(2-) square net layer was grown by newly developed multilayer solid phase epitaxy. High reactivity of the nanometer-scale multilayered precursor enabled efficient formation of single crystalline Y2O2Bi phase with one-step heating. The reductive state of Bi(2-) square net was observed by X-ray photoemission spectroscopy. The electrical resistivity was one order lower than that of polycrystalline powder in previous study. The magnetotransport showed weak antilocalization effect well fitted by the Hikami-Larkin-Nagaoka model, exhibiting two-dimensional electronic nature with strong spin-orbit coupling in the Bi(2-) square net.

Physical properties of Cu(In,Ga)Se2 film on flexible stainless steel substrate for solar cell application: A multi-layer precursor method

The process named “multi-layer precursor method”, consisting of Ga–Se/In–Se/Cu–Se stacked precursors, is proposed to prepare Cu(In,Ga)Se2 (CIGS) films on flexible stainless steel (SUS) substrates. In this work, precursor deposition temperature (TPRE), varying from about 250 to 430°C, is first scrutinized. From Raman scattering measurement, it is suggested that the increase in the TPRE enhances Cu2−xSe secondary phase during film deposition, thus enlarging CIGS grain size, while decreases ordered vacancy compound (OVC) near surface of the finished film, caused by desorption of In2Se during the precursor deposition. Suitable TPRE is in a range of approximately 370–400°C, resulting in long carrier lifetime. Next, according to the examinations of material compositions of CIGS absorbers, the optimized [Cu]/([In]+[Ga]) contributes to the absorbers with large grain size due to the help of Cu2−xSe phase during film deposition and OVC near their surfaces for pn homo-junction. The appropriate [Ga]/([In]+[Ga]) leads to optimized band-gap energy with high CIGS quality implied by long carrier lifetime. Ultimately, the effective [Cu]/([In]+[Ga]) and [Ga]/([In]+[Ga]) ratios for the flexible CIGS solar cell with high conversion efficiency under the so-called “multi-layer precursor method” are in ranges of about 0.74–0.84 and 0.28–0.35, respectively.

Estimation of open-circuit voltage of Cu(In,Ga)Se2 solar cells before cell fabrication

Cu(In,Ga)Se2 (CIGS) absorbers with several Ga/III, Ga/(In + Ga), profiles were fabricated by the so-called “multi layer precursor method” under the control of Ga flux rate during film's deposition. Open-circuit voltage (VOC) of CIGS solar cell is principally dependent on average band-gap energy (Eg) in space-change region (SCR) of below 1.3 eV. This average Eg in SCR, principally controlled by average Ga/III ratio in SCR, is estimated by the peak position of (220/204)-oriented CIGS films on soda-lime grass (SLG) substrates investigated by grazing incidence X-ray diffraction (GIXRD) with 0.1° incident angle, whereas the average Eg in SCR is predicted by Raman or photoluminescence (PL) peak positions of CIGS absorbers on both SLG and stainless steel (SUS) substrates. Ultimately, with the average Eg in SCR of below 1.3 eV, the (220/204) peak position (GIXRD) can be well used as a predictor of the VOC on rigid SLG substrates. On the other hand, Raman peak and PL peak positions can be well utilized as indicators of the VOC on not only rigid SLG but also flexible SUS substrates before solar cell fabrication. These are fast and non-destructive methods to evaluate the Ga content, Eg near CIGS surface, and corresponding VOC for high cell performance.

Controlled back slope of Ga/(In+Ga) profile in Cu(In,Ga)Se2 absorber fabricated by multi layer precursor method for improvement of its photovoltaic performance

Cu(In,Ga)Se2 (CIGS) absorbers with several Ga/III, Ga/(In+Ga) ratio, profiles were deposited by the so-called “multi layer precursor method” consisting of Ga-Se/In-Se/Cu-Se stacks. The effects of average Ga/III ratios and back slopes of the Ga/III profiles on the photovoltaic performance were investigated. The optimum average Ga/III ratio of approximately 0.36 leads to the appropriate average band-gap energy as well as sufficiently long carrier lifetime in CIGS absorber, thus enhancing open-circuit voltage. In addition, the back slope of 0.50μm−1, defined as the ratio of the change in Ga/III ratio to the change in the depth range from 1 to 2μm from CIGS surface, induces back surface field of 0.34V/μm, thereby increasing short-circuit current density. Ultimately, the CIGS absorber on flexible stainless steel substrate with the double graded Ga/III profile (the average Ga/III of 0.36 and the back slope of 0.50μm−1) was fabricated by the multi layer precursor method. This results in the 14.36%-efficient CIGS solar cell on the flexible substrate without an anti-reflective layer.

