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Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) mixed with single-wall nanotubes (SWNTs) (10:1) and doped with (0.1 M) perchloric acid (HClO4) in a solution-processed film, working as an excellent thin transparent conducting film (TCF) in organic solar cells, was investigated. This new electrode structure can be an outstanding substitute for conventional indium tin oxide (ITO) for applications in flexible solar cells due to the potential of attaining high transparency with enhanced conductivity, good flexibility, and good durability via a low-cost process over a large area. In addition, solution-processed vanadium oxide (VOx) doped with a small amount of PEDOT-PSS(PH1000) can be applied as a hole transport layer (HTL) for achieving high efficiency and stability. From these viewpoints, we investigate the benefit of using printed SWNTs-PEDOT-PSS doped with HClO4 as a transparent conducting electrode in a flexible organic solar cell. Additionally, we applied a VOx-PEDOT-PSS thin film as a hole transporting layer and a blend of PTB7 (polythieno[3,4-b] thiophene/benzodithiophene): PC71BM (phenyl-C71-butyric acid methyl ester) as an active layer in devices. Zinc oxide (ZnO) nanoparticles were applied as an electron transport layer and Ag was used as the top electrode. The proposed solar cell structure showed an enhancement in short-circuit current, power conversion efficiency, and stability relative to a conventional cell based on ITO. This result suggests a great carrier injection throughout the interfacial layer, high conductivity and transparency, as well as firm adherence for the new electrode.

International audience; Transparent flexible organic solar cells (OSCs) are attracting increasing attention as an essential constituent for constructing smart window technologies and integrated photovoltaics (PVs). However, silver nanowire (AgNW) electrodes with negligible sheet resistance, good transmittance, and low costs are especially appealing in the design of flexible OSCs that require similar power conversion efficiency (PCE) values and superior flexibility compared with devices based on indium tin oxide (ITO) electrodes. Herein, the new digital printing technology of digital materials deposition to print the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer and AgNWs as top and bottom electrodes for transparent flexible OSCs with an active layer as poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) are used. All other thin layers are deposited on the polyethylene terephthalate (PET) substrate by the conventional process. The PV performance of the devices under inverted structure PET/AgNWs/ZnO/P3HT:PCBM/PEDOT/AgNWs is short circuit current density (Jsc) = 9.8 mA cm−2, open circuit voltage (Voc) = 0.53 V, fill factor (FF) = 0.60, and PCE = 2.9% with visible light transparency = 45%.

Photoelectrochemical devices based on p-type nanostructured semiconducting materials show strong potentialities for various applications, such as photovoltaics and photocatalysis. While only one study was reported on the use of the reference dye P1 for solid-state p-type dye-sensitized solar cells (DSSC), in this work we have systematically investigated two diketopyrrolopyrrole (DPP) derivatives as sensitizers for solid-state p-type DSSC based on NiO and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as solid-state electron transporter material. We report on the performance in solid-state p-type DSSC of a simple DPP dye bearing a thienyl carboxylic acid as the binding group and a parent compound substituted by a pyromellitimide (PYRO) playing the role of a secondary inner electron acceptor. By focusing on the dye/PCBM interface, we specifically show using transient photoluminescence measurements that the presence of a secondary electron acceptor unit can efficiently favor the formation of the (dye+/PCB...

This work explores the potentiality of Mo6 clusters as new inorganic sensitizers with amphoteric properties for photoelectronic applications being non-toxic and stable. It reports on the design of photoelectrodes by electrophoretic deposition (EPD) of molybdenum octahedral metal cluster iodide (CMI) onto mesoporous TiO2 and NiO layers before being deposited on FTO (i. e. CMI@TSO@FTO, TSO = TiO2 or NiO). Indeed, the low-cost, low-waste and industrially scalable EPD method has allowed for the achievement of transparent, homogeneous orange/red [Mo6Ii8]4+ cluster core-based films, and appears suitable for the sensitization of TiO2- and NiO-based electrodes of n- and p-type solar cells inspired from dye-sensitized solar cells (DSSCs). First, the EPD process was optimized by the direct deposition of CMI onto an FTO substrate (CMI@FTO) leading to the realization of highly transparent colored films. Second, strongly colored CMI@TSO@FTO photoelectrodes were achieved and integrated into solar cell devices. Hence, compared to the classical soaking method, the EPD process significantly improves the quality (i.e., its homogeneity and absorption properties) of the photoelectrodes, leading consequently to much better photovoltaic performances.

