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Christophe Ballif - One of the best experts on this subject based on the ideXlab platform.

  • a scalable and inexpensive surface texturization method for advanced transparent front electrodes in microcrystalline and micromorph thin Film Silicon solar cells
    Physica Status Solidi (a), 2015
    Co-Authors: Dejun Bu, Franz-josef Haug, Mathieu Boccard, Christophe Ballif, J Bailat, Linus Lofgren, Yang Wang
    Abstract:

    As the thin Film Silicon solar cell technology reaches a pivotal point to keep competing in the photovoltaic industry where crystalline Silicon and other technologies currently dominate, it has become an urgent task to revolutionize some of its state-of-the-art key processes which have reached their cost barriers for decades. We have devised a more cost-effective method for mass production of transparent front electrodes for thin Film Silicon solar modules. It involves sputtering deposition and a novel surface-texturization process. The new method produces microscopic U-shaped surface textures of aluminum-doped zinc oxide (AZO) and other transparent conductive oxides (TCOs) which lead to higher open circuit voltages, higher fill factors, and comparable short circuit current densities for microcrystalline and micromorph Silicon solar cells. We experimentally demonstrate that solar cells using these TCO front electrodes reach comparable efficiency levels to those using any other commercialized TCO electrodes suchasfluorine-doped tin oxide (FTO) and boron-doped zinc oxide (BZO). An analysis shows that the manufacturing costs of the new method can be significantly lower than those of the commercial counterparts. The possibilities brought about by this method may pave a new path for future developments of thin Film Silicon solar cells. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Highly transparent modulated surface textured front electrodes for high-efficiency multijunction thin-Film Silicon solar cells
    Progress in Photovoltaics: Research and Applications, 2015
    Co-Authors: Hairen Tan, Jan Willem Schüttauf, Franz-josef Haug, Etienne Moulin, Fai Tong Si, Michael Stuckelberger, Christophe Ballif, Olindo Isabella, Miro Zeman, Arno H. M. Smets
    Abstract:

    Copyright © 2015 John Wiley & Sons, Ltd. To further increase the efficiency of multijunction thin-Film Silicon (TF-Si) solar cells, it is crucial for the front electrode to have a good transparency and conduction, to provide efficient light trapping for each subcell, and to ensure a suitable morphology for the growth of high-quality Silicon layers. Here, we present the implementation of highly transparent modulated surface textured (MST) front electrodes as light-trapping structures in multijunction TF-Si solar cells. The MST substrates comprise a micro-textured glass, a thin layer of hydrogenated indium oxide (IOH), and a sub-micron nano-textured ZnO layer grown by low-pressure chemical vapor deposition (LPCVD ZnO). The bilayer IOH/LPCVD ZnO stack guarantees efficient light in-coupling and light trapping for the top amorphous Silicon (a-Si:H) solar cell while minimizing the parasitic absorption losses. The crater-shaped micro-textured glass provides both efficient light trapping in the red and infrared wavelength range and a suitable morphology for the growth of high-quality nanocrystalline Silicon (nc-Si:H) layers. Thanks to the efficient light trapping for the individual subcells and suitable morphology for the growth of high-quality Silicon layers, multijunction solar cells deposited on MST substrates have a higher efficiency than those on single-textured state-of-the-art LPCVD ZnO substrates. Efficiencies of 14.8% (initial) and 12.5% (stable) have been achieved for a-Si:H/nc-Si:H tandem solar cells with the MST front electrode, surpassing efficiencies obtained on state-of-the-art LPCVD ZnO, thereby highlighting the high potential of MST front electrodes for high-efficiency multijunction solar cells.

