Hot-wire CVD deposited n-type μc-Si films for μc-Si/c-Si heterojunction solar cell applications

Phosphorous-doped microcrystalline silicon (μc-Si) films were prepared using hot-wire chemical vapor deposition (HWCVD). Structural, electrical and optical properties of these thin films were systematically studied as a function of PH₃ gas mixture ratio. We report recent results for p-type crystalline silicon-based heterojunction (HJ) solar cells using the HWCVD n-μc-Si film to form an n-p junction. The surface morphology of the crystalline Si substrate after hydrogen treatment was examined using atomic force microscopy. A transfer length method was used to modify the indium-tin-oxide (ITO) deposition parameters in order to reduce front ITO/n-μc-Si contact resistance. In our best solar cell sample (1 cm²) without any buffer layer, the conversion efficiency of 15.1% has been achieved with an open circuit voltage of 0.615 V, fill factor of 0.71 and short circuit current density of 34.6 mA/cm² under 100 mW/cm² condition. The spectral response of this cell will also be discussed.     

High Rate Growth of a-Si and μc-Si Thin Films with Facing-target PECVD

The first investigation on high rate growth of uniform a-Si and μc-Si thin films with facingtarget plasma enhanced chemical vapour deposition (FTPECVD) has been presented here. It has been shown that by employing FTPECVD both a-Si and μc-Si thin films can be fabricated with rates of up to 10μm/h and l μm/h, respectively, around 10 times higher than those of the conventional PECVD, and the correspondent gas utility is about 20 times higher. As indicated by Raman spectroscopy measurement, the crystallinity of the materials is as high as 85%. A columnar structure in the films has been revealed by TEM analysis, a reflection of epitaxial growth in the deposition process.     

Optical and structural characterization of inhomogeneities in a-Si:H TO μc-Si transition

The a-Si:H films with different thickness and microstructure have been deposited with rf-PECVD using a plasma of silane diluted with hydrogen. The structure and optical analysis were carried out by X-ray diffraction, UV-VIS and Raman spectroscopy. Spectral refractive indices, optical energy band gaps, extinction coefficients, phases ratio and grain size were determined as a function of the hydrogen dilution (R = H₂/SiH₄). Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to micro-crystalline hydrogenated silicon (μc-Si:H). XRD analysis indicated that films with R = 0 and R = 20 were amorphous and homogeneous, while films with R = 40 and higher were micro-crystalline consisting medium range ordered silicon hydride (Si₄H) and μc-Si phases with different size of crystallites, which was confirmed also by Raman spectroscopy.     

Improvement of μc-Si:H n-i-p cell efficiency with an i-layer made by hot-wire CVD by reverse H2-profiling

The technique of maintaining a proper crystalline ratio in microcrystalline silicon (μc-Si:H) layers along the thickness direction by decreasing the H₂ dilution ratio during deposition (H₂ profiling) was introduced by several laboratories while optimizing either n-i-p or p-i-n μc-Si:H cells made by PECVD. With this technique a great increase in the energy conversion efficiency was obtained. Compared to the PECVD technique, the unique characteristics of HWCVD, such as the catalytic reactions, the absence of ion bombardment, the substrate heating by the filaments and filament aging effects, necessitate a different strategy for device optimization. We report in this paper the result of our method of using a reverse H₂ profiling technique, i.e. increasing the H₂ dilution ratio instead of decreasing it, to improve the performance of μc-Si:H n-i-p cells with an i-layer made by HWCVD. The principle behind this technique is thought to be a compensation effect for the influence of progressing silicidation of the filaments during the growth of μc-Si:H, if the filament current is held constant during growth. The dependence of the material crystallinity on thickness with and without H₂ profiling is discussed and solar cell J-V parameters are presented. Thus far, the best efficiency of μc-Si:H n-i-p cells made on a stainless steel substrate with an Ag/ZnO textured back reflector made in house has been improved to 8.5%, which is the highest known efficiency obtained for n-i-p cells with a hot-wire μc-Si:H i-layer.     

Wide optical bandgap p-type μc-Si:Ox:H prepared by Cat-CVD and comparisons to p-type μc-Si:H

Oxygen-impurity boron-doped hydrogenated microcrystalline silicon (p-μc-Si:O_x:H) films have been deposited using catalytic chemical vapor deposition (Cat-CVD). Pure silane (SiH₄), hydrogen (H₂), oxygen (O₂), and diluted diborane (B₂H₆) gases were used. The tungsten catalyst temperature (T_fil) was varied from 1900 to 2100 °C and films were deposited on glass substrates at temperatures of 100 to 300 °C. Different catalyst-to-substrate distances were employed and single- or double-coiled filaments were used. In addition to p-μc-Si:O_x:H deposition, we have also deposited conventional p-type microcrystalline silicon (p-μc-Si:H) in order to compare their electrical and optical properties to p-μc-Si:O_x:H.     