Much research has been conducted to improve the performance of photovoltaic solar cells. Transparent conductive film and interconnection layers have a significant impact on the performance of photovoltaic cells. In this work, we analyze the experimental results obtained on tandem organic photovoltaic solar cells with simple inverted structures using silver nanowires AgNW as transparent conductive electrode (TE) and as interconnection layer (ICL) between PEDOT: PSS and ZnO. This type of contact leads to a strong ohmic contact in both sub-cells having P3HT: ICBA as the lower active layer and having PTB7: PC71BM (1: 1.5) as the upper active layer with a good complement of the absorption spectrum. To study the advantages of using AgNWs as an interconnection layer (PEDOT: PSS/AgNWs/ZnO) in tandem photovoltaic solar cells and as an anode and its impact on the performance of these organic cells, we have simulated the electrical characteristics obtained by these tandem organic photovoltaic cells using an equivalent circuit model. This model is based on a single diode model with five photovoltaic parameters. We therefore extracted all the physical parameters of the illuminated photovoltaic cell from its experimental characteristics (J–V), such as the diode saturation current density (J0), the series and shunt resistors (RS, RSh), the ideality factor (n) and the photogenerated current density (JPh). For this we have solved the analytical equations of the current density using Newton Raphson's method. The equations are derived from the single diode equivalent circuit proposed to simulate the measured current density as a function of the voltage of the manufactured tandem type organic solar cells. A good agreement was obtained between the theoretical model and the experimental electrical characteristics. This confirms that the use of AgNWs between PEDOT: PSS and ZnO as an interconnection layer in reverse geometry of these tandem devices, has improved the efficiency (PCE = 9.24%) and is proving to be an efficient recombination layer for tandem organic photovoltaic solar cells.

Funding: European Research Council (grant number 321305) and the EPSRC (grant number EP/L017008/1). IDWS is a Royal Society Wolfson Research Merit award holder. Hybrid materials combining a wide bandgap metal oxide semiconductor, metal chalcogenide nanocrystals and molecular systems represent very attractive materials for fabricating devices with new function or improved photoelectrochemical performances. This study deals with sensitization of NiO, which is a p-type semiconductor, by quantum dots (QDs) of PbS with an average diameter of 3 nm. The PbS QDs were attached to the monocrystalline film of NiO by mercaptopropionic acid linker and were subsequently capped with methyl-pyridine naphthalene diimide (NDI) units to prepare quantum dot sensitized solar cells (p-QDSSCs) on NiO electrodes. Time-resolved photoluminescence measurements of the PbS emission were used to determine the rate constants for charge transfer from the PbS exciton to the NiO, cobalt based redox mediator and NDI. Notably, it was shown that NDI quenches the PbS exciton by electron transfer with a quite fast rate constant (6.9 x 107 s-1). The PbS QDs sensitized NiO films were finally used to fabricate solar cells with tris(4,4’-ditert-butyl-2,2’-bipyridine) cobalt(III/II) as redox mediator. It was observed that the presence of NDI on PbS improved the photovoltaic performance by 50% relative to that of cells without NDI, leading to a device with the following characteristics: Jsc = 5.75 mA/cm2, Voc = 226 mV, ff = 34% and PCE = 0.44%. This study demonstrates that photogalvanic processes can be a productive pathway to better performing sensitized p-type semiconductor for p-QDSSC. In other words, photoinduced electron transfer from the QDs towards the electrolyte rather than initial photoinduced charge injection into the p-type semiconductor can be a favorable operative mechanism in QD sensitized NiO films and might be exploited further for the construction of better performing solar cells or photocatalytic devices. Postprint Postprint