  • Recent advances and remaining challenges in thin-Film Silicon photovoltaic technology
    Materials Today, 2015
    Co-Authors: F Meillaud, Jan Willem Schüttauf, Grégory Bugnon, Michael Stuckelberger, Mathieu Boccard, Matthieu Despeisse, Simon Hänni, F.-j. Haug, J. Persoz, Christophe Ballif
    Abstract:

    This contribution reviews some of the latest achievements and challenges in thin-Film Silicon photovoltaic (PV) technology based on amorphous and nanocrystalline Silicon and their alloys. We address material and device developments, including (i) improved plasma deposition processes to achieve high-quality dense absorber materials; (ii) absorber layers based on Silicon tetrafluoride, which lead to enhanced absorption in the near-infrared and yield outstanding short-circuit current densities; (iii) dedicated optimization of the interfaces and device architecture, as well as (iv) enhanced light harvesting by means of multi-scale textured substrates and reduced parasitic absorption in the non-active layers. This paper will describe how, by combining all of these advances along with precise control of plasmas over large areas, key results have been achieved in recent years, at both the cell and large-area module level, with stabilized efficiencies of over 13 and 12%, respectively.

  • High-Stable-Efficiency Tandem Thin-Film Silicon Solar Cell With Low-Refractive-Index Silicon-Oxide Interlayer
    IEEE Journal of Photovoltaics, 2014
    Co-Authors: Mathieu Boccard, Jordi Escarré, Grégory Bugnon, Matthieu Despeisse, F Meillaud, Xavier Niquille, Simon Hänni, Maximilien Bonnet-eymard, Christophe Ballif
    Abstract:

    We report the recent advances and key requirements for high-efficiency “micromorph” tandem thin-Film Silicon solar cells composed of an amorphous Silicon top cell and a microcrystalline Silicon bottom cell. The impact of inserting a low-refractive-index Silicon-oxide (SiOx) Film as intermediate reflecting layer (IRL) is highlighted. We show that refractive indexes as low as 1.75 can be obtained for layers still conducting enough to be implemented in solar cells, and without no additional degradation. This allows for high top-cell current densities with thin top cells, enabling low degradation rates. A micromorph cell with a certified efficiency of 12.63% (short-circuit current density of 12.8 mA/cm2) is obtained for an optimized stack. Furthermore, short-circuit current densities as high as 15.9 mA/cm2 are reported in the amorphous Silicon top-cell of micromorph devices by combining a 150-nm-thick SiOx-based IRL and a textured antireflecting coating at the air-glass interface.

  • experimental study of flat light scattering substrates in thin Film Silicon solar cells
    Solar Energy Materials and Solar Cells, 2012
    Co-Authors: Karin Soderstrom, Grégory Bugnon, Sylvain Nicolay, F.-j. Haug, Christophe Ballif
    Abstract:

    In this work, a novel type of substrate for thin-Film Silicon solar cells is studied. The substrate has the advantage of being physically flat to allow the growth of cells with excellent material quality while being optically rough for enhanced light trapping that leads to high short-circuit current density. The substrate is made of rough zinc oxide (ZnO) which is grown on a flat silver reflector. The ZnO is then covered with amorphous Silicon and the stack is polished to expose the tips of the pyramidal ZnO surface. The ZnO embedded in the amorphous matrix provides the desirable scattering of light while the surface onto which the cell is deposited is flat and allows for the growth of good-quality material. We present results of ∼4 μm thick microcrystalline Silicon solar cells prepared on such substrates with high open-circuit voltages of 520 mV. We also demonstrate a large relative efficiency gain of 10% compared to a state-of-the-art cell which is grown directly on an optimized textured substrate.

F Meillaud - One of the best experts on this subject based on the ideXlab platform.

  • Recent advances and remaining challenges in thin-Film Silicon photovoltaic technology
    Materials Today, 2015
    Co-Authors: F Meillaud, Jan Willem Schüttauf, Grégory Bugnon, Michael Stuckelberger, Mathieu Boccard, Matthieu Despeisse, Simon Hänni, F.-j. Haug, J. Persoz, Christophe Ballif
    Abstract:

    This contribution reviews some of the latest achievements and challenges in thin-Film Silicon photovoltaic (PV) technology based on amorphous and nanocrystalline Silicon and their alloys. We address material and device developments, including (i) improved plasma deposition processes to achieve high-quality dense absorber materials; (ii) absorber layers based on Silicon tetrafluoride, which lead to enhanced absorption in the near-infrared and yield outstanding short-circuit current densities; (iii) dedicated optimization of the interfaces and device architecture, as well as (iv) enhanced light harvesting by means of multi-scale textured substrates and reduced parasitic absorption in the non-active layers. This paper will describe how, by combining all of these advances along with precise control of plasmas over large areas, key results have been achieved in recent years, at both the cell and large-area module level, with stabilized efficiencies of over 13 and 12%, respectively.

