MVSystems Inc.

Golden, CO, United States

MVSystems Inc.

Golden, CO, United States
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Kiriluk K.G.,Colorado School of Mines | Williamson D.L.,Colorado School of Mines | Bobela D.C.,National Renewable Energy Laboratory | Taylor P.C.,Colorado School of Mines | And 5 more authors.
Materials Research Society Symposium Proceedings | Year: 2010

We have used small-angle x-ray scattering (SAXS) in conjunction with X-ray diffraction (XRD) to study the nanostructure of hydrogenated nanocrystalline silicon (nc-Si:H). The crystallite size in the growth direction, as deduced from XRD data, is 24 nm with a preferred [220] orientation in the growth direction of the film. Fitting the SAXS intensity shows that the scattering derives from electron density fluctuations of both voids in the amorphous phase and H-rich clusters in the film, probably at the crystallite interfaces. The SAXS results indicate ellipsoidal shaped crystallites about 6 nm in size perpendicular to the growth direction. We annealed the samples, stepwise, and then measured the SAXS and ESR. At temperatures below 350°C, we observe an overall increase in the size of the scattering centers on annealing but only a small change in the spin density, which suggests that bond reconstruction on the crystallite surfaces takes place with high efficacy. © 2010 Materials Research Society.

Kiriluk K.G.,Abengoa Solar | Fields J.D.,Colorado School of Mines | Simonds B.J.,Colorado School of Mines | Pai Y.P.,Colorado School of Mines | And 9 more authors.
Applied Physics Letters | Year: 2013

We demonstrate that in nanostructured films of nanocrystalline silicon imbedded in a hydrogenated amorphous silicon matrix, carriers generated in the amorphous region are transported out of this region and therefore do not recombine in the amorphous phase. Electron paramagnetic resonance (EPR) and photoluminescence (PL) measurements show that the EPR and PL from the amorphous phase are rapidly quenched as the volume fraction of Si nanocrystals exceeds about 30 vol. . We propose the use of similar structures to dramatically increase the open circuit voltages in solar cell devices. © 2013 American Institute of Physics.

Matulionis I.,MVSystems Inc. | Hua J.,MVSystems Inc. | Zhu F.,MVSystems Inc. | Gallon J.,MVSystems Inc. | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Photoelectrochemical (PEC) water dissociation into hydrogen and oxygen at a semiconductor-liquid interface offers an environmentally benign approach to hydrogen production. We have developed an integrated PEC device using hydrogenated amorphous silicon carbide (a-SiC or a-SiC:H) material as photoelectrode in conjunction with an amorphous silicon (a-Si) tandem photovoltaic device. Such a "hybrid PV/a-SiC" PEC cell produces photocurrent of about 1.3 mA/cm2 in a short-circuit configuration and is durable in a pH2 electrolyte. On the other hand, the aforementioned structure finished with ITO contacts and measured as a solid-state device features a current density of 5 mA/cm2, indicating a potential solar-to-hydrogen (STH) conversion efficiency of about 6% in the hybrid PV/a-SiC PEC cell. The much lower photocurrent measured in the hybrid PEC cell suggests that there exists an interfacial barrier between the a-SiC and electrolyte, which hinders the photocurrent extraction. In order to mitigate against the interfacial barrier and hence improve the photo-generated charge carrier transport through the a-SiC/electrolyte interface, we have explored several surface modification techniques, namely the use of metallic nano-particles (such as platinum or palladium) and the growth of an additional thin layer (a-SiNx, carbon-rich a-SiC, a-SiF, etc.) on the top of a-SiC by PECVD. In the latter case, it is observed that the addition of a thin PECVD-fabricated layer does not significantly improve the photocurrent, presumably due to a poor band alignment at the a-SiC/electrolyte interface. The use of lower work function nanoparticles like titanium has led to promising results in terms of photocurrent enhancement and an a nodic shift in the onset potential. © 2010 SPIE.

Zhu F.,MVSystems Inc. | Hu J.,MVSystems Inc. | Matulionis I.,MVSystems Inc. | Gallon J.,MVSystems Inc. | Madan A.,MVSystems Inc.
Materials Research Society Symposium Proceedings | Year: 2012

We describe the properties of nano-crystalline silicon based alloy (nc-SiXY) prepared by a very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) technique with silane (SiH4) and XY gas mixtures and diluted in hydrogen (H2) at low deposition temperature. Varying the gas ratio among SiH4, H2 and XY gasses could alter the optical bandgap and structure. The nc-Si films with high crystalline volume fraction were first prepared, and then the XY gasses were added in order to tune the microstructure and opto-electronic properties of this nano-crystalline silicon based alloy. We have characterized the materials using UV-VIS-NIR, Raman, Constant Photocurrent Method (CPM), dark- and photo-conductivity. As XY gas flows were increased, the optical bandgap of nc-SiXY films increased, while its crystalline volume fraction and conductivity decreased. With proper control of the silane concentration, XY/SiH4 gas ratio, and deposition pressure, we have fabricated the nc-SiXY film with optical bangap of about 1.5eV. Applying this material as the absorber layer in p-i-n devices with configuration of textured ZnO/nc-p+/nc-SiXY/a-n+/Ag, the efficiency is 7.25% (Voc=0.616V, Jsc=17.69mA/cm2, FF=0.666) with thickness of ∼0.8μm. © 2012 Materials Research Society.