We report the synthesis of three new push-pull dyes specially designed for the sensitization of mesoporous p type semi-conductor NiO for the construction of p type dye sensitized solar cells (pDSC). Their structure stems from the conjugation of the well-known tris(carboxy-arlyamine) anchoring moiety to a benzothiadiazole acceptor through a fluorene ( PP1 ) or thiophene-fluorene linker ( PP2 ). Appending a NDI secondary acceptor onto PP2 yielded a dyad ( PP2-NDI ). The push-pull structure is here particularly adapted to the sensitization of p-type semi-conducting materials. All three dyes were investigated by spectroscopic and electrochemical techniques, and their electronic properties were modelled by TD-DFT. In all cases, the new sensitizers exhibit adequate absorption features (spanning from 400 nm to 600 nm, extinction coefficients between 20000 and 27000 M −1 cm −1 ) and their thermodynamic parameters are all in favor of efficient interfacial charge transfers involving NiO. pDSC were constructed with all three dyes; high photoconversion efficiencies (PCE) were reached, especially in the case of dyad PP2-NDI (Jsc = 5.90 mA/cm 2 , Voc = 143 mV, FF = 33.8%, PCE = 0.29%), due to a combination of outstanding electronic properties and increased charge separation state lifetime. Tandem DSC (tDSC) composed of a TiO 2 photoanode sensitized by the dye D35 and a NiO photocathode sensitized by PP2-NDI were assembled with two different electrolytes (I 3 − /I − or T 2 /T − based electrolytes). The latter gave PCE among the best ever reported for tDSC (Jsc = 5.90 mA/cm 2 ; Voc = 896 mV; FF = 63%, PCE = 2.80% in the case of the I 3 − /I − electrolyte, Jsc = 4.52 mA/cm 2 , Voc = 840 mV, FF = 60% and PCE = 2.27% for T 2 /T − based devices) unraveling the significance of the new dyes presented in this study.

International audience; Due to the potential of achieving high conductivity and high transparency, low-cost, large-area and flexibility for versatile applications as organic solar cells, silver nanowires (AgNWs) have attracted great attention as a good alternative to conventional ITO. However, design and production of conducting transparent film and interconnecting layers plays a very important role to achieve a high device performance. We discuss the benefit of the AgNWs inserted in the organic tandem solar cell devices as transparent electrode (TE) and as interconnecting layer (ICL) between the two subcells having actives layers with complementary absorption and made of poly(3-hexylthiophene):indene-C60 bisadduct and polythieno [3,4-b]thiophene/benzodithiophene: phenyl-C71-butyric acid methyl ester. ZnO nanoparticles have been used as interfacial layer in the ICL and lead to a decrease of the AgNWs roughness. The tandem cells on AgNWs show a good efficiency (PCE=9.23%), a short circuit current density of 11.23 mA/cm2 close to the lower short circuit current of the two solar subcells, and an open circuit voltage (Voc=1.47 V) matching the sum of the two subcells Voc. This suggests that the ICL provides a good carrier injection through the interfacial layer and an efficient recombination of the current coming from each subcells. Moreover, optical modeling is done in order to calculate the optimized active layers thicknesses and short term stability in open air evaluated.

ANR is gratefully acknowledged for the financial support of these researches through the QuePhelec project (n° ANR-13-BS10-0011-01). Région des Pays de la Loire and Nantes University for the project LUMOMAT are also acknowledged. We acknowledge support from the European Research Council (grant number 321305) and the EPSRC (grant number EP/L017008/1). IDWS is a Royal Society Wolfson Research Merit award holder. The research data supporting this publication can be accessed at http://dx.doi.org/10.17630/ddaebfb9-e127-43cb-9048-966a572b50ac. Quantum dots (QDs) are very attractive materials for solar cells due to their high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to quantum confinement. Particularly interesting are the PbS QDs owing to their broad spectral absorption until the long wavelengths, their easy processability and low cost. Here, we used control of the PbS QDs size to understand charge transfer processes at the interfaces of NiO semiconductor and explain the optimal QDs size in photovoltaic devices. Towards this goal, we have synthesized a series of PbS QDs with different diameters (2.8 A until 4A) and investigated charge transfer dynamics by time resolved spectroscopy and their ability to act as sensitizers in nanocrystalline NiO based solar cells using the cobalt tris(4,4'-diterbutyl-2,2'-bipyridine) complex as redox mediator. We found that PbS QDs with average diameter of 3.0 nm are optimal size in terms of efficient charge transfers and light harvesting efficiency for photovoltaic performances. Our study showed that an hole injection from PbS QDs to NiO valence band (VB) is an efficient process even with low injection driving force (0.3 eV) and occurs in 6-10 ns. Furthermore we found that the direct electrolyte reduction (photoinduced electron transfer to the cobalt redox mediator) also occurs in parallel to the hole injection with rate constant of similar magnitude (10-20 ns). In spite of its large driving force, the rate constant of the oxidative quenching of PbS by Co(III) diminishes more steeply than hole injection on NiO when the diameter of PbS increases. This is understood as the consequence of increasing the trap states that limit electron shift. We believe that our detailed findings will advance the future design of QD sensitized photocathodes. Postprint