Composition-structure-function diagrams of Ti-Ni-Au thin film shape memory alloys.

Ti-Ni-Au thin film materials libraries were prepared from multilayer precursors by combinatorial sputtering. The materials libraries were annealed at 500, 600, and 700 °C for 1 h and then characterized by high-throughput methods to investigate the relations between composition, structure and functional properties. The identified relations were visualized in functional phase diagrams. The goal is to identify composition regions that are suitable as high temperature shape memory alloys. Phase transforming compositions were identified by electrical resistance measured during thermal cycles in the range of -20 and 250 °C. Three phase transformation paths were confirmed: (1) B2-R, (2) B2-R-B19', and (3) B2-B19. For the materials library annealed at 500 °C only the B2-R transformation was observed. For the materials libraries annealed at 600 and 700 °C, all transformation paths were observed. High transformation temperatures (M(s) ≈ 100 °C) were only obtained by annealing at 600 or 700 °C, and with compositions of Ti ≈ 50 at. % and Au > 20 at. %. This is the composition range that undergoes B2-B19 transformation. The phase transformation behaviors were explained according to the compositional and annealing temperature dependence of phase/structure formation, as revealed by X-ray diffraction analysis of the materials libraries.

Raman scattering peak position of Cu(In,Ga)Se2 film to predict its near-surface [Ga] / ([Ga] + [In]) and open-circuit voltage

Abstract Cu(In,Ga)Se 2 (CIGS) solar cells were fabricated on both rigid soda-lime glass (SLG) and flexible stainless steel (SUS) substrates. Their absorbers, with several [Ga] / ([Ga] + [In]) profiles, were deposited using the so-called “multi-layer precursor method”, consisting of Ga–Se/In–Se/Cu–Se stacked precursors. It was revealed that the open-circuit voltage ( V OC ) of the CIGS solar cell is well correlated with the near-surface GGI, defined as the average [Ga] / ([Ga] + [In]) ratio within 200 nm of the CIGS surface. The near-surface GGI could be predicted when the Raman scattering peak position of the CIGS film was known. The estimated penetration depth of Raman scattering light into the CIGS layer was approximately 100–140 nm from its surface. Moreover, a relationship between V OC and the Raman scattering peak position was observed. Ultimately, the Raman scattering peak position, corresponding to the near-surface GGI of below 0.45, could be utilized as an indicator of V OC of CIGS solar cells on both rigid SLG and flexible SUS substrates without cell fabrication, which is measured by the rapid and non-destructive method.

Investigation of Cu(In,Ga)Se2 absorber by time-resolved photoluminescence for improvement of its photovoltaic performance

Time-resolved photoluminescence (TRPL) measurement has been performed on Cu(In,Ga)Se2 (CIGS) absorbers. In this contribution, CIGS films on both rigid soda-lime glass and flexible stainless steel (SUS) substrates are fabricated by the so-called “multi-layer precursor method” consisting of Ga–Se/In–Se/Cu–Se stacks. The TRPL lifetime, demonstrating a positive relationship with PL intensity, exhibits a close correlation with all photovoltaic parameters. According to TRPL and sensitive capacitance measurements, the average band-gap energy (Eg) should be in a range of 1.25–1.30eV, giving rise to sufficiently long TRPL lifetimes. Ultimately, CIGS absorber is fabricated with double graded Eg profile with a proper average Eg of 1.27eV and back-surface field of 0.22V/μm, defined as a ratio of the change in Eg divided by the change in a depth range from 1 to 2μm from CIGS surface. This graded Eg profile results in the improvement of the efficiency of the CIGS solar cell on a flexible SUS substrate up to 16.22% without an anti-reflective layer.