Ahnood A.,University College London | Suzuki Y.,University College London | Madan A.,MVSystems Inc. | Nathan A.,University of Cambridge
Thin Solid Films | Year: 2012

The growth of low temperature silicon nitride using radio frequency (RF) plasma enhanced chemical vapour deposition (PECVD) is associated with high porosity and surface roughness due to the short surface diffusion length of adsorbed radicals during the deposition. In this work we present pulsed-RF PECVD as a means of achieving a film with smoother surface and reduced density of voids. The growth process and the longer surface diffusion length are discussed as the main reason behind improvement of film density while maintaining the substrate temperatures. The deposited films exhibit improved electrical performance with 72% reduction in breakdown probability compared with conventional continuous-wave RF PECVD films. A low interfacial defect density with a field effect mobility of 1.1 cm 2/V.s and subthreshold slope of 0.3 V/dec, was achieved when used as a gate dielectric in thin film transistors. © 2012 Elsevier B.V. All rights reserved.

Fields J.D.,Colorado School of Mines | Gallon J.B.,MVSystems Inc. | Hu J.,MVSystems Inc. | Valentich E.,MVSystems Inc. | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Our efforts focus on developing a method to produce hydrogenated nanocrystalline silicon (nc-Si:H) with larger crystallites to enhance carrier transport properties. A new PECVD methodology, called double pulsed PECVD (DPPECVD), employs alternating low frequency and high frequency discharge sub-cycles to sequentially grow and etch the evolving film, respectively. This confers enhanced process control compared to conventional methods, and provides a pathway to achieve our goal of enhanced carrier mobility. Preliminary results demonstrate nc-Si:H films possessing grains as large as 29 nm, with (220) preferred orientation, which is suitable for solar cell applications. Reactions between plasma species in a SiF4:H2:SiH4 glow discharge, which expectedly contribute to evolution of large grains, are also discussed. Our findings suggest the double pulse strategy is a valuable method for manipulating the microstructural evolution of PECVD grown thin film materials. © 2012 SPIE.

Lee S.-Y.,University of Utah | Paik S.-Y.,University of Utah | McCamey D.R.,University of Utah | Hu J.,MVSystems Inc. | And 3 more authors.
Applied Physics Letters | Year: 2010

A study of spin-dependent charge carrier transitions in silicon-rich hydrogenated amorphous silicon-nitride (a-SiNx:H) p-i-n devices is presented. Pulsed electrically detected magnetic resonance allows us to determine the paramagnetic states that influence the photocurrent and provides insights into the nature of spin-coupling between charge carriers. We show that, in contrast to hydrogenated amorphous silicon, a-SiNx:H allows strongly spin-coupled, correlated (geminate) pairs of charge carriers to dissociate into nongeminate pairs that contribute to the photocurrent. This is discussed with regard to the application of a-SiNx:H as a photoelectrochemical electrode material. © 2010 American Institute of Physics.

Lee S.,University College London | Ahnood A.,University College London | Sambandan S.,Indian Institute of Science | Madan A.,MVSystems Inc. | Nathan A.,University of Cambridge
IEEE Electron Device Letters | Year: 2012

We present an analytical field-effect method to extract the density of subgap states (subgap DOS) in amorphous semiconductor thin-film transistors (TFTs), using a closed-form relationship between surface potential and gate voltage. By accounting the interface states in the subthreshold characteristics, the subgap DOS is retrieved, leading to a reasonably accurate description of field-effect mobility and its gate voltage dependence. The method proposed here is very useful not only in extracting device performance but also in physically based compact TFT modeling for circuit simulation. © 2012 IEEE.

Hu J.,MVSystems Inc. | Zhu F.,MVSystems Inc. | Kunrath A.,MVSystems Inc. | Gaillard N.,Hawaii Natural Energy Institute
Materials Research Society Symposium Proceedings | Year: 2014

In this communication, we report our efforts to develop amorphous silicon carbide (a-SiC) thin film photoelectrodes integrated with Si solar cells to form a monolithic, hybrid photovoltaic (PV)/a-SiC device capable of water splitting using sunlight as the only energy source. The main photoelectrochemical (PEC) properties of both the a-SiC photoelectrode and complete hybrid device fabricated by the plasma enhanced chemical vapor deposition (PECVD) technique at low temperature (≤ 200°C) are discussed. The surface modification with metal nanoparticles, which is critical to PEC performances of the hybrid device, is also described. We show that, with the an a-SiC photoelectrode of p-i-n configuration and a high performance silicon heterojunction solar cell as driver, the photocurrent of the hybrid PV/a-SiC device has reached ∼5 mA/cm2. Additionally, the durability of such device has reached ∼800 hours in acidic electrolyte. Finally, we describe a roadmap for achieving the solar-to-hydrogen efficiency of >10% by optimizing the device configuration. Copyright © Materials Research Society 2014.

Hu J.,MVSystems Inc. | Zhu F.,MVSystems Inc. | Kunrath A.,MVSystems Inc. | Prasher D.,Hawaii Natural Energy Institute | Gaillard N.,Hawaii Natural Energy Institute
2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014 | Year: 2014

In this paper, we present results on fabrication of the hybrid photovoltaic/photoelectrochemical device consisting of an amorphous silicon carbide photoelectrode and silicon solar cells. Driven by the solar cells, a photocurrent density of nearly 5 mA/cm2 was achieved in a mechanical stack fashion, equivalent to a solar-to-hydrgoen (STH) coversion efficiency up to 6.1%. An even higher STH efficiency is expected in a monolithic hybrid device by eliminating varous optical and electrical losses occurring in the mechanical stack. © 2014 IEEE.

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