  • High-Stable-Efficiency Tandem Thin-Film Silicon Solar Cell With Low-Refractive-Index Silicon-Oxide Interlayer
    IEEE Journal of Photovoltaics, 2014
    Co-Authors: Mathieu Boccard, Jordi Escarré, Grégory Bugnon, Matthieu Despeisse, F Meillaud, Xavier Niquille, Simon Hänni, Maximilien Bonnet-eymard, Christophe Ballif
    Abstract:

    We report the recent advances and key requirements for high-efficiency “micromorph” tandem thin-Film Silicon solar cells composed of an amorphous Silicon top cell and a microcrystalline Silicon bottom cell. The impact of inserting a low-refractive-index Silicon-oxide (SiOx) Film as intermediate reflecting layer (IRL) is highlighted. We show that refractive indexes as low as 1.75 can be obtained for layers still conducting enough to be implemented in solar cells, and without no additional degradation. This allows for high top-cell current densities with thin top cells, enabling low degradation rates. A micromorph cell with a certified efficiency of 12.63% (short-circuit current density of 12.8 mA/cm2) is obtained for an optimized stack. Furthermore, short-circuit current densities as high as 15.9 mA/cm2 are reported in the amorphous Silicon top-cell of micromorph devices by combining a 150-nm-thick SiOx-based IRL and a textured antireflecting coating at the air-glass interface.

  • resistive interlayer for improved performance of thin Film Silicon solar cells on highly textured substrate
    Applied Physics Letters, 2010
    Co-Authors: Matthieu Despeisse, Adrian Billet, Grégory Bugnon, Peter Cuony, F Meillaud, A Feltrin, M Stueckelberger, Christophe Ballif
    Abstract:

    The deposition of thin-Film Silicon solar cells on highly textured substrates results in improved light trapping in the cell. However, the growth of Silicon layers on rough substrates can often lead to undesired current drains, degrading performance and reliability of the cells. We show that the use of a Silicon oxide interlayer between the active area and the back contact of the cell permits in such cases to improve the electrical properties. Relative increases of up to 7.5% of fill factor and of 6.8% of conversion efficiency are shown for amorphous Silicon cells deposited on highly textured substrates, together with improved yield and low-illumination performance.

  • in situ Silicon oxide based intermediate reflector for thin Film Silicon micromorph solar cells
    Applied Physics Letters, 2007
    Co-Authors: P Buehlmann, Adrian Billet, J Bailat, D Domine, F Meillaud, A Feltrin, Christophe Ballif
    Abstract:

    We show that SiO-based intermediate reflectors (SOIRs) can be fabricated in the same reactor and with the same process gases as used for thin-Film Silicon solar cells. By varying input gas ratios, SOIR layers with a wide range of optical and electrical properties are obtained. The influence of the SOIR thickness in the micromorph cell is studied and current gain and losses are discussed. Initial micromorph cell efficiency of 12.2% (Voc=1.40V, fill factor=71.9%, and Jsc=12.1mA∕cm2) is achieved with top cell, SOIR, and bottom cell thicknesses of 270, 95, and 1800nm, respectively.