Effect of crystal orientation in Cu(In,Ga)Se 2 fabricated by multi-layer precursor method on its cell performance

Abstract Cu(In,Ga)Se2 (CIGS) films with different crystal orientations and Ga/(In + Ga), Ga/III, profiles are fabricated by the so-called “multi-layer precursor method”, utilizing multi-layer co-evaporation of material sources. In this literature, the crystal orientation and averaged Ga/III near the CIGS surface, estimated from the Ga/III profile, are investigated to improve the cell performance, especially open-circuit voltage (VOC). It is revealed that the VOC increases and more enhances with (220/204)-oriented CIGS absorbers, when the averaged Ga/III near the CIGS surface increases. The conversion efficiency of the solar cell on flexible stainless steel substrate is ultimately improved by the manipulations of the crystal orientation, namely, I(220/204)/I(112) of approximately 1.7, and the averaged Ga/III near the CIGS surface of 0.38 under the multi-layer precursor method.

Multi layer precursor method for Cu(In,Ga)Se2 solar cells fabricated on flexible substrates

Cu(In,Ga)Se2 (CIGS) solar cells are deemed one of the highest conversion efficiency thin-film solar cells, and the utilization of flexible (stainless steel; SUS) substrates offers several advantages in terms of lowering manufacturing costs. In this work, CIGS films on SUS substrates are deposited by the so-called “multi layer precursor method” using multi layer co-evaporation of material sources. The examination concentrates on the influence of growth temperature and Ga/III, Ga/(In + Ga), profiles of CIGS layers on the cell performance. According to the results, CIGS crystallization is primarily manipulated by growth temperature. Ultimately, the deposition of CIGS on a flexible SUS substrate can be readily controlled to obtain a suitable double Ga/III-grading profile with large grains of CIGS for a high cell efficiency of 16.05%.

Cu(In, Ga)Se2 thin films prepared from stacked precursors by post-selenization process

The copper–indium–gallium metallic precursors were fabricated corresponding to the sequence CuGa/CuIn/CuGa/soda-lime-glass by sequential direct current magnetron sputtering. The as-sputtered precursors were comprised of Cu11In9, Cu16In9, In, Cu9Ga4, and CuGa2 phases, which may be closely correlated to the deposition sequences of multi-layered metallic precursors. Cu(In, Ga)Se2 (CIGS) absorber films were prepared from the stacked precursors by post-selenization process with solid Se powder, and the morphological, structural, and compositional properties were investigated. The as-selenized CIGS film exhibited a smooth, compact, and densely packed morphology with well-defined and faceted crystal grains. The film was Cu-deficient and had a low Ga content. X-ray diffractometer results indicated the formation of single-chalcopyrite structure CIGS absorber layers. Depth-resolved Raman patterns showed the formation of a dominant CIGS phase in the as-selenized layer, and an ordered vacancy compound phase like Cu(In, Ga)3Se5 at the surface and inner region. With increasing the sputtering time, the full width at half maximum of the chalcopyrite A1 Raman peak increased. Band broadening can be interpreted as a result of a higher density of defects within the chalcopyrite CIGS phase. The A1 peak shifts with increasing sputtering depths were not apparent, which was related to a uniform distribution of Ga in the CIGS thin film.

Optimization of Selenization and Sintering Conditions of DC Magnetron Sputtered Ag/In/Ag/In Multi-Layer Metal Precursor for Preparation of AgInSe2 Thin Films

Optimization of Selenization and Sintering Conditions of DC Magnetron Sputtered Ag/In/Ag/In Multi-Layer Metal Precursor for Preparation of AgInSe₂ Thin Films

Stoichiometry effect on Cu2ZnSnS4 thin films morphological and optical properties

Thin films of Cu2ZnSnS4 (CZTS) were prepared by sulfurization of multilayered precursors of ZnS, Cu, and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray spectroscopy, and SEM were used for structural, compositional, and morphological analyses, respectively. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric measurements and Photothermal Deflection Spectroscopy. These films show a clear dependence of the optical and microstructural properties on the tin content. As the tin content increases we found: (i) an increase in both crystalline domain and grain size, (ii) an abrupt increase of the energy gap of about 150 meV, from 1.48 to 1.63 eV, and (iii) a decrease of sub-gap absorption up to two orders of magnitude. The results are interpreted assuming the formation of additional defects as the tin content is reduced.