Development of n-type microcrystalline SiO<Subscript>x</Subscript>:H films and its application by innovative way to improve the performance of single junction µc-Si:H solar cell

Light trapping is one of the fundamental necessities of thin film based solar cell for its performance elevation. Back reflection of unused light of first pass is the key way to improve the light trapping phenomena. In this study we have reported the development of n-type hydrogenated microcrystalline silicon oxide (n-µc-SiO:H) layers of different characteristics. The deposition has been done by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. The detailed characterization of the films include the following: (1) electrical properties (2) optical properties like E₀₄ (3) structural studies which include crystalline fraction by Raman spectroscopy and grain size by X-ray diffraction measurement, FTIR spectroscopy, AFM and TEM studies. n-µc-SiO:H layer has been introduced as the n-layer of single junction p–i–n structure µc-Si solar cells. By various techniques the optimum use of n-µc-SiO:H layer for enhancing the performance of µc-Si:H solar cells has been done. It has been found that by using suitable bilayer of two different n-µc-SiO:H layers, it is possible to increase the solar cell performances. The maximum efficiency obtained without any back reflector is 8.44% that is about 8.9% higher than that obtained by using n-µc-Si:H layer as n-layer in the solar cells.     

Optimization of process parameters for sputtering of ceramic ZnO:Al2O3 targets for a-Si:H/μc-Si:H solar cells

Aluminum doped ZnO layers with a thickness of 800 nm were deposited dynamically by d.c. magnetron sputtering from a ceramic planar ZnO: Al₂O₃ target (1 wt.%). A wide range of process parameters, namely oxygen partial pressure, total pressure and power, was covered, while temperature was held constant at 300 °C. Visual absorption in the range of 2.3-4.7% and resistivities between 380 and 2150 µΩcm were obtained. In addition static imprints were performed to reveal the dependence of layer properties on target erosion. It was shown, that films deposited from targets with a race track deeper than 1.8 mm had very stable etching morphologies as well as optical and electrical properties in the range of the observed process parameters. In contrast, a new target yields very different etching structures and an increased resistivity.     

Insulating oxide buffer layer formed by sol–gel method for planarization of stainless steel substrate of a-Si:H thin film solar cell

The planarization of flexible stainless steel (SS) foils was investigated for the application of flexible solar cells. The sol–gel SiO₂ film containing nanoparticles was evaluated for a buffer layer on SS foils, and methods to improve the adhesion of SiO₂ film to SS foil were studied. The improvement of adhesion by adding Al₂O₃ matrix was discussed by analyzing the interface between Al₂O₃–SiO₂ film and SS foil. The usefulness of sol–gel buffer layer was also verified by comparing the performance of single junction a-Si:H thin film solar cells fabricated on bare SS foil and buffer layer-coated SS foil. The cell characteristics such as V_oc, J_sc, fill factor, and efficiency were all improved by adopting the buffer layer. The efficiency of the cell on buffer layer-coated and non-textured SS foil was 6.1% whereas the efficiency was 4.9% on bare SS foil.     

Influence of the electro-optical properties of an α-Si:H single layer on the performances of a pin solar cell

We analyze the results of an extensive characterization study involving electrical and optical measurements carried out on hydrogenated amorphous silicon (α-Si:H) thin film materials fabricated under a wide range of deposition conditions. By adjusting the synthesis parameters, we evidenced how conductivity, activation energy, electrical transport and optical absorption of an α-Si:H layer can be modified and optimized. We analyzed the activation energy and the pre-exponential factor of the dark conductivity by varying the dopant-to-silane gas flow ratio. Optical measurements allowed to extract the absorption spectra and the optical bandgap. Additionally, we report on the temperature dependence of the activation energy to satisfy the Meyer-Neldel rule. Finally, the influence of the individual films parameters upon the final performances of a single junction pin α-Si:H have been studied. The measurements show how a more than doubled enhancement in energy conversion efficiency can be obtained in an α-Si:H solar cell with a proper selection of synthesis conditions.     

Exploring ternary organic photovoltaics for the reduced nonradiative recombination and improved efficiency over 17.23％with a simple large-bandgap small molecular third component

Ternary strategy is one of the most effective methods to further boost the power conversion efficiency(PCE)of organic photovoltaic cells(OPVs).In terms of high-...     