International audience; Copper phthalocyanine-3,4′,4″,4‴ tetra-sulfonated acid tetrasodium salt (TS-CuPc) are promising interfacial materials fororganic photovoltaics (OPVs) because of their electrical properties, solution process ability and stability. In this article,we report the fabrication of poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) OPV devicesincorporating solution-based TS-CuPc as electron transport layers that show promising enhancements of the devicephotocurrent and stability. We also discuss the impact of the mechanism of Photochemical and photophysical behaviorand all parameters on device performance as well as the ambient degradation of these devices. In these results we showedcharge extraction improvement by the use of the TS-CuPc.

Sensitized NiO based photocathode is a new field of investigation with increasing scientific interest in relation with the development of tandem dye-sensitized solar cells (photovoltaic) and dye-sensitized photoelectrosynthetic cells (solar fuel). We demonstrate herein that PbS quantum dots (QDs) represent promising inorganic sensitizers for NiO-based quantum dot-sensitized solar cells (QDSSCs). The solar cell sensitized with PbS quantum dot exhibits significantly higher photoconversion efficiency than solar cells sensitized with a classical and efficient molecular sensitizer (P1 dye = 4-(Bis-{4-[5-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl}-amino)-benzoic acid). Furthermore, the system features an IPCE (Incident Photon-to-Current Efficiency) spectrum that spreads into the infra-red region, reaching operating wavelengths of 950 nm. The QDSSC photoelectrochemical device works with the complexes tris(4,4′-ditert-butyl-2,2′-bipyridine)cobalt(III/II) redox mediators, underscoring the formation of a long-lived charge-separated state. The electrochemical impedance spectrocopy measurements are consistent with a high packing of the QDs upon the NiO surface, the high density of which limits the access of the electrolyte and results in favorable light absorption cross-sections and a significant hole lifetime. These notable results highlight the potential of NiO-based photocathodes sensitized with quantum dots for accessing and exploiting the low-energy part of the solar spectrum in photovoltaic and photocatalysis applications.

Recently many investigations have been done to improve the performance of solar cells photovoltaic. One of this devices developed is the Bulk Heterojunction (BHJ) solar cells based on poly (3-hexylthiophene) (P3HT)/[6, 6]-phenyl C-61-butyric acid methyl ester (PCBM) blend which have been fabricated by spin-coating. It is known that the nano structure of the active layer of this device has an important impact on the photovoltaic performances. In this work, we analyze the results obtained on solar cells using a copolymer P3HT-b-PS based on poly (3-hexylthiophene) (P3HT) as a donor block and polystyrene (PS) as a soft block, their compatibility with the blend of P3HT/PCBM at various weight percentages (0%-5%). The addition of this weight percentage is in order to improve the performance of polymer solar cells. It has been demonstrated that the addition of a small amount of P3HT-b-PS (from 0.5%-1.5%) led to an increase in photovoltaic efficiency compared to devices made from P3HT/PCBM only. To study the impact of the added amount of the P3HT-b-PS on the performances of the fabricated organic cells, we used an equivalent circuit model based on single diode model with five photovoltaic parameters. Then, we extracted these physical parameters of the organic photovoltaic cells such as the saturation current density, the series and shunt resistances, the ideality factor and the photogenerated current density from the experimental characteristics (J-V) in the dark and under illumination. We proposed and developed the used procedure based on this model and we resolved the analytic equations of the density-current using the Lambert W-function. A good agreement between the theoretical model and the experimental data of electrical characteristks is obtained illustrating the enhancement of the addition of a small amount of P3HT-b-PS (