Relationship between open-circuit voltage in Cu(In,Ga)Se2 solar cell and peak position of (220/204) preferred orientation near its absorber surface

Cu(In,Ga)Se2 (CIGS) absorbers with various Ga/III, Ga/(In+Ga), profiles are prepared by the so-called “multi-layer precursor method” using multi-layer co-evaporation of material sources. It is revealed that open-circuit voltage (VOC) of CIGS solar cell is primarily dependent on averaged Ga/III near the surface of its absorber. This averaged Ga/III is well predicted by peak position of (220/204) preferred orientation of CIGS film near its surface investigated by glancing-incidence X-ray diffraction with 0.1° incident angle. Finally, the peak position of (220/204) preferred orientation is proposed as a measure of VOC before solar cell fabrication.

Determination of open-circuit voltage in Cu(In,Ga)Se2 solar cell by averaged Ga/(In + Ga) near its absorber surface

The Cu(In,Ga)Se2 (CIGS) solar cells are fabricated, where CIGS absorbers with various Ga/III, Ga/(In + Ga), profiles are prepared by the so-called “multi-layer precursor method” using multi-layer co-evaporation of material sources. The dependence of cell parameters upon several averaged Ga/III ratios, calculated in different depth ranges of the Ga/III profiles from the absorber surfaces, is performed. It is revealed that open-circuit voltage (VOC) is mainly dependent on the averaged Ga/III, calculated near the surface area of the CIGS absorber (or in space charge region; SCR). The SCR width of ∼0.32 μm can be predicted, corresponding to the calculated value. Finally, the averaged Ga/III near the absorber surface is proposed as an indicator of VOC before solar cell fabrication, as long as carrier concentration is almost constant.

CZTS stoichiometry effects on the band gap energy

Abstract The considerable spread of Cu2ZnSnS4 (CZTS) optical properties reported in the literature is discussed in terms of material stoichiometry. To this purpose, kesterite thin films were prepared by sulfurization of multilayered precursors of ZnS, Cu and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy were used for structural and compositional analysis. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric and Photothermal Deflection Spectroscopy (PDS) measurements to assess the absorption coefficient of samples with different compositions. The PDS data show an increase of the sub-band absorption as the Sn content decreases. The results are interpreted assuming the formation of additional defects as the tin content is reduced. Those defects can also be responsible for the decrease of the band gap energy value as the Sn/Cu ratio is decreased.

Surface grafted glycopolymer brushes to enhance selective adhesion of HepG2 cells

This work demonstrates the application of carbohydrate based methacrylate polymer brush, poly(2-lactobionamidoethyl methacrylate), for the purpose of cell adhesion studies. The first part of the work illustrates the effects of the structure of the aminosilane based ATRP initiator layer on the polymerization kinetics of 2-lactobionamidoethyl methacrylate) (LAMA) monomer on thermally oxidized silicon wafer. Both monolayer and multilayered aminosilane precursor layers have been prepared followed by reaction with 2-bromoisobutyrylbromide to form the ATRP initiator layer. It is inferred from the kinetic studies that the rate of termination is low on a multilayered initiator layer compared to a disordered monolayer structure. However both initiator types results in similar graft densities. Furthermore, it is shown that thick comb-like poly(LAMA) brushes can be constructed by initiating a second ATRP process on a previously formed poly(LAMA) brushes. The morphology of human hepatocellular carcinoma cancer cells (HepG2) on the comb-like poly(LAMA) brush layer has been studied. The fluorescent images of the HepG2 cells on the glycopolymer brush surface display distinct protrusions that extend outside of the cell periphery. On the other hand the cells on bare glass substrate display spheroid morphology. Further analysis using ToF-SIMS imaging shows that the HepG2 cells on glycopolymer surfaces is enriched with protein fragment along the cell periphery which is absent in the case of cells on bare glass substrate. It is suggested that the interaction of the galactose units of the polymer brush with the asialoglycoprotein receptor (ASGPR) of HepG2 cells has resulted in the protein enrichment along the cell periphery.