NUV/VIS sensitive multicolor thin film detector based on a-SiC:H/a-Si:H/μc-SiGeC:H alloys with an in-situ structured transparent conductive oxide front contact without etching

An innovative family of hydrogenated amorphous silicon (a-Si:H) multicolor p-i-n photo sensors, sensitive in the VIS and the near UV spectrum, is presented. Typical values of the quantum efficiency at 350 nm and 580 nm are 5.4% and 54.7%, respectively, with − 0.4 V and − 12 V bias. Electro-optical studies were performed to explore the effect of combining linearly graded a-SiGe:H/μc-SiGeC:H layers with linearly graded a‐SiC:H-layers. The devices presented additionally contain a buried a-Si:H region. Low-reflective aluminum doped zinc oxide (ZnO:Al) back contacts improve the spectral color separation. μτ-products and absorption coefficients of graded absorbers were determined. Discrete absorbers were substituted by a linear graded a-SiC:H absorption zone in the top structure, an interior a-Si:H region and a graded a-SiGe:H/a-SiC:H alloy combination. In this paper we demonstrate a reduction of interference fringes and operation at low bias voltages, combined with a highly precise adjustment of the spectral sensitivity, even in the near UV-spectrum. The device dynamic range exceeds 50 dB at 1000 lx white-light illumination. As the deposited upper layers adopt the roughness of μc-SiGeC:H clusters in the rear absorber, we present an in-situ structured front contact without etching ZnO:Al.     

Triple Helix innovation in China’s dye-sensitized solar cell industry: hybrid methods with semantic TRIZ and technology roadmapping

In recent years, the Triple Helix model has identified feasible approaches to measuring relations among universities, industries, and governments. Results have been extended to different databases, regions, and perspectives. This paper explores how bibliometrics and text mining can inform Triple Helix analyses. It engages Competitive Technical Intelligence concepts and methods for studies of Newly Emerging Science & Technology (NEST) in support of technology management and policy. A semantic TRIZ approach is used to assess NEST innovation patterns by associating topics (using noun phrases to address subjects and objects) and actions (via verbs). We then classify these innovation patterns by the dominant categories of origination: Academy, Industry, or Government. We then use TRIZ tags and benchmarks to locate NEST progress using Technology Roadmapping. Triple Helix inferences can then be related to the visualized patterns. We demonstrate these analyses via a case study for dye-sensitized solar cells.     

Thermal,mechanical and chemical effects in the degradation of the plasma-deposited α-SiC:H passivation layer in a multilayer thin-film device

Amorphous, hydrogenated silicon carbide (-SiC:H) deposited by a plasma-enhanced-chemical-vapour-deposition (PECVD) process has been used as the topmost passivation layer in a multilayer thin-film device, namely, a thermal ink-jet printhead. Normal operations of the device involve rapid heating of the multilayer structure at several kHz, repetitively forming vapour bubbles that grow and collapse in an otherwise liquid environment. During such operations, the -SiC:H layer is subjected to a variety of thermal, mechanical and chemical stresses that are detrimental to its integrity. It is found that thermally activated failures may occur when the multilayer structure is driven for extended periods of time or by pulses of excessive magnitude or duration, or when the -SiC:H film is so thick as to store excessive elastic energy due to large differential thermal expansion effects. It is also found that severe mechanical (namely, cavitation) effects associated with bubble collapse cause early device failures if the surface of the device is exposed to an unlimited liquid reservoir; however, such adverse effects are greatly mitigated by the presence of a nozzle plate in the vicinity of the top surface. Finally, it is shown that high pH and various chemicals tend to etch the -SiC:H thin film through an oxidation-dissolution process, removing the passivating material rapidly and leading to device failures.     

High Pressure Synthesis of (La1?xSrx)8O20, (0.25 ≤ x ≤ 0.65) with a Wide Solubility Range and High Cu-Valence

With an attempt to increase the Cu valence, we synthesized the (La_1–x Sr _x )₈Cu₈O_20– (8-8-20 phase) compounds with large x using an O₂-HIP apparatus. By heat treatment in a high-pressure of oxygen gas (40 MPa), the 8-8-20 compounds were stabilized in the range of 0.25 x 0.65. Their crystal structures, characterized by x-ray Rietveld refinement and electron diffraction, are tetragonal, space group P4/mbm. The formal copper valence was found to increase with Sr concentration from 2.24 at x = 0.25 to 2.63 at x = 0.65, keeping the oxygen content constant around 20.0. Electrical resistivity and magnetic susceptibility showed only metallic behavior from room temperature down to 5 K with no sign of superconductivity.     