  • towards very low cost mass production of thin Film Silicon photovoltaic pv solar modules on glass
    Thin Solid Films, 2006
    Co-Authors: Arvind Shah, Jerome Steinhauser, J Meier, U Kroll, F Meillaud, H Schade, A Buechel, D Domine
    Abstract:

    Production volume of PV modules increases at > 35% per year, but one is yet far from making a global impact on energy supply. One of the obstacles is given by the present high production costs of PV modules. A possibility to reduce costs are thin-Film PV modules on glass. The specific option of thin-Film Silicon is considered. The combination of amorphous and microcrystalline Silicon thin Films within a tandem solar cell corresponds to a theoretical optimum. In practice, stabilized efficiencies of 10% to 12% have so far been obtained in the laboratory with such tandem solar cells. Silicon being a material with an indirect band gap, its absorption coefficient is relatively low, and therefore light management in the solar cell has to be further optimized. Thin-Film Silicon can be deposited by plasma-enhanced CVD, as used for AM-LCD displays. The use of modified fabrication equipment from the AM-LCD Display Industry is therefore a promising way to implement low-cost mass production. © 2005 Elsevier B.V. All rights reserved.

Michio Kondo - One of the best experts on this subject based on the ideXlab platform.

  • high efficiency thin Film Silicon solar cells realized by integrating stable a si h absorbers into improved device design
    Japanese Journal of Applied Physics, 2015
    Co-Authors: Takuya Matsui, Takashi Suezaki, Takashi Koida, Isao Yoshida, Hitoshi Sai, Keigou Maejima, Adrien Bidiville, Mitsuhiro Matsumoto, Kimihiko Saito, Michio Kondo
    Abstract:

    We report that thin-Film Silicon solar cells exhibiting high stabilized efficiencies can be obtained by depositing hydrogenated amorphous Silicon (a-Si:H) absorbers using triode-type plasma-enhanced chemical vapor deposition. The improved light-soaking stability and performance of solar cells are also realized by optimizing the device design, such as p and p–i buffer layers. As a result, we attain independently confirmed stabilized efficiencies of 10.1–10.2% for a-Si:H single-junction solar cells (absorber thickness: ti = 220–310 nm) and 12.69% for an a-Si:H (ti = 350 nm)/hydrogenated microcrystalline Silicon (µc-Si:H) tandem solar cell fabricated using textured SnO2 and ZnO substrates, respectively. The relative efficiency degradations of these solar cells are ~10 and 3%, respectively, under 1 sun illumination at 50 °C for 1000 h.

  • triple junction thin Film Silicon solar cell fabricated on periodically textured substrate with a stabilized efficiency of 13 6
    Applied Physics Letters, 2015
    Co-Authors: Takuya Matsui, Takashi Koida, Koji Matsubara, Michio Kondo, Shuichiro Sugiyama, Hirotaka Katayama, Yoshiaki Takeuchi, Isao Yoshida
    Abstract:

    We report a high-efficiency triple-junction thin-Film Silicon solar cell fabricated with the so-called substrate configuration. It was verified whether the design criteria for developing single-junction microcrystalline Silicon (μc-Si:H) solar cells are applicable to multijunction solar cells. Furthermore, a notably high short-circuit current density of 32.9 mA/cm2 was achieved in a single-junction μc-Si:H cell fabricated on a periodically textured substrate with a high-mobility front transparent contacting layer. These technologies were also combined into a-Si:H/μc-Si:H/μc-Si:H triple-junction cells, and a world record stabilized efficiency of 13.6% was achieved.

  • full wave optoelectrical modeling of optimized flattened light scattering substrate for high efficiency thin Film Silicon solar cells
    Progress in Photovoltaics, 2014
    Co-Authors: Olindo Isabella, Michio Kondo, Miro Zeman
    Abstract:

    The flattened light-scattering substrate (FLiSS) is formed by a combination of two materials with a high refractive index mismatch, and it has a flat surface. A specific realization of this concept is a flattened two-dimensional grating. When applied as a substrate for thin-Film Silicon solar cells in the nip configuration, it is capable to reflect light with a high fraction of diffused component. Furthermore, the FLiSS is an ideal substrate for growing high-quality microcrystalline Silicon (µc-Si:H), used as bottom cell absorber layer in most of multijunction solar cell architectures. FLiSS is a three-dimensional structure; therefore, a full-wave analysis of the electromagnetic field is necessary for its optimal implementation. Using finite element method, different shapes, materials, and geometrical parameters were investigated to obtain an optimized FLiSS. The application of the optimized FLiSS in µc-Si:H single junction nip cell (1-µm-thick i-layer) resulted in a 27.4-mA/cm2 implied photocurrent density. The absorptance of µc-Si:H absorber exceeded the theoretical Yablonovitch limit for wavelengths larger than 750 nm. Double and triple junction nip solar cells on optimal FLiSS and with thin absorber layers were simulated. Results were in line with state-of-the-art optical performance typical of solar cells with rough interfaces. After the optical optimization, a study of electrical performance was carried out by simulating current–voltage characteristics of nip solar cells on optimized FLiSS. Potential conversion efficiencies of 11.6%, 14.2%, and 16.0% for single, double, and triple junction solar cells with flat interfaces, respectively, were achieved. Copyright © 2012 John Wiley & Sons, Ltd.

  • flattened light scattering substrate in thin Film Silicon solar cells for improved infrared response
    Applied Physics Letters, 2011
    Co-Authors: Hitoshi Sai, Yoshiaki Kanamori, Michio Kondo
    Abstract:

    Surface texturing is a technique commonly used to enhance light absorption in thin Film Silicon solar cells; it should be noted that highly textured substrates often induce structural defects in the active layer, which deteriorates the photovoltaic performance. In this paper, we propose a flattened light-scattering substrate (FLiSS) with a large refractive index contrast in plane as an approach to overcome this trade-off. A FLiSS composed of a two-dimensional ZnO grating and a Ag reflector is applied to μc-Si:H cells, in order to improve the spectral response in the infrared region while maintaining a high VOC and FF.

  • mie scattering enhanced near infrared light response of thin Film Silicon solar cells
    Applied Physics Letters, 2010
    Co-Authors: S Nunomura, A Minowa, H Sai, Michio Kondo
    Abstract:

    Light trapping is of importance in thin-Film Silicon solar cells for achieving a higher photocurrent. In this letter, we propose a unique cell structure incorporating submicron-sized light scatterers to enhance light trapping in the near-infrared (NIR) region. The effect of NIR light trapping is demonstrated in substrate-type hydrogenated amorphous/microcrystalline Silicon tandem solar cells. By introducing the light scatterers at the interface between the top and bottom subcells, the NIR response of the solar cell is improved, where Mie scattering plays an essential role in increasing the optical path length of the NIR light.

Grégory Bugnon - One of the best experts on this subject based on the ideXlab platform.

  • Recent advances and remaining challenges in thin-Film Silicon photovoltaic technology
    Materials Today, 2015
    Co-Authors: F Meillaud, Jan Willem Schüttauf, Grégory Bugnon, Michael Stuckelberger, Mathieu Boccard, Matthieu Despeisse, Simon Hänni, F.-j. Haug, J. Persoz, Christophe Ballif
    Abstract:

    This contribution reviews some of the latest achievements and challenges in thin-Film Silicon photovoltaic (PV) technology based on amorphous and nanocrystalline Silicon and their alloys. We address material and device developments, including (i) improved plasma deposition processes to achieve high-quality dense absorber materials; (ii) absorber layers based on Silicon tetrafluoride, which lead to enhanced absorption in the near-infrared and yield outstanding short-circuit current densities; (iii) dedicated optimization of the interfaces and device architecture, as well as (iv) enhanced light harvesting by means of multi-scale textured substrates and reduced parasitic absorption in the non-active layers. This paper will describe how, by combining all of these advances along with precise control of plasmas over large areas, key results have been achieved in recent years, at both the cell and large-area module level, with stabilized efficiencies of over 13 and 12%, respectively.