International audience; Si (001)-oriented substrates (p-type) were implanted at 10 keV with He ion doses in the 5 x 10(15) cm(-2) range. They were annealed at 973 K for 1 h to create a buried layer of nano-sized bubbles. Layers of Si0.37Ge0.23 about 215 nm thick were grown by low pressure chemical vapor deposition at 848 K on these silicon wafers. The surface roughness and morphology were checked by atomic force microscopy and optical microscopy before and after etching with a modified Shimmel recipe to reveal etch pit dislocations. The thickness, composition, crystalline quality and relaxation-state of the SiGe layer were assessed by Rutherford backscattering spectroscopy and high-resolution X-ray diffraction. A fully relaxed strain-state was obtained for Si0.77Ge0.23 layers that did not exhibit the classical cross-hatched pattern morphology while having a threading-dislocations density below 10(3) cm(-2). This low dislocation density was confirmed by photoluminescence spectroscopy. From high resolution transmission electron microscopy observations, the quasi-total strain-relief is assumed to take place by emission of dislocation loops protruding down into the Si substrate from the SiGe/Si interface and terminating at void surfaces of the buried-nanoporous layer. Possible annihilation of dislocation segments coming from either the SiGe/Si interface or punched out in glide planes by overpressurized nanobubbles may also occur. This near surface porous Si is well adapted for multiple junction solar cell manufacturing. (C) 2014 Elsevier B.V. All rights reserved.

Ultra-thin magnesium oxide layers were elaborated by atomic layer deposition and oxidation process on silicon (100) starting from (2 × 1) thermally-reconstructed or hydrogen-terminated Si surfaces. Low-energy electron diffraction experiments show (2 × 3) and (3 × 3) reconstructions while depositing a magnesium monolayer on Si clean surfaces, and a 3-dimentional growth of the oxide as confirmed by ex-situ atomic force microscopy. For hydrogen-terminated or clean surfaces previously physisorbed by oxygen, uniform cobalt/magnesium-oxide/silicon stacks of layers are observed by transmission electron microscopy. Annealing above 150 °C leads to MgO dissolution and formation of an interfacial complex compound by inter-diffusion of Si and Co.

International audience; In this study, we focus on transparent electrodes for organic solar cells prepared from aqueous solutions consisting of single wall carbon nanotubes (SWCNTs) and a copper-phthalocyanine derivative (TSCuPc). We first investigated their electrical conductivity and optical properties. The high solubility level of the TSCuPc/SWCNTs enables the production of stable inks with high conductivity which allows obtaining flexible photovoltaic devices based TSCuPc/SWCNTs films with good performances. A power conversion efficiency of 3.2% was achieved in a device with a blend of poly (3-hexylthiophene-2,5-diyl): phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as the active layer with a TSCuPc/SWCNTs sprayed electrode on a polyethylene terephthalate (PET) substrate. TSCuPc and TSCuPc/SWCNTs were also employed as the electron transport layer (ETL) and the interconnecting layer (ICL) in an inverted tandem organic solar cell based on front P3HT-ICBA and back [70] PCBM-PCDTBT active layers, achieving an efficiency of 7.40%.

International audience; A fullerene end-capped polymer-compatibilizer based on poly(3-hexylthiophene) (P3HT) was synthesized and demonstrated to have a remarkable effect on both the stability and efficiency of devices made from exemplar P3HT and [6,6]-phenyl C-61-butyric acid methyl ester (PCBM). P3HT with ethynyl chain-ends and alpha-azido-omega-bromo-PS were prepared via Grignard metathesis (GRIM) and atom transfer radical polymerisation, respectively. "Click" chemistry resulted in the preparation of poly(3-hexylthiophene)block- omega-bromo-polystyrene (P3HT-b-PS-Br), and subsequent atom transfer radical addition chemistry with fullerene (C-60) yielded the donor-acceptor block copolymer P3HT-b-PS-C-60. Both P3HT-b-PS-Br and P3HT-b-PS-C-60 were considered as compatibilizers with P3HT/PCBM blends, with the study detailing effects on active-layer morphology, device efficiency and stability. When used at low concentrations, both P3HT-b-PS-Br (1%) and P3HT-b-PS-C-60 (0.5%) resulted in considerable 28% and 35% increases in efficiencies with respect to devices made from P3HT/PCBM alone. Furthermore, P3HT-b-PS-C-60 (0.5%) resulted in an important improvement in device stability.