Processing and thermal stability of a Cfiber/SiCfiller/Si–C–Nmatrix composite: effect of oligomer vaporization and the surface oxide layer of SiC filler

The processing of carbon fiber-reinforced ceramic matrix composites (CMC) made by the precursor impregnation and pyrolysis (PIP) method was improved, and factors which deteriorate the thermal stability of the CMC were investigated. The processing time for cross-linking of a precursor polymer was substantially reduced by the application of a sealed metal container due to the suppression of the vaporization of oligomers. The strength of the as-fabricated CMC was 286 MPa and 77% of the original strength was retained after a heating at 1350 °C for 24 h in Ar. The reduction of the strength after the heating was due to the decomposition of SiO₂ which remained at the surface of the SiC filler particles. The decomposition reaction induced deterioration of carbon fibers and the matrix of the CMC at high temperature.     

Design and analysis of a new structure of InAs/GaAs QDIP for 8–12 μm infrared windows with low dark current

Based on the effective mass Schrödinger equation and eight-band k.p method, we study optical absorption in the 8–12 µm infrared window through the conduction subbands of self-assembled InAs/GaAs pyramidal shape quantum dots (QDs) using the finite difference method. Considering homogeneous and inhomogeneous broadening effects, the absorption spectra of QDs are calculated. Regarding the simulation results, we design a QD infrared photodetector (QDIP) with a double barrier resonant tunnelling (DBRT) at λ = 10 µm. We calculate the responsivity, detectivity and dark current for the device, considering the coverage factor of QDs. To enhance the performance of the presented DBRT especially at near room temperature, we propose a modified QDIP with asymmetric multiple barrier resonant tunnelling structure. With the modified structure, the dark current reduces to about half an order of magnitude compared with DBRT–QDIP, and detectivity increases to 1.4 × 10⁹ cm Hz^1/2/W at 200 K.     

Tribological properties and high-speed drilling performance of Zr–C:H:Nx% coatings with different amounts of nitrogen addition

Zr–C:H:N _x% coatings with nitrogen additions ranging from 0 to 29 at.% are deposited on AISI M2 steel substrates and micro-drills using a closed field unbalanced magnetron (CFUBM) sputtering technique. The tribological properties of the coatings are tested against AISI 52100 steel balls under loads of 10 and 100 N, respectively, using an oscillating friction and wear tester. The drilling performance of the coated micro-drills is evaluated by performing high-speed through-hole drilling tests using printed circuit boards as a test material. The wear testing results reveal that the Zr–C:H:N_8% coating has excellent tribological properties, including a low wear depth, a low friction coefficient, and an extended lifetime. Meanwhile, the drilling tests reveal that the Zr–C:H:N_8% coating increases the tool life of the micro-drill by a factor of five compared to an uncoated micro-drill when used for the high-speed through-hole drilling of PCBs and yields a considerable improvement in the machining quality of the drilled hole.     

Radiation Resistance of α-Si:H/Si Heterojunction Solar Cells with a Thin <Emphasis Type="Italic">i</Emphasis>-α-Si:H Inner Layer

We have studied the degradation of photoelectric characteristics of heterojunction solar cell samples based on α-Si:H/Si structures upon irradiation by electrons with an energy of 3.8 MeV and fluences of 1 × 10¹²–1 × 10¹⁴ cm^–2. It is shown that the efficiency of the samples of heterojunction solar cell elements under the conditions of AM0 illumination (0.136 W/cm²) is reduced by 25% at a fluence of 2 × 10¹³ cm^–2. This is more than an order of magnitude higher than the critical fluence value achieved previously when silicon solar cells with a p–n junction and an n-type base were irradiated by high-energy electrons.     

Synthesis and characterization of Mu-11: a porous sodium trisilicate Na2Si3O7·H2O with 10-membered ring openings

The title compound (named Mu-11) is a new type of sodium trisilicate which was synthesized by using the quasi non-aqueous route in the presence of ethylene glycol as solvent. This material was characterized by XRD, SEM, ²⁹Si solid-state MAS NMR spectroscopy, elemental and thermal analyses. The structure was determined by single-crystal X-ray diffraction. The symmetry is monoclinic, space group P2₁/c, a=7.3087(8)Å, b=12.7246(13)Å, c=9.0913(11)Å, β=119.01(1)° and V=739.39(10) ų. The structure consists of corrugated sheets built from four-, six- and eight-membered ring units. The connection of such sheets leads to a three-dimensional framework with a monodimensional channel system delimited by a 10-ring aperture. After heating to 300°C another novel phase crystallizes, which is stable up to 600°C.