  • High-Stable-Efficiency Tandem Thin-Film Silicon Solar Cell With Low-Refractive-Index Silicon-Oxide Interlayer
    IEEE Journal of Photovoltaics, 2014
    Co-Authors: Mathieu Boccard, Jordi Escarré, Grégory Bugnon, Matthieu Despeisse, F Meillaud, Xavier Niquille, Simon Hänni, Maximilien Bonnet-eymard, Christophe Ballif
    Abstract:

    We report the recent advances and key requirements for high-efficiency “micromorph” tandem thin-Film Silicon solar cells composed of an amorphous Silicon top cell and a microcrystalline Silicon bottom cell. The impact of inserting a low-refractive-index Silicon-oxide (SiOx) Film as intermediate reflecting layer (IRL) is highlighted. We show that refractive indexes as low as 1.75 can be obtained for layers still conducting enough to be implemented in solar cells, and without no additional degradation. This allows for high top-cell current densities with thin top cells, enabling low degradation rates. A micromorph cell with a certified efficiency of 12.63% (short-circuit current density of 12.8 mA/cm2) is obtained for an optimized stack. Furthermore, short-circuit current densities as high as 15.9 mA/cm2 are reported in the amorphous Silicon top-cell of micromorph devices by combining a 150-nm-thick SiOx-based IRL and a textured antireflecting coating at the air-glass interface.

  • experimental study of flat light scattering substrates in thin Film Silicon solar cells
    Solar Energy Materials and Solar Cells, 2012
    Co-Authors: Karin Soderstrom, Grégory Bugnon, Sylvain Nicolay, F.-j. Haug, Christophe Ballif
    Abstract:

    In this work, a novel type of substrate for thin-Film Silicon solar cells is studied. The substrate has the advantage of being physically flat to allow the growth of cells with excellent material quality while being optically rough for enhanced light trapping that leads to high short-circuit current density. The substrate is made of rough zinc oxide (ZnO) which is grown on a flat silver reflector. The ZnO is then covered with amorphous Silicon and the stack is polished to expose the tips of the pyramidal ZnO surface. The ZnO embedded in the amorphous matrix provides the desirable scattering of light while the surface onto which the cell is deposited is flat and allows for the growth of good-quality material. We present results of ∼4 μm thick microcrystalline Silicon solar cells prepared on such substrates with high open-circuit voltages of 520 mV. We also demonstrate a large relative efficiency gain of 10% compared to a state-of-the-art cell which is grown directly on an optimized textured substrate.

  • Nanoimprint lithography for high-efficiency thin-Film Silicon solar cells
    Nano Letters, 2011
    Co-Authors: Corsin Battaglia, Kerstin Söderström, Lukas Erni, Laura Ding, Jordi Escarré, Adrian Billet, Grégory Bugnon, Loris Barraud, Mathieu Boccard, Stefaan De Wolf
    Abstract:

    We demonstrate high-efficiency thin-Film Silicon solar cells with transparent nanotextured front electrodes fabricated via ultraviolet nanoimprint lithography on glass substrates. By replicating the morphology of state-of-the-art nanotextured zinc oxide front electrodes known for their exceptional light trapping properties, conversion efficiencies of up to 12.0% are achieved for micromorph tandem junction cells. Excellent light incoupling results in a remarkable summed short-circuit current density of 25.9 mA/cm(2) for amorphous top cell and microcrystalline bottom cell thicknesses of only 250 and 1100 nm, respectively. As efforts to maximize light harvesting continue, our study validates nanoimprinting as a versatile tool to investigate nanophotonic effects of a large variety of nanostructures directly on device performance.

  • mixed phase p type Silicon oxide containing Silicon nanocrystals and its role in thin Film Silicon solar cells
    Applied Physics Letters, 2010
    Co-Authors: Peter Cuony, Grégory Bugnon, Mathieu Boccard, Michael Marending, Duncan T L Alexander, Matthieu Despeisse, Christophe Ballif
    Abstract:

    Lower absorption, lower refractive index, and tunable resistance are three advantages of amorphous Silicon oxide containing nanocrystalline Silicon grains (nc-SiOx) compared to microcrystalline Silicon (μc-Si), when used as a p-type layer in μc-Si thin-Film solar cells. We show that p-nc-SiOx with its particular nanostructure increases μc-Si cell efficiency by reducing reflection and parasitic absorption losses depending on the roughness of the front electrode. Furthermore, we demonstrate that the p-nc-SiOx reduces the detrimental effects of the roughness on the electrical characteristics, and significantly increases μc-Si and Micromorph cell efficiency on substrates until now considered too rough for thin-Film Silicon solar cells.