Efficient bulk-heterojunction polymer solar cells based on poly(3-hexylthiophene) (P3HT) blended with a fullerene derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were fabricated in inverted configuration by using copper phthalocyanine-3,4′,4′′,4′′′tetra-sulfonated acid tetrasodium salt (TS-CuPc) as the electron collecting layer and MoO 3 as hole collecting layer. TS-CuPc is observed to be critical for the device performance, significantly enhancing the Jsc and the PCE compared to devices based on TiO x . The optimal thicknesses of MoO 3 and TS-CuPc were 10 nm and 15 nm, respectively. Based on these optimal parameters, the PCE of 3.6% was obtained compared to 3.4% for the reference TiO x /P3HT:PCBM/MoO 3 /Ag.

International audience; Optical emission spectroscopy of sputtered species during ion bombardment, Auger electron spectroscopy and high-resolution transmission electron microscopy were used to study the cobalt and silicon diffusion through the interfaces of Co/AlO/Si(0 0 1) hetero-structure. The results are discussed as a function of the annealing temperature of sample and show that the diffusion process at the interfaces starts for annealing temperatures above 200 °C without detectable modification of the oxide layer.

Auger electron spectroscopy, secondary neutral mass spectrometry and high-resolution transmission electron microscopy were used to assess the chemical, morphological and structural modifications after annealing of cobalt/aluminum oxide/silicon(001) hetero-structure. The results show that the aluminum oxide forms a diffusion barrier for temperatures lower than 200 °C. Beyond this temperature, cobalt atoms diffuse in the silicon region without apparent modification of the barrier. At 340 °C, the asymmetric diffusion could be explained by the formation of an AlCoO complex oxide playing the role of a diffusion barrier for Si atoms.

To weight the importance of a nanocavity buffer in a SiGe deposition substrate, some P type (001) FZ Si wafers are implanted (A samples) or not (B samples) at room temperature with 5×1016 He+ cm–2 at 10keV. They are annealed at 700°C for one hour to form a nanocavity layer close to the Si surface. Then, the wafers are carefully chemically cleaned in a clean room to remove both organic and metallic impurities from the surface. They are coated either by 210 nm (A) or 430 nm (B) Si1−xGex (x=0.20±0.02) alloy grown at 575°C for 0.42 hour by low pressure chemical vapor deposition (LP-CVD) with a growth rate of 8 to 17 nm.mn−1. Both kinds of samples are studied by cross section transmission electron microscopy, X-rays diffraction, Rutherford backscattering, atomic force microscopy and etch pit counts. The association of these techniques demonstrates that the thin SiGe layer which is deposited on sample A is fully relaxed and that the threading dislocation density (estimated to hardly reach 4×103cm−2) is at least one order of magnitude lower than what is obtained so far using ion implantation assistance in SiGe layer growth on Silicon. The roughness of the SiGe surface is low enough to stand a further Si epitaxy. Nevertheless, the mechanism involved responsible for the threading dislocation annihilation and/or confinement is still unclear.

P‐type (100) float zone Si wafers were implanted at room temperature by Ne or He at high dose (5×1016 cm−2) and low energy (50keV or 10keV respectively). Some of them were annealed at low (700°C) and high (1050°C) temperatures to form a close surface buried layer of tiny cavities and to test their thermal stability. Microscopic studies of these samples revealed that He‐implanted wafers were adequate substrates for epitaxial growth. Hence, as‐implanted He samples were carefully chemically cleaned to grow by low pressure chemical vapor deposition thin Si0.80Ge0.20 layers (about 170nm thick) at 600°C with a growth rate of (11.6±0.5) nm.mn−1. X‐ray diffraction measurements demonstrated that the final layer was fully relaxed. Meanwhile atomic force microscopic scans revealed that the surface roughness was low enough (0.3nm) to stand further silicon deposition. Etch pit counts yield a threading dislocation density of (2.3±0.7)×104 cm−2. Since this density value is about two orders of magnitude lower than what w...