Joan Ramon Morante - One of the best experts on this subject based on the ideXlab platform.

  • Multilayered Hematite Nanowires with Thin-Film Silicon Photovoltaics in an All-Earth-Abundant Hybrid Tandem Device for Solar Water Splitting.
    Chemsuschem, 2019
    Co-Authors: Félix Urbain, Pengyi Tang, Katharina Welter, Vladimir Smirnov, Jordi Arbiol, Friedhelm Finger, Teresa Andreu, Joan Ramon Morante
    Abstract:

    : The concept of hybrid tandem device structures that combine metal oxides with thin-Film semiconducting photoabsorbers holds great promise for large-scale, robust, and cost-effective bias-free photoelectrochemical water splitting (PEC-WS). This work highlights important steps toward the efficient coupling of high-performance hematite photoanodes with multijunction thin-Film Silicon photocathodes providing high bias-free photocurrent density. The hybrid PEC-WS device is optimized by testing three types of multijunction Silicon photocathodes with the hematite photoanode: amorphous Silicon (a-Si:H) tandem: a-Si:H/a-Si:H and triple junction with microcrystalline Silicon (μc-Si:H): a-Si:H/a-Si:H/μc-Si:H and a-Si:H/μc-Si:H/μc-Si:H. The results provide evidence that the multijunction structures offer high flexibility for hybrid tandem devices with regard to tunable photovoltages and spectral matching. Furthermore, both photoanode and photocathode are tested under various electrolyte and light concentration conditions, respectively, with respect to their photoelectrochemical performance and stability. A 27 % enhancement in the solar-to-hydrogen conversion efficiency is observed upon concentrating light from 100 to 300 mW cm-2 . Ultimately, bias-free water splitting is demonstrated, with a photocurrent density of 4.6 mA cm-2 (under concentrated illumination) paired with excellent operation stability for more than 24 h of the all-earth-abundant and low-cost hematite/Silicon tandem PEC-WS device.

  • Solar vanadium redox-flow battery powered by thin-Film Silicon photovoltaics for efficient photoelectrochemical energy storage
    Journal of Physics D, 2018
    Co-Authors: Félix Urbain, Sebastián Murcia-lópez, Nicole Nembhard, Javier Vázquez‐galván, Katharina Welter, Cristina Flox, Vladimir Smirnov, Friedhelm Finger, Teresa Andreu, Joan Ramon Morante
    Abstract:

    Solar-powered vanadium redox-flow batteries (VRFB) have emerged as an attractive method for large-scale and efficient energy storage and conversion. However, due to the stringent charging voltage requirements of vanadium-based systems (1.4–1.7 V), common photobatteries, applying standard photovoltaics with nonoptimized photovoltages, cannot be completely charged bias-free, i.e. by only using bias-free solar energy, or if they can be, only at unpractical low current densities of just a few mA cm-2. In response to this critical challenge, the present study aimed to design and test a compact device combining a high photovoltage Silicon multijunction solar cell with an all-vanadium continuous-flow battery. In particular, we applied a monolithic triple junction solar cell, which can provide photovoltage of up to 2.2 V. Additionally, we have introduced the concept of increased illumination intensity for the solar VRFB. As a first demonstration, a complete bias-free solar charging at 25 mAcm-2 (300 mW cm-2 illumination) is reported. Moreover, we investigated the influence of the operation parameters of the redox-flow battery itself: the membrane type and the vanadium concentration in the electrolyte (i.e. storage capacity). The presented results provide evidence that the low-cost thin-Film Silicon based solar VRFB can be considered as an outstanding alternative for practical energy storage and conversion usage. A maximum bias-free solar conversion efficiency of 12.3% was achieved during charging, combined with promising and competitive energy efficiencies for the complete charge–discharge process that can guarantee an overall solar-to-electricity conversion efficiency of >10%.